Effect of Saturation Temperature Change Due to Pressure Loss of Refrigerants on Heat Transfer Capacity of Heat Exchanger

Heat exchanger is an essential component in the HVAC&R applications. The heat exchanger development methods are divided into simulation and experiment. Simulation is often used by researchers because it can save a lot of time and money over experimental method. However, it is difficult to model all physical phenomena in simulation. Some phenomena are simulated with ideal assumptions based on experience. To analyze an ideal heat exchanger without pressure loss of the refrigerant, the saturation temperature of the heat exchanger is assumed to be constant. Whereas, saturated temperature drop occurs due to the pressure loss of the refrigerant in a real case scenario which affects the heat transfer capacity of the heat exchanger. In this study, a theoretical method to evaluate the effect of saturated pressure loss of refrigerant on the heat transfer capacity in heat exchanger was proposed and analyzed. The proposed method was verified by simulation. R134a, R410A, R600a, R32, and R1234yf were selected as refrigerants for analysis which are used in air conditioners and refrigerators. As a result, the heat transfer capacity ratio of the cycle using R134a showed 96.11% under the condensing condition of 15 kPa pressure loss, and 108.97% and 123.17% for air conditioner and refrigerator evaporating conditions, respectively. Moreover, R600a showed the greatest performance change, and R32 showed the smallest performance change

Concurrent learning adaptive control with directional forgetting

This paper proposes a new concurrent learning-based adaptive control algorithm. The main objective behind our proposition is to relax the persistent excitation requirement for the stability guarantee, while providing the ability to identify time-varying parameters. To achieve the objective, this paper designs a directional forgetting algorithm, which is then integrated with the adaptive law. The theoretical stability analysis shows that the tracking and parameter estimation error is exponentially stable with the signal only finitely excited, not persistently excited. The analysis also shows that the proposed algorithm can guarantee the stability under time-varying parameters. Moreover, the necessary and sufficient conditions for the stability given the time-varying parameters are derived. The results of numerical simulations confirm the validity of the theoretical analysis results and demonstrate the performance of the proposed algorithm

Cupping for Treating Pain: A Systematic Review

The objective of this study was to assess the evidence for or against the effectiveness of cupping as a treatment option for pain. Fourteen databases were searched. Randomized clinical trials (RCTs) testing cupping in patients with pain of any origin were considered. Trials using cupping with or without drawing blood were included, while trials comparing cupping with other treatments of unproven efficacy were excluded. Trials with cupping as concomitant treatment together with other treatments of unproven efficacy were excluded. Trials were also excluded if pain was not a central symptom of the condition. The selection of studies, data extraction and validation were performed independently by three reviewers. Seven RCTs met all the inclusion criteria. Two RCTs suggested significant pain reduction for cupping in low back pain compared with usual care (P < .01) and analgesia (P < .001). Another two RCTs also showed positive effects of cupping in cancer pain (P < .05) and trigeminal neuralgia (P < .01) compared with anticancer drugs and analgesics, respectively. Two RCTs reported favorable effects of cupping on pain in brachialgia compared with usual care (P = .03) or heat pad (P < .001). The other RCT failed to show superior effects of cupping on pain in herpes zoster compared with anti-viral medication (P = .065). Currently there are few RCTs testing the effectiveness of cupping in the management of pain. Most of the existing trials are of poor quality. Therefore, more rigorous studies are required before the effectiveness of cupping for the treatment of pain can be determined

"Teaching to beat" in a Korean Academic High School

1994This paper presents the results of an intensive two-year ethnographic study focusing on what teachers do when they teach in college preparatory academic high schools in Korea. The main concern is how they select, organize, and present classroom knowledge, while keeping order in the classes. Usually the teaching practices in academic high schools have been characterized as rote memory oriented, and this has become the major strategy to prepare the students for the College Entrance Examination (hereafter C.E.E.). This study, however, reveals that the practices are more than teaching students how and what to memorize. The teachers select what they judge important out of the nationally standardized textbooks, break it down, restucture it in a way that makes classroom knowledge readily "digestible stuffs", and "put it into their mouths" so that the students can easily transfer welldigested bits of knowledge into scores on the C.E.E.. This teaching method is prevalent only among "competent" teachers across the school subjects

UAV collision avoidance considering no-fly-zones

This paper proposes a collision avoidance algorithm that ensures minimum separation between the vehicles considering multiple no-fly-zones. The proposed algorithm aims to provide a practical and efficient tactical de-confliction solution for Unmanned Aerial Vehicles (UAVs). The main idea is to utilise the differential geometry concept that computes the minimum heading angle change to avoid the obstacles, and to expand its applicability to polygonal obstacles. This paper validates the minimum separation and efficiency of the proposed algorithm both analytically and numericall

Acupuncture for the treatment of tinnitus: a systematic review of randomized clinical trials

BACKGROUND: Complementary and alternative medicine (CAM) has frequently been used to treat tinnitus, and acupuncture is a particularly popular option. The objective of this review was to assess the evidence concerning the effectiveness of acupuncture as a treatment for tinnitus. METHODS: Fourteen databases were searched from the dates of their creation to July 4th, 2012. Randomized clinical trials (RCTs) were included if acupuncture was used as the sole treatment. The Cochrane risk of bias tool was used to assess the risk of bias. RESULTS: A total of 9 RCTs met all the inclusion criteria. Their methodological quality was mostly poor. Five RCTs compared the effectiveness of acupuncture or electroacupuncture with sham acupuncture for treating tinnitus. The results failed to show statistically significant improvements. Two RCTs compared a short one-time scalp acupuncture treatment with the use of penetrating sham acupuncture at non-acupoints in achieving subjective symptom relief on a visual analog scale; these RCTs demonstrated significant positive effects with scalp acupuncture. Two RCTs compared acupuncture with conventional drug treatments. One of these RCTs demonstrated that acupuncture had statistically significant effects on the response rate in patients with nervous tinnitus, but the other RCT did not demonstrate significant effects in patients with senile tinnitus. CONCLUSIONS: The number, size and quality of the RCTs on the effectiveness of acupuncture for the treatment of tinnitus are not sufficient for drawing definitive conclusions. Further rigorous RCTs that overcome the many limitations of the current evidence are warranted

Fatty acid desaturase (FADS) gene polymorphisms and insulin resistance in association with serum phospholipid polyunsaturated fatty acid composition in healthy Korean men: cross-sectional study

<p>Abstract</p> <p>Background</p> <p>We investigated the relationship between fatty acid desaturase (<it>FADS</it>) gene polymorphisms and insulin resistance (IR) in association with serum phospholipid polyunsaturated fatty acid (FA) composition in healthy Korean men.</p> <p>Methods</p> <p>Healthy men (n = 576, 30 ~ 79 years old) were genotyped for rs174537 near <it>FADS1 </it>(<it>FEN1</it>-10154G>T), <it>FADS2 </it>(rs174575C>G, rs2727270C>T), and <it>FADS3 </it>(rs1000778C>T) SNPs. Dietary intake, serum phospholipid FA composition and HOMA-IR were measured.</p> <p>Results</p> <p>Fasting insulin and HOMA-IR were significantly higher in the rs174575G allele carriers than the CC homozygotes, but lower in the rs2727270T allele carriers than the CC homozygotes. The proportion of linoleic acid (18:2ω-6, LA) was higher in the minor allele carriers of <it>FEN1</it>-10154G>T, rs174575C>G and rs2727270C>T than the major homozygotes, respectively. On the other hand, the proportions of dihomo-γ-linolenic acid (20:3ω-6, DGLA) and arachidonic acid (20:4ω-6, AA) in serum phospholipids were significantly lower in the minor allele carriers of <it>FEN1</it>-10154 G>T carriers and rs2727270C>T than the major homozygotes respectively. AA was also significantly lower in the rs1000778T allele carriers than the CC homozygotes. HOMA-IR positively correlated with LA and DGLA and negatively with AA/DGLA in total subjects. Interestingly, rs174575G allele carriers showed remarkably higher HOMA-IR than the CC homozygotes when subjects had higher proportions of DLGA (≥1.412% in total serum phospholipid FA composition) (<it>P </it>for interaction = 0.009) or of AA (≥4.573%) (<it>P </it>for interaction = 0.047).</p> <p>Conclusion</p> <p>HOMA-IR is associated with <it>FADS </it>gene cluster as well as with FA composition in serum phospholipids. Additionally, HOMA-IR may be modulated by the interaction between rs174575C>G and the proportion of DGLA or AA in serum phospholipids.</p

Parameter-robust linear quadratic Gaussian technique for multi-agent slung load transportation

This paper copes with parameter-robust controller design for transportation system by multiple unmanned aerial vehicles. The transportation is designed in the form of string connection. Minimal state-space realization of slung-load dynamics is obtained by Newtonian approach with spherical coordinates. Linear quadratic Gaussian / loop transfer recovery (LQG/LTR) is implemented to control the position and attitude of all the vehicles and payloads. The controller's robustness against variation of payload mass is improved using parameter-robust linear quadratic Gaussian (PRLQG) method. Numerical simulations are conducted with several transportation cases. The result verifies that LQG/LTR shows fast performance while PRLQG has its strong point in robustness against system variation

Sample greedy based task allocation for multiple robot systems

This paper addresses in-schedule dependent task allocation problems for multi-robot systems. One of the main issues with those problems is the inherent NP-hardness of combinatorial optimisation. To handle this issue, this paper develops a decentralised task allocation algorithm by leveraging the submodularity concept and a sampling process of task sets. Our theoretical analysis reveals that the proposed algorithm can provide an approximation guarantee of 1/2 of the optimal solution for the monotone submodular case and 1/4 for the non-monotone submodular case, both with polynomial time complexity. To examine the performance of the proposed algorithm and validate the theoretical analysis, we introduce two task allocation scenarios and perform numerical simulations. The simulation results confirm that the proposed algorithm achieves a solution quality which is comparable to state-of-the-art algorithms in the monotone case and much better quality in the non-monotone case with significantly lower computational complexity