Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

Small scale characterization experiments using only 1–5 g of a baseline ammonium nitrate plus fuel oil (ANFO) explosive are discussed and simulated using an ignition and growth reactive flow model. There exists a strong need for the small scale characterization of non-ideal explosives in order to adequately survey the wide parameter space in sample composition, density, and microstructure of these materials. However, it is largely unknown in the scientific community whether any useful or meaningful result may be obtained from detonation failure, and whether a minimum sample size or level of confinement exists for the experiments. In this work, it is shown that the parameters of an ignition and growth rate law may be calibrated using the small scale data, which is obtained from a 35 GHz microwave interferometer. Calibration is feasible when the samples are heavily confined and overdriven; this conclusion is supported with detailed simulation output, including pressure and reaction contours inside the ANFO samples. The resulting shock wavevelocity is most likely a combined chemical-mechanical response, and simulations of these experiments require an accurate unreacted equation of state (EOS) in addition to the calibrated reaction rate. Other experiments are proposed to gain further insight into the detonation failure data, as well as to help discriminate between the role of the EOS and reaction rate in predicting the measured outcome

The Influence of Thermal Damage and Phase Transition on Impact and Shock Sensitivity in HMX Systems

Information on the sensitivity of explosives is highly valuable, and the short time scales in which chemical reactions occur in explosives, along with the ability of microstructure to have significant effects on sensitivity, often make this information difficult and expensive to acquire and interpret. Significant changes in impact and shock sensitivity are expected as a result of inducing structural damage in an explosive sample, and thermally damaged HMXbased samples can incur a solid-solid phase transition from β → δ with non-extreme thermal inputs. Changes in sensitivity due to this phase transition, as well as the simultaneously induced damage, and their relative influence on sensitivity, are of interest to determine experimentally. Drop-weight impact tests are a commonly used measure of explosive impact sensitivity. Often, simply the L50 of a given material is reported and compared with that of other materials to give a sense of its impact sensitivity. The practice of reporting the impact sensitivity as a single number, the L50, is likely inadequate. It is important to additionally report a measure of the spread of the distribution of reaction probabilities in order to assess the hazard of reaction in situations that may induce a stimulus level well below the L50 of a material. Additionally, multiple distribution forms have been suggested previously for fitting of binary sensitivity data; these distributions typically deviate from each other most near the tails (low and high stimulus levels). The consequences of choosing one distribution form over another in the analysis of explosive drop-weight impact results is explored. Changes in impact sensitivity due to phase change have received some previous exploration, though the phase change influence is generally conflated with the induced damage upon said phase transition; however, sensitivity changes in the shock regime due to β → δ phase change have received little attention. Work is shown which includes methods to isolate variables of HMX phase transition and damage typically incurred upon said phase transition

A Novel Method for Quantifying The Sensitivity of a Non-Ideal Explosive

High costs and safety risks are incurred when large-scale characterization tests on non-ideal explosives are performed, and may not be feasible with some explosives due to the lack of available material required to sustain a steady detonation. The physics governing a detonation failure event, which will occur if the diameter of an explosive charge is below the critical diameter, and it\u27s relationship to mechanisms of initiation have not been fully explored. An understanding of this relationship may increase the ability to predict the behavior of explosives using only a few grams per test of the given material for characterization. Here, experiments in which detonation failure in non-ideal ammonium nitrate based explosives occur are observed in order to explore the relationship between rate of failure and the shock sensitivity of an explosive. Microwave interferometry is used to measure the rate of detonation failure in AN-based explosives doped with various sizes of aluminum particles or solid glass beads, and it is observed that the rate of detonation failure has a relationship with aluminum particle size. The size of glass beads at this mixture ratio appears to have no eect on the rate of detonation failure, and it is concluded that the contribution of aluminum to the failing reaction wave is chemically dominated

An analysis of the differences in the acute hospitalization charges following minimally invasive versus open posterior lumbar interbody fusion Presented at the 2009 Joint Spine Section Meeting Clinical article

Object. Minimally invasive spine (MIS) procedures are increasingly being recognized as equivalent to open procedures with regard to clinical and radiographic outcomes. These techniques are also believed to result in less pain and disability in the immediate postoperative period. There are, however, little data to assess whether these procedures produce their intended result and even fewer objective data to demonstrate that they are cost effective when compared with open surgery. Methods. The authors performed a retrospective analysis of hospital charges for 1- and 2-level MIS and open posterior interbody fusion for lumbar spondylotic disease, disc degeneration, and spondylolisthesis treated at a single academic medical center. Patients presenting with bilateral neurological symptoms were treated with open surgery, and those with unilateral symptoms were treated with MIS. Overall hospital charges and surgical episode related charges, length of stay (LOS), and discharge status were obtained from the hospital finance department and adjusted for multi-/single-level surgeries. Results. During a 14-month period, 74 patients (mean age 55 years) were treated. The series included 59 single-level operations (75% MIS and 25% open), and 15 2-level surgeries (53% MIS and 47% open). The demographic profile, including age and Charlson Comorbidity Index, were similar between the 4 groups. The mean LOS for patients undergoing single-level surgery was 3.9 and 4.8 days in the MIS and open cases, respectively (p = 0.017). For those undergoing 2-level surgery, the mean LOS was 5.1 for MIS versus 7.1 for open surgery (p = 0.259). With respect to hospital charges, single-level MIS procedures were associated with an average of $70,159 compared with$78,444 for open surgery (p = 0.027). For 2-level surgery, mean charges totalled $87,454 for MIS versus$108,843 for open surgery (p = 0.071). For single-level surgeries, 5 and 20% of patients undergoing MIS and open surgery, respectively, were discharged to inpatient rehabilitation. For 2-level surgeries, the rates were 13 and 29%, respectively. Conclusions. While hospital setting, treatment population, patient selection, and physician expectation play major roles in determining hospital charges and LOS, this pilot study at an academic teaching hospital shows trends for quicker discharge, reduced hospital charges, and lower transfer rates to inpatient rehabilitation with MIS. However, larger multicenter studies are necessary to validate these findings and their relevance across diverse US practice environments. (DOI: 10.3171/2009.12.SPINE09621

A comparison of complications and clinical and radiologic outcome between the mini-open prepsoas and mini-open transpsoas approaches for lumbar interbody fusion: a meta-analysis

STUDY DESIGN: Systematic review and meta-analysis. OBJECTIVE: To compare complication rates and clinical and radiologic outcome between the mini-open prepsoas and mini-open transpsoas approaches for lateral lumbar interbody fusion. SUMMARY OF BACKGROUND DATA: Both approaches are believed to be safe with similar complication rates. Previous studies suggest that the rate of neurological injury might be higher in the transpsoas group, whereas visceral or vascular injury might be more frequent in the prepsoas group. METHODS: A systematic review of the literature was performed. Data were extracted from original publications up until December 26, 2018. Evidence was extracted from well-designed case-control or cohort studies and sorted in 2 groups, the prepsoas and transpsoas approaches. A meta-analysis was performed using a random-effects model (I statistic >50% for all analyses). RESULTS: A total of 115 studies included data of 13,260 patients, 2450 in the prepsoas group and 10,810 in the transpsoas group. Demographics for prepsoas versus transpsoas group were (N-weighted means): age 61.9 versus 60.9 years; %female sex 53% versus 63%, levels fused 1.4 versus 2.6, blood loss 52.4 versus 122.3 mL, and operating time 125.1 versus 200.7 min. The following statistically significant differences in complication rates between prepsoas and transpsoas approaches were found: transient psoas weakness or thigh/groin numbness 4% versus 26% [95% confidence interval (CI): 11%-17%], motor neural injury 0.4% versus 1.3% (95% CI: 16%-62.3%); no statistically significant differences were found for: major vascular injury 2% versus 1% (95% CI: 1.04%-2.31%), kidney or ureter injury 0.04% versus 0.08% (95% CI: 0.057%-5.2%), injury pleural/peritoneal structures 0.6% versus 0.2% (95% CI: 0.89%-6.58%), cage subsidence 5% versus 4% (95% CI: 0.9%-1.97%), surgical site infection 1% versus 1% (95% CI: 0.57%-1.66%), abdominal wall pseudohernia 1% versus 1% (95% CI: 0.07%-21.22%), sympathetic chain injury 5% versus 0% (95% CI: 0.34%-97.86%), and directly procedure-related death 0.04% versus 0% (95% CI: 0.127%-76.8%). Pooled mean perioperative changes between prepsoas and transpsoas approaches were: segmental sagittal Cobb angle 3.07 versus 1.99 degrees; foraminal height 2 versus 6.96 mm. CONCLUSIONS: The prepsoas had fewer complications than the transpsoas approach. Furthermore, the prepsoas approach showed superior restoration of segmental lordosis, whereas foraminal height restoration was superior with the transpsoas approach. This could be explained by the differences in location of the interbody device placement in relation to the center of rotation of the spine between the 2 surgical techniques