Study on mechanical properties of interbedded rock masses with microcrack based on thermal-mechanical coupling.

The mechanical properties of deep rock masses are significantly influenced by temperature and other factors. The effect of temperature on the strength of deep rock masses will pose a serious challenge to deep resource exploitation and engineering construction. In this paper, the thermal-mechanical coupling calculation model is established by particle flow code (PFC2D) to study the uniaxial compression response of rock masses with microcracks after temperature load. The strength of failure, microcracks, and strain was analyzed. The results show that: (i) When the soft rock thickness ratio Hs/H < 0.5, the displacement caused by the applied temperature is concentrated at the structural plane, and the contact force is concentrated at the end of the initial microcrack. When Hs/H ≥ 0.5, the displacement caused by the applied temperature is concentrated on both sides of the initial microcrack, and the contact force is concentrated in the hard rock area. (ii) The number of microcracks decreases with the increase of soft rock thickness under different working conditions. When the soft rock thickness ratio Hs/H < 0.5, the relationship curve between the number of microcracks and the vertical strain shows two stages of change. When Hs/H ≥ 0.5, the relationship curve between the number of cracks and the vertical strain changes shows three stages of change. (iii) When the soft rock thickness ratio Hs/H < 0.5, the failure strength decreases with the increase of soft rock thickness ratio at T = 100°C and 200°C. When T = 300°C and 400°C, the failure strength decreased first and then increased. When Hs/H ≥ 0.5, the failure strength increases with the increase of soft rock thickness at T = 200°C, 300°C, and 400°C. At T = 100°C, the failure strength decreases with the increase of soft rock thickness.

Cracks propagation characteristics of double-hole delay blasting in soft-hard composite rock mass.

By researching the distance between blasthole and interface of soft-hard rock strata, as well as the time of delay detonation, blasting effect of the rock mass will be more controllable. Firstly, validity of numerical method was authenticated from three angles: blasting coupled stress field, ratio of crushing zone radius to blasthole radius, and crack network state. Under the condition of soft-hard rock strata, numerical model of double-hole blasting was established by using PFC2D. Then delay blasting experiments were carried out under different relative positions of blasthole and interface. Ultimately, results were analyzed from three perspectives: crack network, crack quantity and rock fragment. Results show that: (1) When detonated in hard rock, if between interface and blasthole distance is greater than twice crushing zone radius, the closer blasthole is to the interface, the more obvious the "hook" phenomenon between the two blastholes is. With increasing delayed initiation time, "hook" phenomenon will weaken or even disappear. (2) Based on the crack information initiated in hard rock, the law of crack number varying with thickness of hard rock and delay time is obtained. (3) For initiation in hard rock, crack extension range is large, but less fragments are formed. The law is opposite to that initiation in structural plane and soft rock. Fragmentation area increases exponentially with increasing soft rock thickness, and exponential function is obtained.

Perioperative Results and Risk Factors for In-Hospital Mortality In Patients With Stanford Type A Aortic Dissection Undergoing Sun's Procedure - A Single Center Study.

BACKGROUND: The study was to analyze the therapeutic effect and risk factors of in-hospital mortality in patients with acute Stanford type A aortic dissection operated by Sun's procedure. METHODS: From Jan. 2010 to March 2016, 72 patients whose data was fully accessible underwent Sun's procedure in our hospital due to acute Stanford type A aortic dissection. Patients were divided into the survival group and the death group, and the risk factors for in-hospital mortality were collected and analyzed. RESULTS: All 72 patients were diagnosed as acute Stanford type A aortic dissection by CT angiography in which the ascending aorta, aortic arch and descending aorta were involved; these patients were operated by Sun's procedure. The operation of proximal aorta included 39 Bentall procedure, one David surgery, and 32 ascending aorta replacement. The in-hospital mortality rate was 19.4% (14 patients). Studies showed the risk factors for the in-hospital mortality included the body mass index, cardiopulmonary bypass time, operation time, intraoperative transfusion of red blood cells and plasma volume, and the total perioperative transfusion of red blood cells, plasma and cryoprecipitate volume. Independent risk factors included the body mass index and cardiopulmonary bypass time. CONCLUSION: Acute Stanford type A aortic dissection is a severe, complex disease with high in-hospital mortality, though the Sun's procedure is an effective surgical approach in treating this kind of disease in some center. Body mass index and cardiopulmonary bypass time are independent risk factors for in-hospital mortality.

[Three-step sperm retrieval for 73 non-obstructive azoospermia patients].

OBJECTIVE: To investigate the value and clinical application of the Three-Step Sperm Retrieval method in improving the sperm retrieval rate for non-obstructive azoospermia (NOA) patients. METHODS: Seventy-three NOA patients underwent Three-Step Sperm Retrieval in the following order of procedures: testicular fine needle aspiration (TFNA), testicular sperm extraction (TSE), and microdissection testicular sperm extraction (MD-TSE). The testicular tissue obtained from each step was observed for spermatozoa under the 400-fold inverted microscope. If spermatozoa were found in one step, the operation would be stopped; otherwise, the next step would be carried out. The testicular tissue was subjected to pathological examination. RESULTS: Spermatozoa was found in the testicular tissue in 38.4% of the cases (28/73) at TFNA as the first step, in 52.1% (38/73) at TFNA and TSE, and in 64.4% (47/73) at TFNA, TSE and MD-TSE. Pathological examination showed 25 of the cases to be Sertoli cell-only syndrome, 21 to be sperm maturation arrest and the other 27 to be hypospermatogenesis, in which spermatozoa were found in 10, 14 and 23 cases, respectively. CONCLUSION: The Three-Step Sperm Retrieval method can significantly improve the sperm retrieval rate for NOA patients. And the sperm retrieval rate is associated with the pathological type of the testicular tissue, a higher rate with hypospermatogenesis.

[Reparative isolation and purification of flavones from Pericarpium Citri Reticulatae by high-speed counter-current chromatography].

Three flavones were prepared, isolated and purified from Pericarpium Citri Reticulatae by high-speed counter-current chromatography (HSCCC). A two-phase solvent system composed of light petroleum-ethyl acetate-methanol-water (2:4:3:3, v/v/v/v) was used. Within 6 hours, 10.1 mg of heseridin, 49.8 mg of 5,6,7,8,4'-pentamethoxyflavone and 50.6 mg of 5-hydroxy-6,7,8,3',4'-pentamethoxyflavone with their purities over 97.0% were obtained from 4.0 g of the crude extract of Pericarpium Citri Reticulatae in one-step elution under the conditions of a flow rate of 1.70 mL/min, 800 r/min and the detection wavelength of 280 nm. The obtained fractions were analyzed by high performance liquid chromatography (HPLC), and identified by mass spectrometry (MS), 1H-nuclear magnetic resonance (NMR) and 13C-NMR. The results indicate that HSCCC is a powerful technique for the purification of flavones from Citrus reticulata Blanco.

Dual-directional optokinetic nystagmus elicited by the intermittent display of gratings in primary open-angle glaucoma and normal eyes.

PURPOSE: To compare optokinetic nystagmus (OKN) responses to the intermittent display of stimuli between normal subjects and patients with primary open-angle glaucoma (POAG). METHODS: Optokinetic nystagmus (OKN) was recorded in 9 glaucomatous patients and 7 normal subjects. The computer-generated stimuli displayed sinusoidal luminance gratings (16 cd/m(2) mean luminance, 0.5 cyc/deg) with a pi/2 phase shift between successive stimulus gratings. These stimulus gratings were separated by an interstimulus interval (ISI), during which a homogeneous luminance field of 16 cd/m(2) was presented. The ISI duration and the luminance contrast were set at different values. RESULTS: For normal subjects, dual-directional alternating OKN could be evoked in the ISI range from 33 to 100 ms. The dual-directional alternating OKN was defined as that OKN slow phase alternatively tracked in the direction of pi/2 shift (forward OKN) and against the pi/2 shift (reverse OKN). By contrast, for most glaucomatous eyes, nearly no reverse OKN could be evoked at any ISI value. CONCLUSIONS: The lack of reverse OKN in POAG patients in the present experiments is a meaningful finding. The occurrence of reverse OKN during a certain range of ISI duration could be related to the biphasic characteristics of the temporal impulse response in normal subjects, whereas, the lack of reverse OKN might suggest the plausible damage of magnocellular cells in POAG.