bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative workplace behavior and coping strategies among nurses: A cross‐sectional study
Authors: Hawkins Natasha , Jeong Sarah , Smith Tony
Published: September 2020

Negative workplace behavior affecting nurses is an internationally recognized problem. This study examines the types and extent of negative workplace behavior experienced by nurses in non‐metropolitan, regional acute care settings and their ways of coping when subject to that behavior. A cross‐sectional study was conducted involving 74 nurse participants in four regional hospitals in Australia. The structured questionnaire consisted of four parts: demographic questions, the Negative Acts Questionnaire – Revised, questions on exposure to bullying and/or incivility and policy awareness and use of pathways, and the Ways of Coping Questionnaire. Overall, 34% of participants were exposed to bullying and 49% to incivility over the previous month. The most common type of negative workplace behavior reported was “work‐related bullying,” which included exposure to excessive workloads, unrealistic deadlines, and information being withheld. Nurses reported the use of a variety of coping mechanisms, including problem‐focused coping strategies and seeking social support. The findings imply that negative workplace behaviors occur not only at individual nursesʼ level but also derive from the broader contexts of organizational management and systemic factors.
Consistent assignment in long‐term care homes: Avoiding the pitfalls to capitalise on the promises
Authors: Caspar Sienna , Brassolotto Julia M. , Cooke Heather A.
Published: September 2020

Background

Consistent assignment (CA) is the practice within long‐term care (LTC) by which care staff work with the same residents almost every shift for an indefinite period of time. CA is considered by many to be essential to person‐centred care.

Objectives

This paper explores how staff assignment practices impact the caregiving experience from the perspectives of resident care aides (RCAs), residents and family members and, by doing so, describe the nuanced conditions under which CA may or may not be beneficial to all, and why.

Methods

Data are drawn from 40 in‐depth interviews conducted as part of a larger institutional ethnography exploring the social organisation of care in three purposively selected LTC homes in Western Canada. Data analysis was based on the principles of constant comparison.

Results

RCAs, residents and family members described the primary benefit of CA as being able to ‘get to know’ each other well and form meaningful relationships. However, the RCAs also indicated that CA can contribute to feelings of isolation, which has negative effects on worker comfort and satisfaction, care team dynamics and communication, and resident care.

Conclusions

Management initiatives are needed to ensure that the implementation of CA does not result in the unintended consequences of decreasing RCAs' experience of teamwork, decreasing RCAs’ exchange of individualised resident care information, or negatively impacting RCAs’ ability and desire to care for each other as well as the residents.

Implications for practice

The staffing practice of consistent assignment in long‐term care homes provides increased opportunities for the development of stronger staff‐resident and staff‐family member relationships. Findings from this study enable us to offer several, evidenced‐based recommendations for ensuring the successful implementation of consistent assignment, such that it may be beneficial to all.
Elective caesarean section and bronchiolitis hospitalization: A retrospective cohort study
Authors: Douglas Lindsey C. , Leventer‐Roberts Maya , Levinkron Ohad , Wilson Karen M.
Published: September 2020

Background

We sought to evaluate whether elective caesarean section is associated with subsequent hospitalization for bronchiolitis.

Methods

This is a retrospective cohort study that used the electronic medical record database of Clalit Health Services, the largest healthcare fund in Israel, serving over 4.5 million members and over half of the total population. The primary outcome was bronchiolitis admission in the first 2 years of life. We performed logistic regression analyses to identify independent associations. We repeated the analysis using boosted decision tree machine learning techniques to confirm our findings.

Results

There were 124 553 infants enrolled between 2008 and 2010, and 5168 (4.1%) were hospitalized for bronchiolitis in the first 2 years of life. In logistic regression models stratified by seasons, elective caesarean section birth was associated with 15% increased odds (95% CI: 1.02‐1.30) for infants born in the fall season, 28% increased odds (95% CI: 1.11, 1.47) for those born in the winter, 35% increased odds (95% CI: 1.12‐1.62) for those born in the spring and 37% increased odds (95% CI: 1.18‐1.60) for those born in the summer. In the boosted gradient decision tree analysis, the area under the curve for risk of bronchiolitis admission was 0.663 (95% CI: 0.652, 0.674) with timing of birth as the most important feature.

Conclusion

Elective caesarean section, a potentially modifiable risk factor, is associated with increased odds of hospitalization for bronchiolitis in the first 2 years of life. These data should be considered when scheduling elective caesarean sections especially for infants born in spring and summer months.
Attachment style, partner communication, and physical well‐being among couples coping with cancer
Authors: Ramos Katherine , Langer Shelby L. , Todd Michael , Romano Joan M. , Ghosh Neeta , Keefe Francis J. , Baucom Donald H. , Syrjala Karen L. , Porter Laura S.
Published: September 2020

Attachment styles may influence interpersonal strategies used to cope with stress. We examined links between attachment style, communicative behaviors, and physical well‐being among 166 couples coping with cancer. Results of actor–partner interdependence mediation models indicated that insecure attachment styles were associated with greater self‐report of two different and seemingly contradictory communicative behaviors (disclosure and holding back), which in turn were associated with poorer physical well‐being. These effects were intrapersonal for both patients and spouses, with the exception of anxious attachment and holding back for spouses. They were also interpersonal in that spouse insecure attachment was associated with poorer patient physical well‐being through spouse communication (greater holding back and disclosure). Couple‐based communication interventions to support adjustment should consider attachment style.
Auditor or Adviser? Auditor (In)Dependence and Its Impact on Financial Management
Authors: Yang Lang (Kate)
Published: September 2020

Fiscal transparency entails government financial reporting and independent audits. This study postulates and tests the dual functions of external auditors: an examiner who assesses government compliance with accounting rules and an adviser who supplements government financial management capacity. Computational text analyses show that localities, especially those with lower financial management capacity, are likely to adopt similar languages in summarizing the governments’ financial conditions if they share the same auditor, suggesting auditor input in government disclosure. The auditor advisory role intensifies with a longer tenure. Further analyses show that auditor tenure is positively associated with the timeliness of audited financial reports. On the other hand, a long tenure reduces the likelihood of auditors' identifying internal control deficiencies and thus points to accountability concerns. These findings highlight the importance of government capacity‐building in fiscal transparency initiatives and the unique challenges to auditor independence in the public sector.
Investigating the association between students' strategy use and mathematics achievement
Authors: Sahin Nesrin , Dixon Juli K. , Schoen Robert C.
Published: September 2020

This observational study used data from 270 second‐grade students to investigate the association between students' strategy use for multidigit addition and subtraction and their mathematics achievement. Based on strategies they used during a mathematics interview, students were classified into the following strategy groups: (a) standard algorithm, (b) invented, (c) mixed, and (d) unclassified. We used two‐level hierarchical linear regression to investigate the association between students' strategy use and their performance on a standardized test in mathematics. Results indicated that students in the mixed strategy groups had significantly higher mathematics achievement than those in the standard algorithm and the unclassified groups.
Interpreting intercultural encounters with 90 Day Fiancé in the world religions' classroom
Authors: Mikles Natasha L.
Published: September 2020

While many college courses on “world religions” have as their foundation an assortment of institutionally‐authoritative, primary sources selected from a canon of sacred texts, this paper argues for a critical reevaluation of such textually‐based teaching methodologies in light of the religious literacy standards set by the American Academy of Religion. When professors are asked to defend the value of a degree in religious studies, they may tout such skills as cultural literacy or being able to conduct business in a globalized marketplace. These are not necessarily the skills one acquires from reading translations of texts like the Bhagavad Gita or the Quran. More often, these texts are assigned because the professor themself studied them in college, in a lineage that dates back to Max Müller and the beginnings of the “World Religions Paradigm.” This article uses the recent standards for religious literacy proposed by the American Academy of Religion to suggest a different object of analysis for obtaining these skills and framing intercultural encounters: the reality television franchise 90 Day Fiancé. This is presented as a case study of how a re‐imagined World Religions course may feature more creative and deliberate choices in order to achieve the skills promised.
Active cholesterol 20 years on
Authors: Lange Yvonne , Steck Theodore L.
Published: September 2020

This review considers the following hypotheses, some well‐supported and some speculative. Almost all of the sterol molecules in plasma membranes are associated with bilayer phospholipids in complexes of varied strength and stoichiometry. These complexes underlie many of the material properties of the bilayer. The small fraction of cholesterol molecules exceeding the binding capacity of the phospholipids is thermodynamically active and serves diverse functions. It circulates briskly among the cell membranes, particularly through contact sites linking the organelles. Active cholesterol provides the upstream feedback signal to multiple mechanisms governing plasma membrane homeostasis, pegging the sterol level to a threshold set by its phospholipids. Active cholesterol could also be the cargo for various inter‐organelle transporters and the form excreted from cells by reverse transport. Furthermore, it is integral to the function of caveolae; a mediator of Hedgehog regulation; and a ligand for the binding of cytolytic toxins to membranes. Active cholesterol modulates a variety of plasma membrane proteins—receptors, channels and transporters—at least in vitro.
Treatment of canine oral papillary squamous cell carcinoma using definitive‐intent radiation as a monotherapy—a case series
Authors: van der Steen Francine , Zandvliet Maurice
Published: September 2020

Canine oral papillary squamous cell carcinoma (COPSCC) is a rare neoplasm and although locally invasive it carries a favourable prognosis following wide surgical excision. Radiotherapy has been reported to be effective as an adjunct treatment to surgery. However, limited information is available on the role of radiotherapy as single treatment. This single‐institution retrospective study describes a series of 10 dogs diagnosed with macroscopic COPSCC that were treated with definitive‐intent radiotherapy (DRT) as a monotherapy. These dogs had a median age of 4 years (range: 0.4‐9.6 years). The tumour was located in the rostral oral cavity in all cases with a median tumour size of 2.5 cm (range: 0.8‐6.8 cm). No local or distant metastases were identified. All dogs were treated with electron beam DRT (>32Gy, 10‐16 daily fractions of 3.2Gy). The median follow‐up time was 961 days (range: 333‐3.498 days) with nine dogs achieving a complete response and one dog a partial response. The dog with the partial response developed disease progression at 228 days after initiation of radiotherapy. Two dogs died from non‐tumour‐related causes. The remaining seven dogs were still alive and in complete remission at the time of last follow‐up. Median progression‐free survival time and median survival time were not reached. DRT was generally well tolerated, but all dogs experienced self‐limiting acute radiation mucositis (grade 2‐3) and/or dermatitis (grade 1). No late radiation toxicity was observed. Macroscopic COPSCC appears to be a radiosensitive tumour that can be successfully treated with DRT eliminating the need for aggressive surgery in advanced cases.
Prophylactic anti‐glaucoma therapy in dogs with primary glaucoma: A practitioner survey of current medical protocols
Authors: Plummer Caryn E. , Bras Dineli , Grozdanic Sinisa , Komáromy András M. , McLellan Gillian , Miller Paul , Sapienza John S. , Teixeira Leandro , Webb Terah
Published: September 2020

Aim

To examine the use of prophylactic anti‐glaucoma medications in the normotensive fellow eye in dogs with unilateral overt primary glaucoma by veterinary ophthalmology clinicians.

Methods

A survey of veterinary ophthalmology clinicians was distributed over two international list serves servicing veterinary ophthalmologists, trainees, and individuals whose practice consisted primarily of ophthalmic patients. The survey was developed following analysis of historical and currently available medical options for control of intraocular pressure and for neuroprotection.

Results

Responses from 199 veterinary ophthalmology clinicians were evaluated. While a large variety of topical anti‐hypertensive drugs and protocols were used, the most commonly used medications were aqueous humor production suppressors such as dorzolamide 2.0% ophthalmic solution, timolol 0.5% ophthalmic solution, and a combination product containing both drugs. Latanoprost 0.005% ophthalmic solution was used infrequently for prophylaxis by comparison. The majority of respondents do not use concurrent anti‐inflammatory medications (61.22%), although a sizeable minority used prednisolone acetate, dexamethasone, or ketorolac as prophylactic treatment. Systemically administered ocular anti‐hypertensive agents were rarely used. Only 40% of respondents used neuroprotectant agents; the most commonly prescribed were the calcium channel blocker amlodipine and the nutraceutical Ocu‐Glo™. Recommended intervals between re‐examination by the clinician ranged from one month to one year, with most re‐evaluations occurring every 3 to 6 months. The majority of respondents recommended more frequent assessments of IOP at intervals between once monthly and once every 3 months.

Conclusions

Data analysis of medical therapy for the normotensive fellow eye of dogs previously diagnosed with primary glaucoma suggests that there is a great need for well‐designed, prospective, controlled, multi‐center studies to determine which protocols have the greatest efficacy in delaying an overt attack in the previously normotensive eye in dogs with a genetic predisposition to glaucoma. Prospective studies utilizing a carbonic anhydrase inhibitor such as dorzolamide and a prostaglandin analogue such as latanoprost would be reasonable as these two drugs are widely used in the treatment of overt glaucoma and would allow for an exploration of the impact of different mechanisms of action of lowering IOP on the pathophysiology of primary glaucoma.
Effects of e‐cigarettes and vaping devices on cardiac and pulmonary physiology
Authors: Tsai MuChun , Byun Min Kwang , Shin John , Crotty Alexander Laura E.
Published: September 2020

E‐cigarette aerosols are exceedingly different from conventional tobacco smoke, containing dozens of chemicals not found in cigarette smoke. It is highly likely that chronic use of e‐cigarettes will induce pathological changes in both the heart and lungs. Here we review human and animal studies published to date and summarize the cardiopulmonary physiological changes caused by vaping. In terms of cardiac physiology, acute exposure to e‐cigarette aerosols in human subjects led to increased blood pressure and heart rate, similar to traditional cigarettes. Chronic exposure to e‐cigarette aerosols using animal models caused increased arterial stiffness, vascular endothelial changes, increased angiogenesis, cardiorenal fibrosis and increased atherosclerotic plaque formation. Pulmonary physiology is also affected by e‐cigarette aerosol inhalation, with increased airway reactivity, airway obstruction, inflammation and emphysema. Research thus far demonstrates that the heart and lung undergo numerous changes in response to e‐cigarette use, and disease development will depend on how those changes combine with both environmental and genetic factors. E‐cigarettes have been advertised as a healthy alternative to cigarette smoking, and users are under the impression that vaping of e‐cigarettes is harmless, but these claims that e‐cigarettes are safer and healthier are not based on evidence. Data from both humans and animal models are consistent in demonstrating that vaping of e‐cigarettes causes health effects both similar to and disparate from those of cigarette smoking. Further work is needed to define the long‐term cardiopulmonary effects of e‐cigarette use in humans.

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Design and Evaluation of Torque Compensation Controllers for a Lower Extremity Exoskeleton
Authors: Zhou Xianlian , Chen Xinyu
Published: September 2020

In this article, we present an integrated human-in-the-loop simulation paradigm for the design and evaluation of a lower extremity exoskeleton that is elastically strapped onto human lower limbs. The exoskeleton has three rotational DOFs on each side and weighs 23 kg. Two torque compensation controllers of the exoskeleton are introduced, aiming to minimize interference and maximize assistance, respectively. Their effects on the wearer's biomechanical loadings are studied with a running motion and predicted ground reaction forces (GRFs). It is found that the added weight of the passive exoskeleton substantially increases the wearer's musculoskeletal loadings. The maximizing assistance controller reduces the knee joint torque by 31% when compared with the normal running (without exoskeleton) and by 50% when compared with the passive exoskeleton case. When compared with the normal running, this controller also reduces the hip flexion and extension torques by 31% and 38%, respectively. As a result, the peak activations of the biceps short head, gluteus maximus, and rectus femoris muscles are reduced by more than a half. Nonetheless, the axial knee joint reaction force increases for all exoskeleton cases due to the added weight and higher ground reaction forces. In summary, the results provide sound evidence of the efficacy of the proposed controllers on reducing the wearer's musculoskeletal loadings. And it is shown that the human-in-the-loop simulation paradigm presented here can be used for virtual design and evaluation of powered exoskeletons and pave the way for building optimized exoskeleton prototypes for experimental evaluation.
An Efficient Technique for Fractional Coupled System Arisen in Magnetothermoelasticity With Rotation Using Mittag–Leffler Kernel
Authors: Veeresha P. , Prakasha D. G. , Baleanu Dumitru
Published: September 2020

In this paper, we find the solution for fractional coupled system arisen in magnetothermoelasticity with rotation using q-homotopy analysis transform method (q-HATM). The proposed technique is graceful amalgamations of Laplace transform technique with q-homotopy analysis scheme, and fractional derivative defined with Mittag–Leffler kernel. The fixed point hypothesis is considered to demonstrate the existence and uniqueness of the obtained solution for the proposed fractional order model. To illustrate the efficiency of the future technique, we analyzed the projected model in terms of fractional order. Moreover, the physical behavior of q-HATM solutions has been captured in terms of plots for different arbitrary order. The attained consequences confirm that the considered algorithm is highly methodical, accurate, very effective, and easy to implement while examining the nature of fractional nonlinear differential equations arisen in the connected areas of science and engineering.
Heat Transfer Analysis of Regenerative Thermo-Mechanical Refrigeration System
Authors: Sleiti Ahmad K. , Al-Khawaja Mohammed
Published: September 2020

Refrigeration systems contribute to the critical environmental concerns including global warming and ozone depletion. It is necessary to develop new systems that use renewable energy resources and waste heat to perform the cooling function with eco-friendly working fluids. This improves the energy efficiency of the power systems and minimizes the harmful effects of conventional refrigeration systems. This paper introduces an analysis of a regenerative thermo-mechanical refrigeration system that is powered with renewable heat sources (solar, geothermal) or waste heat (from internal combustion engines, gas power plants, and steam power plants). The system operates at the supercritical conditions of the working fluids. The performance of the system is evaluated based on power efficiency, the COP, and the expander-compressor diameters. Also, a number of working fluids were compared with each other based on their performance and environmental effects. There is a trade-off between high-performance fluids and their environmental effects. Using R32 as a working fluid at Th = 150 °C and Tc1 = 40 °C, the system produces a cooling capacity of 1 kW with power efficiency of 10.23%, expander diameter of 53.12 mm and compressor diameter of 75.4mm. The regenerator increases the power efficiency by about 1%. However, the size of the regenerator is small (Dr = 6.5 mm, Lr = 142 mm].
Evaporation of Silver-Graphene Hybrid Nanofluid Droplet on its Nanostructured Residue and Plain Copper Surfaces at Elevated Temperatures
Authors: Siddiqui Farooq Riaz , Tso Chi Yan , Fu Sau Chung , Qiu Huihe , Chao Christopher Yu Hang
Published: September 2020

Droplet evaporation is an efficient process as it removes a large amount of heat by using the latent energy, making it suitable for heat transfer applications. In this research, evaporation of the silver-graphene hybrid nanofluid (SGHF) droplet, because of its synergistic thermal conductivity, is investigated for substrate temperature in a range of 25–100 °C. The experiments for droplet evaporation were performed in an environmental facility for two droplet sizes, 3 μL and 30 μL volume, on a copper plate. A 100 W silicone heater mat was used to heat the copper plate from the underside, while two T-type thermocouples were used to monitor its surface temperature. As droplet evaporation ended, a porous residue was formed on the copper surface. Subsequently, a 3 μL volume of the SGHF droplet was dispensed on the porous residue surface. The results showed a tremendous rise in the evaporation rate (up to 160%) for the subsequent SGHF droplet sitting on the porous residue as compared to the non-wetted copper surface. Moreover, the evaporation rate of the SGHF droplet on the copper surface increased up to 56% as compared to the water droplet for a substrate temperature range of 25–100 °C.
Saturation Boiling of HFE-7000 Liquid on Inclined Rough Copper Surfaces
Authors: El-Genk Mohamed S. , Pourghasemi Mahyar
Published: September 2020

Pool boiling experiments are performed to investigate the effects of inclination angle, θ, and average roughness, Ra, of uniformly heated 10 × 10 mm copper surfaces on saturation boiling of HFE-7000 dielectric liquid. Ra varied from 0.039 to 0.1.44 μm and θ from 0° (upward facing) to 180° (downward facing). In addition, high speed images and still photographs of nucleate boiling in the various regions and near CHF are captured to assist the interpretation of experimental results. The values of CHF and the maximum nucleate boiling heat transfer coefficient, hMNB, which occurs near the fully developed nucleate boiling region, increase with increasing Ra and/or decreasing θ. The corresponding surface superheats, however, decrease with increasing θ and/or Ra. In the upward facing orientation, CHF increases from ∼20.7 to ∼30.9 W/cm2 with increasing Ra from 0.039 to 0.144 μm, and the corresponding CHF values in the downward facing orientation are 7.1 and 8.9 W/cm2, respectively. Nucleate boiling heat transfer coefficient, hNB, in the discrete bubbles region at low surface superheats increases, while in the fully developed nucleate boiling region at high superheats it increases with increasing Ra and/or decreasing θ. The developed correlations for CHF and hMNB and corresponding superheats, as functions of Ra and θ, are in good agreement with the experimental data.
Nanoscale and Macroscale Effects of Mineral Deposition During Water Evaporation on Nanoporous Surfaces
Authors: McClure Emma R. , Carey Van P.
Published: September 2020

Recent studies have indicated that droplet evaporation heat transfer can be substantially enhanced by fabricating a thin nanoporous superhydrophilic layer on a metal substrate. Such surfaces have immense potential to improve spray cooling processes, however, little durability testing of the surfaces have been performed. In spray cooling applications, as water evaporates any impurities in the water will be deposited onto the surface. Primarily, this investigation serves to demonstrate how minerals in hard water deposit on the surface and interact with the ZnO nanopillars of the superhydrophilic surface. Quantifying the effects of mineral scale on droplet spreading and vaporization heat transfer on the surface is important in determining implementation requirements to advance the surface into industry applications. Micrographs of the surface demonstrate minerals deposit nonuniformly, and quickly fill the nanostructure. Despite a reduction in the extent of droplet spreading due to the mineral deposition, scaled surfaces still demonstrated improved thermal performance compared to the uncoated, smooth copper surface. Scale tended to build up on previously deposited scale leaving largely uncoated areas where droplets chose to preferentially spread resulting in a continued low contact angle. Maintaining these uncoated areas and reducing the contaminants present in the water will extend the life and performance of the nanostructured surface.
Temperature Distribution in a Turbulent Flow in the Heat Pollution Phenomena
Authors: Radulescu Victorita
Published: September 2020

The thermal pollution, with major effects on the water quality degradation by any process involving the temperature transfer, represents nowadays a major concern for the entire scientific world. The turbulent heat and the mass transfer have an essential role in the processes of thermal pollution, mainly in problems associated with the transport of hot fluids in long heating pipes, thermal flows associated with big thermo-electric power plants, etc. In the last decades, the problems of the turbulent heat and mass transfer were analyzed for different dedicated applications. The present paper, in the first part, estimates the universal law of the velocity distribution near a solid wall, with a specific interpretation of the fluid viscosity, valid for all types of flows. Most of the scientific researches associate nowadays both the turbulent heat and the mass transfer with the Prandtl number. In the turbulent fluid flow near a solid and rigid surface, there are three flowing domains, laminar, transient, and fully turbulent, each one with its characteristics. In this paper, it is assumed that the friction effort at the wall remains valid at any distance from the wall, but with different forms associated with the dynamic viscosity. By using the superposition of the molecular and turbulent viscosity and by creating the interdependence between the molecular and turbulent transfer coefficients is estimated the mathematical model of the velocity profile for the fluid flow and temperature distribution. Three supplementary hypotheses have been assumed to estimate the dependence between the laminar and thermal sub-layer and the hydrodynamic sub-layer. The theoretical obtained distribution was compared with some experimental results from the literature and it was observed there is a good agreement between them; the differences are smaller than 3%. In the second part of the paper is determined the temperature field for a fluid flowing also in presence of the solid surfaces with different temperatures, associated not only with the Prandtl number but also with the fluid viscosity and its dependence with the temperature, correlated with the Grashoff number. In the next paragraph is used the concept of the laminar substrate with different thicknesses for the hydrodynamic flows with thermal transfer to the solid walls, and also the inverse transfer from the solid walls affecting the fluid flow and the mass transfer. The obtained mathematical model is correlated with the semi-empirical data from the literature. By numerical modeling, the obtained results were compared with the experimental measurements and it was determined the dependence between the Stanton number and the Prandtl number. The numerical results demonstrate a good agreement with the experimental results in a wide range of the Prandtl numbers from 0.5 to 3000. Finally, are mentioned some conclusions and references.
Mechanical Performance of Concrete Thermal Energy Storage Subject to Operating Thermal Demands
Authors: Wang Shuoyu , Abdulridha Ahmed , Quiel Spencer , Naito Clay , Sulieman Muhannad , Caspar Justin , Bravo Julio , Neti Sudhakar , Romero Carlos , Yao Zheng , Oztekin Alparslan
Published: September 2020

This paper presents a lab-scale investigation of the use of structural concrete for sensible heat storage in power plants. Transient thermal and mechanical analyses are simulated via coupled finite element models to study the thermo-mechanical performance of a cylindrical concrete block with 4-in diameter and 8-in length under thermal loading. The model is validated by performing experiments on high strength concrete (HSC) cylinders with this geometry in an oven, which heats the specimens from the outside. The models are then modified to simulate thermal energy storage (TES) application with thermal loading applied at the interior surface of a hole running through the longitudinal center of the cylinder. Thermal cycles have a varying heating rate (5, 10, or 24 hours) followed by consistent durations of soaking (2 hours) and cooling (13 hours). In the TES simulations, a steel jacket is also applied to the external surface of the concrete cylinder to provide confinement. The resulting thermal distribution and maximum principal stresses during heating and cooling are observed as a function of time. This study provides insight into the mechanical requirements and impact on material integrity for concrete modules subjected to representative TES heating regimes.
Experimental Study on the Thermal-Hydraulic Performance of Louvered Fin and Flat Tube Heat Exchangers
Authors: Khan Tariq Amin , Li Wei , Xiaolong Yan , Yang Zhuo
Published: September 2020

In this study, the air side heat transfer and pressure drop characteristics of flat tube with louvered fins compact heat exchangers have been experimentally investigated. Three samples of heat exchangers, i.e., one without fins, one with flat louver fins and one with corrugated louver fins are studied. The louvers in the present samples have small louver pitch (Lp = 0.8mm) and high louver angle (θl = 37°) due to the space constraints in automotive applications. The performance tests were conducted in a high standard test facility which are composed of an evaporator chamber, condenser chamber and auxiliary units. In our study, only evaporators are tested and hence the condenser section is the same during the tests.

Experimental results under the wet surface conditions show that the cooling capacity and pressure drop performances of evaporator with flat louver fins (HX2) is higher than the one with corrugated louver fins (HX3) while the evaporator without fins has the minimum heat transfer due to no interruptions. This can be due to higher number of tubes in the case of HX2 having small tube pitch. However, the overall performance (ratio of heat transfer per unit volume to pressure drop per unit volume) of HX2 is better than HX3 which signifies the importance of corrugated louver fins.
Copper-Carbon Nanotube Micropillars for Passive Thermal Management of High Heat Flux Electronic Devices
Authors: Rojo Gerardo , Darabi Jeff
Published: September 2020

Miniaturization of electronic products and a consequent rapid increase in power density of advanced microprocessors and electronic components have created a need for improved cooling techniques to efficiently remove heat from such devices. Traditional air-cooled heat sinks have been utilized for several decades as the most cost-effective cooling technique for electronic cooling applications. However, the existing thermal management solutions are unable to maintain the temperature of the next generation of complex electronic systems within acceptable limits without adding considerable weight and complexity. This paper reports a microstructured wick for application in passive thermal management systems such as heat pipes and vapor chambers. The wick structure consists of mushroom-like composite copper-carbon nanotubes (Cu-CNT) micropillars. The small spacing between micropillar heads provides a higher capillary pressure whereas the large spacing between the base of micropillars provides a higher permeability for liquid flow. The micropillar array was fabricated on a copper substrate using an electroplating technique. The micropillar array was then tested in a controlled environment to experimentally measure its thermal performance under several operating conditions. A heat removal capability of 80 W/cm2 was demonstrated at a wall superheat of 15° C. In addition, a computational study was performed using ANSYS Fluent to predict the thermal performance of the micropillar array. Model predictions were compared with the experimental results and good agreement was obtained.
Impact of Micropillar Density Distribution on the Capillary Limit of Heat Pipes
Authors: Hassaine Daoudji Doriane Ibtissam , Struss Quentin , Amnache Amrid , Léveillé Étienne , Salim Shirazy Mahmood Reza , Fréchette Luc G.
Published: September 2020

This paper shows the performance enhancement of heat pipes by tailoring the density distribution of micropillar wicks to minimize viscous pressure loss while maintaining sufficient capillary pumping. In a heat pipe, capillarity and permeability are linked, since small pores create higher capillary pumping while unfortunately inducing more pressure drop along the heat pipe. This pressure loss accumulates along the heat pipe, leading to a non-uniform pressure difference between the liquid and vapor. Therefore, we do not need a uniform capillary pressure to withstand this difference. This provides the opportunity to spatially tailor the wick structure, aiming for a high capillarity to pump the liquid, but a low permeability to induce less pressure loss. Our study offers a compromise between capillarity and permeability by designing the density distribution of the pillar wick structure. This density distribution, which was not studied before, will be shown to enhance the heat pipe performance.

The theoretical models show that a tailored density distribution can enhance the heat pipe performance by a factor of 1.5. To support this result, ‘rate of rise’ measurements along a pillar array demonstrate that the liquid pressure loss in a tailored density array are less compared to a constant pillar density.
Effect of Temperature on Velocity Profiles of Ions and Water Molecules in Charged Nanotubes
Authors: Wang Yu , Liu Zhenyu
Published: September 2020

High surface charge density makes it possible for charge inversion to occur in the electrical double layer, in which cases, flow reversal appears for electroosmotic driven flow that is one of the best-known methods of fluid transport based on the electro-kinetic phenomenon. Reverse electroosmotic flow of an aqueous solution of KCl was studied using MD method in this work. Nonequilibrium molecular dynamics simulations were carried out to investigate the effect of temperature on velocity profiles of ions and water molecules confined in charged carbon nanotubes (CNTs) with a diameter of 3.0 nm. The results demonstrate that the temperature dependence of velocity of ions and water molecules is obviously different for various distances to the tube wall. It is found that the temperature has a direct effect on the ion velocity profiles, that is, as the temperature increases, the velocity of either counter-ion or co-ion in the diffuse layer increases significantly though the velocity drops sharply in the vicinity of the tube wall surface. As for water molecules, the MD simulations show plenty of velocity profiles, in which the velocity is slightly positive near the tube wall, but is negative in most of the rest region. The temperature effect on reverse electroosmotic flow is clearly observed, which is reflected in two aspects: the viscosity of the fluid and the velocity profiles of ion and water molecule.
Numerical Investigation of Single Bubble Dynamics Passing a Mesh-Based Structure
Authors: Alnaimat Fadi , Mathew Bobby , Alhammadi Omar
Published: September 2020

In this article, investigations of the dynamic behaviors of a single bubble flowing across a mesh-based structure domain was conducted using the volume of fluid (VOF) model. The study was investigated in various mesh structure sizes, including hole size and gap distance. The fundamental behavior of bubble deformation and the effects of gap sizes were analyzed. Subsequently, the predicted dynamics of the deforming bubble area and the effect of the surface tension were examined inside the mesh holes. The discharging bubbles from the mesh structure resulted in a slight difference in the physical features from the original bubble dynamics before entering the mesh (flow restriction). This drafted the bubbles in different trajectories and led to behave differently based on the mesh characteristics. The complex interactions and the subsequent deformations were observed between different mesh sizes. For the validation of the bubble dynamics, the results of computational fluid dynamics (CFD) simulation were tested under different mesh sizes detailing the velocity field, exiting trajectory, bubbles deformation, and residence time, which helps to reveal the affected parameters on the separation mechanism of the original bubble.
Technique for Determining Local Nucleate and Film Boiling Correlations for Large Diameter Tubes
Authors: Azih Chukwudi , MacCoy Reilly , Mazhar Hazem , Fraser Chris
Published: September 2020

The boiling behaviour on the surface of large diameter tubes is known to be strongly dependent on the local orientation of the surface around the circumference. Understanding such local variations in boiling behaviour is of particular interest in the CANDU® nuclear industry, where part of the heat removal path for cooling the fuel under postulated accident conditions is via pool-boiling on the surface of the 132 mm diameter calandria tube that is immersed in a pool of the heavy water moderator. While the average pool boiling behaviour of the calandria tubes has been well studied with integrated experiments, local boiling correlations have not been developed for prototypical diameter calandria tubes. Local boiling correlations will allow for more detailed modelling of postulated accident scenarios and better quantification of safety margins. In this study, the nucleate and film pool-boiling characteristics of a large diameter Zircaloy-2 CANDU® calandria tube were tested in a pool of subcooled water. A novel technique is developed to derive the local boiling curve along the circumference of the tube, involving the local heating, measurement of the wall temperature, and heat flux. The adequacy of the technique is determined by comparing the local boiling curves with previous experiments in which averaged pool boiling characteristics were obtained.
Inverse Model for Fire Heat Release Rate Using Deep Neural Networks
Authors: Kou Luyao , Wang Xinzhi , Zhang Hui , Yang Rui , Liu Yi
Published: September 2020

The estimation of heat release rate (HRR) in a building fire is a meaningful yet challenging task to improve first emergency response. Inspired by the capability of deep learning method that mines patterns from raw data, the inverse model based on Gated Recurrent Unit (GRU) is presented for the inversion of HRR. First, a series of fire scenarios is simulated to form the dataset by forward fire modeling. Second, GRU is applied to learn representations from windows of time-series sensor data. Output layer is used to map the learned representations to targets. Third, the HRR is estimated by the trained GRU network with observed data from the fire. Finally, the accuracy and efficiency of the inverse model are evaluated in a multi-compartment configuration. Preliminary results indicate that GRU network can be applied to the inversion of fire HRR with higher accuracy and efficiency.
Experimental Investigation on Heat Transfer of Water Spray Cooling by Addition of n-Butanol
Authors: Cai Chang , Liu Hong , Chen Han , Zhao Chuanqi , Gao Jiuliang , Jia Ming , Yan Yan'an
Published: September 2020

Heat transfer characteristics of water spray cooling with n-butanol additive were experimentally studied in this paper. The results indicated that adding n-butanol can effectively enhance the heat dissipation and control the surface temperature. The optimal concentration of n-butanol corresponding to the best heat transfer performance is 0.5 vol%. The experimental Nusselt numbers also agree well with a previous correlation with Weber, Prandtl, Jacob and Reynolds numbers, evidenced by a maximum absolute error of 6.34%. The measurement also showed that the decrease of surface tension and contact angle of the n-butanol-water mixture is the main mechanism to enhance the spray cooling heat transfer, while other physical properties also play an important role. The surface temperature non-uniformity in the radial direction is more apparent at a high heat flux while the addition of different contents of n-butanol has a negligible effect.
Experimental Investigation of a PCM-Based Topology Optimized Heat Sink for Passive Cooling of Electronics
Authors: Ho Jin Yao , Leong Kai Choong
Published: September 2020

A thermal energy storage unit filled with phase change material (PCM) can serve as a heat sink for the cooling of electronics with intermittent or periodic heat dissipation rates. The use of thermal conductive structures (TCS) is an effective method of improving the thermal performance of a PCM-based heat sink. In this paper, topology optimization is explored to develop a new class of TCS with a tree-like structure to enhance the thermal performance of a trapezoidal heat sink. The topology-optimized heat sink was then fabricated by Selective Laser Melting (SLM) using an aluminum alloy, AlSi10Mg, as the base powder. Experiments were performed to evaluate the thermal performance of the topology-optimized heat sink with the tree-like structure. In addition, a conventional longitudinal-fin heat sink of the same solid volume fraction (φ = 16.2%) and a heat sink without enhanced structure were also fabricated and experimentally investigated for comparison. Rubitherm RT-35HC paraffin wax was used as the PCM. Three different heat fluxes of 4.00 kW/m2, 5.08 kW/m2 and 7.24 kW/m2 were applied at the base of each specimen by a silicone rubber heater. The structure wall and the PCM temperatures were measured over time. Our results show that, for all heat rates tested, the topology-optimized heat sink was able to maintain a lower base temperature as compared to the fin-structure and the plain heat sinks. A thermal enhancement ratio (ε) is defined to evaluate the performance of the heat sinks with and without the use of PCM. From the experimental results, the highest ε value of 8.6 was achieved by the topology-optimized heat sink. These results indicate the better performance of the topology-optimized heat sink in dissipating heat as compared to the other specimens.
Improved Accuracy of a Machining Tool With a Constant Cutting Speed Vector and Outside Approach Path
Authors: Suzuki Takamaru , Iwama Shoya , Hirogaki Toshiki , Aoyama Eiichi , Ikegami Takakazu , Akai Takayuki
Published: September 2020

A five-axis machining center is equipped with a direct drive motor on a rotary axis and is capable of synchronous control, which makes it a feasible tool for quickly and accurately machining complicated three-dimensional surfaces such as propellers and hypoid gears. However, the accuracy of the machined shape and consistency of the freeform machined surface both need to be improved. We developed a method for maintaining the feed speed vector at the milling point by controlling three axes of the five-axis machining center (two linear and one rotary) to improve the quality of the machined surface considering differences in the servo characteristics of the three axes during the actual process. Experimental results showed that using the proposed method with an outside approach path for the machining tool greatly reduced the shape error. The effectiveness of the proposed method was verified by using a wireless Internet of Things holder to monitor the machining force.
Design of a Two-Piece Brassiere Cup From its Data Points Toward its Automation
Authors: Yoshida Kotaro , Wakamatsu Hidefumi , Morinaga Eiji , Kubo Takahiro
Published: September 2020

A method to design the two-dimensional shapes of patterns of two piece brassiere cup is proposed when its target three-dimensional shape is given as a cloud of its data points. A brassiere cup consists of several patterns and their shapes are designed by repeatedly making a paper cup model and checking its three-dimensional shape. For improvement of design efficiency of brassieres, such trial and error must be reduced. As a cup model for check is made of paper not cloth, it is assumed that the surface of the model is composed of several developable surfaces. When two lines that consist in the developable surface are given, the surface can be determined. Then, the two-piece brassiere cup can be designed by minimizing the error between the surface and given data points. It was mathematically verified that the developable surface calculated by our propose method can reproduce the given data points which is developable surface.
Study on Adhesion With Stress and Temperature in Drilling of Aluminum Alloy
Authors: Matsumura Takashi , Arakawa Satoshi , Tamura Shoichi
Published: September 2020

Aluminum alloys have been widely used for automobile and aircraft parts. In cutting of aluminum alloy, adhesion sometimes occurs to deteriorate surface finish. The study discusses the adhesion characteristics in drilling of aluminum alloy (A7075) with a flat tool at a point angle of 180 degrees.

The adhesion volumes on the rake face of the tool were measured in drillings of blind holes for the cutting speeds and the feed rates. Then, the stress and the temperature distributions were estimated in the cutting simulation. In the simulation, the cutting force is predicted in the chip flow model based on the minimum cutting energy. The cutting temperature is analyzed in Finite volume method using the result in the cutting force prediction. The adhesion volumes are associated with the stress and temperature on the rake face. The adhesion volume becomes large in the temperature ranged from 400 to 500 K. The adhesion volume increases with the stress up to 500 MPa.