Vertex Deletion Problems on Chordal Graphs

Containing many classic optimization problems, the family of vertex deletion problems has an important position in algorithm and complexity study. The celebrated result of Lewis and Yannakakis gives a complete dichotomy of their complexity. It however has nothing to say about the case when the input graph is also special. This paper initiates a systematic study of vertex deletion problems from one subclass of chordal graphs to another. We give polynomial-time algorithms or proofs of NP-completeness for most of the problems. In particular, we show that the vertex deletion problem from chordal graphs to interval graphs is NP-complete

An Updated Quantification Method for Liquid Refrigerant Distribution in Microchannel Evaporators Using Infrared Thermography

Refrigerant distribution in the parallel tubes of a microchannel evaporator significantly affects its heat transfer performance, which can further affect the coefficient of performance of the whole air-conditioning or refrigeration system. This paper proposes an easy-to-implement quantification method using infrared thermography for the liquid refrigerant distribution in microchannel evaporators to update the original method developed by Li and Hrnjak (2015). Before the detailed discussion of the new quantification method, the effect of surface emissivity on the infrared thermography is investigated, and the calibration process of the infrared thermography is presented for a microchannel heat exchanger sample. Then, the updated quantification method is introduced in detail. The ε-NTU approach is clarified for the formula derivation. A new mathematical method is introduced for the determination of the transition between the two-phase region and the single-phase region. A facility with pump-driven two-phase refrigerant R134a has been built to demonstrate the updated quantification method for the liquid refrigerant distribution in a microchannel evaporator with vertical parallel tubes. The tests have been run at the conditions of 41.7 g/s refrigerant flow rate and 5 oC evaporation temperature with the evaporator inlet vapor quality of 0.15 and 0.25, respectively. The infrared images and the reduced liquid refrigerant mass flow rate distributions are presented to demonstrate the effectiveness of the updated quantification method

Flow Boiling Heat Transfer And Pressure Drop Characteristics Of R1234yf In A Dimpled Flat Duct

Among various heat transfer enhancement technologies, the dimpled surface, which is inspired by the resistance reduction characteristics of the specific concaves on golf balls, has the potential to improve heat transfer with a relatively low pressure-drop penalty. More and more applications of dimpled surfaces in heat exchangers have shown up in industries. However, the lack of experimental data, especially the heat transfer and pressure drop data for liquidand-vapor two-phase flow, inside the dimpled flow channels prevents the good design of the dimpled heat exchangers. In this study, a facility has been designed and built to investigate the heat transfer and pressure drop of flow-boiling R1234yf in a dimpled flat duct. The details of the facility, especially the test section, are presented. A microscope is used to measure the geometrical dimensions of the dimpled flat tube. The heat loss is tested and the heat balance is -2 -1 checked before the experiments. The experiments are performed at mass flux from 100 to 200 kg m s , heat flux of 5 kW m-2, saturation temperature of 15 oC, and vapor quality from 0.1 to 0.95. The experimental results are presented and discussed in detail

A knee-point-based evolutionary algorithm using weighted subpopulation for many-objective optimization

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Among many-objective optimization problems (MaOPs), the proportion of nondominated solutions is too large to distinguish among different solutions, which is a great obstacle in the process of solving MaOPs. Thus, this paper proposes an algorithm which uses a weighted subpopulation knee point. The weight is used to divide the whole population into a number of subpopulations, and the knee point of each subpopulation guides other solutions to search. Besides, Additionally, the convergence of the knee point approach can be exploited, and the subpopulation-based approach improves performance by improving the diversity of the evolutionary algorithm. Therefore, these advantages can make the algorithm suitable for solving MaOPs. Experimental results show that the proposed algorithm performs better on most test problems than six other state-of-the-art many-objective evolutionary algorithms

Deferoxamine regulates neuroinflammation and iron homeostasis in a mouse model of postoperative cognitive dysfunction

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a common complication after surgery, especially amongst elderly patients. Neuroinflammation and iron homeostasis are key hallmarks of several neurological disorders. In this study, we investigated the role of deferoxamine (DFO), a clinically used iron chelator, in a mouse model of surgery-induced cognitive dysfunction and assessed its neuroprotective effects on neuroinflammation, oxidative stress, and memory function. METHODS: A model of laparotomy under general anesthesia and analgesia was used to study POCD. Twelve to 14 months C57BL/6J male mice were treated with DFO, and changes in iron signaling, microglia activity, oxidative stress, inflammatory cytokines, and neurotrophic factors were assessed in the hippocampus on postoperative days 3, 7, and 14. Memory function was evaluated using fear conditioning and Morris water maze tests. BV2 microglia cells were used to test the anti-inflammatory and neuroprotective effects of DFO. RESULTS: Peripheral surgical trauma triggered changes in hippocampal iron homeostasis including ferric iron deposition, increase in hepcidin and divalent metal transporter-1, reduction in ferroportin and ferritin, and oxidative stress. Microglia activation, inflammatory cytokines, brain-derived neurotropic factor impairments, and cognitive dysfunction were found up to day 14 after surgery. Treatment with DFO significantly reduced neuroinflammation and improved cognitive decline by modulating p38 MAPK signaling, reactive oxygen species, and pro-inflammatory cytokines release. CONCLUSIONS: Iron imbalance represents a novel mechanism underlying surgery-induced neuroinflammation and cognitive decline. DFO treatment regulates neuroinflammation and microglia activity after surgery