The non-isothermal gravimetric method for study the thermal decomposition kinetic of HNBB and HNS explosives

The hexanitrostilben (HNS) is a thermally stable explosive that can be prepared from hexanitrobibenzyl (HNBB). Therefore, the investigation of thermal stability of HNBB can be important in the yield of preparation of HNS. The decomposition kinetic of HNBB and HNS are studied by non-isothermal gravimetric method. The TG/DTG curves in non-isothermal method are obtained in range of 25°C–400 °C at heating rates of 3 °C/min, 5 °C/min, 8 °C/min, 10 °C/min and 12 °C/min. The data of weight-temperature are used for calculation of activation energy (E_a) of thermal decomposition reactions by methods of Ozawa, Kissinger, Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) as model-free methods and Strink's equation as model-fitting method. The compensation effect is used for prediction of mechanism and determination of pre-exponential factor (lnA) of the decomposition reaction. A reduction 60 kj/mol for the average of activation energy of thermal decomposition reaction of HNBB is obtained versus HNS. This result shows the lower thermal stability of HNBB in comparison to HNS. The Avrami equation (A_3/2) with function f(α) = 3/2(1-α)[-ln(1-α)]^1/3 indicates the predicted mechanism for thermal decomposition reaction both explosives.     

Tuning the reactivity of Al–Ni by fine coating of halogen-containing energetic composites

In this paper, various core-shell structured Al–Ni@ECs composites have been prepared by a spray-drying technique. The involved ECs refer to the energetic composites (ECs) of ammonium perchlorate/nitrocellulose (AP/NC, NA) and polyvinylidene fluoride/hexanitrohexaazaisowurtzitane (PVDF/CL-20, PC). Two Al–Ni mixtures were prepared at atomic ratios of 1:1 and 1:3 and named as Al/Ni and Al/3Ni, respectively. The thermal reactivity and combustion behaviors of Al–Ni@ECs composites have been comprehensively investigated. Results showed that the reactivity and combustion performance of Al–Ni could be enhanced by introducing both NA and PC energetic composites. Among which the Al/Ni@NA composite exhibited higher reactivity and improved combustion performance. The measured flame propagation rate (v = 20.6 mm/s), average combustion wave temperature (T_max = 1567.0 °C) and maximum temperature rise rate (γ_t = 1633.6 °C/s) of Al/Ni@NA are higher than that of the Al/Ni (v = 15.8 mm/s, T_max = 858.0 °C, and γ_t = 143.5 °C/s). The enhancement in combustion properties could be due to presence of the acidic gaseous products from ECs, which could etch the Al₂O₃ shell on the surface of Al particles, and make the inner active Al to be easier transported, so that an intimate and faster intermetallic reaction between Al and Ni would be realized. Furthermore, the morphologies and chemical compositions of the condensed combustion products (CCPs) of Al–Ni@ECs composites were found to be different depending on the types of ECs. The compositions of CCPs are dominated with the Al–Ni intermetallics, combining with a trace amount of Al₅O₆N and Al₂O₃.     

A decomposable transshipment algorithm for a multiperiod transportation problem

A dynamic version of the transportation (Hitchcock) problem occurs when there are demands at each of n sinks for T periods which can be fulfilled by shipments from m sources. A requirement in period t₂ can be satisfied by a shipment in the same period (a linear shipping cost is incurred) or by a shipment in period t₁ < t₂ (in addition to the linear shipping cost a linear inventory cost is incurred for every period in which the commodity is stored). A well known method for solving this problem is to transform it into an equivalent single period transportation problem with mT sources and nT sinks. Our approach treats the model as a transshipment problem consisting of T, m source — n sink transportation problems linked together by inventory variables. Storage requirements are proportional to T² for the single period equivalent transportation algorithm, proportional to T, for our algorithm without decomposition, and independent of T for our algorithm with decomposition. This storage saving feature enables much larger problems to be solved than were previously possible. Futhermore, we can easily incorporate upper bounds on inventories. This is not possible in the single period transportation equivalent.     

Insensitive energetic microspheres DAAF/RDX fabricated by facile molecular self-assembly

Insensitive energetic materials are promising in the defense weapons field. However, energetic materials still suffer from great challenges and the concern about their safety limits their utilization. In this work, insensitive energetic explosive 3,3′-diamino-4,4′-azoxyfurazan/hexahydro-1,3,5-trinitro-1,3,5-triazine (DAAF/RDX) microspheres were fabricated by self-assembly method. Rod-like DAAF/RDX was prepared by mechanical ball milling for comparison. DAAF/RDX composites with different mass ratios (90:10, 80:20, and 70:30) were obtained. The morphologies and structures of as-obtained DAAF/RDX composites were characterized by scanning electron microscopy (SEM), powder x-ray diffraction (PXRD) and fourier transform infrared spectroscopy (FT-IR). The results showed that DAAF/RDX microspheres exhibited regular shaped microspheres with sizes from 0.5 to 1.2 μm. There was no crystal transition during the modification process. The thermal properties of as-obtained materials were then evaluated by differential scanning calorimetry (DSC) and materials studio software. DAAF/RDX microspheres showed an advanced decomposition peak temperature compared with rod-like DAAF/RDX. The binding energy and peak temperature values at zero β_i (T_P0) of DAAF/RDX (90:10) increased by 36.77 kJ/mol, 1.6 °C, and 58.11 kJ/mol, 12.3 °C compared to DAAF/RDX (80:20) and DAAF/RDX (70:30), indicating the better thermal stability of DAAF/RDX (90:10). The characteristic drop height (H₅₀) of DAAF/RDX (higher than 100 cm) composites was higher than that of raw RDX (25 cm), suggesting significant improvements in mechanical safety. The preparation of DAAF/RDX microspheres is promising for the desensitization of RDX and useful for the formation of other materials and future wide applications.     

On the first time a separately maintained parallel system has been down for a fixed time

Consider a system consisting of n separately maintained independent components where the components alternate between intervals in which they are “up” and in which they are “down”. When the i^th component goes up [down] then, independent of the past, it remains up [down] for a random length of time, having distribution F_i[G_i], and then goes down [up]. We say that component i is failed at time t if it has been “down” at all time points s ?[t-A.t]: otherwise it is said to be working. Thus, a component is failed if it is down and has been down for the previous A time units. Assuming that all components initially start “up,” let T denote the first time they are all failed, at which point we say the system is failed. We obtain the moment-generating function of T when n = l, for general F and G, thus generalizing previous results which assumed that at least one of these distributions be exponential. In addition, we present a condition under which T is an NBU (new better than used) random variable. Finally we assume that all the up and down distributions F_i and G_i i = l,….n, are exponential, and we obtain an exact expression for E(T) for general n; in addition we obtain bounds for all higher moments of T by showing that T is NBU.     

A new look on the electric spark sensitivity of nitramines

Electric spark energy, E_ES, for a 50% probability of initiation of the 14 nitramines was determined using a measuring instrument in which the electrodes are in direct contact with the sample. Indirectly proportional relationships were established between the logarithm of the E_ES values and the length of the longest N–N bond in the nitramine molecule. This finding is compatible with the mechanism of the first step in the electro-reduction of the nitramine grouping. Directly proportional relationships were found to exist between the E_ES values and the crystal lattice free volumes, ΔV (i.e. an increase in the ΔV values increases the nitramine's resistance to electric sparks) but there were several nitramines with the opposite course of this relationship. Also a semilogarithic relationships between the E_ES values and a ratio of intrinsic volumes of molecule, V_int, to the ΔV values were described as well as ambiguous linear dependence between these energies and a sum of the positive and negative extremes of the molecular surface electrostatic potentials, V_S,Σ. Several nitramines studied (always the same ones) display roughly the same distribution in the coordinate systems of relationships with lengths of the longest N–N bonds, the V_int/ΔV ratio and the sum V_S,Σ as the independent variables. It was found that, typically, such relationships start from a single identical point, in effect a point corresponding to data for a structural unit from which the studied nitramines can be hypothetically generated, and/or are converging on another point, often the one corresponding to the data for HNIW. All the findings point to a fundamental influence of the intermolecular forces on reactivity of nitramines exposed to electric sparks.     

An integral equation for the second moment function of a geometric process and its numerical solution

In this article, an integral equation satisfied by the second moment function M₂(t) of a geometric process is obtained. The numerical method based on the trapezoidal integration rule proposed by Tang and Lam for the geometric function M(t) is adapted to solve this integral equation. To illustrate the numerical method, the first interarrival time is assumed to be one of four common lifetime distributions, namely, exponential, gamma, Weibull, and lognormal. In addition to this method, a power series expansion is derived using the integral equation for the second moment function M₂(t), when the first interarrival time has an exponential distribution.     

Burning characteristics of high density foamed GAP/CL-20 propellants

The monolithic foamed propellants with high densities were prepared by casting and two-step foaming processes. Glycidyl azide polymer (GAP) and isocyanate were used as the binder system and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, CL-20) was employed as the energetic component. The newly designed formulation containing 60 % CL-20 produced a force constant of 1077 J/g and low flame temperature of 2817 K. Two foamed propellants with densities of 1.32 g/cm³ and 1.53 g/cm³ were fabricated by a confined foaming process and examined by closed bomb tests. The results revealed that porosity significantly affects burning performance. A size effect on combustion behaviors was observed for the foamed propellant with 5.56 % porosity, and a double-hump progressive dynamic vivacity curve was obtained. At last, the 30 mm gun test was carried out to demonstrate the interior ballistic performance, and the muzzle velocity increased by 120 m/s at the same maximum chamber pressure when monolithic propellant was added in the charge.     

Nonlinear one-parametric linear programming and t-norm transportation problems

Previous methods for solving the nonlinear one-parametric linear programming problem min {c(t)^Tx |Ax = b, x ≥ 0} for t ? [α,β] were based on the simplex method using a considerably extended tableau. The proposed method avoids such an extension. A finite sequence of feasible bases (B^k | k = 1, 2, …, r) optimal in [t^k, t^k+1] for k = 1, 2, …,^r with α = t¹ < t² < … < t^r+1 = β is determined using the zeroes of a set of nonlinear functions. Computational experience is discussed in the special case of t-norm transportation problems.     

Stochastic control of queueing systems

Suppose that the state of a queueing system is described by a Markov process { Y_t, t ≥ 0}, and the profit from operating it up to a time t is given by the function f(Y_t). We operate the system up to a time T, where the random variable T is a stopping time for the process Yt. Optimal stochastic control is achieved by choosing the stopping time T that maximizes Ef(Y_T) over a given class of stopping times. In this paper a theory of stochastic control is developed for a single server queue with Poisson arrivals and general service times.     

Peak rate of occurrence of a poisson process

Suppose that a nonhomogeneous Poisson process is observed for a length of time T, say Let λ (t) denote the mean value function of the process. It is assumed that λ (t) is first increasing then decreasing inside the interval (0, T) with peak at t = t₀, say. Three methods are given for estimating to. One of these methods is nonparametric, and the other two methods are based on the standard regression technique and the maximum likelihood principle The given resull has application in a problem of determining the azimuth of a target from the radar-impulse data. The time series of incoming signals may be approximated by the occurrence of a nonhomogeneous Poisson process with mean value function λ (t). The azimuth of the target is reasonably determined from the direction of the axis of the radar beam at the instant to, corresponding to the peak value of λ (t).     

Fullerene bisadduct stabilizers: The effect of different addition positions on inhibiting the autocatalytic decomposition of nitrocellulose absorbed nitroglycerin

To explore the effect of different positions and number of pyrrolidine bound to the carbon cage on the stabilization effect of fulleropyrrolidine derivatives to nitrocellulose (NC)/nitroglycerine (NG), we synthesized N-(4-methoxy) phenylpyrrolidine-C₆₀ and four different of bis(N-(4-methoxy) phenylpyrrolidine)-C₆₀ compounds through Prato reaction. Their structures were characterized by UV–vis, ¹H NMR, ¹³C NMR, high-resolution mass spectroscopy, and single-crystal X-ray diffraction. Their stabilization effect to NC/NG were investigated using differential scanning calorimetry, methyl violet, vacuum stabilization effect, weight loss, and accelerating rate calorimeter tests. The results indicated these compounds had excellent stabilization effect to NC/NG. The stabilization effect of the fulleropyrrolidine bisadducts to NC/NG is significantly better than that of fulleropyrrolidine monoadduct and C₆₀. Moreover, the position where pyrrolidine binds to fullerene in fulleropyrrolidine bisadducts is different, and its stabilization effect to NC is also different. The stabilization effect order of different bisadduct isomers to nitrocellulose is as follows: e-edge > trans-2> cis-2> trans-3. Electron paramagnetic resonance (EPR) and FT-IR were used to study the stabilization mechanism of fulleropyrrolidine derivatives to NC/NG. The EPR results also show that fulleropyrrolidine bisadducts with different addition sites have different abilities to absorb nitroxide, and their ability is better than that of the monoadduct and C₆₀, which is consistent with the results of stabilization effect performance test.     

A note on a prediction interval for a first-order Gauss Markov process

Let X_t, t = 1,2, ?, be a stationary Gaussian Markov process with E(X_t) = μ and Cov(X_t, X_t+k) = σ²ρ^k. We derive a prediction interval for X_2n+1 based on the preceding 2n observations X₁,X₂, ?,X_2n.     

Steady-state analysis of load balancing with Coxian-2 distributed service times

This paper studies load balancing for many-server (N servers) systems. Each server has a buffer of size b ? 1, and can have at most one job in service and b ? 1 jobs in the buffer. The service time of a job follows the Coxian-2 distribution. We focus on steady-state performance of load balancing policies in the heavy traffic regime such that the normalized load of system is λ = 1 ? N^?α for 0 < α < 0.5. We identify a set of policies that achieve asymptotic zero waiting. The set of policies include several classical policies such as join-the-shortest-queue (JSQ), join-the-idle-queue (JIQ), idle-one-first (I1F) and power-of-d-choices (Po d) with d = O(N^α log N). The proof of the main result is based on Stein's method and state space collapse. A key technical contribution of this paper is the iterative state space collapse approach that leads to a simple generator approximation when applying Stein's method.     

Application of renewal theory to continuous sampling plans

Renewal theory is used to study the effectiveness of a class of continuous sampling plans first introduced by Dodge. This approach provides a simple way of viewing and computing the long-run Average Outgoing Quality (AOQ) and its maximum AOQL. More importantly, it is used to study the average outgoing quality in a short production run through an approximation formula AOQ^*(t). Formulas for AOQ and AOQ^*(t) are provided. By simulation, it is found that AOQ^*(t) is sufficiently accurate in situations corresponding to actual practice.     

Thermal decomposition of ammonium perchlorate catalyzed with CuO nanoparticles

Ammonium perchlorate (APC) is the most common oxidizer in use for solid rocket propulsion systems. However its initial thermal decomposition is an endothermic process that requires 102.5 J·g⁻¹. This manner involves high activation energy and could render high burning rate regime. This study reports on the sustainable fabrication of CuO nanoparticles as a novel catalyzing agent for APC oxidizer. Colloidal CuO nanoparticles with consistent product quality were fabricated by using hydrothermal processing. TEM micrographs demonstrated mono-dispersed particles of 15 nm particle size. XRD diffractogram demonstrated highly crystalline material. The synthesized colloidal CuO particles were effectively coated with APC particles via co-precipitation by using fast-crash solvent–antisolvent technique. The impact of copper oxide particles on APC thermal behavior has been investigated using DSC and TGA techniques. APC demonstrated an initial endothermic decomposition stage at 242 °C with subsequent two exothermic decomposition stages at 297.8 °C and 452.8 °C respectively. At 1 wt%, copper oxide offered decrease in initial endothermic decomposition stage by 30%. The main outcome of this study is that the two main exothermic decomposition peaks were merged into one single peak with an increase in total heat release by 53%. These novel features can inherit copper oxide particles unique catalyzing ability for advanced highly energetic systems.     

Maximum matching in a convex bipartite graph

A special matching problem arising in industry is shown to be solvable by an algorithm of the form: match objects a_i and b_j if they satisfy a local optirnality criterion based on a ranking of currently unmatched objects. When no a_i and b_i remain that can be matched, the largest number of acceptable matches has been found.     

Readiness and the optimal redeployment of resources

This paper considers the problem of the optimal redeployment of a resource among different geographical locations. Initially, it is assumed that at each location i, i = 1,…, n, the level of availability of the resource is given by a₁ ≧ 0. At time t > 0, requirements R_f(t) ≧ 0 are imposed on each location which, in general, will differ from the a₁. The resource can be transported from any one location to any other in magnitudes which will depend on t and the distance between these locations. It is assumed that ΣR_j > Σa_t The objective function consideis, in addition to transportation costs incurred by reallocation, the degree to which the resource availabilities after redeployment differ from the requirements. We shall associate the unavailabilities at the locations with the unreadiness of the system and discuss the optimal redeployment in terms of the minimization of the following functional forms: \documentclass{article}\pagestyle{empty}\begin{document}$ \sum\limits_{j = 1}^n {kj(Rj - yj) + } $\end{document} transportation costs, Max \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {Max}\limits_j \,[kj(Rj - yj)] + $\end{document} transportation costs, and \documentclass{article}\pagestyle{empty}\begin{document}$ \sum\limits_{j = 1}^n {kj(Rj - yj)^2 + } $\end{document} transportation costs. The variables y_j represent the final amount of the resource available at location j. No benefits are assumed to accrue at any location if y_j > R_j. A numerical three location example is given and solved for the linear objective.     

On the conditional residual lifetime of coherent systems under double regularly checking

In this paper, we consider a coherent system with n independent and identically distributed components under the condition that the system is monitored at time instances t₁ and t₂ (t₁ < t₂). First, various mixture representations for reliability function of the conditional residual lifetime of the coherent system are derived under different scenarios at times t₁ and t₂ (t₁ < t₂). Several stochastic comparisons between two systems are also made based on the proposed conditional random variables. Then, we consider the conditional residual lifetime of the functioning components of the system given that j components have failed at time t₁ and the system has failed at time t₂. Some stochastic comparisons on the proposed conditional residual lifetimes are investigated. Several illustrative graphs and examples are also provided.     

对高温超导层状特性的解释

基于高温超导材料结构的准二维性,建立了高温超导的层状理论,得到了高温超导材料的临界温度Tc与Cu-O面数l间的关系,指出高物质密度N_i~0和高电子密度N_e~0的超导材料可能有更高的Tc。