The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Svatopluk Zeman - One of the best experts on this subject based on the ideXlab platform.
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a modified vacuum Stability Test in the study of initiation reactivity of nitramine explosives
Thermochimica Acta, 2017Co-Authors: Svatopluk Zeman, Ahmed Elbeih, Tamer Elshenawy, Ahmed K Hussein, Marcela JungovaAbstract:Abstract The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) in the first six hours of decomposition were measured by means of the Czech vacuum Stability Test, STABIL. The PBXs were filled by RDX (1,3,5-trinitro-1,3,5-triazinane), β−HMX (β−1,3,5,7-tetranitro-1,3,5,7-tetrazocane), BCHMX and ϵ-CL20 (ϵ-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, ϵ-HNIW) and, in one case, on a mixture of BCHMX and 3-nitro-1,2,4-triazol-5-one (NTO), in a 1:1 wt. ratio. These nitramines were bonded by 9% by wt. of softened polyisobutylene matrix, 13% by wt. of softened polystyrene-butadiene matrix, 18% by wt. of crosslinked hydroxyl-terminated polybutadiene, 12% by wt. of polydimethylsiloxane and by 40% of TNT. The relationships of specific rate constants with experimental detonation velocities, impact and friction sensitivities of these PBXs are shown and discussed. It is postulated that this approach provides results which are applicable to studies of initiation reactivity of energetic materials and which are fully comparable with those of other methods of investigation in this area.
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note on the use of the vacuum Stability Test in the study of initiation reactivity of attractive cyclic nitramines in formex p1 matrix
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Svatopluk Zeman, Ahmed Elbeih, Qilong YanAbstract:The zero-order reaction rates (specific rate constants) for isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum Stability Test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d] imidazole (BCHMX), and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, e-CL-20) with 9 wt.% of the C4 type matrix, i.e., a matrix containing 25 wt.% of polyisobutylene, 59 wt.% of dioctyl sebacate and 16 wt.% of the oil HM46. Dependencies were found between the specific rate constants mentioned and the detonation velocities of the PBXs, and consequently between these constants and the impact of pure explosive fillers, i.e., RDX, β-HMX, e-HNIW, RS-e-HNIW, and BCHMX and, at the same time, the corresponding PBXs. The results obtained are compared with those from a recent analogous study of PBXs using an SBR (Formex P1) binder which could increase the PBXs’ reactivity in comparison with C4 matrix. These results also help to dispel a widely held view about HNIW being a relatively sensitive explosive.
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study of initiation reactivity of some plastic explosives by vacuum Stability Test and non isothermal differential thermal analysis
Thermochimica Acta, 2007Co-Authors: Martina Chovancova, Svatopluk ZemanAbstract:Abstract On the basis of measurements of 18 high explosives by means of the Czech Vacuum Stability Test (VST) STABIL, a relationship has been specified between the results of this Test and those of Russian manometric method. The said relationship was used to predict the Arrhenius parameters ( E a and log A values) of four plastic explosives based on RDX and one high explosive based on PETN (Semtex). The slopes E a R −1 of Kissinger's equation were specified by means of non-isothermal differential thermal analysis (DTA) and evaluation of the measurement results by means of the Kissinger method. The role played by binders and plasticizers in thermal decomposition of nitramines was pointed out on the basis of relationship between the E a values obtained from VST and the E a R −1 values obtained from DTA, both for plastic explosives, eight nitramines, Composition B and PETN. The relationships between the E a R −1 values and thermoStability threshold was specified for the given group of explosives. The relationship classify some of the studied plastic explosives as belonging to nitramines with steric hindrance in the molecule (CPX, TNAZ and HNIW). The relationship between E a R −1 values and drop energies, E dr , sharply differentiates between plastic explosives and individual nitramines. From the relationship between the E dr and D 2 values it was found that the increasing performance of the studied nitramines and plastic explosives is connected with the decrease in their impact sensitivity. Also specified are the approximate linear dependences between the peak temperatures of exothermic decomposition of all the explosives studied and their ignition temperatures, T ig , or critical temperatures, T c ; these dependences were applied to prediction of T ig and T c of both the studied plastic explosives and some of the nitramines.
Karl W Birkeland - One of the best experts on this subject based on the ideXlab platform.
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changes in Stability Test usage by snowpilot users
Proceedings 2012 International Snow Science Workshop Anchorage Alaska, 2012Co-Authors: Karl W Birkeland, Doug ChabotAbstract:Professionals and recreationists utilize Stability Tests to assess snow Stability. Our goal is to determine whether or not people are changing the types of Tests they conduct. We utilized the SnowPilot database of over 3,600 snow pits from nine winters, with about 83% of these pits being dug by avalanche professionals. We found a dramatic shift in the Tests conducted since 2004. SnowPilot users have moved away from rutschblocks and stuffblocks and moved more toward extended column Tests (ECTs) and propagation saw Tests (PSTs), while still conducting a large number of compression Tests (CTs). ECTs are now the most popular Test, being conducted in nearly 80% of all pits. Not surprisingly, this shift toward ECTs and PSTs has coincided with an increasing emphasis on the importance of propagation potential in our Stability assessments. As we learn more about snow and the way it fractures, newer and more effective Tests might well be advanced. Our results demonstrate that our community will quickly adopt new Tests when they are useful and scientifically validated.
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on optimal Stability Test spacing for assessing snow avalanche conditions
Journal of Glaciology, 2010Co-Authors: Karl W Birkeland, Jordy Hendrikx, Martyn P ClarkAbstract:Assessing snow Stability requires a holistic approach, relying on avalanche, snowpack and weather observations. Part of this assessment utilizes Stability Tests, but these Tests can be unreliable due in part to the spatial variability of Test results. Conducting more than one Test can help to mitigate this uncertainty, though it is unclear how far apart to space Tests to optimize our assessments. To address this issue we analyze the probability of sampling two relatively strong Test results over 25 spatial datasets collected using a variety of Stability Tests. Our results show that the optimal distance for spacing Stability Tests varies by dataset, even when taking the sampling scheme and Stability-Test type into account. This suggests that no clear rule currently exists for spacing Stability Tests. Our work further emphasizes the spatial complexity of snow Stability measurements, and the need for holistic Stability assessments where Stability Tests are only one part of a multifaceted puzzle.
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minimizing false stable Stability Test results why digging more snowpits is a good idea
Proceedings of the 2006 International Snow Science Workshop Telluride Colorado, 2006Co-Authors: Karl W Birkeland, Doug ChabotAbstract:The worst nightmare for an avalanche worker is to assess an unstable slope as stable since the consequence of such an assessment is that you, your clients or the public could be caught in an avalanche. Thus, a primary goal in avalanche forecasting is to minimize such "false-stable" errors. In this paper we analyze the first season of data from the SnowPilot database. Starting with nearly 1,000 snowpits and 3,500 Stability Tests, we use Stability Test scores, shear quality, and weak layer depth to identify what we term the "critical weak layer" in each pit. We also divide the pits into "stable" and "unstable" categories based on the assessed snow Stability and observations of obvious signs of inStability (collapsing, cracking and recent avalanche activity). This filtering leaves us with 289 compression, rutschblock and stuffblock Stability Tests that fractured on the critical weak layer on unstable slopes. Of those 289 Tests, 38 of them (13%) presented "false-stable" results, which we define as CT21 or greater, RB5 or greater, or SB drop heights 40 cm or greater. If we include shear quality and consider strong Test results with a Q1 shear to be unstable, we decrease our false-stable cases to around 9% of the total. This implies that - if we use only Stability Test results - around 1 in 10 times we assess unstable slopes we will conclude that it is stable, which is unacceptably high. Recently spatial variability research has led some to argue that digging snowpits is unnecessary or futile, but we believe our data reinforce the idea that the key to analyzing snow Stability lies in digging more rather than fewer pits, and using a holistic approach that considers much more than simple Stability Test results. Though our dataset is limited, it suggests that digging multiple pits might be an effective strategy for minimizing false-stable situations. In fact, having Stability Tests and associated shear quality from two different, but representative locations on the slope might decrease the chance of a false-stable error from around 10% to closer to 1%.
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integrating shear quality into Stability Test results
2002 International Snow Science Workshop Penticton British Columbia, 2002Co-Authors: Ron Johnson, Karl W BirkelandAbstract:This study investigates whether collecting shear quality data in conjunction with Stability Test results improves snowpack evaluations. Over the past six seasons we have consistently evaluated shear quality when evaluating snowpack Stability. Shear quality is subjectively evaluated on a 3-tiered scale from Q1 (clean, fast shears) to Q2 (average shears) to Q3 (irregular or dirty shears). Our method is a formalization of what ski patrollers and others have been doing in the U.S. and elsewhere for at least several decades. We used a dataset of nearly 700 individual Stability Tests (rutschblock, stuffblock and compression Tests) collected by seven observers on slopes from Alaska to Chile. In addition to Stability Test results, observers noted whether slopes they felt were similar to their snowpit location had avalanches, or collapsing or cracking snowpacks, on that day. Results suggest that shear quality provides important Stability information, especially when Stability Test results appear to indicate relatively stable conditions, but the shear quality is rated Q1. This might be because Stability Test results are often spatially variable, while our experience indicates that shear quality is more homogeneous. Given these results, we believe formally integrating some description of shear characteristics into Stability assessments may be important for avalanche workers and backcountry enthusiasts.
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the stuffblock snow Stability Test comparability with the rutschblock usefulness in different snow climates and repeatability between observers
Cold Regions Science and Technology, 1999Co-Authors: Karl W Birkeland, Ron JohnsonAbstract:Abstract The stuffblock is a new snow Stability Test developed by the Gallatin National Forest Avalanche Center and used operationally since 1993. The Test involves stressing an isolated column of snow 0.30 m 2 by dropping a nylon sack filled with 4.5 kg onto the column from 0.10 m increments until weak layer failure occurs. Results over several winters correlate the stuffblock Test with the more widely used rutschblock Test, and validate the usefulness of the Test for evaluating snow Stability in several different climates. Further, the Test provides results that are consistent between observers, a favorable attribute for regional avalanche forecasting operations which use numerous observers.
Ahmed Elbeih - One of the best experts on this subject based on the ideXlab platform.
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a modified vacuum Stability Test in the study of initiation reactivity of nitramine explosives
Thermochimica Acta, 2017Co-Authors: Svatopluk Zeman, Ahmed Elbeih, Tamer Elshenawy, Ahmed K Hussein, Marcela JungovaAbstract:Abstract The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) in the first six hours of decomposition were measured by means of the Czech vacuum Stability Test, STABIL. The PBXs were filled by RDX (1,3,5-trinitro-1,3,5-triazinane), β−HMX (β−1,3,5,7-tetranitro-1,3,5,7-tetrazocane), BCHMX and ϵ-CL20 (ϵ-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, ϵ-HNIW) and, in one case, on a mixture of BCHMX and 3-nitro-1,2,4-triazol-5-one (NTO), in a 1:1 wt. ratio. These nitramines were bonded by 9% by wt. of softened polyisobutylene matrix, 13% by wt. of softened polystyrene-butadiene matrix, 18% by wt. of crosslinked hydroxyl-terminated polybutadiene, 12% by wt. of polydimethylsiloxane and by 40% of TNT. The relationships of specific rate constants with experimental detonation velocities, impact and friction sensitivities of these PBXs are shown and discussed. It is postulated that this approach provides results which are applicable to studies of initiation reactivity of energetic materials and which are fully comparable with those of other methods of investigation in this area.
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application of vacuum Stability Test to determine thermal decomposition kinetics of nitramines bonded by polyurethane matrix
Acta Astronautica, 2017Co-Authors: Ahmed Elbeih, Mohamed Abdelghany, Tamer ElshenawyAbstract:Abstract Vacuum Stability Test (VST) is mainly used to study compatibility and Stability of energetic materials. In this work, VST has been investigated to study thermal decomposition kinetics of four cyclic nitramines, 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, CL-20), bonded by polyurethane matrix based on hydroxyl terminated polybutadiene (HTPB). Model fitting and model free (isoconversional) methods have been applied to determine the decomposition kinetics from VST results. For comparison, the decomposition kinetics were determined isothermally by ignition delay technique and non-isothermally by Advanced Kinetics and Technology Solution (AKTS) software. The activation energies for thermolysis obtained by isoconversional method based on VST technique of RDX/HTPB, HMX/HTPB, BCHMX/HTPB and CL20/HTPB were 157.1, 203.1, 190.0 and 176.8 kJ mol−1 respectively. Model fitting method proved that the mechanism of thermal decomposition of BCHMX/HTPB is controlled by the nucleation model while all the other studied PBXs are controlled by the diffusion models. A linear relationship between the ignition temperatures and the activation energies was observed. BCHMX/HTPB is interesting new PBX in the research stage.
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note on the use of the vacuum Stability Test in the study of initiation reactivity of attractive cyclic nitramines in formex p1 matrix
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Svatopluk Zeman, Ahmed Elbeih, Qilong YanAbstract:The zero-order reaction rates (specific rate constants) for isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum Stability Test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d] imidazole (BCHMX), and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, e-CL-20) with 9 wt.% of the C4 type matrix, i.e., a matrix containing 25 wt.% of polyisobutylene, 59 wt.% of dioctyl sebacate and 16 wt.% of the oil HM46. Dependencies were found between the specific rate constants mentioned and the detonation velocities of the PBXs, and consequently between these constants and the impact of pure explosive fillers, i.e., RDX, β-HMX, e-HNIW, RS-e-HNIW, and BCHMX and, at the same time, the corresponding PBXs. The results obtained are compared with those from a recent analogous study of PBXs using an SBR (Formex P1) binder which could increase the PBXs’ reactivity in comparison with C4 matrix. These results also help to dispel a widely held view about HNIW being a relatively sensitive explosive.
Rifat Sipahi - One of the best experts on this subject based on the ideXlab platform.
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delay independent Stability Test for systems with multiple time delays
IEEE Transactions on Automatic Control, 2012Co-Authors: Ismail Ilker Delice, Rifat SipahiAbstract:Delay-independent Stability (DIS) of a general class of linear time-invariant (LTI) multiple time-delay system (MTDS) is investigated in the entire delay-parameter space. Stability of such systems may be lost only if their spectrum lies on the imaginary axis for some delays. We build an analytical approach that requires the inspection of the roots of finite number of single-variable polynomials in order to detect if the spectrum ever lies on the imaginary axis for some delays, excluding infinite delays. The approach enables to Test the necessary and sufficient conditions of DIS of LTI-MTDS, technically known as weak DIS, as well as the robust Stability of single-delay systems against all variations in delay ratios. The proposed approach, which does not require any parameter sweeping and graphical display, becomes possible by establishing a link between the infinite spectrum and algebraic geometry. Case studies are provided to show the effectiveness of the approach.
Tamer Elshenawy - One of the best experts on this subject based on the ideXlab platform.
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a modified vacuum Stability Test in the study of initiation reactivity of nitramine explosives
Thermochimica Acta, 2017Co-Authors: Svatopluk Zeman, Ahmed Elbeih, Tamer Elshenawy, Ahmed K Hussein, Marcela JungovaAbstract:Abstract The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) in the first six hours of decomposition were measured by means of the Czech vacuum Stability Test, STABIL. The PBXs were filled by RDX (1,3,5-trinitro-1,3,5-triazinane), β−HMX (β−1,3,5,7-tetranitro-1,3,5,7-tetrazocane), BCHMX and ϵ-CL20 (ϵ-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, ϵ-HNIW) and, in one case, on a mixture of BCHMX and 3-nitro-1,2,4-triazol-5-one (NTO), in a 1:1 wt. ratio. These nitramines were bonded by 9% by wt. of softened polyisobutylene matrix, 13% by wt. of softened polystyrene-butadiene matrix, 18% by wt. of crosslinked hydroxyl-terminated polybutadiene, 12% by wt. of polydimethylsiloxane and by 40% of TNT. The relationships of specific rate constants with experimental detonation velocities, impact and friction sensitivities of these PBXs are shown and discussed. It is postulated that this approach provides results which are applicable to studies of initiation reactivity of energetic materials and which are fully comparable with those of other methods of investigation in this area.
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application of vacuum Stability Test to determine thermal decomposition kinetics of nitramines bonded by polyurethane matrix
Acta Astronautica, 2017Co-Authors: Ahmed Elbeih, Mohamed Abdelghany, Tamer ElshenawyAbstract:Abstract Vacuum Stability Test (VST) is mainly used to study compatibility and Stability of energetic materials. In this work, VST has been investigated to study thermal decomposition kinetics of four cyclic nitramines, 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, CL-20), bonded by polyurethane matrix based on hydroxyl terminated polybutadiene (HTPB). Model fitting and model free (isoconversional) methods have been applied to determine the decomposition kinetics from VST results. For comparison, the decomposition kinetics were determined isothermally by ignition delay technique and non-isothermally by Advanced Kinetics and Technology Solution (AKTS) software. The activation energies for thermolysis obtained by isoconversional method based on VST technique of RDX/HTPB, HMX/HTPB, BCHMX/HTPB and CL20/HTPB were 157.1, 203.1, 190.0 and 176.8 kJ mol−1 respectively. Model fitting method proved that the mechanism of thermal decomposition of BCHMX/HTPB is controlled by the nucleation model while all the other studied PBXs are controlled by the diffusion models. A linear relationship between the ignition temperatures and the activation energies was observed. BCHMX/HTPB is interesting new PBX in the research stage.
