Torsional fracture of viscoelastic liquid bridges.

Short liquid bridges are stable under the action of surface tension. In applications like electronic packaging, food engineering, and additive manufacturing, this poses challenges to the clean and fast dispensing of viscoelastic fluids. Here, we investigate how viscoelastic liquid bridges can be destabilized by torsion. By combining high-speed imaging and numerical simulation, we show that concave surfaces of liquid bridges can localize shear, in turn localizing normal stresses and making the surface more concave. Such positive feedback creates an indent, which propagates toward the center and leads to breakup of the liquid bridge. The indent formation mechanism closely resembles edge fracture, an often undesired viscoelastic flow instability characterized by the sudden indentation of the fluid's free surface when the fluid is subjected to shear. By applying torsion, even short, capillary stable liquid bridges can be broken in the order of 1 s. This may lead to the development of dispensing protocols that reduce substrate contamination by the satellite droplets and long capillary tails formed by capillary retraction, which is the current mainstream industrial method for destabilizing viscoelastic liquid bridges.

Exceeding traditional curvature limits of concentric tube robots through redundancy resolution.

Understanding elastic instability has been a recent focus of concentric tube robot research. Modeling advances have enabled prediction of when instabilities will occur and produced metrics for the stability of the robot during use. In this paper, we show how these metrics can be used to resolve redundancy to avoid elastic instability, opening the door for the practical use of higher curvature designs than have previously been possible. We demonstrate the effectiveness of the approach using a three-tube robot that is stabilized by redundancy resolution when following trajectories that would otherwise result in elastic instabilities. We also show that it is stabilized when teleoperated in ways that otherwise produce elastic instabilities. Lastly, we show that the redundancy resolution framework presented here can be applied to other control objectives useful for surgical robots, such as maximizing or minimizing compliance in desired directions.

Composite FOXL2 Mutation-positive Adult Granulosa Cell Tumor and Serous Borderline Tumor of the Ovary.

We report a case of a cystic ovarian neoplasm in a 76-yr-old female composed of 2 distinct and intimately associated components: a macrocystic adult granulosa cell tumor (AGCT) and a serous borderline tumor. The granulosa cell nature of the tumor was confirmed with positive immunohistochemical staining for inhibin, calretinin, and WT1, while the neoplastic nature of the granulosa cell proliferation was supported by the presence of a point mutation of the FOXL2 gene. A review of 19 previously reported mixed AGCT and epithelial neoplasms of the ovary is included. Of the eight mixed AGCT and epithelial tumors, including our case, that were tested for FOXL2 mutation, 4 of the 5 mutation-positive cases were notable for demonstrating a macroscopically visible nodule or mass of AGCT at the time of gross examination, while 2 of the 3 mutation-negative cases lacked a mass-producing granulosa cell component. This feature by itself may be sufficient to predict the true neoplastic nature of the granulosa cell proliferation. This is the first reported case of a composite neoplastic AGCT and serous borderline tumor. We also discuss the current histogenetic models for these rare mixed AGCT and epithelial tumors.

Ciliated Carcinoma of the Endometrium.

We report a case of ciliated carcinoma of the endometrium in a 55-yr-old woman with stromal hyperthecosis of the ovaries. The patient presented with postmenopausal uterine bleeding and an endometrial curetting revealed an atypical epithelial proliferation that met the criteria for endometrioid adenocarcinoma notwithstanding an abundance of ciliated cells. Cilia were present not only within typical endometrioid glands but also within microacini of quasi-solid areas as well as inside intracytoplasmic vacuoles. The subsequent hysterectomy specimen demonstrated a well-differentiated adenocarcinoma of the endometrium with a predominance of neoplastic glands lined by ciliated epithelial cells, thus confirming the initial suspicion for ciliated carcinoma. Since the first description of ciliated adenocarcinoma of the endometrium in 1983, only a handful of additional cases have been reported in the literature. We review the spectrum of histologic presentations of this endometrial neoplasm and elaborate on its distinction from cilia-bearing mimickers and its histogenesis.

Perineal Clear Cell Hidradenoma: A GATA3-positive Neoplasm With Potential for Misdiagnosis.

We report a case of clear cell hidradenoma of the perineum that was initially misinterpreted as a papillary urothelial carcinoma, either metastatic or of Bartholin gland origin, on initial excisional biopsy. The misinterpretation may have been due to the pseudopapillary architecture and GATA3-positivity of the biopsy tissue. Clear cell hidradenomas often show a range of histologic growth patterns and cellular differentiation and are one of many tumors that react immunohistochemically with GATA3. Although rare, these tumors can occur in the genital region and can mimic malignant tumors such as metastatic renal cell carcinoma and carcinomas of the genitourinary tract. This report details the morphologic and immunohistochemical pitfalls that make accurate diagnosis of clear cell hidradenoma in this unusual location challenging.

Conjugation of hydrophobic moieties enhances potency of antisense oligonucleotides in the muscle of rodents and non-human primates.

We determined the effect of attaching palmitate, tocopherol or cholesterol to PS ASOs and their effects on plasma protein binding and on enhancing ASO potency in the muscle of rodents and monkeys. We found that cholesterol ASO conjugates showed 5-fold potency enhancement in the muscle of rodents relative to unconjugated ASOs. However, they were toxic in mice and as a result were not evaluated in the monkey. In contrast, palmitate and tocopherol-conjugated ASOs showed enhanced potency in the skeletal muscle of rodents and modest enhancements in potency in the monkey. Analysis of the plasma-protein binding profiles of the ASO-conjugates by size-exclusion chromatography revealed distinct and species-specific differences in their association with plasma proteins which likely rationalizes their behavior in animals. Overall, our data suggest that modulating binding to plasma proteins can influence ASO activity and distribution to extra-hepatic tissues in a species-dependent manner and sets the stage to identify other strategies to enhance ASO potency in muscle tissues.

Behavior of viscoelastic models with thermal fluctuations.

Fluctuating viscoelasticity for conformation-tensor-based models is studied at equilibrium, in simple-shear deformation, and in uniaxial extension. The models studied are the upper-convected Maxwell model, the FENE-P model with finite chain-extensibility, and the Giesekus model with anisotropic drag. Using numerical simulations, the models are compared in detail both with each other and with analytical predictions for the Maxwell model. At equilibrium, the models differ only marginally, both in terms of static and dynamic characteristics. When deformed, the average mechanical response of the Maxwell model is unaffected by the strength of thermal fluctuations, while the mechanical response of the FENE-P and Giesekus models show a slight decrease the stronger the fluctuations in simple shear, whereas the decrease in uniaxial extension is marginal. For all models, the standard deviation of the mechanical response increases with increasing strength of fluctuations, and the magnitude of the standard deviation relative to the average for given fluctuation strength generally decreases the stronger the deformation, this effect being stronger for uniaxial extension than for simple-shear deformation.

Assessing Chemical Mechanisms Underlying the Effects of Sunflower Pollen on a Gut Pathogen in Bumble Bees.

Many pollinator species are declining due to a variety of interacting stressors including pathogens, sparking interest in understanding factors that could mitigate these outcomes. Diet can affect host-pathogen interactions by changing nutritional reserves or providing bioactive secondary chemicals. Recent work found that sunflower pollen (Helianthus annuus) dramatically reduced cell counts of the gut pathogen Crithidia bombi in bumble bee workers (Bombus impatiens), but the mechanism underlying this effect is unknown. Here we analyzed methanolic extracts of sunflower pollen by LC-MS and identified triscoumaroyl spermidines as the major secondary metabolite components, along with a flavonoid quercetin-3-O-hexoside and a quercetin-3-O-(6-O-malonyl)-hexoside. We then tested the effect of triscoumaroyl spermidine and rutin (as a proxy for quercetin glycosides) on Crithidia infection in B. impatiens, compared to buckwheat pollen (Fagopyrum esculentum) as a negative control and sunflower pollen as a positive control. In addition, we tested the effect of nine fatty acids from sunflower pollen individually and in combination using similar methods. Although sunflower pollen consistently reduced Crithidia relative to control pollen, none of the compounds we tested had significant effects. In addition, diet treatments did not affect mortality, or sucrose or pollen consumption. Thus, the mechanisms underlying the medicinal effect of sunflower are still unknown; future work could use bioactivity-guided fractionation to more efficiently target compounds of interest, and explore non-chemical mechanisms. Ultimately, identifying the mechanism underlying the effect of sunflower pollen on pathogens will open up new avenues for managing bee health.

A Dynamic Model for Concentric Tube Robots.

Existing static and kinematic models of concentric tube robots are based on the ordinary differential equations of a static Cosserat rod. In this paper, we provide the first dynamic model for concentric tube continuum robots by adapting the partial differential equations of a dynamic Cosserat rod to describe the coupled inertial dynamics of precurved concentric tubes. This generates an initial-boundary-value problem that can capture robot vibrations over time. We solve this model numerically at high time resolutions using implicit finite differences in time and arc length. This approach is capable of resolving the high-frequency torsional dynamics that occur during unstable "snapping" motions and provides a simulation tool that can track the true robot configuration through such transitions. Further, it can track slower oscillations associated with bending and torsion as a robot interacts with tissue at real-time speeds. Experimental verification of the model shows that this wide range of effects is captured efficiently and accurately.

Laser sintering of polymer particle pairs studied by in situ visualization.

Merging of particle pairs during selective laser sintering (SLS) of polymers is vital in defining the final part properties. Depending on the sintering conditions, polymers can undergo full or partial sintering whereby incomplete sintering results in poor mechanical properties. At present, the underlying mechanisms and related conditions leading to various consolidation phenomena of polymer particles are not well understood. In the present work, a novel in-house developed experimental setup is used to perform laser sintering experiments on polystyrene (PS) particle doublets while performing in situ visualization of the sintering dynamics. From the recorded images, the evolution of the growth of the neck radius formed between both particles is analyzed as a function of time. Sintering conditions such as heating chamber temperature, laser pulse energy and duration, laser spot size and particle size are precisely controlled and systematically varied. A non-isothermal viscous sintering model is developed that allows qualitative prediction of the observed effects of the various parameters. It is shown that the sintering kinetics is determined by a complex interplay between the transient rheology caused by the finite relaxation times of the polymer and the time-dependent temperature profile which also affects the polymer viscosity. The combination of a full material characterization with sintering experiments under well-defined conditions has resulted in a general understanding of the effects of material and process parameters on laser sintering. Thereby a strong foundation is laid for the route towards rational design of laser sintering.

Shear-Induced Migration of Rigid Particles near an Interface between a Newtonian and a Viscoelastic Fluid.

Simulations of rigid particles suspended in two-phase shear flow are presented, where one of the suspending fluids is viscoelastic, whereas the other is Newtonian. The Cahn-Hilliard diffuse-interface model is employed for the fluid-fluid interface, which can naturally describe the interactions between the particle and the interface (e.g., particle adsorption). It is shown that particles can migrate across streamlines of the base flow, which is due to the surface tension of the fluid-fluid interface and a difference in normal stresses between the two fluids. The particle is initially located in the viscoelastic fluid, and its migration is investigated in terms of the Weissenberg number Wi (shear rate times relaxation time) and capillary number Ca (viscous stress over capillary stress). Four regimes of particle migration are observed, which can roughly be described by migration away from the interface for Wi = 0, halted migration toward the interface for low Wi and low Ca, particle adsorption at the interface for high Wi and low Ca, and penetration into the Newtonian fluid for high Wi and high Ca. It is found that the angular velocity of the particle plays a large role in determining the final location of the particle, especially for high Wi. From morphology plots, it is deduced that the different dynamics can be described well by considering a balance in the first-normal stress difference and Laplace pressure. However, it is shown that other parameters, such as the equilibrium contact angle and diffusion of the fluid, are also important in determining the final location of the particle.

First Canadian experience with donation after cardiac death simultaneous pancreas and kidney transplants.

BACKGROUND: Compared with neurologic determination of death (NDD) donor organs, donation after cardiac death (DCD) donor organs have traditionally been considered of inferior quality owing to warm ischemia experienced during procurement. We present, to our knowledge, the first analysis of simultaneous pancreas and kidney (SPK) transplants using DCD donor organs in Canada. METHODS: We carried out a retrospective cohort study of SPK transplants from 13 DCD and 68 NDD donors performed between October 2008 and July 2016. In all patients immunosuppression was induced with thymoglobulin and continued with tacrolimus, mycophenolate mofetil and prednisone maintenance therapy. RESULTS: Donor and recipient characteristics of DCD and NDD groups were similar with respect to age, sex, body mass index, kidney and pancreas cold ischemia times, and donor terminal creatinine. Mean DCD graft warm ischemia time was 0.5 (range 0.4-0.7) hours. Median follow-up was 2.2 (range 0.1-6.7) years and 2.7 (range 0.3-6.3) years for the DCD and NDD groups, respectively. The DCD and NDD groups were similar with regards to recipient percent panel reactive antibody and presence of human leukocyte antigen antibodies. The groups also received similar total doses of thymoglobulin. In total 38% of patients in the DCD group experienced renal delayed graft function (DGF) compared with 10% in the NDD group (p = 0.027). There were 7 cases of pancreas graft thrombosis requiring relaparotomy in the NDD group compared with none in the DCD group. No patients from either group required insulin at any time after transplant. Although the estimated glomerular filtration rate (eGFR) was lower in the DCD than the NDD group on postoperative days 7 and 14 (p = 0.025), no difference was noted on day 30 or through 4 years after transplant. No differences were seen between the groups with respect to amylase, lipase, or glycosated hemoglobin (HbA1c) up to 4 years after transplant, or in kidney, pancreas, or patient survival at any time after transplant. CONCLUSION: Our results show that, apart from a higher renal DGF rate, SPK transplants with DCD donor organs have comparable outcomes to standard transplants with NDD donor organs.

CONTEXTE: Comparativement aux organes prélevés après détermination de la mort cérébrale (ou détermination du décès neurologique [DDN]), les organes prélevés après détermination du décès cardiocirculatoire (DDC) sont en général considérés de moindre qualité en raison du phénomène d'ischémie chaude inhérent à ce type de prélèvement. Nous présentons, à notre connaissance, la première analyse sur la double greffe rein-pancréas effectuée avec des organes prélevés après DDC au Canada. MÉTHODES: Nous avons procédé à une étude de cohorte rétrospective sur les doubles greffes rein-pancréas effectuées entre octobre 2008 et juillet 2016, soit 13 après DDC et 68 après DDN. Chez tous les patients, l'immunosuppression a été induite par la thymoglobuline et a été maintenue au moyen d'un traitement d'entretien par le tacrolimus, le mycophénolate mofétil et la prednisone. RÉSULTATS: Les caractéristiques des donneurs et des receveurs des 2 groupes (DDC et DDN) étaient semblables sur les plans de l'âge, du sexe, de l'indice de masse corporelle, de la durée de l'ischémie froide du rein et du pancréas, et de la créatinine terminale (donneur). La durée moyenne de l'ischémie chaude des greffons prélevés après DDC a été de 0,5 (étendue : 0,4-0,7) heure. Le suivi médian a été d'une durée de 2,2 (étendue : 0,1-6,7) ans et de 2,7 (étendue : 0,3-6,3) ans, respectivement, pour les groupes DDC et DDN. Les 2 groupes étaient similaires pour ce qui est des pourcentages d'anticorps réactifs et de la présence d'anticorps anti-HLA (human leukocyte antigen) chez les receveurs. Les 2 groupes avaient aussi reçu des doses totales semblables de thymoglobuline. En tout, 38 % des patients du groupe DDC ont manifesté un retard de fonctionnement du greffon rénal, contre 10 % dans le groupe DDN (p = 0,027). On a dénombré 7 cas de thrombose du greffon pancréatique ayant nécessité une réintervention dans le groupe DDN, contre aucun dans le groupe DDC. Aucun des patients n'a eu besoin d'insuline après la transplantation. Le débit de filtration glomérulaire estimé (DFGe) était moins élevé dans le groupe DDC que dans le groupe DDN aux jours 7 et 14 (p = 0,025), mais on n'a plus noté de différence à ce chapitre au jour 30 ni au cours des 4 années suivant la greffe. On n'a observé aucune différence entre les groupes pour ce qui est de l'amylase, de la lipase ou de l'HbA1c jusqu'à 4 ans suivant la greffe, ni pour ce qui est de la survie des greffons rénaux ou pancréatiques ou celle des patients, peu importe le temps écoulé depuis la greffe. CONCLUSION: Selon nos résultats, si ce n'est un taux plus élevé de retard de fonctionnement du greffon rénal, les receveurs d'une double greffe rein-pancréas après DDC obtiennent des résultats semblables à ceux qui subissent une greffe standard d'organes prélevés après DDN.

Heparin infusion in simultaneous pancreas and kidney transplantation reduces graft thrombosis and improves graft survival.

INTRODUCTION: Thrombosis of the pancreas after transplantation is the most common cause of relaparotomy and resultant graft loss. There is currently no standard protocol consistently proven to prevent thrombosis following transplantation. Our objective was to determine whether our protocol of post-operative low-dose intravenous (IV) heparin infusion would prevent graft thrombosis without additional complications in our patients. METHODS: A total of 66 simultaneous pancreas kidney (SPK) transplants were performed at our institution from 2004 to 2014. Patients were divided into 2 retrospective cohort groups. Group 1 patients received only acetylsalicylic acid (ASA) 81 mg/d started on post-operative day 1. Group 2 patients received IV heparin infusion beginning in the recovery room at a rate of 500 IU/h for the first 24 hours, reduced by 100 IU/h every day to stop on day 5, and then received ASA 81 mg/d afterward. Outcome and complication rates were compared between the two groups for 5 years post-transplant. RESULTS: We observed a significant reduction in graft thrombosis and graft loss with (0/29) patients in the heparin group vs (7/33) 25.7% from the non-heparin (P<.01) with no differences in complication rates. CONCLUSIONS: We present a heparin infusion protocol which may help prevent graft thrombosis and graft loss in SPK transplantation.

Toughening Immiscible Polymer Blends: The Role of Interface-Crystallization-Induced Compatibilization Explored Through Nanoscale Visualization.

This study explores the novel approach of interface-crystallization-induced compatibilization (ICIC) via stereocomplexation as a promising method to improve the interfacial strength in thermodynamically immiscible polymers. Herein, two distinct reactive interfacial compatibilizers, poly(styrene-co-glycidyl methacrylate)-graft-poly(l-lactic acid) (SAL) and poly(styrene-co-glycidyl methacrylate)-graft-poly(d-lactic acid) (SAD) are synthesized via reactive melt blending in an integrated grafting and blending process. This approach is demonstrated to enhance the interfacial strength of immiscible polyvinylidene fluoride/poly l-lactic acid (PVDF/PLLA) 50/50 blends via ICIC. IR nanoimaging indicates a cocontinuous morphology in the blends. The blend compatibilized with SAD exhibits a higher storage modulus, as unveiled by small amplitude oscillatory shear (SAOS) in the melt state at a temperature below the melting temperature of the stereocomplex (SC) crystals and by DMTA measurements in the solid state. This increase is attributed to the formation of a 200-300 nm thick rigid interfacial SC crystalline layer that is directly visible using AFM imaging and chemically characterized via IR nanospectroscopy. This ICIC also results in a significant toughening of the blend, with the elongation at break increasing more than 20-fold. Moreover, the fracture toughness factor obtained from single edge-notch bending (SENB) tests is doubled with ICIC as compared to the uncompatibilized blend, indicating the strong crack-resistance capability as a result of ICIC. This improvement is also evident in SEM images, where thinner and longer fibrillation is observed on the fractured surface in the presence of ICIC.

The impact of robotic surgery access on the management of patients with clinical stage I kidney tumors.

INTRODUCTION: Robotic surgery is used in the treatment of kidney tumors. We aimed to determine if robotic access was associated with initial choice of management for patients with a clinical stage I kidney mass. METHODS: Patients with a clinical stage I kidney mass were identified from the Canadian Kidney Cancer information system (CKCis) cohort. Sites were classified by year and access to robotic surgery. Associations between robotic access and initial management were determined using logistic regression. Univariable and multivariable analyses were performed, adjusting for tumor size and stage, and presented as relative risks (RR ) or adjusted RR (aRR) and 95% confidence intervals (CI). RESULTS: Overall, 4160 patients were included. Among patients treated with surgery, the proportion of partial nephrectomy compared to radical nephrectomy was significantly higher in robotic sites (77.3% for robotic sites vs. 65.9% for non-robotic sites; RR 1.17, 95% CI 1.12-1.23, p<0.0001; aRR 1.12, 95% CI 1.08-1.17, p<0.0001). Patients receiving partial nephrectomy at sites with robotic access were more likely to receive a minimally invasive approach compared to patients at non-robotic sites (61.4% vs. 50.9%, RR 1.21, 95% CI 1.12-1.30; aRR 1.16, 95% CI 1.08-1.25, p<0.0001). The proportion of patients managed by active surveillance was not significantly different between robotic (405, 16.9%) and non-robotic (258, 14.7%) sites (RR 1.15, 95% CI 0.99-1.32; aRR 0.97, 95% CI 0.84-1.12). CONCLUSIONS: Access to robotic kidney surgery was associated with increased use of partial nephrectomy and minimally invasive partial nephrectomy. Use of active surveillance was similar at robotic and non-robotic institutions. Limitations of this study include lack of data on perioperative complications and cancer recurrence.

Effective gene therapy with nonintegrating lentiviral vectors.

Retroviral and lentiviral vector integration into host-cell chromosomes carries with it a finite chance of causing insertional mutagenesis. This risk has been highlighted by the induction of malignancy in mouse models, and development of lymphoproliferative disease in three individuals with severe combined immunodeficiency-X1 (refs. 2,3). Therefore, a key challenge for clinical therapies based on retroviral vectors is to achieve stable transgene expression while minimizing insertional mutagenesis. Recent in vitro studies have shown that integration-deficient lentiviral vectors can mediate stable transduction. With similar vectors, we now show efficient and sustained transgene expression in vivo in rodent ocular and brain tissues. We also show substantial rescue of clinically relevant rodent models of retinal degeneration. Therefore, the high efficiency of gene transfer and expression mediated by lentiviruses can be harnessed in vivo without a requirement for vector integration. For therapeutic application to postmitotic tissues, this system substantially reduces the risk of insertional mutagenesis.

Dorsally and ventrally derived oligodendrocytes have similar electrical properties but myelinate preferred tracts.

In the developing spinal cord, most oligodendrocyte precursors (OLPs) arise from the ventral ventricular zone (VZ) under the influence of Sonic Hedgehog, but a minority are generated from the dorsal VZ in a Hedgehog-independent manner. In the developing forebrain too, OLPs arise from both the ventral and the dorsal VZ. It is not known whether dorsally and ventrally derived oligodendrocyte (OL) lineage cells have different properties. We generated a dual reporter mouse line to color code ventrally and dorsally derived OLPs (vOLPs and dOLPs) and their differentiated oligodendrocyte progeny (vOLs and dOLs) for functional studies. We found that ∼80% of OL lineage cells in the postnatal spinal cord and ∼20% in the corpus callosum are ventrally derived. In both spinal cord and corpus callosum, vOLPs and dOLPs had indistinguishable electrical properties, as did vOLs and dOLs. However, vOLPs and dOLPs had different migration and settling patterns. In the spinal cord, vOLPs appeared early and spread uniformly throughout the cord, whereas dOLPs arrived later and remained mainly in the dorsal and dorsolateral funiculi. During adulthood, corticospinal and rubrospinal tracts became myelinated mainly by dOLs, even though vOLs dominated these tracts during early postnatal life. Thus, dOLPs are electrically similar to vOLPs but appear to outcompete them for dorsal axons.

D-amino acid oxidase knockdown in the mouse cerebellum reduces NR2A mRNA.

Virus mediated RNA-interference (RNAi) is a powerful approach to study genes in vivo. Here we report a method using lentivirus-delivered RNAi to knockdown the glial enzyme, D-amino acid oxidase (DAO), in the mouse cerebellum. After initial characterisation in vitro, we achieved a 40-50% reduction of DAO mRNA in the cerebellum 7 and 28 days after a single injection of lentivirus encoding a DAO-specific, short-hairpin RNA. Injections also decreased DAO immunoreactivity (-33%). The major substrate for DAO is D-serine, an N-methyl-D-aspartate receptor (NMDAR) co-agonist. Thus, we also measured whether DAO knockdown impacted on d-serine, or expression of NMDAR subunits, and found that DAO RNAi led to increased cerebellar D-serine levels (+77%), and decreased NMDAR subunit NR2A mRNA (-22%), but did not affect NR1 or NR2C mRNAs. These data demonstrate the utility of lentiviruses to deliver RNAi to glial cells within the cerebellum, and confirm the role of DAO in D-serine metabolism. They also provide a tool to investigate DAO, an enzyme currently of considerable interest in the pathophysiology and therapy of schizophrenia.

Synergy of Fiber Surface Chemistry and Flow: Multi-Phase Transcrystallization in Fiber-Reinforced Thermoplastics.

Fiber-reinforced polymer composites are largely employed for their improved strength with respect to unfilled matrices. Considering semi-crystalline materials under relevant processing conditions, the applied pressure and flow induce shear stresses at the fiber-polymer interface. These stresses may strongly enhance the nucleation ability of the fiber surface with respect to the quiescent case. It is thus possible to assume that the fiber features are no longer of importance and that crystallization is dominated by the effect of flow. However, by making use of an advanced experimental technique, i.e., polarization-modulated synchrotron infrared microspectroscopy (PM-SIRMS), we are able to show that the opposite is true for the industrially relevant case of isotactic polypropylene (iPP). With PM-SIRMS, the local chain orientation is measured with micron-size spatial resolution. This orientation can be related to the polymer nucleation density along the fiber surface. For various combinations of an iPP matrix and fiber, the degree of orientation in the cylindrical layer that develops during flow correlates well with the differences in nucleation density found in quiescent conditions. This result shows that the morphological development during processing of polymer composites is not solely determined by the flow field, nor by the nucleating ability of the fiber surface alone, but rather by a synergistic combination of the two. In addition, using finite element modeling, it is demonstrated that, under the experimentally applied flow conditions, the interphase structure formation is mostly dominated by the rheological characteristics of the material rather than perturbations in experimental conditions, such as shear rate, layer thickness, and temperature. This once again highlights the importance of matrix-filler interplay during flow and, thus, of material selection in the design of hybrid and lightweight composite technologies.

Assessing vegetation recovery from energy development using a dynamic reference approach.

Ecologically relevant references are useful for evaluating ecosystem recovery, but references that are temporally static may be less useful when environmental conditions and disturbances are spatially and temporally heterogeneous. This challenge is particularly acute for ecosystems dominated by sagebrush (Artemisia spp.), where communities may require decades to recover from disturbance. We demonstrated application of a dynamic reference approach to studying sagebrush recovery using three decades of sagebrush cover estimates from remote sensing (1985-2018). We modelled recovery on former oil and gas well pads (n = 1200) across southwestern Wyoming, USA, relative to paired references identified by the Disturbance Automated Reference Toolset. We also used quantile regression to account for unmodelled heterogeneity in recovery, and projected recovery from similar disturbance across the landscape. Responses to weather and site-level factors often differed among quantiles, and sagebrush recovery on former well pads increased more when paired reference sites had greater sagebrush cover. Little (<5%) of the landscape was projected to recover within 100 years for low to mid quantiles, and recovery often occurred at higher elevations with cool and moist annual conditions. Conversely, 48%-78% of the landscape recovered quickly (within 25 years) for high quantiles of sagebrush cover. Our study demonstrates advantages of using dynamic reference sites when studying vegetation recovery, as well as how additional inferences obtained from quantile regression can inform management.