An innovative test method for mechanical properties of sandstone under instantaneous unloading confining pressure

With the increase of underground engineering construction depth,the phenomenon of surrounding rock sudden failure caused by supporting structure failure occurs frequently.The conventional unloading con-fining pressure(CUCP)test cannot simulate the plastic yielding and instantaneous unloading process of supporting structure to rock.Thus,a high stress loading-instantaneous unloading confining pressure(HSL-IUCP)test method was proposed and applied by considering bolt’s fracture under stress.The wall thickness of confining pressure plates and the material of bolts were changed to realize different confin-ing pressure loading stiffness(CPLS)and lateral maximum allowable deformation(LMAD).The superio-rity of HSL-ICPU method is verified compared with CUCP.The rock failure mechanism caused by sudden failure of supporting structure is obtained.The results show that when CPLS increases from 1.35 to 2.33 GN/m,rock’s peak strength and elastic modulus increase by 25.18%and 23.70%,respectively.The fracture characteristics change from tensile failure to tensile-shear mixed failure.When LMAD decreases from 0.40 to 0.16 mm,rock’s residual strength,peak strain,and residual strain decrease by 91.80%,16.94%,and 21.92%,respectively,and post-peak drop modulus increases by 140.47%.The test results obtained by this method are closer to rock’s real mechanical response characteristics compared with CUCP.

Vibration characteristics of rotor system with tilting-pad journal bearing of elastic and damped pivots

In view of an entire dynamic model of tilting-pad journal bearing(TPJB) in which the pads swing and vibrate along geometric direction of preload, a TPJB of elastic and damped pivots was designed and manufactured. Vibration experiments were carried out under the conditions of different rotor bending stiffness and oil supply pressure to find out the relationship between the new bearing's vibration depression effect and other dynamic parameters of the rotor. The result shows that critical amplitudes can be efficaciously reduced while system's stability can be remarkably improved by this bearing. Besides, the bearing's effect of vibration depression weakens as the rotor bending stiffness increases, but heightens it as the oil supply pressure increases.

Effects of antihypertensives on arterial responses associated with obstructive sleep apneas

Background Many patients with obstructive sleep apnea syndrome (OSAS) have complicated with hypertension and may be prescribed with antihypertension medications to control their blood pressure But whether antihypertension medications can also decrease arterial stiffness or control the blood pressure increasing following obstructive events is not well described This study aimed to investigate whether antihypertensive medications can ameliorate the changes in arterial stiffness and blood pressure associated with OSA Methods Sixtyone OSAS patients [13 women, 48 men, mean age (534±123) years], 26 normotensive patients (N), 7 hypertensive patients on no antihypertension medications (H), and 28 hypertensive patients on various combination antihypertension therapy (HM), were prospectively diagnosed with standard nocturnal polysomnography Beattobeat blood pressure was continuously recorded from the radial artery by applanation tonometry during baseline sleep As a measure of arterial stiffness, arterial augmentation index (AAI) was calculated as the ratio of augmented systolic blood pressure (SBP) to pulse pressure and expressed as a percentage for the following conditions: awakening, the first 10 ('early apnea') and last 10 ('late apnea') cardiac cycles of obstructive events (apnea or hypopnea), and the first 15 cardiac cycles following event termination ('post apnea') for all events with nadir O2 saturation ≤89% Results Systolic blood pressure (SBP) postapnea [(14274±1306) mmHg (N), (13706±2656) mmHg (H), (13694±141) mmHg (HM)] was significantly increased from awakening [(13576±1476) mmHg (N), (13558±2317) mmHg (H), (12977±1400) mmHg (HM)], early apnea [(13053±1265) mmHg (N), (12447±2497) mmHg (H), (12604±1312) mmHg (HM)], and late apnea [(1298±1268) mmHg(N), (12478±2515) mmHg (H), (12448±1382) mmHg (HM)] respectively (P<0001, repeated measures ANOVA) AAI was significantly increased for the N group (P<0001) from awakening to late apnea [(1045±262)% vs (1443±321)%] and from early apnea to late apnea [(1061±234)% vs (1443±321)%], and also for H group (P<005) from awakening to late apnea [(1123±387)% vs (1632±802)%] and from early apnea to late apnea [(1175±379)% vs (1632±802)%] Meanwhile, no significant differences in AAI among awakening, early apnea, late apnea, and postapnea conditions were found in HM group Conclusions The current data demonstrate that systemic blood pressure increases significantly during the postapneic phase of OSAS, compared with that during awakening and intraapnea phases even with the use of combined antihypertensive therapy which could normalize BP during awakening in the hypertensive patients However, increases in arterial stiffness during obstructive events could be ameliorated by combined antihypertension medications