bluuebunny/crossref_metadata_2025 huggingface dataset:
The aging population: demographics and the biology of aging
Authors: Kanasi Eleni , Ayilavarapu Srinivas , Jones Judith
Published: August 2016

Epidemiologic studies show that 11% of the world's population is over 60 years of age; this is projected to increase, by 2050, to 22% of the population. Oral aging is a current focus of several organizations including the Federation Dentaire Internationale, the World Health Organization and the American and Japanese Dental Associations. In their Tokyo Declaration, the Japanese Association identified the elderly population as one of its main target groups. One of the WHO goals is for each person to retain more than 20 teeth by age 80, despite the fact that the prevalence of periodontal disease is continuously rising as the population is aging. Every species has its own characteristic lifespan, which is determined by its evolutionary history and is modified by multiple diverse factors, including biological mechanisms. In humans, the gradual accumulation of products of cellular metabolism and extensive DNA damage contribute to the aging process. Aging is thought to be associated with a low‐grade inflammatory phenotype in mammals, called ‘inflammaging’, and is the result of autophagic capacity impairing so‐called ‘housekeeping activities’ in the cells, resulting in protein aggregation, mitochondrial dysfunction and oxidative stress. Delayed stem‐cell proliferation, associated with aging, may impact the maintenance and survival of a living being, but excessive proliferation could also result in depleted reserves of stem cells. Studies are needed to address the association of delayed cell proliferation and wound healing with the onset of periodontal diseases and response to treatment. The effects of systemic diseases, medications, psychological effects and decreased interest or ability in performing oral‐hygiene practices are thought to result in periodontal diseases, and ultimately in tooth loss, in aged individuals. Together with an aging population comes a responsibility for ‘healthy’ and ‘successful’ aging. This article describes the changing global demographic profile and the effects of an aging society on the prevalence and incidence of periodontal diseases. We review the definitions of normal and successful aging, the principles of geriatric medicine and the highlights of biological aging at cellular, tissue and systems levels.
From restoration to regeneration: periodontal aging and opportunities for therapeutic intervention
Authors: Huang Lan , Salmon Benjamin , Yin Xing , Helms Jill A.
Published: August 2016

With the march of time our bodies start to wear out: eyesight fades, skin loses its elasticity, teeth and bones become more brittle and injuries heal more slowly. These universal features of aging can be traced back to our stem cells. Aging has a profound effect on stem cells: DNA mutations naturally accumulate over time and our bodies have evolved highly specialized mechanisms to remove these damaged cells. Whilst obviously beneficial, this repair mechanism also reduces the pool of available stem cells and this, in turn, has a dramatic effect on tissue homeostasis and on our rate of healing. Simply put: fewer stem cells means a decline in tissue function and slower healing. Despite this seemingly intractable situation, research over the past decade now demonstrates that some of the effects of aging are reversible. Nobel prize‐winning research demonstrates that old cells can become young again, and lessons learned from these experiments‐in‐a‐dish are now being translated into human therapies. Scientists and clinicians around the world are identifying and characterizing methods to activate stem cells to reinvigorate the body's natural regenerative process. If this research in dental regenerative medicine pans out, the end result will be tissue homeostasis and healing back to the levels we appreciated when we were young.
The aging mouth: differentiating normal aging from disease
Authors: Lamster Ira B. , Asadourian Lynda , Del Carmen Tessa , Friedman Paula K.
Published: August 2016

Aging is the physiologic change that occurs over time. In humans, this change occurs at different rates and are related to lifestyle, environment and genetics. It can be challenging to differentiate normal aging from disease. In the oral cavity, with increasing age the teeth demonstrate wearing of the enamel, chipping and fracture lines, and a darker color. The pulp chamber and canals are reduced in size as a result of the deposition of secondary dentin. Coronal or root caries, however, represent disease. A limited amount of periodontal attachment loss occurs in association with aging, usually manifesting as recession on the buccal surface of teeth. Severe periodontitis occurs in 10.5–12% of the population, with the peak incidence being observed at 35–40 years of age. Changes to the mucosal tissue that occur with age include reduced wound‐healing capacity. However, environmental factors, such as smoking, dramatically increase the risk of mucosal pathology. Reduced salivary gland function is often seen in association with medication usage, as well as with disorders such as diabetes mellitus. Both medication use and chronic disorders are more common in older adults. Masticatory function is of particular importance for older adults. Maintenance of a nutritionally complete diet is important for avoiding sarcopenia and the frailty syndrome. Successful oral aging is associated with adequate function and comfort. A reduced, but functional, dentition of 20 teeth in occlusion has been proposed as a measure of successful oral aging. Healthy oral aging is important to healthy aging from both biological and social perspectives.
Implants for the aged patient: biological, clinical and sociological considerations
Authors: Bartold P. Mark , Ivanovski Saso , Darby Ivan
Published: August 2016

Until recently, age, particularly old age, was considered a contraindication to the placement of dental implants. However, this was based largely on anecdotal dogma rather than on empirical information. This review considers the biological, clinical and socio‐economic implications of implants placed in the aged population. Aging has been shown to have an influence on the biological aspects of soft‐ and hard‐tissue wound healing and tissue remodeling, which may influence the establishment and maintenance of implant integration. However, information to date indicates that age should not be an a priori contraindication for implant placement and there is good evidence to indicate that dental implants can be placed successfully in the elderly with good clinical and socio‐economic outcomes.
Oral health and the frailty syndrome
Authors: MacEntee Michael I. , Donnelly Leeann R.
Published: August 2016

The frailty syndrome is an ever‐growing area of study among older adults because of its association with an increased risk of falls, hospitalization, institutionalization, dependency and mortality. Frailty is neither a disease nor a disability but is better understood as a medical syndrome of multisystem dysregulation that results in a diminished ability to overcome everyday stressors. The prevalence of frailty in any given population can vary widely, in part because of the way in which it is defined and measured, but in general it is higher among women and in those with advanced age and declining health. Whilst it is largely understood that older adults will differ biologically, psychologically and socially, and that each of these domains can impact oral health, we are only beginning to investigate how the mouth is affected in frailty. Given that both hard and soft structures contribute to oral health and disease status among older adults with varying degrees of impairment and disability, frailty adds yet another dimension to be considered. This paper will discuss how frailty can influence and be influenced by oral disorders, as well as the potential relationship to oral neglect and the resultant consequences among this vulnerable population.
Can There Be an Artifact Theory of Law?
Authors: Burazin Luka
Published: August 2016

The idea that particular legal institutions are artifacts is not new. However, the idea that the “law” or “legal system” is itself an artifact has seldom been directly put forward, due perhaps to the ambiguities surrounding philosophical inquiries into law. Nevertheless, such an idea has recently been invoked more often, though not always developed in detail in terms of what the characterization of the “law” or “legal system” as an artifact entails ontologically, and what consequences, if any, this has for philosophical accounts of law. As a result, the primary aim of this paper is to attempt an inquiry into what the claim that “law” by its nature or character is an artifact entails, and what an artifact theory of law might look like.
Protocols for treating patients with end‐stage renal disease: a survey of undergraduate dental programs
Authors: Sturgill Jeremiah , Howell Scott , Perry Maureen Munnelly , Kothari Hemali
Published: August 2016

Rationale/Background

Approximately 14% of Americans are living with chronic kidney disease (CKD). The prevalence of end‐stage renal disease (ESRD), the result of progressing CKD continues to rise by 21,000 per year. There are no updated, evidence‐based antibiotic prophylaxis guidelines for patients with renal disease undergoing dental treatment. The most recent was a scientific statement from the American Heart Association (AHA) in 2003. Presented in three parts, the goal of the first part of this study is to determine the current protocol being used to treat renal patients at U.S. dental schools.

Methods and Materials

A 21 multiple‐choice question survey was e‐mailed to 58 clinic deans of accredited dental schools in the United States regarding renal treatment protocol details including antibiotic prophylaxis.

Results

Fifty‐two percent of programs report having no established renal patient treatment protocol. For programs with a protocol, when using prophylactic antibiotics, 54% followed AHA protocol, whereas 62% used a modified protocol.

Conclusion

There is a lack of consistent, established protocols among undergraduate dental programs. It is suggested that evidence‐based guidelines for the safe treatment of patients be developed.
The impact of knowledge and religion on organ donation as seen by immigrants in Sweden
Authors: Krupic Ferid , Sayed‐Noor Arkan S. , Fatahi Nabi
Published: August 2016

Background

Transplantation of organs is one of the most successful medical advances of the past 60 years and transplantation is the treatment of choice for severe organ failure worldwide. Despite this situation, and the general acknowledgement of organ donation as a global priority, demand for organs outstrips supply in virtually every country in the world.

Aim

The aim of the study was to elucidate factors that influence immigrant's decisions regarding organ donation.

Methods

Data were collected through three group interviews using open‐ended questions and qualitative content analysis. 32 participants, 16 men and 16 women from Bosnia and Herzegovina, Somalia, Lebanon and Kosovo participated in focus group interviews (FGI).

Results

Analysis of the collected data resulted in two main categories: ‘Information about organ donation’ and ‘Religious aspects of organ donation and a number of subcategories’. Some of the influencing factors concerning organ donation were mainly related to limited information from society as well as limited information from healthcare professionals. Religious aspects, fear and prejudices about organ donation were other factors that mentioned by participants as hamper regarding organ donation.

Conclusion

In order to improve immigrants' attitude towards organ donation, information about this issue and identification of the hampering factors, particularly culturally related factors such as the religious aspect, is essential. In this context, different intervention studies are needed to increase monitories groups' attitude towards organ donations.
A randomized, controlled trial comparing skin health effects and comfort of two adult incontinence protective underwear
Authors: Trowbridge M. M. , Wang B. , Gutshall D. , Rodenberg C. A. , Farage M. A.
Published: August 2016

Background/Purpose

It is important to confirm product use effects on skin health for products intended for prolonged skin contact. This study compared experimental and marketed reference adult incontinence protective underwear.

Methods

Randomized, single‐blind (examiner), parallel study evaluating skin health effects in predominantly obese incontinent women normally using protective underwear (approximately 20% Type II Diabetes). Subjects wore experimental or marketed reference protective underwear daily, 14 consecutive days. Visual skin grading, transepidermal water loss (TEWL) assessed before, after 1 and 2 weeks of product wear. Overall assessment of comfort assessed.

Results

Of the 122 subjects (60 experimental and 62 marketed reference), 22 were diabetic and 88 were postmenopausal. Under the conditions of this study, there were no statistically significant differences in overall change from baseline for visual grading and TEWL between the experimental product and the marketed reference product for all subjects. Changes from baseline for skin erythema and skin marking were generally small for both products for all subjects as well as for both diabetics and non‐diabetics. There were no serious adverse events (AEs), and no withdrawals due to AEs. Overall comfort assessments of size and fit were ‘just right,’ and skin comfort in the leg, waist and crotch areas were ‘comfortable’ or ‘very comfortable’ for both products.

Conclusions

In‐use 14‐day testing demonstrated few statistical differences between experimental product with unique odor neutralizing technology and currently marketed product for skin assessments and comfort. Both products were comfortable and well‐tolerated.
Visceral leishmaniasis in a lung transplant recipient: usefulness of highly sensitive real‐time polymerase chain reaction for preemptive diagnosis
Authors: Opota O. , Balmpouzis Z. , Berutto C. , Kaiser‐Guignard J. , Greub G. , Aubert J.‐D. , Prod'hom G. , Manuel O. , Jaton K.
Published: August 2016

We report the case of a lung transplant recipient in whom the diagnosis of visceral leishmaniasis (VL) was made by detection of parasites in a peripheral blood smear when the parasite load already reached 8.9 × 103 parasites/mL. We demonstrated that the VL diagnosis could have been done months before the development of symptoms by the use of Leishmania‐specific real‐time polymerase chain reaction (PCR), suggesting the role of preemptive PCR‐based diagnosis in transplant recipients at risk for VL.
Fulminant Epstein–Barr virus‐associated hemophagocytic syndrome in a renal transplant patient and review of the literature
Authors: Romiopoulos I. , Pyrpasopoulou A. , Onoufriadis I. , Massa E. , Mouloudi E. , Kydona C. , Giasnetsova T. , Gerogianni N. , Myserlis G. , Solonaki F. , Nikodimopoulou M. , Mandala E. , Antachopoulos C. , Roilides E.
Published: August 2016

We describe a rare fulminant case of Epstein–Barr virus‐associated hemophagocytic syndrome (HPS) in a 37‐year‐old female renal transplant patient, indistinguishable from severe sepsis clinically and in the laboratory. HPS involves rapidly escalating immune system activation, resulting in a cytokine cascade, which can, especially in immunocompromised patients, lead to multi‐organ failure, and even death. Thirty‐two Herpesviridae‐associated HPS cases in renal transplant patients have been reported and are reviewed. Overall mortality is 47% (15/32 cases).
Incidence and outcomes of bloodstream infections among hematopoietic cell transplant recipients from species commonly reported to be in over‐the‐counter probiotic formulations
Authors: Cohen S.A. , Woodfield M.C. , Boyle N. , Stednick Z. , Boeckh M. , Pergam S.A.
Published: August 2016

Background

Probiotic supplementation has been promoted for numerous health conditions; however, safety in immunosuppressed patients is unknown. We evaluated bloodstream infections (BSIs) caused by common probiotic organisms in hematopoietic cell transplant recipients.

Methods

All blood culture (BC) results from a cohort of hematopoietic cell transplant recipients transplanted at Fred Hutchinson Cancer Research Center in Seattle, Washington, between 2002 and 2011 were reviewed. Patients with at least 1 positive BC for common probiotic organisms (Lactobacillus species, Bifidobacterium species, Streptococcus thermophilus, and Saccharomyces species) within 1 year post hematopoietic cell transplantation (HCT) were considered cases. Data were collected from center databases, which contain archived laboratory data, patient demographics, and clinical summaries.

Results

A total of 19/3796 (0.5%) patients developed a BSI from one of these organisms within 1 year post HCT; no Bifidobacterium species or S. thermophilus were identified. Cases had a median age of 49 years (interquartile range [IQR]: 39–53), and the majority were allogeneic hematopoietic cell transplant recipients (14/19, 74%). Most positive BCs were Lactobacillus species (18/19) and occurred at a median of 84 days (IQR: 34–127) post transplant. The incidence rate of Lactobacillus bacteremia was 1.62 cases per 100,000 patient‐days; the highest rate occurred within 100 days post transplant (3.3 per 100,000 patient‐days). Eight patients (44%) were diagnosed with acute graft‐versus‐host disease of the gut prior to the development of bacteremia. No mortality was attributable to any of these infections.

Conclusion

Organisms frequently incorporated in available over‐the‐counter probiotics are infrequent causes of bacteremia after HCT. Studies evaluating the use of probiotics among high‐risk patients are needed.
ABA‐dependent inhibition of the ubiquitin proteasome system during germination at high temperature in Arabidopsis
Authors: Chiu Rex Shun , Pan Shiyue , Zhao Rongmin , Gazzarrini Sonia
Published: August 2016

During germination, endogenous and environmental factors trigger changes in the transcriptome, translatome and proteome to break dormancy. In Arabidopsis thaliana, the ubiquitin proteasome system (UPS) degrades proteins that promote dormancy to allow germination. While research on the UPS has focused on the identification of proteasomal substrates, little information is known about the regulation of its activity. Here we characterized the activity of the UPS during dormancy release and maintenance by monitoring protein ubiquitination and degradation of two proteasomal substrates: Suc‐LLVY‐AMC, a well characterized synthetic substrate, and FUSCA3 (FUS3), a dormancy‐promoting transcription factor degraded by the 26S proteasome. Our data indicate that proteasome activity and protein ubiquitination increase during imbibition at optimal temperature (21°C), and are required for seed germination. However, abscisic acid (ABA) and supraoptimal temperature (32°C) inhibit germination by dampening both protein ubiquitination and proteasome activity. Inhibition of UPS function by high temperature is reduced by the ABA biosynthesis inhibitor, fluridone, and in ABA biosynthetic mutants, suggesting that it is ABA dependent. Accordingly, inhibition of FUS3 degradation at 32°C is also dependent on ABA. Native gels show that inhibition of proteasome activity is caused by interference with the 26S/30S ratio as well as free 19S and 20S levels, impacting the proteasome degradation cycle. Transfer experiments show that ABA‐mediated inhibition of proteasome activity at 21°C is restricted to the first 2 days of germination, a time window corresponding to seed sensitivity to environmental and ABA‐mediated growth inhibition. Our data show that ABA and high temperature inhibit germination under unfavourable growth conditions by repressing the UPS.
The composition of surface wax on trichomes of Arabidopsis thaliana differs from wax on other epidermal cells
Authors: Hegebarth Daniela , Buschhaus Christopher , Wu May , Bird David , Jetter Reinhard
Published: August 2016

To protect plants against biotic and abiotic stress, the waxy cuticle must coat all epidermis cells. Here, two independent approaches addressed whether cell‐type‐specific differences exist between wax compositions on trichomes and other epidermal cells of Arabidopsis thaliana, possibly with different protection roles. First, the total waxes from a mutant lacking trichomes (gl1) were compared to waxes from wild type and a trichome‐rich mutant (cpc tcl1 etc1 etc3). In the stem wax, compounds with aliphatic chains longer than 31 carbons (derived from C32 precursors) increased in relative abundance in cpc tcl1 etc1 etc3 over gl1. Similarly, the leaf wax from the trichome‐rich mutant contained higher amounts of C32+ compounds as compared to gl1. Second, leaf trichomes were isolated, and their waxes were analyzed. The wax mixtures of the trichome‐rich mutant and the wild type were similar, comprising alkanes and alkenes as well as branched and unbranched primary alcohols. The direct analyses of trichome waxes confirmed that they contained relatively high concentrations of C32+ compounds, compared with the pavement cell wax inferred from analysis of gl1 leaves. Finally, the cell‐type‐specific wax compositions were put into perspective with expression patterns of wax biosynthesis genes in trichomes and pavement cells. Analyses of published transcriptome data (Marks et al., ) revealed that core enzymes involved in elongation of wax precursors to various carbon chain lengths are expressed differentially between epidermis cell types. By combining the chemical and gene expression data, we identified promising gene candidates involved in the formation of C32+ aliphatic chains.
Integrating metabolomics and transcriptomics data to discover a biocatalyst that can generate the amine precursors for alkamide biosynthesis
Authors: Rizhsky Ludmila , Jin Huanan , Shepard Michael R. , Scott Harry W. , Teitgen Alicen M. , Perera M. Ann , Mhaske Vandana , Jose Adarsh , Zheng Xiaobin , Crispin Matt , Wurtele Eve S. , Jones Dallas , Hur Manhoi , Góngora‐Castillo Elsa , Buell C. Robin , Minto Robert E. , Nikolau Basil J.
Published: August 2016

The Echinacea genus is exemplary of over 30 plant families that produce a set of bioactive amides, called alkamides. The Echinacea alkamides may be assembled from two distinct moieties, a branched‐chain amine that is acylated with a novel polyunsaturated fatty acid. In this study we identified the potential enzymological source of the amine moiety as a pyridoxal phosphate‐dependent decarboxylating enzyme that uses branched‐chain amino acids as substrate. This identification was based on a correlative analysis of the transcriptomes and metabolomes of 36 different E. purpurea tissues and organs, which expressed distinct alkamide profiles. Although no correlation was found between the accumulation patterns of the alkamides and their putative metabolic precursors (i.e., fatty acids and branched‐chain amino acids), isotope labeling analyses supported the transformation of valine and isoleucine to isobutylamine and 2‐methylbutylamine as reactions of alkamide biosynthesis. Sequence homology identified the pyridoxal phosphate‐dependent decarboxylase‐like proteins in the translated proteome of E. purpurea. These sequences were prioritized for direct characterization by correlating their transcript levels with alkamide accumulation patterns in different organs and tissues, and this multi‐pronged approach led to the identification and characterization of a branched‐chain amino acid decarboxylase, which would appear to be responsible for generating the amine moieties of naturally occurring alkamides.
Phase 3 evaluation of HP802‐247 in the treatment of chronic venous leg ulcers
Authors: Kirsner Robert S. , Vanscheidt Wolfgang , Keast David H. , Lantis John C. , Dove Cyaandi R. , Cazzell Shawn M. , Vartivarian Mher , Augustin Matthias , Marston William A. , McCoy Nicholas D. , Cargill D. Innes , Lee Tommy D. , Dickerson Jaime E. , Slade Herbert B. ,   for the HP802‐247 Study Group
Published: August 2016

In 2012 we reported promising results from a phase 2 clinical trial of HP802‐247, a novel spray‐applied investigational treatment for chronic venous leg ulcers consisting of human, allogeneic fibroblasts and keratinocytes. We now describe phase 3 clinical testing of HP802‐247, its failure to detect efficacy, and subsequent investigation into the root causes of the failure. Two randomized, controlled trials enrolled a total of 673 adult outpatients at 96 centers in North America and Europe. The primary endpoint was the proportion of ulcers with confirmed closure at the end of 12 weeks of treatment. An investigation into the root cause for the failure of HP802‐247 to show efficacy in these two phase 3 trials was initiated immediately following the initial review of the North American trial results. Four hundred twenty‐one patients were enrolled in the North American (HP802‐247, 211; Vehicle 210) and 252 in the European (HP802‐247, 131; Vehicle 121) trials. No difference in proportion of closed ulcers at week 12 was observed between treatment groups for either the North American (HP802‐247, 61.1%; Vehicle 60.0%; p = 0.5896) or the European (HP802‐247, 47.0%; Vehicle 50.0%; p = 0.5348) trials. Thorough investigation found no likelihood that design or execution of the trials contributed to the failure. Variability over time during the trials in the clinical response implicated the quality of the cells comprising HP802‐247. Concordance between the two separate, randomized, controlled trials with distinct, nonoverlapping investigative sites and independent monitoring teams renders the possibility of a Type II error vanishingly small and provides strong credibility for the unexpected lack of efficacy observed. The most likely causative factors for the efficacy failure in phase 3 was phenotypic change in the cells (primarily keratinocytes) leading to batch to batch variability due to the age of the cell banks.
Mitochondria‐specific antioxidant supplementation does not influence endurance exercise training‐induced adaptations in circulating angiogenic cells, skeletal muscle oxidative capacity or maximal oxygen uptake
Authors: Shill Daniel D. , Southern W. Michael , Willingham T. Bradley , Lansford Kasey A. , McCully Kevin K. , Jenkins Nathan T.
Published: August 2016

Key points

Reducing excessive oxidative stress, through chronic exercise or antioxidants, can decrease the negative effects induced by excessive amounts of oxidative stress. Transient increases in oxidative stress produced during acute exercise facilitate beneficial vascular training adaptations, but the effects of non‐specific antioxidants on exercise training‐induced vascular adaptations remain elusive.

Circulating angiogenic cells (CACs) are an exercise‐inducible subset of white blood cells that maintain vascular integrity.

We investigated whether mitochondria‐specific antioxidant (MitoQ) supplementation would affect the response to 3 weeks of endurance exercise training in CACs, muscle mitochondrial capacity and maximal oxygen uptake in young healthy men.

We show that endurance exercise training increases multiple CAC types, an adaptation that is not altered by MitoQ supplementation. Additionally, MitoQ does not affect skeletal muscle or whole‐body aerobic adaptations to exercise training.

These results indicate that MitoQ supplementation neither enhances nor attenuates endurance training adaptations in young healthy men.

Antioxidants have been shown to improve endothelial function and cardiovascular outcomes. However, the effects of antioxidants on exercise training‐induced vascular adaptations remain elusive. General acting antioxidants combined with exercise have not impacted circulating angiogenic cells (CACs). We investigated whether mitochondria‐specific antioxidant (MitoQ) supplementation would affect the response to 3 weeks of endurance exercise training on CD3+, CD3+/CD31+, CD14+/CD31+, CD31+, CD34+/VEGFR2+ and CD62E+ peripheral blood mononuclear cells (PBMCs), muscle mitochondrial capacity, and maximal oxygen uptake () in healthy men aged 22.1 ± 0.7 years, with a body mass index of 26.9 ± 0.9 kg m–2, and 24.8 ± 1.3% body fat. Analysis of main effects revealed that training induced 33, 105 and 285% increases in CD14+/CD31+, CD62E+ and CD34+/VEGFR2+ CACs, respectively, and reduced CD3+/CD31− PBMCs by 14%. There was no effect of MitoQ on CAC levels. Also independent of MitoQ supplementation, exercise training significantly increased quadriceps muscle mitochondrial capacity by 24% and by roughly 7%. In conclusion, endurance exercise training induced increases in multiple CAC types, and this adaptation is not modified by MitoQ supplementation. Furthermore, we demonstrate that a mitochondrial‐targeted antioxidant does not influence skeletal muscle or whole‐body aerobic adaptations to exercise training.
Building reaction kinetic models for amiloid fibril growth
Authors: Markov Svetoslav Marinov
Published: August 2016

In this work weВ  discuss some methodological aspects of the creation and formulation of mathematicalВ  models describing the growth of species from the point of view of reaction kinetics. Our discussion is based on familiar examples of growth models such as logistic growth and enzyme kinetics. WeВ В  propose several reaction networkВ  modelsВ  forВ  the amiloid fibrillation processes in the citoplasm. The solutions of the models are sigmoidal functions graphically visualized usingВ  the computer algebra system В  Mathematica.
Stability Analysis of Multiharmonic Nonlinear Vibrations for Large Models of Gas Turbine Engine Structures With Friction and Gaps
Authors: Petrov E. P.
Published: August 2016

An efficient method is proposed for the multiharmonic frequency-domain analysis of the stability for nonlinear periodic forced vibrations in gas turbine engine structures and turbomachines with friction, gaps, and other types of nonlinear contact interfaces. The method allows using large-scale finite element models for structural components together with detailed description of nonlinear interactions at contact interfaces between these components. The highly accurate reduced models are applied in the assessment of stability of periodic regimes for large-scale model of gas turbine structures. An approach is proposed for the highly accurate calculation of motion of a structure after it is perturbed from the periodic nonlinear forced response. Efficiency of the developed approach is demonstrated on a set of test cases including simple models and large-scale realistic bladed disk models with different types of nonlinearities: friction, gaps, and cubic nonlinear springs.
Morphing Continuum Theory: Incorporating the Physics of Microstructures to Capture the Transition to Turbulence Within a Boundary Layer
Authors: Wonnell Louis B. , Chen James
Published: August 2016

A boundary layer with Re = 106 is simulated numerically on a flat plate using morphing continuum theory. This theory introduces new terms related to microproperties of the fluid. These terms are added to a finite-volume fluid solver with appropriate boundary conditions. The success of capturing the initial disturbances leading to turbulence is shown to be a byproduct of the physical and mathematical rigor underlying the balance laws and constitutive relations introduced by morphing continuum theory (MCT). Dimensionless equations are introduced to produce the parameters driving the formation of disturbances leading to turbulence. Numerical results for the flat plate are compared with the experimental results determined by the European Research Community on Flow, Turbulence, and Combustion (ERCOFTAC) database. Experimental data show good agreement inside the boundary layer and in the bulk flow. Success in predicting conditions necessary for turbulent and transitional (T2) flows without ad hoc closure models demonstrates the theory's inherent advantage over traditional turbulence models.
Hybrid RANS-LES Modeling of the Aerothermal Field in an Annular Hot Streak Generator for the Study of Combustor–Turbine Interaction
Authors: Andreini A. , Bacci T. , Insinna M. , Mazzei L. , Salvadori S.
Published: August 2016

The adoption of lean-burn technology in modern aero-engines influences the already critical aerothermal conditions at turbine entry, where the absence of dilution holes preserves the swirl component generated by burners and prevents any control on pattern factor. The associated uncertainty and lack of confidence entail the application of wide safety margins in turbine cooling design, with a detrimental effect on engine efficiency. Computational fluid dynamics (CFD) can provide a deeper understanding of the physical phenomena involved in combustor–turbine interaction, especially with hybrid Reynolds-averaged Navier–Stokes (RANS) large eddy simulation (LES) models, such as scale adaptive simulation (SAS), which are proving to overcome the well-known limitations of the RANS approach and be a viable approach to capture the complex flow physics. This paper describes the numerical investigation on a test rig representative of a lean-burn, effusion cooled, annular combustor developed in the EU Project Full Aerothermal Combustor-Turbine interactiOns Research (FACTOR) with the aim of studying combustor–turbine interaction. Results obtained with RANS and SAS were critically compared to experimental data and analyzed to better understand the flow physics, as well as to assess the improvements related to the use of hybrid RANS-LES models. Significant discrepancies are highlighted for RANS in predicting the recirculating region, which has slight influence on the velocity field at the combustor outlet, but affects dramatically mixing and the resulting temperature distribution. The accuracy of the results achieved suggests the exploitation of SAS model with a view to the future inclusion of the nozzle guide vanes in the test rig.
Oil-Free Automotive Turbochargers: Drag Friction and On-Engine Performance Comparisons to Oil-Lubricated Commercial Turbochargers
Authors: Ryu Keun , Ashton Zachary
Published: August 2016

Oil-free bearings for automotive turbochargers (TCs) offer unique advantages eliminating oil-related catastrophic TC failures (oil coking, severe bearing wear/seizure, and significant oil leakage, for example), while increasing overall system reliability and reducing maintenance costs. The main objective of the current investigation is to advance the technology of the gas foil bearings (GFBs) for automotive TCs by demonstrating their reliability, durability, and static/dynamic force characteristics desirable in extreme speed and temperature conditions. The paper compares drag friction and on-engine performances of an oil-free TC supported on GFBs against an oil-lubricated commercial production TC with identical compressor and turbine wheels. Extensive coastdown and fast acceleration TC rotor speed tests are conducted in a cold air-driven high-speed test cell. Rotor speed coastdown tests demonstrate that the differences in the identified rotational viscous drag coefficients and drag torques between the oil-free and production TCs are quite similar. In addition, rotor acceleration tests show that the acceleration torque of the oil-free TC rotor, when airborne, is larger than the production TC rotor due to the large mass and moment of inertia of the oil-free TC rotor even though air has lower viscosity than the TC lubricant oil. Separate experiments of the oil-free TC installed on a diesel engine demonstrate the reliable dynamic-forced performance and superior rotor dynamic stability of the oil-free TC over the oil-lubricated TC. The post on-engine test inspection of the oil-free TC test hardware reveals no evidence of significant surface wear between the rotor and bearings, as well as no dimensional changes in the rotor outer surfaces and bearing top foil inner surfaces. The present experimental characterization and verified robustness of the oil-free TC system continue to extend the GFB knowledge database.
Foreign Object Damage in an Oxide/Oxide Ceramic Matrix Composite Under Prescribed Tensile Loading
Authors: Kedir Nesredin , Faucett David , Sanchez Luis , Choi Sung R.
Published: August 2016

Foreign object damage (FOD) behavior of an N720/alumina oxide/oxide ceramic matrix composite (CMC) was characterized at ambient temperature by using spherical projectiles impacted at velocities ranging from 100 to 350 m/s. The CMC targets were subject to ballistic impact at a normal incidence angle while being loaded under different levels of tensile loading in order to simulate conditions of rotating aeroengine airfoils. The impact damage of frontal and back surfaces was assessed with respect to impact velocity and load factor. Subsequent postimpact residual strength was also estimated to determine quantitatively the severity of impact damage. Impact force was predicted based on the principles of energy conservation.
Ferrofluid Capillary Rise in Porous Medium Under the Action of Nonuniform Magnetic Field
Authors: Zakinyan Arthur , Mkrtchyan Levon , Grunenko Victoria , Dikansky Yuri
Published: August 2016

The capillary flow of a ferrofluid in a single cylindrical capillary tube and through a sandy porous medium under the action of a nonuniform magnetic field is studied experimentally. The dynamics of the capillary rise and the static case have been considered. It has been shown that the nonuniform magnetic field with upward directed gradient accelerates the capillary rise; contrary, the nonuniform magnetic field with downward directed gradient decelerates the capillary rise. Time dependences of the ferrofluid height and maximum reachable height of ferrofluid have been analyzed. The method of the study of ferrofluid capillary rise based on the use of magnetic measurements has been proposed. It has been demonstrated that porous material parameters can be extracted from the results of measurements of the inductances of the solenoid with porous medium inside and the small sensing coil within a single experiment.
Cavitation-Induced Unsteady Flow Characteristics in the First Stage of a Centrifugal Charging Pump
Authors: Zhang Fan , Yuan Shouqi , Fu Qiang , Pei Ji , Böhle Martin , Jiang Xusong
Published: August 2016

Cavitation is the main factor that causes reliability problems in centrifugal charging pumps (CCPs) in nuclear power plants. In this study, the cavitation-induced unsteady flow characteristics of a CPR1000 CCP were investigated by numerical and experimental methods. The vapor distribution in the impeller, velocity fluctuation, and pressure fluctuation results in the time and frequency domains were considered for several typical monitoring points in the impeller and volute. The pressure fluctuations in the impeller occurred at an impeller rotating frequency of fR and its integer harmonics, whereas those in the volute mainly occurred at an impeller blade-passing frequency of fB and its integer harmonics. The absolute error between the simulated and measured NPSHr was 3.6%, and that between the calculated and measured head was 2.9%, validating the simulation of the cavitation performances of a CCP.
Effect of Microstructure Geometric Form on Surface Shear Stress
Authors: Rangharajan Kaushik K. , Gerber Matthew J. , Prakash Shaurya
Published: August 2016

Low Reynolds number flow of liquids over micron-sized structures and the control of subsequently induced shear stress are critical for the performance and functionality of many different microfluidic platforms that are extensively used in present day lab-on-a-chip (LOC) domains. However, the role of geometric form in systematically altering surface shear on these microstructures remains poorly understood. In this study, 36 microstructures of diverse geometry were chosen, and the resultant overall and facet shear stresses were systematically characterized as a function of Reynolds number to provide a theoretical basis to design microstructures for a wide array of applications. Through a set of detailed numerical calculations over a broad parametric space, it was found that the top facet (with respect to incident flow) of the noncylindrical microstructures experiences the largest surface shear stress. By systematically studying the variation of the physical dimensions of the microstructures and the angle of incident flow, a comprehensive regime map was developed for low to high surface shear structures and compared against the widely studied right circular cylinder in cross flow.
Instability of a Curved Pipe Flow With a Sudden Expansion
Authors: Shusser Michael , Ramus Artyom , Gendelman Oleg
Published: August 2016

Numerical calculations of laminar flow of an incompressible fluid through an axisymmetric sudden expansion followed by a curved pipe recently done by the authors discovered an early instability of this flow for a certain expansion ratio, as it becomes unsteady with periodic oscillations of the flow variables at a Reynolds number when both curved pipe flow and flow in a straight pipe with an axisymmetric sudden expansion remain stable. This study describes in detail the created oscillatory flow and suggests that the early instability of the ratio 3 flow could be caused by the higher velocity gradient near the outer wall of the bend.
Computational Fluid Dynamics-Based Pump Redesign to Improve Efficiency and Decrease Unsteady Radial Forces
Authors: Yan Peng , Chu Ning , Wu Dazhuan , Cao Linlin , Yang Shuai , Wu Peng
Published: August 2016

In this study, a double volute centrifugal pump with relative low efficiency and high vibration is redesigned to improve the efficiency and reduce the unsteady radial forces with the aid of unsteady computational fluid dynamics (CFD) analysis. The concept of entropy generation rate is applied to evaluate the magnitude and distribution of the loss generation in pumps and it is proved to be a useful technique for loss identification and subsequent redesign process. The local Euler head distribution (LEHD) can represent the energy growth from the blade leading edge (LE) to its trailing edge (TE) on constant span stream surface in a viscous flow field, and the LEHD is proposed to evaluate the flow field on constant span stream surfaces from hub to shroud. To investigate the unsteady internal flow of the centrifugal pump, the unsteady Reynolds-Averaged Navier–Stokes equations (URANS) are solved with realizable k–ε turbulence model using the CFD code FLUENT. The impeller is redesigned with the same outlet diameter as the baseline pump. A two-step-form LEHD is recommended to suppress flow separation and secondary flow encountered in the baseline impeller in order to improve the efficiency. The splitter blades are added to improve the hydraulic performance and to reduce unsteady radial forces. The original double volute is substituted by a newly designed single volute one. The hydraulic efficiency of the centrifugal pump based on redesigned impeller with splitter blades and newly designed single volute is about 89.2%, a 3.2% higher than the baseline pump. The pressure fluctuation in the volute is significantly reduced, and the mean and maximum values of unsteady radial force are only 30% and 26.5% of the values for the baseline pump.
Nonlinear Control of a Quadrotor With Deviated Center of Gravity
Authors: Xian Bin , Zhao Bo , Zhang Yao , Zhang Xu
Published: August 2016

In this paper, a new adaptive tracking controller is developed for a quadrotor unmanned aerial vehicle (UAV) via immersion and invariance (I&I) approach. The controller is able to compensate parametric uncertainties such as the unmeasurable effects of the deviated center-of-gravity (CoG), as well as the aerodynamic coefficients. The globally asymptotic tracking of the desired attitude trajectories is proven via the Lyapunov-based stability analysis and LaSalle's invariance theorem. Real-time experiment results performed on a quadrotor attitude control testbed are given to show the good control performance of the proposed scheme.
Propagation and Attenuation of Pressure Waves in Dispersed Two-Phase Flows
Authors: Costa Martins Jaqueline , Seleghim Paulo
Published: August 2016

The propagation and attenuation of pressure waves in highly dispersed gas–liquid flows are investigated in this work, and an indirect measurement method is proposed to assess the attenuation coefficient in short pipelines. Additionally, a mechanistic acoustic energy dissipation model is derived from the oscillatory solutions of one-dimensional (1D) nondimensionalized mass and momentum equations to facilitate the interpretation of the results. Tests were performed on a 1500 m long, 50 mm internal diameter pipeline in which pressure disturbances were induced by suddenly opening leak valves. The results are consistent and in good agreement with the proposed attenuation model (±10% for 103 < Re < 104), therefore validating the proposed model and indirect measurement method.
Simultaneous Influence of Static Load and Temperature on the Electromechanical Signature of Piezoelectric Elements Bonded to Composite Aeronautic Structures
Authors: Rebillat Marc , Guskov Mikhail , Balmes Etienne , Mechbal Nazih
Published: August 2016

Electromechanical (EM) signature techniques have raised a huge interest in the structural health-monitoring community. These methods aim at assessing structural damages and sensors degradation by analyzing the EM responses of piezoelectric components bonded to aeronautic structures. These structures are subjected simultaneously to static loads and temperature variations that affect the metrics commonly used for damage detection and sensor diagnostics. However, the effects of load and temperature on these metrics have mostly been addressed separately. This paper presents experimentations conducted to investigate the simultaneous influence of static load and temperature on these metrics for two kinds of piezoelectric elements (lead zirconate titanate (PZT) and macrofiber composite (MFC)) bonded on sandwich composite materials, for the full range of real-life conditions encountered in aeronautics. Results obtained indicate that both factors affect the metrics in a coupled manner in particular due to the variations of the mechanical properties of the bonding layer when crossing its glass transition temperature. Furthermore, both piezoelectric elements globally behave similarly when subjected to temperature variations and static loads. Simultaneous accounting of both temperature and static load is thus needed in practice in order to design reliable structural health-monitoring systems based on these metrics.
Reduction of Jet Impingement Noise by Addition of Swirl
Authors: Balakrishnan P. , Srinivasan K.
Published: August 2016

Experimental investigations are carried out with an objective of reducing impingement jet noise using coaxial swirl jets. Two nozzle-to-plate distances have been considered and the Mach number values ranged from 0.95 to 1.83. The vane angles of the coaxial swirlers ranged from 0 deg to 60 deg, corresponding to swirl numbers that ranged from weak to high. Flow visualization has also been conducted to understand the shock-cell structure for each case. The results indicate that swirl jets are highly efficient in the control of impingement noise. Transonic, screech, and impinging tones are completely eliminated by the swirl jets. A weak swirl seems efficient for lower Mach numbers while higher amounts of swirl are efficient at higher Mach numbers.