Membrane inlet mass spectrometry method (REOX/MIMS) to measure 15N-nitrate in isotope-enrichment experiments

Using 15N stable isotope as a tracer to quantify N transformation rates in isotope-enrichment experiments improves understanding of the N cycle in various ecosystems. However, measuring 15N-nitrate (15NO3−) in small volumes of water for these experiments is a major challenge due to the inconvenience of preparing samples by traditional techniques. We developed a “REOX/MIMS” method by applying membrane inlet mass spectrometry (MIMS) to determining 15NO3− concentrations in a small volumes of water from isotope-enrichment experiments after converting the dissolved inorganic N to N2. The nitrates (NO3− + NO2−) were reduced to NH4+ with zinc powder, and the ammonium (NH4+) was then oxidized to N2 by hypobromite iodine solution. The resulting 29N2 and 30N2 were measured via MIMS. This optimized protocol provides a sensitive (~0.1 μM) and precise (relative standard deviation = 0.1–4.37%) approach to quantify 15NO3− concentrations (0.1–500 µM) in water samples over a wide range of salinities (0–35‰) and in 2 M KCl solution with excellent calibration curves (R2 ≥ 0.9996, p \u3c 0.0001). The method was combined with 15NO3− isotope-enrichment incubation experiments to measure gross nitrification and gross NO3− immobilization rates in various ecosystems. It was rapid, accurate, and cost-effective. Future applications of this efficient approach will inform scientists, modelers and decision makers about mechanisms, sources, fates, and effects of NO3− delivered to or produced in numerous aquatic and terrestrial ecosystems

Sound insulation performance of plate with interconnected distributed piezoelectric patches

The intensive use of light plate-like structures in aircraft industry and transport industry result in more serious vibration and noise issues for their higher dynamical sensitivities. To deal with these problems, techniques based on piezoelectric materials have been proposed and numerous papers have contributed to their development and application[1-7]. In these applications, periodically distributed piezoelectric control strategies[4-7] attracted many researchers for their abilities to modify the equivalent dynamical parameters of the piezo-mechanical system to obtain new desired vibro-acoustic functionalities, i.e., materializing ?integrated smart structure? or ?metacomposite?[8]. However, previous works who used the periodically distributed piezoelectric techniques mainly focused on controlling vibration, associated sound radiation[9] or wave propagation on the structures, few of research concerns control sound transmission. In our work, wave propagation properties and sound insulation performance of a thin plate with interconnected distributed piezoelectric patches via an inductive circuit network were studied. Firstly, analytical dynamical equations for this piezo-electromechanical plate (PEM plate for short) were established by using homogenization method under sub-wavelength assumption. Then, dispersion relationships and energy density of the wave modes propagating in PEM plate were analyzed. At last, the coincidence frequency as well as the sound transmission loss (STL) were studied. The results obtained lead to the following conclusions: (1) Two free bending waves exist in PEM plate with different wave speeds and translate energy both in mechanical field and in electric field. (2) There exists a region for the incident angle of sound wave of PEM plate, if the incident angle of sound wave lies in the region then there is not the coincidence frequency around where the insulation effect is worst. (3) The disappearance of coincidence frequency can be used to optimize the value of inductance to considerably improve the sound insulation performance of PEM plate in coincidence region

Thermal Environment Analysis and Improvement on Isolated Cold Aisle Data Centers

Isolated cold aisle airflow distribution is a transitional form from non-isolated airflow distribution to closed cold aisle airflow distribution. With the increase of the power of racks, cooling failure may happen in the layout of the isolated cold aisle. This paper presents the study on cooling performance of the racks which are improved through bottom ventilating reform and adjustment. Inlet/outlet air temperature and mass flow rate of the racks are investigated in detail under conditions of various bottom ventilated areas and various porosities of the raised floor. The characteristics of airflow distribution are contrastively analyzed through calculating indexes of the thermal environment of data centers. Results show that adequate ventilation through the bottom of the racks is good for improvement of the state of airflow distribution. There is an optimization range (0.1-0.3 m and 0.05-0.15 m, respectively) of the ventilated area at the bottom of the racks. And high porosity (above 50%) of the ventilated area can reduce the inlet and outlet temperatures of the racks and the racks in different positions have a better temperature uniformity. In conclusion, bottom ventilation of racks is a feasible plan to improve airflow distribution, and schemes of ventilated area and porosity of corresponding raised floor should be designed respectively under consideration of the layout of racks and AC

Environmental and Microbial Factors in Inflammatory Bowel Disease Model Establishment: A Review Partly through Mendelian Randomization

Inflammatory bowel disease (IBD) is a complex condition resulting from environmental, microbial, immunologic, and genetic factors. With the advancement of Mendelian randomization research in IBD, we have gained new insights into the relationship between these factors and IBD. Many animal models of IBD have been developed using different methods, but few studies have attempted to model IBD by combining environmental factors and microbial factors. In this review, we examine how environmental factors and microbial factors affect the development and progression of IBD, and how they interact with each other and with the intestinal microbiota. We also summarize the current methods for creating animal models of IBD and compare their advantages and disadvantages. Based on the latest findings from Mendelian randomization studies on the role of environmental factors in IBD, we discuss which environmental and microbial factors could be used to construct a more realistic and reliable IBD experimental model. We propose that animal models of IBD should consider both environmental and microbial factors to better mimic human IBD pathogenesis and to reveal the underlying mechanisms of IBD at the immune and genetic levels. We highlight the importance of environmental and microbial factors in IBD pathogenesis and offer new perspectives and suggestions for improving experimental animal modeling. Our goal is to create a model that closely resembles the clinical picture of IBD

A simulation based research on chance constrained programming in robust facility location problem

Since facility location decisions problem include long-term character and potential parameter variations, it is important to consider uncertainty in its modeling. This paper examines robust facility location problem considering supply uncertainty, in which we assume the supply of the facility in the actual operation is not equal to the supply initially established, the supply is subject to random fluctuation. The chance constraints are introduced when formulating the robust facility location model to make sure the system operate properly with a certain probability while the supply fluctuates. The chance constraints are approximated safely by using Hoeffding’s inequality and the problem is transformed to a general deterministic linear programming. Furthermore, how the facility location cost change with confidence level is investigated through a numerical example. The sensitivity analysis is conducted for important parameters of the model and we get the main factors that affect the facility location cost

Experimental study on multi-split air conditioner with digital scroll compressor

A set of 10 horse powers (HP) multi-split air conditioner with a digital scroll compressor and a standard compressor was designed. The control strategy of compressor switching and the control model of compressor output capacity were presented. The output ratio of the digital compressor was determined in the control strategy. Furthermore, in the control model of compressor output capacity, considering the pressure disturbance, a certain suction pressure range was used as the pressure control target to adjust the output capacity. Experiments show that the system ran unstably, the standard compressor frequently appeared on off phenomenon, and some operation parameters such as the output ratio of the digital compressor, the opening of electric expansive valve (EEV), the cooling capacity and the air outlet temperature fluctuated. A new control model of the output capacity was proposed, in which the average suction pressure in an adjustment period was taken as the current pressure to regulate the output capacity. Experimental results demonstrate that the control model can be used to solve the frequent on off phenomenon of the standard compressor and oscillation of the operation parameters, realize control accuracy of less than 0.2 degrees C deviation of the air outlet temperature. (C) 2011 Elsevier Ltd. All rights reserved