Study of Methane Explosion Suppression Characteristics of N2 and CO2 in Variable Cross-Section Ducts.

To investigate the effect of concentration of N2 and CO2 (0, 10, 20, 30, 40, and 50%) on the flame propagation characteristics of CH4/air premixed gases with stoichiometric ratios in variable cross-section ducts, experiments were conducted in four combinations of ducts at initial conditions of 298 K and 1 atm. The results show that the flame propagation velocity, propagation time, and overpressure are greater in the suddenly contracted duct than in the suddenly expanded duct if the dimensions of the ducts are kept constant. However, an increase in inert gas concentration leads to a decrease in flame propagation speed, an increase in flame propagation time, and changes in flame structure and pressure. "Tulip" flames appeared when a duct with a cross section of 100 mm × 100 mm was combined with a duct with a cross section of 70 mm × 70 mm, whether N2 or CO2 was added or what its concentration was. However, when a duct with a cross section of 140 mm × 140 mm was combined with a 70 mm × 70 mm duct, a "tulip" flame is formed only at a CO2 concentration of 50%. As the concentration of inert gas increases, the explosion pressure first decreases and then stabilizes, while the rate of pressure increase showed a monotonically decreasing trend. The explosion pressure is minimized when the concentration of CO2 and N2 is 30 and 40%, respectively.

Effect of Abrupt Changes in the Cross-Sectional Area of a Pipe on Flame Propagation Characteristics of CH4/Air Mixtures.

To study the flame propagation characteristics of methane/air premixed gas in the pipeline with a sudden change of the pipe cross-sectional area, six kinds of customized pipes are used to study the methane/air premixed gas with a concentration of 9.5%. The results show that when the initial smooth flame front encounters an abrupt change in the cross-sectional area, the flame front becomes disordered and a turbulent flame is formed. A greater change in the cross-sectional area results in more severe flame turbulence. Compared with larger cross-section pipes set at the ignition end and downstream end, when the large cross-sectional area pipe is set in the middle of the pipe, the flame propagation process receives the secondary mutation induction effect of the abrupt cross section and the turbulence effect is stronger. The maximum propagation velocity and pressure are observed in configuration with the larger pipe in the middle of the pipe network. Moreover, when the cross-sectional area of this larger pipe increases, the flame is more substantially influenced by longitudinal expansion, the maximum propagation velocity and maximum overpressure increase accordingly, and the pressure oscillations are more obvious.

Experimental study on the effects of chemical composite additive on the microscopic characteristics of spontaneous combustion coal.

In order to study the effects of chemical composite additive (CCA) on the microscopic characteristics of spontaneous combustion coal, atomic force microscope and Fourier transform infrared spectroscopy technology were used to study the microstructure and active groups of spontaneous combustion coal. The roughness, three-dimensional surface morphology, microscopic pore structure, infrared spectrum, and active group content of raw coal samples and coal samples treated with water or different concentrations of CCA were analyzed. The experimental results showed that compared with the raw coal, the roughness Rq and Ra of the CCA-treated coal samples decreased with increasing CCA concentration, and the surface topography of the microscopic structure tended to be flat and smooth, and the size becomes smaller and the depth becomes shallow of pore. In the raw coal samples and coal samples treated with water and CCA, the main types of active groups remained constant. However, the contents of these groups changed, and the order of the contents of main types of active groups is water-treated > raw coal (untreated) > CCA-1% treated > CCA-5% treated > CCA-10% treated > CCA-20% treated. In addition, the mechanism of the CCA inhibition of coal spontaneous combustion was discussed and analyzed.

Effect of blockage ratios on the characteristics of methane/air explosion suppressed by BC powder.

To investigate the effect of blockage ratios on the explosion suppression by powder suppressant, an experimental study was performed to suppress the methane-air explosion in a 5L duct with different blockage ratios and various concentrations of BC dry powder. The results indicate that flames experienced both the spherical and finger-shaped stages. Furthermore, the smoothness of flame front initially decreased and then increased. Flame propagation velocities were higher with larger blockage ratios except for φ = 1. The maximum peak overpressure (MPP) with the blockage ratio was slightly increased till φ reached 0.7 then surged sharply. The MPP decreased as the powder concentration increased. The maximum drop rate in the MPP being 34.8%-59.9%, depending on powder concentrations, occurred at the blockage ratio between 0.4 and 0.6. The result is ascribed to the competition between the suppression augmentation by the higher venting-generated turbulence and the suppression attenuation by the shorter residence time of the particle. However, the drop rate was relatively less promoted by increasing the concentration from 80 g/m3 to 240 g/m3. The inhibitor at higher concentration was less effective. An inhibition mechanism is explained by analogy to droplet group combustion, in which the decomposition regime of NaHCO3 differs at different concentrations.

Methane explosion suppression characteristics based on the NaHCO3/red-mud composite powders with core-shell structure.

The NaHCO3/red-mud (RM) composite powders were successfully prepared by the solvent-anti-solvent method for methane explosion suppression. The RM was used as a carrier, and the NaHCO3 was used as a loaded inhibitor. The NaHCO3/RM composite powders showed a special core-shell structure and excellent endothermic performance. The suppression properties of NaHCO3/RM composite for 9.5% CH4 explosion were tested in a 20L spherical explosion vessel and a 5L Perspex duct. The results showed that the NaHCO3/RM composite powders displayed a much better suppression property than the pure RM or NaHCO3 powders. The loading amount of NaHCO3 has an intensive influence on the inhibition property of NaHCO3/RM composite powders. The best loaded content of NaHCO3 is 35%. It exhibited significant inhibitory effect that the explosion max-pressure declined 44.9%, the max-pressure rise rate declined 96.3% and the pressure peak time delayed 366.7%, respectively.

Riemannian Variance Filtering: An Independent Filtering Scheme for Statistical Tests on Manifold-valued Data.

Performing large scale hypothesis testing on brain imaging data to identify group-wise differences (e.g., between healthy and diseased subjects) typically leads to a large number of tests (one per voxel). Multiple testing adjustment (or correction) is necessary to control false positives, which may lead to lower detection power in detecting true positives. Motivated by the use of so-called "independent filtering" techniques in statistics (for genomics applications), this paper investigates the use of independent filtering for manifold-valued data (e.g., Diffusion Tensor Imaging, Cauchy Deformation Tensors) which are broadly used in neuroimaging studies. Inspired by the concept of variance of a Riemannian Gaussian distribution, a type of non-specific data-dependent Riemannian variance filter is proposed. In practice, the filter will select a subset of the full set of voxels for performing the statistical test, leading to a more appropriate multiple testing correction. Our experiments on synthetic/simulated manifold-valued data show that the detection power is improved when the statistical tests are performed on the voxel locations that "pass" the filter. Given the broadening scope of applications where manifold-valued data are utilized, the scheme can serve as a general feature selection scheme.

[Histopathologic changes after tracheal reconstruction with a scraped partial mucosa jejunal autograft].

OBJECTIVE: To explore the histopathological changes of the new trachea reconstruction with a scraped partial mucosa jejunal autograft hy microscope and transmission electron microscope. METHOD: Eight canine models of extensive circumferential tracheal defects with revascularized jejuna combined with NiTi alloy mesh tube were established. Operations were performed on these dogs under general anesthesia by intravenous ketamine. A 6.5 cm length of segment of the jejunum was resected. The graft was prepared by scraping the partial mucosa with operating knife blade and dry gauze. During the resecting course, micro-vascular anastomoses were done between the mesenteric artery and the right common carotid artery,and the mesenteric vein with the right common carotid vein. The silicone intraluminal stent was placed in the lumen of the jejunal segment and was removed the fourth week after operation. A Ni-Ti alloy prothesis was placed over the jejunal segment, with the mesenteric vascular supply egressing through the longitudinal defect of the mesh tube. Then the free jejunum was used to reconstruct the tracheal defects. Biopsy were performed and recorded at the 1 at, 2nd, 3rd and 4th postoperative months. All specimens were observed by microscope and transmission electron microscope examinations. RESULT: Eight dogs postoperative all survived expected time. One month after operation, the tracheointestinal snastomosis showed smooth and was covered by continuous internal lining. The mucosa of the jejunum was slightly atrophied. Two months after operation, examination of the jejunal mucosa of the autografts demonstrated obviously thinned. The lumen of the reconstructed trachea was covered by squamous epithelium entirely at 3 months postoperatively. The partial squamous epithelium has transformed ciliated columnar epithelium at 4 months postoperatively. CONCLUSION: A free scraped partial jejunum reconstructed trachea can accelerated the atrophying process of mucous epithelization and promoted mucosal metaplasia of the jejunum. The reconstructed tracheal lumen has completely transformed squamous epithelium at 3 months postoperatively and partial squamous epithelium has transformed ciliated columnar epithelium at 4 months postoperatively.

[A case report with esophageal foreign body of muskmelon].

A male patient, 41 years old, swallowed a chunk of muskmelon because his attention was not centralized. Odynophagia and dysphagia were the two main clinical manifestations. The esophagus barium swallow examination showed a foreign body in the upper esophagus. The patient did the rigid esophagoscope examination in the operating room under general anesthesia. There was a chunk of muskmelon in the upper esophagus and could not take it out from the esophagus by using foreign body forceps because the muskmelon was very crisp. In the end the muskmelon was sent in the stomach. The patient's symptoms were alleviated after operation.

Benzyl 2-benzyl-4-[(3aS,7aR)-2,3,3a,4,5,6,7,7a-octa-hydro-1H-isoindol-2-yl]-4-oxobutano-ate.

In the title compound, C(26)H(31)NO(3), the octa-hydro-1H-isoindole ring is not planar and the two rings are twisted with a C-C-C-C torsion angle of 73.6 (4)°. The six-membered ring has a chair conformation while the five-membered ring has an envelope conformation on the C-atom in position 7a. The H atoms in the 3a- and 7a-psitions are cis and the H-C-C-H torsion angle is 42.36°.

[Clinical classification of osteoradionecrosis of temporal bone and the treatment of massive osteonecrosis].

OBJECTIVE: To explore the effective treatment regimen for osteoradionecrosis of temporal bone. METHOD: Twenty-seven patients with massive osteoradionecrosis in temporal bone were included and retrospectively analyzed, in which, 15 cases received surgery and the other 12 cases adopted non-surgical treatment. RESULT: In the surgery group, three cases died one year postoperatively and died of massive hemorrhage due to internal carotid blowout. One case died four years after surgery without clear cause of death, and two cases were lost to follow up. Out of the nine survivors, the follow up period ranged from four months to eight years (one was followed up eight years, one was followed up over four years, four were followed up two-three years, one was followed up over one year, one was followed up nine months, and one was followed up four months, respectively). Patients classified as the type III received best outcome, and patients of type V and IV without invasion of the internal carotid artery received good surgical effects, while patients classified as the type IV with internal carotid artery invasion presented low survival rate. Two cases in the non-surgical group died of internal carotid rupture, and the other ten cases presented with repeated infection and expansion of the osteoradionecrosis lesion. CONCLUSION: The new classification criteria is helpful in diagnosis of location of lesions,and can serve as a guide for clinical therapy. Massive osteoradionecrosis in temporal bone responded unfavorably to conservative treatment, compared to that, surgery can effectively control the expansion of the lesion and markedly improve patient quality of life. Long-term follow up is necessary because of the slow development of osteoradionecrosis after surgery.

Synthesis of beta-hederin and Hederacolchiside A1: triterpenoid saponins bearing a unique cytotoxicity-inducing disaccharide moiety.

A facile synthetic approach toward oleanolic acid glycoside bearing alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl moiety, a unique oligosaccharide that strongly induces antitumor activity of oleanane-type triterpenoid saponins, was developed. Based on this approach beta-hederin (oleanolic acid 3-O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranoside) was efficiently prepared from oleanolic acid through stepwise glycosylation in linear eight steps with 52% overall yield, while Hederacolchiside A1 (oleanolic acid 3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->4)]-alpha-L-arabinopyranoside) in linear 13 steps with 20% overall yield.

[The utility boiler low NOx combustion optimization based on ANN and simulated annealing algorithm].

With the developing restrict environmental protection demand, more attention was paid on the low NOx combustion optimizing technology for its cheap and easy property. In this work, field experiments on the NOx emissions characteristics of a 600 MW coal-fired boiler were carried out, on the base of the artificial neural network (ANN) modeling, the simulated annealing (SA) algorithm was employed to optimize the boiler combustion to achieve a low NOx emissions concentration, and the combustion scheme was obtained. Two sets of SA parameters were adopted to find a better SA scheme, the result show that the parameters of T0 = 50 K, alpha = 0.6 can lead to a better optimizing process. This work can give the foundation of the boiler low NOx combustion on-line control technology.