bluuebunny/crossref_metadata_2025 huggingface dataset:
Fleshing out facilitation – reframing interaction networks beyond top‐down versus bottom‐up
Authors: Watson David M.
Published: June 2016

Rather than direct plant–plant interactions, research on the community‐scale influence of mistletoes reveals hitherto unappreciated roles of animals in mediating facilitation. Lacking roots and reliant upon animal vectors, mistletoes represent model systems with which to understand mechanisms underlying interaction networks. In addition to direct effects on nutrient dynamics via enriched litter‐fall, mistletoes are visited by pollinators, seed dispersers and natural enemies, complementing increased heterogeneity in nutrient returns reallocated from infected hosts with increased external inputs. These amplified bottom‐up effects are coupled with top‐down influences of insectivores attracted to infected hosts and stands by increased availability of favoured prey. Simultaneously influencing nutrient dynamics and plant–plant interactions from below and above, visiting animals help explain variation in the context dependence of facilitation.

Contents

Summary
803

I.
Introduction
803

II.
Case study 1 – Mediterranean pine forest
804

III.
Case study 2 – semi‐arid tropical savannah
804

IV.
Mistletoes as facilitators – top‐down, bottom‐up or both?
805

V.
Beyond parasitic plants – do animals drive facilitation cascades?
805

VI.
Conclusions
806

References
807
Symbiodinium sp. cells produce light‐induced intra‐ and extracellular singlet oxygen, which mediates photodamage of the photosynthetic apparatus and has the potential to interact with the animal host in coral symbiosis
Authors: Rehman Ateeq Ur , Szabó Milán , Deák Zsuzsanna , Sass László , Larkum Anthony , Ralph Peter , Vass Imre
Published: June 2016

Coral bleaching is an important environmental phenomenon, whose mechanism has not yet been clarified. The involvement of reactive oxygen species (ROS) has been implicated, but direct evidence of what species are involved, their location and their mechanisms of production remains unknown.

Histidine‐mediated chemical trapping and singlet oxygen sensor green (SOSG) were used to detect intra‐ and extracellular singlet oxygen (1O2) in Symbiodinium cultures.

Inhibition of the Calvin–Benson cycle by thermal stress or high light promotes intracellular 1O2 formation. Histidine addition, which decreases the amount of intracellular 1O2, provides partial protection against photosystem II photoinactivation and chlorophyll (Chl) bleaching. 1O2 production also occurs in cell‐free medium of Symbiodinium cultures, an effect that is enhanced under heat and light stress and can be attributed to the excretion of 1O2‐sensitizing metabolites from the cells. Confocal microscopy imaging using SOSG showed most extracellular 1O2 around the cell surface, but it is also produced across the medium distant from the cells.

We demonstrate, for the first time, both intra‐ and extracellular 1O2 production in Symbiodinium cultures. Intracellular 1O2 is associated with photosystem II photodamage and pigment bleaching, whereas extracellular 1O2 has the potential to mediate the breakdown of symbiotic interaction between zooxanthellae and their animal host during coral bleaching.
Aboveground mammal and invertebrate exclusions cause consistent changes in soil food webs of two subalpine grassland types, but mechanisms are system‐specific
Authors: Vandegehuchte Martijn L. , van der Putten Wim H. , Duyts Henk , Schütz Martin , Risch Anita C.
Published: June 2016

Ungulates, smaller mammals, and invertebrates can each affect soil biota through their influence on vegetation and soil characteristics. However, direct and indirect effects of the aboveground biota on soil food webs remain to be unraveled. We assessed effects of progressively excluding aboveground large‐, medium‐ and small‐sized mammals as well as invertebrates on soil nematode diversity and feeding type abundances in two subalpine grassland types: short‐ and tall‐grass vegetation. We explored pathways that link exclusions of aboveground biota to nematode feeding type abundances via changes in plants, soil environment, soil microbial biomass, and soil nutrients.

In both vegetation types, exclusions caused a similar shift toward higher abundance of all nematode feeding types, except plant feeders, lower Shannon diversity, and lower evenness. These effects were strongest when small mammals, or both small mammals and invertebrates were excluded in addition to excluding larger mammals. Exclusions resulted in a changed abiotic soil environment that only affected nematodes in the short‐grass vegetation. In each vegetation type, exclusion effects on nematode abundances were mediated by different drivers related to plant quantity and quality. In the short‐grass vegetation, not all exclusion effects on omni–carnivorous nematodes were mediated by the abundance of lower trophic level nematodes, suggesting that omni–carnivores also depended on other prey than nematodes.

We conclude that small aboveground herbivores have major impacts on the soil food web of subalpine short‐ and tall‐grass ecosystems. Excluding aboveground animals caused similar shifts in soil nematode assemblages in both subalpine vegetation types, however, mechanisms turned out to be system‐specific.
High genetic and virulence diversity detected in Neofusicoccum luteum and N. australe populations in New Zealand vineyards
Authors: Baskarathevan J. , Jones E. E. , Jaspers M. V. , Ridgway H. J.
Published: June 2016

Genotypic and virulence diversity of Neofusicoccum luteum and N. australe isolates recovered from grapevines displaying symptoms of dieback and decline in New Zealand were investigated. The universally primed PCR (UP‐PCR) method was used to investigate the genetic diversity of 40 isolates of N. luteum and 33 isolates of N. australe. Five UP‐PCR primers produced a total of 51 loci from N. luteum and 57 from N. australe with a greater number of polymorphic loci produced in N. australe (86%) compared with N. luteum (69%). Analysis of UP‐PCR data showed both species found in New Zealand vineyards were genetically diverse at both the inter‐ and intra‐vineyard levels with only a single pair of clonal isolates in N. luteum. Cluster analysis of UP‐PCR data produced four genetic groups in N. luteum and 10 in N. australe (P < 0.05). For both species, there was no relationship between the genetic groups and the origin of isolates. The mean genetic diversity (H) of N. luteum was less than for N. australe, being 0.1791 and 0.2417, respectively. Pathogenicity assays of both species using isolates from either the same or different genetic groups inoculated onto either green shoots or grapevine trunks, showed virulence diversity within the population; however, no correlation was identified between genetic groups and virulence.
Effect of Different Levels of Silymarin and Caproic Acid on Storage of Ram Semen in Liquid Form
Authors: Roostaei‐Ali Mehr M , Parisoush P
Published: June 2016

Contents

Two experiments were designed to evaluate the effect of silymarin on stored spermatozoa using four rams. In experiment 1, silymarin was evaluated as a supplement for Tris–glucose extender. Semen samples (n = 20) were diluted with extender containing 0, 50, 100, 150 and 200 μg/ml silymarin and incubated at 5°C for 72 h. Membrane integrity, acrosome integrity, sperm viability and motility were evaluated at 72 h. Concentration of malondialdehyde (MDA) was determined after 48 h. Membrane integrity was higher in 100 μg/ml silymarin (65.2%) than control group (43.2%, p < 0.05). Acrosome integrity was highest in 100 μg/ml silymarin (71.3%, p < 0.05). Progressive motility was higher in 100 (58.5%), 150 (60.62%) and 200 μg/ml silymarin (54.7%) than control group (30.7%, p < 0.05). The highest MDA concentration was observed in control group (400 mm/10 × 106 sperm; p < 0.05). The goal of experiment 2 was to determine the interaction between silymarin and caproic acid on ram stored sperm. Ejaculates (n = 20) were diluted by Tris–glucose extender, added 0 (S−) or 100 μg/ml (S+) silymarin and 0 (C−) or 0.3125% (C+) caproic acid, and thereafter, aliquots were incubated at 5°C for 72 h. Membrane integrity was lower in C−S− (57.6%) than C−S+ (73.2%), C+S− (80.2%) and C+S+ (72.1%, p > 0.05). The highest sperm viability and acrosome integrity were observed in C+S‐ (82.4 and 80.1%, respectively; p < 0.05). There was no difference between C‐S+ and C+S+ on sperm viability and membrane integrity, progressive motility and MDA concentration (p > 0.05). Therefore, the supplementation of extender with silymarin and caproic acid improved sperm quality and caproic acid was superior to caproic acid plus silymarin.
Nonparametric Tree‐Based Predictive Modeling of Storm Outages on an Electric Distribution Network
Authors: He Jichao , Wanik David W. , Hartman Brian M. , Anagnostou Emmanouil N. , Astitha Marina , Frediani Maria E. B.
Published: June 2016

This article compares two nonparametric tree‐based models, quantile regression forests (QRF) and Bayesian additive regression trees (BART), for predicting storm outages on an electric distribution network in Connecticut, USA. We evaluated point estimates and prediction intervals of outage predictions for both models using high‐resolution weather, infrastructure, and land use data for 89 storm events (including hurricanes, blizzards, and thunderstorms). We found that spatially BART predicted more accurate point estimates than QRF. However, QRF produced better prediction intervals for high spatial resolutions (2‐km grid cells and towns), while BART predictions aggregated to coarser resolutions (divisions and service territory) more effectively. We also found that the predictive accuracy was dependent on the season (e.g., tree‐leaf condition, storm characteristics), and that the predictions were most accurate for winter storms. Given the merits of each individual model, we suggest that BART and QRF be implemented together to show the complete picture of a storm's potential impact on the electric distribution network, which would allow for a utility to make better decisions about allocating prestorm resources.
Domestic Effects of Offshoring High‐skilled Jobs: Complementarities in Knowledge Production
Authors: Abramovsky Laura , Griffith Rachel , Miller Helen
Published: June 2016

We provide evidence on how changes in the use of high‐skilled workers (inventors) in a foreign location affect a firm's domestic use of the same type of worker. We exploit rich data that provide variation in the location of inventors within multinational firms across industries and countries to control for confounding firm–time and industry factors. We find that a 10% increase in the use of foreign inventors leads to a 1.9% increase in the use of domestic inventors. Our results suggest that foreign and domestic inventors are complementary in the production of knowledge.
Endless Pressure: Life on a Low Income in Austere Times
Authors: Pemberton Simon , Fahmy Eldin , Sutton Eileen , Bell Karen
Published: June 2016

Much has been written that details the decline in living standards following the ‘credit crunch’ in the UK. It remains that we understand to a lesser degree the lived reality of poverty through the Great Recession and into the era of austerity. This article draws on testimonies of 62 participants from low income households conducted in three different areas of the UK during 2012–13 to document the pressures that this period brought to bear on these households. According to these testimonies, the experience of poverty intensified in key respects: first, participants reported feeling, more than ever before, that they were ‘existing, rather than living’ due to the meagre budgets they were forced to live on; second, the precarious nature of work and social security contributed to a sense of insecurity that was all pervasive in our participants' lives; third, due to the pejorative political rhetoric and media coverage of poverty, our participants felt that their lives were placed under increased scrutiny which deleteriously impacted their wider relationships and sense of belonging. Our analysis demonstrates the profound consequences for those living on low incomes of the continued shift to residual forms of state welfare and the increased reliance on the ‘Big Society’ as a means to deal with the pressures identified in this article.
Analyses of changes on skin by aging
Authors: Kazanci A. , Kurus M. , Atasever A.
Published: June 2016

Background

This study aimed to evaluate the histological changes occurring in rat skin with increasing age, starting from the intrauterine period.

Methods

Thirty‐two healthy female Sprague–Dawley rats were evaluated in four groups: group 1 – intrauterine day 19, group 2 – postpartum day 21, group 3 – postpartum day 60, and group 4 – postpartum month 19. Skin samples from the back, abdomen, head, and upper and lower limbs were obtained from each subject under anesthesia. Tissue specimens were evaluated statistically and morphologically for the thicknesses of the epidermis, dermis, and basement membrane; the number, height, and width of dermal papillae; and the mast cell and pilosebaceous counts per group. The changes in collagen/elastic fibers and glycosaminoglycans were also assessed.

Results

Epidermal thickness was the highest in the intrauterine group; it decreased in the postpartum period and increased again in the aged group. Basal membrane thickness increased steadily with age. The number, height, and width of dermal papillae and dermal thickness increased up to day 60 after birth although these decreased in the aged group. Mast cell count also reached the maximum in the intrauterine group and gradually decreased with age. Pilosebaceous units of the dermis were fewer in intrauterine specimens; they showed an increase during the postpartum period and a decrease in the aged group.

Conclusion

Skin specimens obtained from rats showed striking differences between the intrauterine and postpartum groups. Moreover, the postpartum group showed considerable intra‐group differences.
Dynamic Deformation of Clamped Circular Plates Subjected to Confined Blast Loading
Authors: Chen P. W. , Liu H. , Ding Y. S. , Guo B. Q. , Chen J. J. , Liu H. B.
Published: June 2016

In this paper, the dynamic deformation of thin metal circular plates subjected to confined blast loading was studied using high‐speed three‐dimensional Digital Image Correlation (3D DIC). A small‐scale confined cylinder vessel was designed for applying blast loading, in which an explosive charge was ignited to generate blast loading acting on a thin metal circular plate clamped on the end of the vessel by a cover flange. The images of the metal plates during the dynamic response were recorded by two high‐speed cameras. The 3D transient displacement fields, velocity fields, strain fields and residual deformation profiles were calculated by using 3D DIC. Some feature deformation parameters including maximum out‐of‐plane displacement, final deflection, maximum principal strain and residual principal strain were extracted, and the result was in good agreement with that simulated by AUTODYN. A dimensionless displacement was introduced to analyse the effects of plate thickness, material types and charge mass on the deflection of metal plates. DIC is also proven to be a powerful technique to measure dynamic deformation under blast loading.
Molecular phylogeny of the Byrrhoidea–Buprestoidea complex (Coleoptera, Elateriformia)
Authors: Kundrata Robin , Jäch Manfred A. , Bocak Ladislav
Published: June 2016

The superfamilies of Elateriformia have been in a state of flux since their establishment. The recent classifications recognize Dascilloidea, Buprestoidea, Byrrhoidea and Elateroidea. The most problematic part of the elateriform phylogeny is the monophyly of Byrrhoidea and the relationships of its families. To investigate these issues, we merged more than 500 newly produced sequences of 18SrRNA, 28SrRNA,rrnLmtDNAandcox1mtDNAfor 140 elateriform taxa with data from GenBank. We assembled an all‐taxa (488 terminals) and a pruned data set, which included taxa with full fragment representation (251 terminals); both were aligned in various programs and analysed using maximum‐likelihood criterion and Bayesian inference. Most analyses recovered monophyletic superfamilies and broadly similar relationships; however, we obtained limited statistical support for the backbone of trees. Dascilloidea were sister to the remaining Elateriformia, and Elateroidea were sister to the clade of byrrhoid lineages including Buprestoidea. This clade mostly consisted of four major lineages, that is (i) Byrrhidae, (ii) Dryopidae + Lutrochidae, (iii) Buprestoidea (Schizopodidae sister to Buprestidae) and (iv) a clade formed by the remaining byrrhoid families. Buprestoidea and byrrhoid lineages, with the exception of Byrrhidae and Dryopidae + Lutrochidae, were usually merged into a single clade. Most byrrhoid families were recovered as monophyletic. Callirhipidae and Eulichadidae formed independent terminal lineages within the Byrrhoidea–Buprestoidea clade. Paraphyletic Limnichidae were found in a clade with Heteroceridae and often also with Chelonariidae. Psephenidae, represented by Eubriinae and Eubrianacinae, never formed a monophylum. Ptilodactylidae were monophyletic only whenParalichas(Cladotominae) was excluded. Elmidae regularly formed a clade with a bulk of Ptilodactylidae; however, elmid subfamilies (Elminae and Larainae) were not recovered. Despite the densest sampling of Byrrhoidea diversity up to date, the results are not statistically supported and resolved only a limited number of relationships. Furthermore, questions arose which should be considered in the future studies on byrrhoid phylogeny.
Opening-wedge high tibial osteotomy: a seven - to twelve-year study
Authors: Pipino Gennaro , Indelli Pier , Tigani Domenico , Maffei Giuseppe , Vaccarisi Davide
Published: June 2016

Purpose: medial opening-wedge osteotomy is a widely performed procedure used to treat moderate isolated medial knee osteoarthritis. Historically, the literature has contained reports showing satisfactory midterm results when accurate patient selection and precise surgical techniques were applied. This study was conducted to investigate the clinical and radiographic seven- to twelve-year results of opening-wedge high tibial osteotomy in a consecutive series of patients affected by varus knee malalignment with isolated medial compartment degenerative joint disease.

Methods: we reviewed a case series of 147 medial opening-wedge high tibial osteotomies at an average follow-up of 9.5 years. Endpoints for evaluation included the reporting of adverse effects, radiographic evidence of bone union, radiographic changes in the correction angle during union, and clinical and functional final outcomes.

Results: good or excellent results were obtained in 94% of the cases: the patients reported no major complications related to the opening-wedge high tibial osteotomy surgical technique, bone graft resorption, implant choice or postoperative rehabilitation protocol. At final follow-up, the average hip-knee angle was 4° of valgus without major loss of correction during the healing process. A statistically significant change in the patellar height was detected postoperatively, with a trend towards patella infera.

Conclusions: medial opening-wedge high tibial osteotomy is still a reliable method for correcting varus deformity while producing stable fixation, thus allowing satisfactory stability, adequate bone healing and satisfactory mid- to long-term results.

Level of evidence: Level IV, therapeutic cases series.
Platelet-rich plasma in the treatment of acute hamstring injuries in professional football players
Authors: Zanon Giacomo , Combi Franco , Combi Alberto , Perticarini Loris , Sammarchi Luigi , Benazzo Francesco
Published: June 2016

Purpose: muscle injuries have a high incidence in professional football and are responsible for the largest number of days lost from competition. Several in vitro studies have confirmed the positive role of plateletrich plasma (PRP) in accelerating recovery and in promoting muscle regeneration, and not fibrosis, in the healing process. This study examines the results of intralesional administration of PRP in the treatment of primary hamstring injuries sustained by players belonging to a major league football club.

Methods: twenty-five hamstring injuries (grade 2 according to MRI classification) sustained by professional football players during a 31-months observation period were treated with PRP and analyzed. sport participation absence (SPA), in days, was considered to correspond to the healing time, and we also considered the re-injury rate, and tissue healing on MRI. The mean follow-up was 36.6 months (range 22-42).

Results: there were no adverse events. The mean SPA for the treated muscle injuries was 36.76±19.02 days. The re-injury rate was 12%. Tissue healing, evaluated on MRI, was characterized by the presence of excellent repair tissue and a small scar.

Conclusions: this study confirmed the safety of PRP in treating hamstring lesions in a large series of professional football players. PRP-treated lesions did not heal more quickly than untreated lesions described in the literature, but they showed a smaller scar and excellent repair tissue.

Level of evidence: Level IV, therapeutic case series.
Failed vascularized fibular graft in treatment of osteonecrosis of the femoral head. A histopathological analysis
Authors: Meloni Maria , Hoedemaeker W. , Fornasier Victor
Published: June 2016

Purpose: vascularized fibular grafting has been used to treat osteonecrosis of the femoral head in younger patients. Although the results described in the literature are promising, the failure rate is still significant, especially in steroid users. This study was undertaken to learn more, on a histopathological level, about the mechanism of vascularized fibular graft failure.

Methods: fifteen femoral heads removed at conversion to total hip arthroplasty were analyzed. The case load comprised 10 men and 5 women. They ranged in age from 28 to 39 years and had a median age of 35 years. The interval between the vascularized fibular implant procedure and the conversion to total hip arthroplasty ranged from 22 months to 30 months; the median interval was 26 months. All the patients were steroid users. The heads were sectioned and axial and coronal sections were taken and stained using the WHO method (hematoxylin, phloxine, saffron and Alcian green). A quantitative and qualitative analysis of graft-host interaction at the head (zone 1), neck (zone 2) and epiphysis (zone 3) was performed.

Results: all the specimens showed recognizable collapse of the articular surface over the area of necrosis. Thirteen femoral heads showed the presence of an osteochondral flap attached only at the margins of the area of avascular necrosis, and 10 of these 13 femoral heads also showed loss of the articulating surface with an ulcer crater corresponding to the exposed area of avascular necrosis.

Conclusions: vascularized fibular graft failure seems to be related to a negative effect of creeping substitution: the revascularization becomes a negative force as it supports unbalanced bone resorption, which, as is well known, is enhanced by corticosteroids.

Clinical relevance: creeping substitution is an undermining force in the repair and revascularization of the necrotic area in the femoral head.
An update on the grading of muscle injuries: a narrative review from clinical to comprehensive systems
Authors: Grassi Alberto , Quaglia Alberto , Canata Gian , Zaffagnini Stefano
Published: June 2016

Muscle injuries are recognized to be among the most frequent injuries occurring in the sporting and athletic population, and they account for more than 30% of all injuries in professional soccer players. Despite their considerable frequency and impact, there is still a lack of uniformity in the categorization, description and grading of muscle injuries.

Dozens of systems based on clinical signs, ultrasound imaging (US) appearance or magnetic resonance imaging (MRI) findings have been proposed over the years. Most of them are three-grade systems that take into account pain, ROM limitation, swelling and hematoma, hypoechoic or hyperintense areas on US or MRI, and muscle gap or tendon involvement; however, they still lack evidence-based prognostic value. Recently, new comprehensive classification systems have been proposed, with the aim of developing uniform muscle injury terminology and giving each severity grade prognostic value.

The systems that combine detailed MRI and US features with the clinical presentation, such as the Munich Muscle Injury Classification, the ISMuLT classification, and the British Athletic Classification, if used extensively, could improve the diagnosis, prognosis and management of muscle injuries.
Outcome evaluation after Achilles tendon ruptures. A review of the literature
Authors: Spennacchio Pietro , Vascellari Alberto , Cucchi Davide , Canata Gian , Randelli Pietro
Published: June 2016

The optimal treatment and the best rehabilitation protocol after an acute Achilles tendon rupture (ATR) remain a matter of controversy in orthopaedic and sports medicine. The use of validated injury-specific outcome instruments is the only way to clarify these issues, in order to ensure that patients receive the best possible treatment.

This article describes the most commonly reported outcome measures used to assess patients treated for ATR. On the basis of the available evidence, the Achilles tendon Total Rupture Score (ATRS) is the most appropriate outcome measure for evaluating the management of acute ATR.
Maximizing Wind Energy Capture for Speed-Constrained Wind Turbines During Partial Load Operation
Authors: Yan Zeyu , Yu Victor , Shaltout Mohamed L. , Cheong Matthew Chu , Chen Dongmei
Published: June 2016

With the development of wind turbine technology, more wind turbines operate in the partial load region, where one of the main objectives is to maximize captured wind energy. This paper presents the development of an optimal control framework to maximize wind energy capture for wind turbines with limited rotor speed ranges. Numerical optimal control (NOC) techniques were applied to search for the achievable maximum power coefficient, thus maximum wind energy capture. Augmentations of these optimal techniques significantly reduced the computational cost. Simulation results show that, in comparison with the traditional torque feedback and conventional optimal control algorithms, the proposed augmented optimal control algorithm increases the harvested energy while minimizing the computational expense for speed-constrained wind turbines during partial load operation.
A Mesoscale Model of Plasticity: Dislocation Dynamics and Patterning (One-Dimensional)
Authors: Taheri-Nassaj Nasrin , Zbib Hussein M.
Published: June 2016

In this study, we developed a physically based mesoscale model for dislocation dynamics systems to predict the deformation and spontaneous formation of spatio-temporal dislocation patterns over microscopic space and time. Dislocations and dislocation patterns are emblematic of plastic deformation, a nonlinear, dissipative process involving the dynamics of underlying dislocations as carriers of plastic deformation. The mesoscale model includes a set of nonlinear partial differential equations of reaction–diffusion type. Here, we consider the equations within a one-dimensional framework and analyze the stability of steady-state solutions for these equations to elucidate the associated patterns with their intrinsic length scale. The numerical solution to the model yields the spatial distribution of dislocation patterns over time and provides respective stress–strain curves. Finally, we compare the stress–strain curves associated with the dislocation patterns with the experimental results noted in the literature.
Dynamic Fracture of Layered Plates Subjected to In-Plane Bending
Authors: Kumar Agnihotri Servesh , Parameswaran Venkitanarayanan
Published: June 2016

Layered structures typically used in applications such as windshields, thermal protection systems, heavy armor, etc., have property jumps at the layer interfaces. Present study focuses on understanding crack initiation and propagation in such systems under dynamic loading particularly when the property jumps are across the crack front. Layered plates were fabricated by joining polymethylmethacrylate (PMMA) and epoxy sheets using an epoxy-based adhesive (Araldite). Single-edge notched (SEN) specimens were subjected to dynamic loading using a modified Hopkinson bar setup. High-speed imaging coupled with dynamic photoelasticity was used to record the crack-tip isochromatic fringes from which the stress intensity factor (SIF) history was obtained. In selected experiments, a pair of strain gages installed on surfaces of specimen was used to record the strain history in the layers, from which the SIF in each layer was obtained. The results indicated that, prior to crack extension, the strain in both layers was identical. The crack tips in the layers start extending at different time instants with the one in the relatively brittle epoxy layer extending first followed by the one in the PMMA layer. At low impact velocity, the delay obtained was significantly higher than that at high impact velocity. The speed of epoxy crack was lower initially due to the bridging of the crack by the uncracked portion of the PMMA layer till initiation of the crack in the PMMA layer. This effect reduced at higher impact velocity for which the delay was much lower and the cracks propagated at a higher-speed.
Lattice Boltzmann Method for Simulating Disturbed Hemodynamic Characteristics of Blood Flow in Stenosed Human Carotid Bifurcation
Authors: Kang Xiuying , Tang Wenwen , Liu Siyuan
Published: June 2016

The local hemodynamic factor plays a vital role in the formation and progression of atherosclerosis. In this study, we simulated pulsatile flow patterns in the three-dimensional stenosed and normal carotid artery bifurcations throughout a cardiac cycle using the multiple-relaxation-time lattice Boltzmann (MRT-LB) method. Additionally, we investigated the time-varied flow rate and its division ratios between the parent and daughter branches, the multidirectionality of the stress field, and the averaged local energy dissipation rate. The results can be used in computational modeling of carotid artery hemodynamics and further investigation of the relationship between hemodynamics and cardiovascular diseases.
Effect of Relaxation on Drag Forces and Diffusivities of Particles Confined in Rectangular Channels
Authors: Dechadilok Panadda , Intum Chakrapong , Manaratha Sasipan , Sathanon Umnart
Published: June 2016

When a particle is moving inside a channel, its hydrodynamic interaction with channel walls increases its drag coefficient, causing a diffusivity reduction. For charged particles moving in an electrolytic solution, there is an additional drag due to the distortion of an electrical double layer caused by particle motion known as the relaxation effect. Effects of relaxation on drag forces on spheres confined in rectangular channels are computed employing perturbations involving particle Peclet number and surface charge densities. Results indicate that confinement amplifies electrokinetic retardation; increasing the relative particle size or decreasing the channel cross section area enhances the relaxation effect. With the relative particle size kept constant, the relaxation effect on the drag exerted on charged spheres in cylindrical pores with its smaller cross section area is stronger than that on charged spheres in rectangular channels and slit pores. However, for certain values of Debye length and particle size, the ratio between excess drag due to relaxation on confined charged spheres and hydrodynamic drag on uncharged spheres confined at the same location is higher for particles in rectangular channels, resulting in higher percentages of diffusivity reduction. Diffusivity reduction due to relaxation of charged particles in square ducts displays a maximum as a function of relative particle size, whereas that of charged particles in rectangular channels with higher cross section aspect ratio increases monotonically as particle size increases.
Biomechanical Analysis of a Filiform Mechanosensory Hair Socket of Crickets
Authors: Joshi Kanishka , Mian Ahsan , Miller John
Published: June 2016

Filiform mechanosensory hairs of crickets are of great interest to engineers because of the hairs' highly sensitive response to low-velocity air-currents. In this study, we analyze the biomechanical properties of filiform hairs of the cercal sensory system of a common house cricket. The cercal sensory system consists of two antennalike appendages called cerci that are situated at the rear of the cricket's abdomen. Each cercus is covered with 500–750 flow sensitive filiform mechanosensory hairs. Each hair is embedded in a complex viscoelastic socket that acts as a spring and dashpot system and guides the movement of the hair. When a hair deflects due to the drag force induced on its length by a moving air-current, the spiking activity of the neuron that innervates the hair changes and the combined spiking activity of all hairs is extracted by the cercal sensory system. Filiform hairs have been experimentally studied by researchers, though the basis for the hairs' biomechanical characteristics is not fully understood. The socket structure has not been analyzed experimentally or theoretically from a mechanical standpoint, and the characterization that exists is mathematical in nature and only provides a very rudimentary approximation of the socket's spring nature. This study aims to understand and physically characterize the socket's behavior and interaction with the filiform hair by examining hypotheses about the hair and socket biomechanics. A three-dimensional computer-aided design (CAD) model was first created using confocal microscopy images of the hair and socket structure of the cricket, and then finite-element analyses (FEAs) based on the physical conditions that the insect experiences were simulated. The results show that the socket can act like a spring; however, it has two-tier rotational spring constants during pre- and postcontacts of iris and hair bulge due to its constitutive nonstandard geometric shapes.
The Impact of Posture on the Mechanical Properties of a Functional Spinal Unit During Cyclic Compressive Loading
Authors: Barrett Jeff M. , Gooyers Chad E. , Karakolis Thomas , Callaghan Jack P.
Published: June 2016

To assess how posture affects the transmission of mechanical energy up the spinal column during vibration, 18 porcine functional spinal units (FSUs) were exposed to a sinusoidal force (1500 ± 1200 N) at 5 Hz for 120 min in either a flexed, extended, or neutral posture. Force and FSU height were measured continuously throughout the collection. From these data, specimen height loss, dynamic stiffness, hysteresis, and parameters from a standard linear solid (SLS) model were determined and analyzed for differences between postures. Posture had an influence on all of these parameters. In extension, the FSU had higher dynamic stiffness values than when neutral or flexed (p < 0.0001). In flexion, the FSU had higher hysteresis than both an extended or neutral posture (p < 0.0001). Height loss was greatest in a flexed posture and smallest in an extended posture (p < 0.0001). In extension, the series spring element in the SLS model had a stiffness value higher than both flexed and neutral posture conditions, whereas the stiffness in the parallel spring was the same between extension and neutral (p < 0.01), both higher than in flexion. Viscosity coefficients were highest in extension compared to both flexed and neutral (p < 0.01). Based on these results, it was determined that posture had a significant influence in determining the mechanical properties of the spine when exposed to cyclic compressive loading.
Mechanical Characteristics of Bovine Glisson's Capsule as a Model Tissue for Soft Collagenous Membranes
Authors: Bircher Kevin , Ehret Alexander E. , Mazza Edoardo
Published: June 2016

An extensive multiaxial experimental campaign on the monotonic, time- and history-dependent mechanical response of bovine Glisson's capsule (GC) is presented. Reproducible characteristics were observed such as J-shaped curves in uniaxial and biaxial configurations, large lateral contraction, cyclic tension softening, large tension relaxation, and moderate creep strain accumulation. The substantial influence of the reference state selection on the kinematic response and the tension versus stretch curves is demonstrated and discussed. The parameters of a large-strain viscoelastic constitutive model were determined based on the data of uniaxial tension relaxation experiments. The model is shown to well predict the uniaxial and biaxial viscoelastic responses in all other configurations. GC, the corresponding model, and the experimental protocols are proposed as a useful basis for future studies on the relation between microstructure and tissue functionality and on the factors influencing the mechanical response of soft collagenous membranes.
Bifurcation Forecasting for Large Dimensional Oscillatory Systems: Forecasting Flutter Using Gust Responses
Authors: Ghadami Amin , Epureanu Bogdan I.
Published: June 2016

Forecasting bifurcations is a significant challenge and an important need in several applications. Most of the existing forecasting approaches focus on bifurcations in nonoscillating systems. However, subcritical and supercritical flutter (Hopf) bifurcations are very common in a variety of systems, especially fluid–structural systems. This paper presents a unique approach to forecast (nonlinear) flutter based on observations of the system only in the prebifurcation regime. The proposed method is based on exploiting the phenomenon of critical slowing down (CSD) in oscillating systems near certain bifurcations. Techniques are introduced to enhance the prediction accuracy for cases of low-frequency oscillations and large-dimensional dynamical systems. The method is applied to an aeroelastic system responding to gust loads. Numerical results are provided to demonstrate the performance of the method in predicting the postbifurcation regime accurately in both supercritical and subcritical cases.
Effect of Design Parameters on Thermomechanical Stress in Silicon of Through-Silicon Via
Authors: Hwang Joo-Sun , Seo Seung-Ho , Lee Won-Jun
Published: June 2016

We examined the effect of the design parameters of a through-silicon via (TSV) on the thermomechanical stress distribution at the bottom of the TSV using finite element analysis. Static analyses were carried out at 350 °C to simulate the maximum thermomechanical stress during postplating annealing. The thermomechanical stress is concentrated in the lower region of a TSV, and the maximum stress in silicon occurs at the bottom of the TSV. The TSV diameter and dielectric liner thickness were two important determinants of the maximum stress in the silicon. The maximum stress decreased with decreasing TSV diameter, whereas the effect of aspect ratio was negligible. A thick dielectric liner is advantageous for lowering the maximum stress in silicon. The minimum dielectric thickness resulting in a maximum stress less than the yield stress of silicon was 520, 230, and 110 nm for via diameters of 20, 10, and 5 μm, respectively. The maximum stress also decreased with the thickness of the copper overburden.
Corrosion Protection Performance of Organic Offshore Coating Systems at −60 °C Temperature Shock
Authors: Momber A. W. , Irmer M. , Glück N. , Plagemann P.
Published: June 2016

Six organic coating systems were investigated according to their corrosion protection performance under simulated Arctic offshore conditions. The investigations involved accelerated aging, coating adhesion measurements, and dynamic mechanical analysis (DMA). The test conditions were adapted to Arctic offshore conditions, which mainly covered temperature shocks between −20 and −60 °C, chloride exposure, dry–wet cycles, and ultraviolet (UV) radiation. Corrosion protection capability dropped for all coatings if temperature decreased from −20 °C to −60 °C. Two types of coatings could be classified according to their response to the corrosive load: temperature-sensitive coatings and insensitive coatings. Adhesive effects (interface between coating system and substrate) were found to be marginal only at low temperatures and did not affect the response of the coatings to the corrosive load. Cohesive effects (mechanical properties of free polymer films) could be identified in terms of a very high storage modulus and changes in the loss modulus for a temperature-sensitive coating at −60 °C.
Effect of Geometrical Modeling on the Prediction of Laser-Induced Heat Transfer in Metal Foam
Authors: Bucher Tizian , Bolger Christopher , Zhang Min , Chen Chang Jun , Lawrence Yao Y.
Published: June 2016

Over the past several decades, aluminum foam (Al-foam) has found increasing popularity in industrial applications due to its unique material properties. Unfortunately, till date Al-foam can only be affordably manufactured in flat panels, and it becomes necessary to bend the foam to the final shape that is required in engineering applications. Past studies have shown that thin cell walls crack and collapse when conventional mechanical bending methods are used. Laser forming, on the other hand, was shown to be able to bend the material without causing fractures and cell collapse. This study was focused on the thermal aspects of laser forming of closed-cell Al-foam. An infrared camera was used to measure the transient temperature response of Al-foam to stationary and moving laser sources. Moreover, three different numerical models were developed to determine how much geometrical accuracy is needed to obtain a good agreement with experimental data. Different levels of geometrical complexity were used, including a simple solid geometry, a Kelvin-cell based geometry, and a highly accurate porous geometry that was based on an X-ray computed tomography (CT) scan. The numerical results were validated with the experimental data, and the performances of the numerical models were compared.
Effects of Workshop Fabrication Processes on the Deformation Capacity of S960 Ultra-high Strength Steel
Authors: Amraei M. , Dabiri M. , Björk T. , Skriko T.
Published: June 2016

Deformation of a direct quenched type of ultra-high strength steel (UHSS) with low-carbon content is studied in this work. Although this material, as manufactured, combines high strength and good ductility, it is highly sensitive to the workshop fabrication processes used. The presence of stress concentration due to structural discontinuity or notch effects can accentuate the effect of fabrication processes on the deformation capacity of the material. To evaluate the influence of fabrication methods on deformation capacity, a series of tensile tests are done on both pure base material (BM) and after the steel has been subjected to heat input (HI) or cold forming (CF). To study the effect of HI due to welding or other heat-based workshop fabrication processes, the surface of the material was dressed by laser beam at controlled speed and laser intensity. CF effects were studied by bending the specimens to a predetermined angle prior to subjecting the steel to tensile testing. Experimental results were compared with numerical simulation using ls-dyna simulation software. The generated results show acceptable agreement between experimental and numerical simulation outcomes.
Effect of Reverse Yielding on the Residual Contact Pressure in Tube-to-Tubesheet Joints
Authors: Bouzid Abdel-Hakim , Kazeminia Mehdi
Published: June 2016

The analytical prediction of the contact stress in tube-to-tubesheet joints subjected to hydraulic expansion is conducted without any consideration to reverse yielding that can occur inside the tube. Most existing models consider the tube and tubesheet to unload elastically when the expansion pressure is released. These models are therefore less conservative as they overestimate the contact pressure. An analytical model that considers strain-hardening material behavior of the tube and tubesheet and accounts for reverse yielding has been developed. The model is based on Henckey deformation theory and the Von Mises yield criteria. The paper shows that reverse yielding that is present in tubes during hydraulic expansion unloading makes the joint less rigid and causes a decrease in the contact pressure depending on the gap clearance and the materials used. A good correlation between the analytical and finite elements results is obtained on different treated cases which gives confidence on the developed model.
Estimating Long-Term Extreme Slamming From Breaking Waves
Authors: Lian Gunnar , Haver Sverre K.
Published: June 2016

Characteristic loads for design of offshore structures are defined in terms of their annual exceedance probability, q. In the Norwegian Petroleum Regulations, q = 10−2 is required for the ultimate limit state (ULS), while q = 10−4 is required for the accidental limit state (ALS). In principle, a full long-term analysis (LTA) is required in order to obtain consistent estimates. This is straightforward for linear response problems, while it is a challenge for nonlinear problems, in particular if they additionally are of an on–off nature. The latter will typically be the case for loads due to breaking wave impacts. In this paper, the challenges related to estimation of characteristic slamming loads are discussed. Measured slamming loads from a model test are presented, and the observed large variability is discussed. The stochastic nature of slamming loads is studied using a simplified linear relation between the sea states and the Gumbel distribution parameter surfaces. The characteristic slamming loads with q-annual probability of exceedance are estimated from an LTA using the short-term distribution of the slamming loads and the long-term distribution of the sea states. The effect of integrating over a smaller area of the scatter diagram of the sea states is studied. The uncertainties in response from slamming loads are compared to a more common response process, and the relation between variability and the number of realizations in each sea state is looked into.