Thickness-dependent structural stability and transition in molybdenum disulfide under hydrostatic pressure

Understanding the physical mechanism of structural stability and transition in various polytypes of layered transition metal dichalcogenides under the external stimulus is of crucial importance for their new applications.Here,we investigate the thickness-dependent structural properties of MoS2 under the condition of hydrostatic pressure in terms of bond relaxation and thermodynamics considerations.For both types of MoS2 structures,we find that the transition and metallization are significantly modulated by hydrostatic pressure and the number of layers.We establish a pressure-size phase diagram to address the transition mechanism.Our study not only provides insights into the thickness-dependent structural properties of MoS2,but also shows a theoretical guidance for the design and fabrication of MoS2-based devices.

EFFECT OF ELECTROACUPUNCTURE ON CANINE PYLORIC PRESSURE AND ITS RELATION WITH BRAIN-GUT PEPTIDE LEVEL IN THE GASTRIC MUCOSAL TISSUES

Aim of the study: To observe the effect of electroacupuncture (EA) on canine pyloric pressure and its relation with contents of motilin (MTL), somatostatin (SS) and nitric oxide synthetase (NOS) in the gastric mucosal tissues. Methods: The total and basic pressure of the pyloric sphincter, and the frequency of the high pressure waves were measured by using a gastrotonometer; and the contents of MTL, SS and NOS in tissues of the gastric body and gastric antrum mucosa were detected by using radioimmunoassay(RIA) and biochemical methods in 20 dogs. Results: After EA of Zusanli (ST 36), the total and basic pressure of the pyloric sphincter, and the frequency of the high pressure waves, the content of SS in the gastric body mucosa, MTL and SS in the gastric antrum mucosa all decreased significantly (P<0.05) and the level of NOS increased clearly (P<0.05). While after EA of Xiajuxu (ST 39), all the indexes had not any striking changes except significant decrease of SS content in the gastric body mucosa (P<0.05). Conclusions: EA has a significant modulating action on gastrointestinal functional activities by lowering canine pyloric pressure and contracted frequency, which is also related with its influence on contents of some brain gut peptides (BGP) and is of specificity in meridians and acupoints.

Impacts of Coagulation Pretreatment on MF Filtration and a Comparative Study of Different Membrane Module Types

Changes in the regulatory requirements and the forthcoming Disinfectant/Disinfection By-Products （D/DBP） Rule will require that drinking water treatment facilities be operated to achieve maximum removals of particles and disinfectant tolerant microorganisms as well as natural organic matter （NOM）. For drinking water production, the use of membrane filtration processes such as microfiltration and ultrafiltration （MF/UF） alone to satisfy the turbidity, particle and microorganism removal a requirement of the surface water treatment regulation （SWTR） is not enough. MF/UF treatment processes can achieve only nominal （10 percent） removal of disinfection by-products （DBP） precursors （James, et al., 1995）. On the other hand, too fast fouling can make the filtration processes more difficult to carry on. To solve these problems, many authors have been interested in installing coagulation pretreatment before membrane filtration to improve membrane performance. However, previous studies reported conflicting results. Some supported the effectiveness of coagulation pretreatment, while others contended that coagulation aggravated membrane performance. This research aims to identify the effects of coagulation pretreatment on membrane filtration through a pilot study using PVDF membrane in combination with analyzing the rationale of coagulation. Another objective of this research was to evaluate the different impacts on membrane performance of using different membrane modules （the submerged module and pressured module）. The results showed that coagulation pretreatment greatly improved the membrane performance, extending the filtration time as well as reducing the permeated organic level, and that the submerged module is much more efficient than the pressured module.