bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of oral ondansetron on QT interval in children with acute gastroenteritis; a retrospective observational study
Authors: Yang Heewon , Jeon Woochan , Ko Yura , Jeong Sooin , Lee Jisook
Published: November 2021

Background

In mildly to moderately dehydrated patients with acute gastroenteritis (AGE), oral rehydration therapy (ORT) is the treatment of choice. Though ondansetron is a very effective antiemetics and leads to succeed ORT, there have been reports QT prolongation in patients using it. We investigated the effect of oral ondansetron on QT interval in mildly to moderately dehydrated children with AGE.

Methods

This retrospective observational study was conducted in a single pediatric emergency department (ED) of a tertiary university hospital. We collected the medical records of patients with a primary diagnosis of AGE who received oral ondansetron and underwent an electrocardiogram between January 2017 and June 2018. A pediatric emergency physician calculated the corrected QT interval (QTc) by Bazett’s method, and the calculations were reviewed by a pediatric cardiologist. QTc values before (preQTc) and after (postQTc) ondansetron administration were analyzed. ΔQTc was calculated as the change from preQTc to postQTc. We also investigated any cardiac complications from oral ondansetron.

Results

Total 80 patients were included. The mean age of the patients was 53.31 ± 32.42 months, and 45% were male. The mean dose of oral ondansetron was 0.18 ± 0.04 mg/kg. The mean interval from administration of ondansetron to performance of the electrocardiogram was 65 ± 26 min. The mean preQTc was 403.3 ± 24.0 ms, and the mean postQTc was 407.2 ± 26.7 ms. Two patients had a preQTc ≥460 ms, and one patient had a postQTc ≥460 ms. ΔQTc was ≥30 ms in seven patients (8.8%). No ΔQTc was ≥60 ms. No pre- or postQTc was ≥500 ms. No patient had a fatal cardiac arrhythmia after taking ondansetron.

Conclusion

Oral administration of a single dose of ondansetron in children with AGE did not cause high-risk QTc prolongation or fatal arrhythmia.
Family alcohol use, rather than childhood trauma, is more likely to cause male alcohol use disorder: findings from a case-control study in northern China
Authors: Chen Xu , Pan Yunmeng , Xu Peiru , Huang Yi , Li Nan , Song Yun
Published: November 2021

Objective

To explore the influence of childhood trauma and family alcohol use on male alcohol use disorder.

Methods

We conducted a case-control study using Childhood Trauma Questionnaire (CTQ) and a structured interview involving 129 men with alcohol use disorder and 129 healthy male volunteers. The two groups were compared in terms of childhood trauma, parental drinking behavior, and attitudes toward childhood drinking.

Results

Patients showed higher scores of CTQ than controls on childhood trauma experiences, including on the subscales of physical abuse, emotional abuse, sexual abuse, and emotional neglect. Higher proportions of patients than controls had fathers who drank seven or more times a week, and had mothers who were opposed to childhood drinking. Conversely, a smaller proportion of patients than controls had fathers who opposed childhood drinking. Patients were more likely than controls to have been induced to drink as children. Logistic regression analysis identified three risk factors for alcohol use disorder: induced drinking during childhood [odds ratio (OR) 6.09, 95% confidence interval (CI) 2.56–14.51], the father’s weekly alcohol consumption during the respondent’s childhood (OR 4.40, 95%CI 2.94–6.58) and history of smoking (OR 3.39, 95%CI 1.48–7.77). Conversely, more years of education were a protective factor against alcohol use disorder (OR 0.88, 95% CI 0.78–0.99).

Conclusions

Men whose fathers drank frequently during their childhood and were encouraged to drink may be at increased risk of alcohol use disorder in adulthood. In fact these factors of family alcohol use appear to increase risk of alcohol use disorder among adult men more than exposure to childhood trauma does.
Dose tranexamic acid reduce blood loss associated with simultaneous bilateral distal tibial tubercle-high tibial osteotomy?
Authors: Wang Zhimeng , Huang Qiang , Liu Lu , Lu Yao , Zhang Congming , Ma Teng , Li Zhong , Wang Qian , Xue Hanzhong , Zhang Kun
Published: November 2021

Background

Simultaneous bilateral distal tibial tubercle high tibial osteotomy (SBDTT-HTO) can result in increased blood loss. The aim of this study is to evaluate the actual hemostatic effect of different tranexamic acid (TXA) treatment regimen in SBDTT-HTO.

Methods

We conducted a retrospective case–control study including 54 patients who underwent SBDTT-HTO. The single-dose group (n = 18) received 1 g of intravenous TXA 15–30 min before surgery, the two-dose group (n = 18) received an additional 1 g of intravenous TXA 6 h after surgery, and the multiple-dose group (n = 18) received an additional 1 g intravenous TXA per-day until discharge. Blood loss, hemoglobin levels, occurrence of any adverse events,functional analysis, quality of life, and pain assessmentswere compared among the three groups.

Results

The total blood loss, hidden blood loss, drainage volumes, and haemoglobin level in the multiple-dose group all occupy a significant advantage.(p < 0.05). In addition, better quality of life were observed in patients belonging to the multiple-dose group then single-dose group.(p < 0.05).

Conclusions

Based on our results, for patients undergoing SBDTT-HTO, sequential intravenous TXA administration can effectively and safely reduce blood loss,maintain postoperative Hb levels,and with the advantage of accelerating recovery.
Health Humanities curriculum and evaluation in health professions education: a scoping review
Authors: Carr Sandra E. , Noya Farah , Phillips Brid , Harris Anna , Scott Karen , Hooker Claire , Mavaddat Nahal , Ani-Amponsah Mary , Vuillermin Daniel M. , Reid Steve , Brett-MacLean Pamela
Published: November 2021

Background

The articulation of learning goals, processes and outcomes related to health humanities teaching currently lacks comparability of curricula and outcomes, and requires synthesis to provide a basis for developing a curriculum and evaluation framework for health humanities teaching and learning. This scoping review sought to answer how and why the health humanities are used in health professions education. It also sought to explore how health humanities curricula are evaluated and whether the programme evaluation aligns with the desired learning outcomes.

Methods

A focused scoping review of qualitative and mixed-methods studies that included the influence of integrated health humanities curricula in pre-registration health professions education with programme evaluate of outcomes was completed. Studies of students not enrolled in a pre-registration course, with only ad-hoc health humanities learning experiences that were not assessed or evaluated were excluded. Four databases were searched (CINAHL), (ERIC), PubMed, and Medline.

Results

The search over a 5 year period, identified 8621 publications. Title and abstract screening, followed by full-text screening, resulted in 24 articles selected for inclusion. Learning outcomes, learning activities and evaluation data were extracted from each included publication.

Discussion

Reported health humanities curricula focused on developing students’ capacity for perspective, reflexivity, self- reflection and person-centred approaches to communication. However, the learning outcomes were not consistently described, identifying a limited capacity to compare health humanities curricula across programmes. A set of clearly stated generic capabilities or outcomes from learning in health humanities would be a helpful next step for benchmarking, clarification and comparison of evaluation strategy.
Two decades (1998 to 2018) of collaborative human immunodeficiency virus clinical pharmacology capacity building in a resource constrained setting
Authors: Maponga Charles C. , Monera-Penduka Tsitsi G. , Mtisi Takudzwa J. , Difrancesco Robin , Makita-Chingombe Faithful , Mazambara Fine , Tooley Kathleen , Mudzviti Tinashe , Morse Gene D.
Published: November 2021

While important advances have been made in the prevention and treatment of Human Immunodeficiency Virus (HIV) infection, limited expertise and resource constraints to effectively manage rollout of HIV programs often contribute to poor treatment outcomes in Sub-Saharan Africa. In 1998, the University of Zimbabwe (UZ) and the University at Buffalo, State University of New York (UB), developed a collaborative clinical pharmacology capacity building program in Zimbabwe to train the next generation of HIV researchers and support rollout of the national HIV program. The collaboration was funded by research and training grants that were competitively acquired through United States of America government funding mechanisms, between 1998 and 2016. Thirty-eight research fellows were trained and a specialty clinical pharmacology laboratory was established during this period. Knowledge and skills transfer were achieved through faculty and student exchange visits. Scientific dissemination output included sixty-two scholarly publications that influenced three national policies and provided development of guidelines for strategic leadership for an HIV infection—patient adherence support group. The clinical pharmacology capacity building program trained fellows that were subsequently incorporated into the national technical working group at the Ministry of Health and Child Care, who are responsible for optimizing HIV treatment guidelines in Zimbabwe. Despite serious economic challenges, consistent collaboration between UZ and UB strengthened UZ faculty scholarly capacity, retention of HIV clinical research workforce was achieved, and the program made additional contributions toward optimization of antiretroviral therapy in Zimbabwe.
Accuracy of one-dimensional templating on linear EOS radiography allows template-directed instrumentation in total knee arthroplasty
Authors: Finsterwald Michael Andreas , Sobhi Salar , Isaac Senthuren , Scott Penelope , Khan Riaz J. K. , Fick Daniel P.
Published: November 2021

Background

Templating for total knee arthroplasty (TKA) is routinely performed on two-dimensional standard X-ray images and allows template-directed instrumentation. To date, there is no report on one-dimensional (1D) anteroposterior (AP) templating not requiring specific templating software. We aim to describe a novel technique and explore its reliability, accuracy and potential cost-savings.

Methods

We investigated a consecutive series of TKAs at one institution between January and July 2019. Patients with preoperative low-dose linear AP EOS radiography images were included. Implant component sizes were retrospectively templated on the AP view with the hospitals imaging viewing software by two observers who were blinded to the definitive implant size. Planning accuracy as well as inter- and intra-observer reliability was calculated. Cost-savings were estimated based on the reduction of trays indicated by the 1D templating size estimations.

Results

A total of 141 consecutive TKAs in 113 patients were included. Accuracy of 1D templating was as follows: exact match in 53% femoral and 63% tibial components, within one size in 96% femoral and 98% tibial components. Overall 58% of TKA components were planned correctly and 97% within one size. Inter- and intra-rater reliability was good (κ = 0.66) and very good (κ = 0.82), respectively. This templating process can reduce instrumentation from six to three trays per case and therefore halve sterilisation costs.

Conclusions

The new 1D templating method using EOS AP imaging predicts component sizes in TKA within one size 97% of the time and can halve the number of instrumentation trays and sterilisation costs.
Honokiol attenuates lipotoxicity in hepatocytes via activating SIRT3-AMPK mediated lipophagy
Authors: Liu Jingxin , Zhang Tian , Zhu Jianzhong , Ruan Shuangchen , Li Rongsong , Guo Bing , Lin Ligen
Published: November 2021

Background

Non-alcoholic fatty liver disease (NAFLD) is characterized by ectopic accumulation of triglycerides in the liver. Emerging evidence has demonstrated that lipophagy regulates lipid mobilization and energy homeostasis in the liver. Sirtuin 3 (SIRT3), a mitochondrial NAD+-dependent deacetylase, modulates the activities of several substrates involving in autophagy and energy metabolism. Honokiol (HK) is a natural lignan from the plants of Magnolia genus that exhibits potent liver protective property.

Methods

AML12 was challenged with 500 μM palmitic acid and 250 μM oleic acid mixture solution to induce lipotoxicity. C57BL/6J mice were fed with a choline-deficient high fat diet (CDHFD) to generate liver steatosis. The expression of autophagy-related and AMP-activated protein kinase (AMPK) pathway proteins was evaluated by Western blotting and immunofluorescence staining. Intracellular lipid accumulation was validated by Nile red staining. Molecular docking analysis was performed on AutoDock 4.2.

Results

HK (5 and 10 μM) was found to attenuate lipid accumulation through promoting SIRT3-AMPK-mediated autophagy, mainly on lipid droplets. HK had hydrophobic interaction with amino acid residues (PHE294, GLU323 and VAL324) and NAD+. Moreover, HK improved mitochondrial function to enhance lipolysis, through decreasing the acetylated long-chain acyl-CoA dehydrogenase level. In CDHFD-fed mice, HK (2.5 and 10 mg/Kg) treatment obviously prevented lipid accumulation in the liver. And co-treatment of the AMPK inhibitor, Compound C, almost abolished the above changes.

Conclusions

These results suggest that HK could ameliorate lipotoxicity in hepatocytes by activating SIRT3-AMPK-lipophagy axis, which might be a potential therapeutic agent against NAFLD.
Can earthen architectural heritage save us?
Authors: Moriset Sebastien , Rakotomamonjy Bakonirina , Gandreau David
Published: November 2021

Contemporary architecture seems to turn its back on the past in terms of the raw materials taken from the environment, their transformation into building components and the way they are assembled to create buildings. The global challenge of preserving the environment forces us to rethink the way we produce architecture today. Within this challenge, the past shows us possible ways to fill the gap between tradition and modernity. However, we need to understand what motivates people to abandon ancestral materials and knowledge for materials that they cannot manufacture or use themselves. Is this transformation to industrial materials and forms irreversible? Is there nothing we can learn from our rich past? How can we revive endogenous knowledge to produce environmentally wise architecture? These are the questions that the authors, who have been working on the revival of earthen heritage for over 20 years, wish to answer.
Lessons Learned From Implementing a Novel Bayesian Adaptive Dose-Finding Design in Advanced Pancreatic Cancer
Authors: Tidwell Rebecca S. S. , Thall Peter F. , Yuan Ying
Published: November 2021

PURPOSE

Novel Bayesian adaptive designs provide an effective way to improve clinical trial efficiency. These designs are superior to conventional methods, but implementing them can be challenging. The aim of this article was to describe what we learned while applying a novel Bayesian phase I-II design in a recent trial.

METHODS

The primary goal of the trial was to optimize radiation therapy (RT) dose among three levels (low, standard, and high), given either with placebo (P) or an investigational agent (A), for treating locally advanced, radiation-naive pancreatic cancer, deemed appropriate for RT rather than surgery. Up to 48 patients were randomly assigned fairly between RT plus P and RT plus A, with RT dose-finding done within each arm using the late-onset efficacy-toxicity design on the basis of two coprimary end points, tumor response and dose-limiting toxicity, both evaluated at up to 90 days. The random assignment was blinded, but within each arm, unblinded RT doses were chosen adaptively using software developed within the institution.

RESULTS

Implementing the design involved double-blind balance-restricted random assignment, real-time assessment of patient outcomes to evaluate the efficacy-toxicity trade-off for each RT dose in each arm to optimize each patient's RT dose adaptively, and transition from a single-center trial to a multicenter trial. We present lessons learned and illustrative documentation.

CONCLUSION

Implementing novel Bayesian adaptive trial designs requires close collaborations between physicians, pharmacists, statisticians, data managers, and sponsors. The process is difficult but manageable and essential for efficient trial conduct. Close collaboration during trial conduct is a key component of any trial that includes real-time adaptive decision rules.
Horror, Trauma, and George A. Romero’sMartin(1978)
Authors: Lowenstein Adam
Published: November 2021

This essay analyzes how George A. Romero, in his underrated psychological vampire film Martin, translates individual trauma (slow, process-based, unrecognized) into collective trauma (sudden, event-based, recognized) through a vocabulary of horror. The language of trauma spoken by Martin is not the one we expect from the horror film, with its traditional investments in fantastic spectacle. Instead, it is a language that combines horror’s fantastic vocabulary and documentary’s realist vocabulary in ways that undermine our attempts to distinguish between the two modes. Romero’s vision urges us to see catastrophe where we are accustomed to seeing only the mundane, and collective trauma where we routinely see only individual trauma. In Martin’s version of horror, the economic decline of Braddock, Pennsylvania, is paired with trauma connected to the Vietnam War and immigration. The film moves between these coordinates to revisualize the distinctions that divide the fantastic from the real as well as the individual from the collective.
The War That Never Happened
Authors: Sankar Nandini Ramesh , Alexander V. Neethi
Published: November 2021

This article examines Mark Z. Danielewski’s House of Leaves (2000), a gothic novel that augments its postmodernist credentials by preemptively imagining and representing the theoretical gaze that would otherwise have been directed on itself. The article suggests that despite the novel’s intense performance of self-reflexivity, it demonstrates a traumatic suppression of its own immediate historical conditions, particularly its temporal proximity to the events of the First Gulf War. This article thus reads the text’s telling silences and its thematization of uncanny spatial violations as indexing a minimally acknowledged guilt over the war in Iraq. The novel’s slippages in self-awareness not only point to an avoidance of its own scotomized history but also foreground the shifting boundaries and dispersed locations of textual self-consciousness.
Corporate Social Policy as a Management Mechanism for the Level of Social Pollution Reducing
Authors: Klimenkova M. , Fedorova A.
Published: November 2021

The article is devoted to the study of the role of corporate social policy as a managerial mechanism for reducing the level of social pollution on the manufacturing enterprise example. The concept of social pollution from the economic activity of economic entities is considered, the main factors of negative impact on the quality of working life and the employees’ well-being are outlined. Evaluation of the effectiveness of the social policy of the investigated enterprise was carried out using the author's methodology for analyzing the relevant socio-economic indicators. The authors studied data on the structure and volume of costs for social policy measures, the main socio-economic indicators of the enterprise and their ratio, calculated indicators of social policy parameters and identified directions for improving social policy and developing management decisions.
INTERNAL DAMAGE PREDICTION IN CFRP LAMINATES USING BVID PROFILES AND MACHINE LEARNING
Authors: HASEBE SAKI , HIGUCHI RYO , YOKOZEKI TOMOHIRO , TAKEDA SHIN-ICHI
Published: November 2021

The purpose of this study is to investigate the possibility of estimating impact information only from the surface profile of impacted CFRP laminates using machine learning. The low-velocity impact test was conducted to collect the data about barely visible impact damage (BVID) under various impact conditions: stacking sequence, impactor shape, and impact energy. A 3D optical profiler and an ultrasonic C-scanning system were utilized to measure external and internal damages. After feature engineering using only the specimen surface data, the machine learning models were able to estimate impactor shape with over 80% accuracy by a classification problem and over 90% by a regression problem, and delamination area and its length with over 70% R2, without significant outliers. It demonstrated that considering both local and total deformation that is unique to the low-velocity impact test is prominent in this estimation.
OPTIMIZATION OF INJECTION PROCESS PARAMETERS OF PLASTIC REINFORCED COMPOSITES USING RESPONSE SURFACE METHODOLOGY AND CENTRAL COMPOSITE DESIGN
Authors: ADEODU ADEFEMI O. , KANAKANA-KATUMBA MUKONDELELI G. , MALADZHI RENDANI W. , DANIYAN ILESANMI A.
Published: November 2021

The injection molding process is among the most efficient processes for mass production of polymer products with complex geometry at optimal cost. This study investigates the effect of the injection parameters on the cavity pressure, tensile and microstructural properties of plastic-reinforced composites and optimized the process to determine the optimum injection parameters using the Response Surface Methodology and central composite design. The two polymer composite materials used for this work are low-density polyethylene reinforced with aluminium powder (LDPE/Al) and low-density polyethylene reinforced with carbon black (LDPE/CB) at 250 and 200oC injection temperature respectively. The analysis of the results obtained from both the numerical and physical experimentations were used to obtain two predictive models which correlate cavity pressure and tensile strength as a function of the independent process parameters namely, injection pressure and time. An injection pressure of 70 MPa and time of 1.00 sec was found to be optimum producing a cavity pressure of 37.658 MPa while an injection pressure of 70 MPa and time of 1.75 sec was found to be optimum producing a material with tensile strength of 7.41 MPa. The results indicate that the cavity pressure increases with an increase in the injection pressure but decreases with an increase in the injection time for the two analyzed polymer composites. The study shows that process parameters have significant effects on the cavity pressure, mechanical and microstructural properties of LDPE/Al and LDPE/CB.
STUDY ON COOLING RATE-DEPENDENT MECHANICAL PROPERTIES OF THERMOPLASTIC COMPOSITES
Authors: HIGUCHI RYO , OSHIMA SOTA , MINAKUCHI SHU , YOKOZEKI TOMOHIRO , AOKI TAKAHIRA
Published: November 2021

This study investigates the effect of solidification conditions on the crystallization behaviors and mechanical properties of thermoplastic resin and carbon fiber reinforced thermoplastics (CFRTP). In particular, the crystallinity, elastic modulus, plastic behavior, strength, and fracture toughness were investigated in Polyphenylene Sulfide (PPS) and CF/PPS manufactured by different cooling rates. Based on experimental results, the cooling-rate-dependent elasto-plastic constitutive law of resin was developed empirically. Finally, the homogenized simulations of CF/PPS were conducted using the developed empirical model, and predicted results were compared with experiments.
PREDICTING PROCESSING INDUCED RESIDUAL- STRESSES IN CARBON FIBER-THERMOPLASTIC MICRO-COMPOSITES
Authors: PARAMBIL NITHIN K. , CHEN BRANNDON R. , DEITZEL JOSEPH M. , GILLESPIE, JR. JOHN W. , VO LOAN T. , SAROSI PETER
Published: November 2021

A computational model of residual stress is developed for AS4/polypropylene composites and implemented via user material subroutine (UMAT) in ABAQUS. The main factors included in the model are the cooling-rate dependent crystallinity, temperature-dependent elastic modulus, and temperature-dependent coefficient of thermal expansion (CTE) of the matrix, and the temperature-independent transversely isotropic properties of the carbon fiber. Numerical results are generated for the case of a single fiber embedded in a thin film of polypropylene sample to replicate the process history and test configuration. During single fiber composite processing, a precalculated weight (tensile preload) is applied at the fiber ends to eliminate buckling/waviness of the carbon fiber induced by matrix shrinkage in the axial direction of the fiber. Experiments and Finite element (FE) analysis have been conducted with different preloads (1g, 4g, and 8g) at 25°C. Micro-Raman spectroscopy is utilized to validate the residual strain with different preloads at the bulk. The measured strain values show a good correlation with the predicted residual strain for various preload conditions.
BENDING SIMULATION OF PRE-GELLED COMPOSITES USING AN EXPLICIT COSSERAT CONTINUUM MODEL
Authors: COURTEAU-GODMAIRE HUBERT , POURSARTIP ANOUSH , VAZIRI REZA
Published: November 2021

Forming simulation of uncured pre-preg can be made more efficient with the use of dedicated finite elements tailored for soft, layered media. These elements are based on the Cosserat continuum theory that introduces a rotational degree of freedom at each node within standard solid elements. In this study, a Cosserat element is developed within a 2D non-linear explicit finite element framework that uses the Carrera Unified Formulation for its spatial discretization. Two benchmark case studies involving bending deformations are presented as the verification of the developed model. It is demonstrated that similar accuracy of predictions can be achieved with much coarser meshes of Cosserat elements than the equivalent classical finite element models consisting of multi-layer stacks of solid elements.
EFFECTS OF STOICHIOMETRY ON PROPERTIES OF DGEBF/DETDA EPOXY USING MOLECULAR DYNAMICS
Authors: PATIL SAGAR , OLAYA MICHAEL , DESHPANDE PRATHAMESH , MAIARÙ MARIANNA , ODEGARD GREGORY
Published: November 2021

This article details the molecular modeling of full and off-stoichiometry models of the DGEBF/DETDA epoxy system using Molecular Dynamics to predict the mechanical properties as a function of the crosslinking density. The Reactive Interface Force Field (IFF-R) is implemented in this work to simulate mechanical deformation. The “fix bond/react” command in LAMMPS is used to simulate crosslinking between epoxy monomers. The results show that the predicted mass density, volumetric shrinkage, and bulk modulus have a strong dependence on the stoichiometry of the epoxy.
EFFECT OF MICROSTRUCTURE ON INITIATION OF DELAMINATION IN CROSS PLY LAMINATES FROM A TRANSVERSE CRACK
Authors: ZHUANG LINQI , MARAGONI LUCIO , TALREJA RAMESH
Published: November 2021

Transverse crack propagating towards a cross-ply interface is investigated in this study. The non-uniform fiber distribution near ply interface is modelled explicitly in order to study the effect of microstructure on crack path and initiation of delamination. The growth of fiber/matrix interfacial debond and debond kinking out of interface are analyzed based on a combination of energy and stress-based approach, which is convenient in predicting matrix crack path. Kinking of transverse crack tip when it approaches ply interface is investigated using an energy-based approach. It is found that predicted matrix crack path and crack tip kinking behavior near interface is strongly influenced by the local microstructure. The obtained results indicate that an induced symmetrical delamination, i.e., interface cracks of equal length on either side of the transverse ply crack, as often assumed in modeling studies, is not always a favorable damage mode.
COMPUTATIONAL DESCRIPTION OF THE GEOMETRY OF ALIGNED CARBON NANOTUBES IN POLYMER NANOCOMPOSITES
Authors: LOMOV STEPAN V. , LEE JEONYOON LEEJEONYOON , WARDLE BRIAN L. , GUDKOV NIKITA A. , AKHATOV ISKANDER S. , ABAIMOV SERGEY G.
Published: November 2021

The paper considers nanocomposites, reinforced with aligned carbon nanotubes (A- CNTs). Nominally aligned, the CNTs in the forest are wavy, which has important consequences in downgraded mechanical properties, and influences electric and thermal performance. The most detailed geometrical model of A-CNTs was proposed by Stein and Wardle (Nanotechnology, 27:035701, 2015). It creates a centerline trajectory of a CNT in steps, each step defining a section of the CNT, growing in the alignment direction with certain deviations. The paper, starting from this framework, formulates a model of the CNT geometry, which is based on the concept of correlation length of the CNT waviness and maximum admissible CNT curvature and torsion. The value of the maximum curvature can be linked to the buckling criteria for CNTs, or derived from ab initio and finite element modelling. It is used as a limiting factor for the growth, defining the waviness and tortuosity of the CNTs. The CNTs in the forest are placed in a random non-regular way, using Voronoi tessellation. The full paper includes investigation of the proposed algorithm for several values of the CNT volume fraction (in the range 0.5%…8%), the dependency of the modelled geometry on the curvature, and the apparent twist of the CNT centerlines. The modelling results are compared with experimental observations in 3D TEM imaging.
FAILURE PERFORMANCE OF BEND-FREE VARIABLE STIFFNESS COMPOSITE PRESSURE VESSELS
Authors: DAGHIGHI SHAHRZAD , WEAVER PAUL M.
Published: November 2021

Pressure vessels are designed to store liquids and gases and have various applications spanning from chemical plants to automotive and aerospace industries. Currently, lightweight composite pressure vessels are desirable, especially in transportation industry applications because of their subsequent benefits in fuel consumption, cost and environmental issues. Using composite materials for pressure vessels along with advanced manufacturing technologies such as automated fiber placement provides excellent scope to tailor stiffness through the structural surface using fiber steering to achieve desirable structural performance. Recently, variable angle tow (VAT) technology has been used to suppress bending in super ellipsoids of revolution composite pressure vessels, resulting in minimizing the inefficient bending stresses and deformations and increasing their load-carrying capacity. It is worth noting that such geometries can provide excellent packing efficiency. These advantages make the bend-free super ellipsoids of revolution composite pressure vessels potential candidates for the next generation of pressure vessels. Therefore, their failure performance as the most important design factor should be studied carefully due to safety reasons. In this study, the maximum allowable internal pressure for VAT bend-free ellipsoidal pressure vessels, using the first-ply failure based on both Tsai-Wu and three-dimensional invariant-based failure criteria is determined. Subsequently, VAT bend-free pressure vessels’ failure performance is compared against that obtained for conventional constant stiffness composite vessels. Among structures considered, the VAT bend-free composite vessel has the best failure performance. Moreover, the predicted failure load using the three-dimensional invariant-based failure criterion for the VAT bend-free design is 34% lower than the failure load predicted by the Tsai- Wu. Finally, the effect of various material properties on the difference in predicted failure load using these criteria is assessed. Results provide physical insight useful for designers in materials selection.
MODELING CFRP OPEN-HOLE COMPRESSION STRENGTH USING ARTIFICIAL NEURAL-NETWORK WITH MANUALLY DERIVED LAYER
Authors: YU SU , COLTON JONATHAN S.
Published: November 2021

This paper models the open-hole compression (OHC) strength of aerospace-grade unidirectional CFRP laminates with standard and non-standard ply angles using deep learning methods. Specifically, an artificial neural-network (ANN) model is developed from experimental test results to predict laminate OHC strength from ply orientation and stacking sequence. This ANN model innovates from conventional models by adding a layer containing an interply compatibility-index that was derived manually from interply failure modes to improve the prediction accuracy. A final root mean square error (RMSE, or standard deviation of prediction errors) of 6.7% of the average failure strength (21.1 MPa) and R2a value of 0.83 is achieved using K-fold cross validation on 16 laminates studied. This paper models all angles from -90° to 90°, not just the standard angles (0°, +/-45°, 90°). This paper shows that interply failure modes are important predictors for laminate OHC strength.
STRESS RELAXATION BEHAVIOR OF THERMOSET POLYMERS AT LARGE STRAINS
Authors: ISLAM RASHEDUL , RADFORD DONALD W. , RODRIGUEZ PATRICK , MURPHEY THOMAS W.
Published: November 2021

Unlike composites used in traditional structural applications, thin ply high strain composites (HSCs) common to deployable space structures often experience long term packing deformations at strains up to, and sometimes exceeding, 2%. Extended stowage of these structures can result in incomplete deployment and often permanent shape change, which is directly related to the stress relaxation of the thermoset matrix materials typical to HSCs. Traditionally, viscoelastic characteristics of polymers are measured at small strains on the order of 0.1% and very little data exists at the much larger 2% strains of HSCs. To address this lack of data, the stress relaxation response of two relevant thermoset matrix materials was characterized, over a range of strains and temperatures, to inform and validate future constitutive models. A large strain test, presented here as the Stepped Strain Extended Recovery (SSER) method, was developed to characterize non-linear viscoelastic and potential plastic polymer behavior. The method was implemented using a dynamic mechanical analyzer (DMA) at a variety of operational strains and temperatures. Specimens were prepared from cured thin films of cyanate ester resin, PMT-F6, and toughened epoxy resin, PMT-F7, for testing in a tensile configuration. Four strains, 0.5, 1.0, 1.5 and 2.0% were sequentially applied to each specimen for 100-minute durations, each separated by a 1000-minute recovery period. Tests were performed isothermally at 30°C, 50°C and 70°C. Despite the test temperatures being well below the glass transition temperature (Tg) of the crosslinked polymers, load decay was measured under constant specimen deformation. Trends in the data indicate a consistent increase in stress relaxation with increasing strain and temperature. Overall, the test protocol offers a consistent, rapid, and relatively automated method for generating stress relaxation data over a range of conditions, a necessity for the development and validation of future predictive engineering tools.
EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF STOCHASTIC THICKNESS EFFECTS IN DISCONTINUOUS FIBER COMPOSITES
Authors: KO SEUNGHYUN , NAKAGAWA TROY , CHEN ZHISONG , DAVEY JAMES , ABDULLAH TALAL , KUKLENSKI LUKE , ADAMS EBONNI J. , SOJA MATTHEW R. , PARK CHUL Y. , AVERY WILLIAM B. , YANG JINKYU , SALVIATO MARCO
Published: November 2021

Discontinuous fiber composites (DFCs) made of chopped prepreg tapes have recently drawn the attention of the aerospace and automobile industries thanks to their flexible manufacturing capability. Because of the discontinuity in a form of prepreg tapes, the fibers easily follow the mold contours while maintaining comparable stiffness and strength to continuous quasi-isotropic laminates. Furthermore, the high production rates and part complexities enabled by DFCs make them a competitive alternative to the use of metals in several applications. However, one of the current roadblocks for the use of DFCs is the lack of reliable analysis methods to predict their mechanical behavior, which depends on different parameters such as platelet sizes, aspect ratios, and spatial distribution. In this paper, we first experimentally investigated tensile elastic modulus and strength of unnotched coupons made of two different platelet aspect ratios (square and narrow) for varying coupon thicknesses. From the experiments, the square platelets showed significant thickness effects on both elastic modulus and strength. The narrow platelets also had significant thickness effects on strength but relatively constant modulus with varying thicknesses. In both modulus and strength, the narrow platelets had higher average values with larger deviations. Next, we computationally examined the relationship between the platelet distributions and the corresponding thickness effects. To get a thorough understanding of the effects of the platelet distribution on the mechanical behavior, the analysis was performed in two steps. In the first step, computational models were generated utilizing a uniform platelet distribution. In the second step, the models were generated leveraging platelet orientation tensors obtained from X-ray micro-computed tomography characterization. It was found that the assumption of a uniform orientation distribution condition was sufficient to capture the average modulus and strength with varying thicknesses for both platelet sizes. However, the associated Coefficient of Variation (CoV) of the results were significantly underpredicted, especially in the case of narrow platelets. On the other hand, numerical results using the orientation tensor obtained via micro-CT provided significantly improved predictions of the CoVs with varying thicknesses. These numerical investigations suggest that, for parts manufactured in conditions of limited platelet flow, the average mechanical performance can be accurately predicted by stochastic Finite Element models featuring a uniform platelet orientation distribution. On the other hand, the prediction of the CoV of moduli and strengths urges the use of an accurate representation of the real platelet morphology.
IMPACT DAMAGE DETECTION LIMITS OF MICROWAVE NDE TECHNIQUE FOR POLYMER COMPOSITES
Authors: BERKOWITZ KATHERINE , GUHA RISHABH D. , IDOLOR OGHENEOVO , PANKOW MARK , GRACE LANDON
Published: November 2021

Despite recent advances, the need for improved non-destructive evaluation (NDE) techniques to detect and quantify early-stage damage in polymer matrix composites remains critical. A recently developed microwave based NDE technique which capitalizes on the ubiquitous presence of moisture within a polymer matrix has yielded positive results. The chemical state of moisture directly affects dielectric properties of a polymer matrix composite. Thus, the preferential diffusion of ‘free’ water into microcracks and voids associated with physical damage allows for damage detection through spatial permittivity mapping using techniques that are sensitive to moisture content and molecular water state. While it has been demonstrated that the method can detect damage at low levels of moisture and impact damage, the specific parameters under which the technique will accurately and reliably capture damage within a composite are unknown. The three variables affecting the performance of the method to detect impact damage are moisture content, extent of damage, and resolution of the dielectric scanning technique. Here, we report on the impact of the latter as a function of the two environmental variables (moisture and damage extent). To understand limits and optimize execution of the technique, the interrelationships between each of the variables must be explored. This study investigates the relationship between moisture content and scan resolution. Two BMI/quartz laminates were impacted at 9 Joules to induce barely visible impact damage. The specimens were inspected at a variety of gravimetric moisture levels, and several variations of the spatial permittivity map were created for each moisture level. Detection standards for the technique were investigated based on moisture content and desired scan accuracy; findings showed at 0.05-0.4% moisture content (by wt.) the technique can detect damage location and size with a minimum of 88% accuracy. Pareto frontiers were generated at each moisture level to optimize scan speed and accuracy.
MICROMECHANICAL FINITE ELEMENT PREDICTION OF INTERLAMINAR TRACTION-SEPARATION LAWS USING J-INTEGRAL APPROACH
Authors: MEYER CHRISTOPHER S. , HAQUE BAZLE Z. , O’BRIEN DANIEL J. , GILLESPIE, JR. OHN W.
Published: November 2021

Dynamic impact loading of woven composites leads to mesoscale damage such as interlaminar transverse cracks and intralaminar tow-tow delamination cracks. At the microscale, this damage may be modeled as fracture between [90/90] and [0/90] unidirectional composite laminates. Microscale finite element model (FEM) resolution of dynamic impact at structural length scale is intractable, but mesoscale FEM resolution is possible with current computational resources. However, mesoscale cohesive zone modeling of this damage requires appropriate tractionseparation laws. These laws are predicted in this work with fiber length-scaleresolved FEMs, which include residual stress, experimentally measured, ratedependent, nonlinear matrix behavior, and experimentally measured, computationally validated, rate-dependent fiber-matrix interface properties. The J-integral from elastoplastic fracture mechanics is computed under mode I and mode II loading and differentiated to determine the traction-separation laws.
QUASI-LINEAR VISCOELASTIC MODELLING OF UNCURED PREPREGS UNDER COMPACTION
Authors: KULKARNI SIDDHESH S. , KHAN KAMRAN A. , UMER REHAN
Published: November 2021

Reinforcement compaction sometimes referred as consolidation process and is one of the key steps in various composite manufacturing processes such as autoclave and out-of-autoclave processing. The prepregs consist of semi-cured thermoset resin system impregnating the fibers. hence, the prepreg shows strong viscoelastic compaction response, which strongly depends on compaction speed and stress relaxation. modeling of time-dependent response is of utmost importance to understand the behavior of prepregs during different stages of composites manufacturing processes. The quasilinear viscoelastic (QLV) theory has been extensively used for the modeling of viscoelastic response of soft tissues in biomedical applications. In QLV approach, the stress relaxation can be expressed in terms of the nonlinear elastic function and the reduced relaxation function. The constitutive equation can be represented by a convolution integral of the nonlinear strain history, and reduced relaxation function. This study adopted a quasilinear viscoelastic modeling approach to describe the time dependent behavior of uncured-prepregs under compression. The model was modified to account for the compaction behavior of the prepreg under a compressive load. The deformation behavior of the prepreg is usually characterized by the fiber volume fraction, V . In this study, the material used was a 2/2 Twill weave glass prepreg (M26T) supplied by Hexcel® Industries USA. We performed a compaction experiment of the uncured prepreg at room temperature at different displacement rate and subsequent relaxation to describe the viscoelastic behavior of the prepreg. The model parameter calibration was performed using the trust-region-reflective algorithm in matlab to a selected number of test data. The calibrated model was then used to predict the rate dependent compaction and relaxation response of prepregs for different fiber volume fractions and strain rates.
I Will Survive: Predicting Business Failures from Customer Ratings
Authors: Naumzik Christof , Feuerriegel Stefan , Weinmann Markus
Published: November 2021

This paper presents a novel method that uses online ratings to predict business failures.
The Pareto Frontier of Inefficiency in Mechanism Design
Authors: Filos-Ratsikas Aris , Giannakopoulos Yiannis , Lazos Philip
Published: November 2021

We study the trade-off between the price of anarchy (PoA) and the price of stability (PoS) in mechanism design in the prototypical problem of unrelated machine scheduling. We give bounds on the space of feasible mechanisms with respect to these metrics and observe that two fundamental mechanisms, namely the first price (FP) and the second price (SP), lie on the two opposite extrema of this boundary. Furthermore, for the natural class of anonymous task-independent mechanisms, we completely characterize the PoA/PoS Pareto frontier; we design a class of optimal mechanisms [Formula: see text] that lie exactly on this frontier. In particular, these mechanisms range smoothly with respect to parameter [Formula: see text] across the frontier, between the first price ([Formula: see text]) and second price ([Formula: see text]) mechanisms. En route to these results, we also provide a definitive answer to an important question related to the scheduling problem, namely whether nontruthful mechanisms can provide better makespan guarantees in the equilibrium compared with truthful ones. We answer this question in the negative by proving that the price of anarchy of all scheduling mechanisms is at least n, where n is the number of machines.
Asymptotic Properties of Stationary Solutions of Coupled Nonconvex Nonsmooth Empirical Risk Minimization
Authors: Qi Zhengling , Cui Ying , Liu Yufeng , Pang Jong-Shi
Published: November 2021

This paper has two main goals: (a) establish several statistical properties—consistency, asymptotic distributions, and convergence rates—of stationary solutions and values of a class of coupled nonconvex and nonsmooth empirical risk-minimization problems and (b) validate these properties by a noisy amplitude-based phase-retrieval problem, the latter being of much topical interest. Derived from available data via sampling, these empirical risk-minimization problems are the computational workhorse of a population risk model that involves the minimization of an expected value of a random functional. When these minimization problems are nonconvex, the computation of their globally optimal solutions is elusive. Together with the fact that the expectation operator cannot be evaluated for general probability distributions, it becomes necessary to justify whether the stationary solutions of the empirical problems are practical approximations of the stationary solution of the population problem. When these two features, general distribution and nonconvexity, are coupled with nondifferentiability that often renders the problems “non-Clarke regular,” the task of the justification becomes challenging. Our work aims to address such a challenge within an algorithm-free setting. The resulting analysis is, therefore, different from much of the analysis in the recent literature that is based on local search algorithms. Furthermore, supplementing the classical global minimizer-centric analysis, our results offer a promising step to close the gap between computational optimization and asymptotic analysis of coupled, nonconvex, nonsmooth statistical estimation problems, expanding the former with statistical properties of the practically obtained solution and providing the latter with a more practical focus pertaining to computational tractability.