Towards the Development of a Strategy to Characterize and Model the Rheological Behavior of Filled, Uncured Rubber Compounds.

In this paper, an experimental strategy is presented to characterize the rheological behavior of filled, uncured rubber compounds. Oscillatory shear experiments on a regular plate-plate rheometer are combined with a phenomenological thixotropy model to obtain model parameters that can be used to describe the steady shear behavior. We compare rate- and stress-controlled kinetic equations for a structure parameter that determines the deformation history-dependent spectrum and, thus, the dynamic thixotropic behavior of the material. We keep the models as simple as possible and the characterization straightforward to maximize applicability. The model can be implemented in a finite element framework as a tool to simulate realistic rubber processing. This will be the topic of another work, currently under preparation. In shaping processes, such as rubber- and polymer extrusion, with realistic processing conditions, the range of shear rates is far outside the range obtained during rheological characterization. Based on some motivated choices, we will present an approach to extend this range.

Short-time behavior of advecting-diffusing scalar fields in Stokes flows.

This article addresses the short-term decay of advecting-diffusing scalar fields in Stokes flows. The analysis is developed in two main subparts. In the first part, we present an analytic approach for a class of simple flow systems expressed mathematically by the one-dimensional advection-diffusion equation w(y)∂(ξ)φ=ε∂(y)(2)φ+iV(y)φ-ε'φ, where ξ is either time or axial coordinate and iV(y) an imaginary potential. This class of systems encompasses both open- and closed-flow models and corresponds to the dynamics of a single Fourier mode in parallel flows. We derive an analytic expression for the short-time (short-length) decay of φ, and show that this decay is characterized by a universal behavior that depends solely on the singularity of the ratio of the transverse-to-axial velocity components V(eff)(y)=V(y)/w(y), corresponding to the effective potential in the imaginary potential formulation. If V(eff)(y) is smooth, then ||φ||(L(2))(ξ)=exp(-ε'ξ-bξ(3)), where b>0 is a constant. Conversely, if the effective potential is singular, then ||φ||(L(2))(ξ)=1-aξ(ν) with a>0. The exponent ν attains the value 5/3 at the very early stages of the process, while for intermediate stages its value is 3/5. By summing over all of the Fourier modes, a stretched exponential decay is obtained in the presence of nonimpulsive initial conditions, while impulsive conditions give rise to an early-stage power-law behavior. In the second part, we consider generic, chaotic, and nonchaotic autonomous Stokes flows, providing a kinematic interpretation of the results found in the first part. The kinematic approach grounded on the warped-time transformation complements the analytical theory developed in the first part.

Direct numerical simulation of a 2D-stented aortic heart valve at physiological flow rates.

We study the nonlinear interaction of an aortic heart valve, composed of hyperelastic corrugated leaflets of finite density attached to a stented vessel under physiological flow conditions. In our numerical simulations, we use a 2D idealised representation of this arrangement. Blood flow is caused by a time-varying pressure gradient that mimics that of the aortic valve and corresponds to a peak Reynolds number equal to 4050. Here, we fully account for the shear-thinning behaviour of the blood and large deformations and contact between the leaflets by solving the momentum and mass balances for blood and leaflets. The mixed finite element/Galerkin method along with linear discontinuous Lagrange multipliers for coupling the fluid and elastic domains is adopted. Moreover, a series of challenging numerical issues such as the finite length of the computational domain and the conditions that should be imposed on its inflow/outflow boundaries, the accurate time integration of the parabolic and hyperbolic momentum equations, the contact between the leaflets and the non-conforming mesh refinement in part of the domain are successfully resolved. Calculations for the velocity and the shear stress fields of the blood reveal that boundary layers appear on both sides of a leaflet. The one along the ventricular side transfers blood with high momentum from the core region of the vessel to the annulus or the sinusoidal expansion, causing the continuous development of flow instabilities. At peak systole, vortices are convected in the flow direction along the annulus of the vessel, whereas during the closure stage of the valve, an extremely large vortex develops in each half of the flow domain.

Pim1 kinase is required to maintain tumorigenicity in MYC-expressing prostate cancer cells.

PIM1 kinase and MYC are commonly co-expressed in human prostate cancer and synergize to induce rapidly progressing prostate cancer in mouse models. Deficiency of the Pim kinase genes is well tolerated in vivo, suggesting that PIM1 inhibition might offer an attractive therapeutic modality for prostate cancer, particularly for MYC-expressing tumors. Here we examine the molecular consequences of Pim1 and MYC overexpression in the prostate as well as the effects of depleting Pim1 in prostate carcinoma cells with high levels of MYC. Overexpression of Pim1 in the mouse prostate induces several pro-tumorigenic genetic programs including cell cycle genes and Myc-regulated genes before the induction of any discernible pathology. Pim1 depletion by RNA interference in mouse and human prostate cancer cells decreased cellular proliferation, survival, Erk signaling and tumorigenicity even when MYC levels were not significantly altered. These results indicate that PIM1 may be necessary to maintain tumorigenicity, and further support efforts aimed at developing PIM1 inhibitors for prostate cancer therapy.

Breaking of symmetry in microfluidic propulsion driven by artificial cilia.

In this Brief Report we investigate biomimetic fluid propulsion due to an array of periodically beating artificial cilia. A generic model system is defined in which the effects of inertial fluid forces and the spatial, temporal, and orientational asymmetries of the ciliary motion can be individually controlled. We demonstrate that the so-far unexplored orientational asymmetry plays an important role in generating flow and that the flow increases sharply with Reynolds number and eventually becomes unidirectional. We introduce the concept of configurational symmetry that unifies the spatial, temporal, and orientational symmetries. The breaking of configurational symmetry leads to fluid propulsion in microfluidic channels.

Nature-inspired microfluidic propulsion using magnetic actuation.

In this work we mimic the efficient propulsion mechanism of natural cilia by magnetically actuating thin films in a cyclic but non-reciprocating manner. By simultaneously solving the elastodynamic, magnetostatic, and fluid mechanics equations, we show that the amount of fluid propelled is proportional to the area swept by the cilia. By using the intricate interplay between film magnetization and applied field we are able to generate a pronounced asymmetry and associated flow. We delineate the functional response of the system in terms of three dimensionless parameters that capture the relative contribution of elastic, inertial, viscous, and magnetic forces.

Transient interfacial tension of partially miscible polymers.

The interfacial tension of three different binary polymer blends has been measured as function of time by means of a pendent drop apparatus, at temperatures ranging from 24 degrees C to 80 degrees C. Three grades of polybutene (PB), differing in average molecular weight and polydispersity, are used as dispersed phase, the continuous phase is kept polydimethylsiloxane (PDMS), ensuring different asymmetry in molecular weight across the interface. The interfacial tension changes with time and, therefore, this polymer blends can not be considered fully immiscible. Changes in interfacial tension are attributed to the migration of low-molecular weight components from the source phase into the interphase and, from there, into the receiving phase. In the early stages of the experiments, just after the contact between the two phases has been established, the formation of an interphase occurs and the interfacial tension decreases with time. As time proceeds, the migration process slows down given the decrease in driving force which is the concentration gradient and, at the same time, molecules accumulated in the interphase start to migrate into the "infinite" matrix phase. A quasi-stationary state is found before depletion of the low-molecular weight fraction in the drop occurs and causes the interfacial tension sigma(t) to increase. The time required to reach the final stationary value, sigma(stat), increases with molecular weight and is a function of temperature. Higher polydispersity leads to lower sigma(stat) and a weaker dependence of sigma(stat) on temperature is found. A model coupling the diffusion equation in the different regimes is applied in order to interpret the experimental results. Numerical solutions of the diffusion equation are proposed in the cases of a constant and a changing interphase thickness. In the latter case, the interphase is defined by tracking with time a fixed limiting concentration in the transient concentration profiles and the variations found in sigma(t) are attributed to the changes in the interphase thickness. A discrete version of this continuous model is proposed and scaling arguments are reported in order to compare the results obtained with the predictions of the continuous model. The kinetic model as proposed by Shi et al. [T. Shi, V.E. Ziegler, I.C. Welge, L. An, B.A. Wolf, Macromolecules 37 (2007) 1591-1599] appears as a special case of the discrete model, when depletion is not taken into account. Using the models, time scales for the diffusion process can be derived, which fit the experimental results quite well.

An attempt to measure the spread of emergency medicine internationally.

OBJECTIVE: To determine the feasibility of using the internet to track the spread of emergency medicine internationally. OVERVIEW: This was an attempt to perform a descriptive cross-sectional study employing a web-based survey. SUBJECTS: Potential respondents were identified from multiple sources. OBSERVATIONS: The primary outcome was the response to 16 questions about EM care and the setting in which it was delivered for acute cardiac, paediatric, obstetrical illnesses and trauma. The questions were divided into six general areas and elicited for urban, semi-urban and rural settings. A series of four e-mails soliciting completion of the survey were sent to potential respondents. ANALYSIS: Simple descriptive statistics. RESULTS: We identified 358 potential respondents with valid e-mail addresses over a period of three years. Overall, 145 (41%) responded and 117 (33% 95% CI 28-38%) of them were complete and interpretable. There was one response from 54 and two responses from 29 countries, representing an overall response rate by country surveyed of 65% (95% CI 57-73%), but of all existing countries of only 43% (95% CI 36-50%). Based on sparse data, it appears that in urban areas, 47% (obstetrics) to 65% (paediatric) of acutely sick or injured patients are taken to an ED-equivalent. For rural areas, this range was 19% (obstetrical) to 40% (trauma). CT scans are available in 78% of urban ED-equivalents but 12% of rural ones. Haematocrits are available in 72% of rural settings. In 60% of responding nations, some type of EM training was available, and in 42% physicians went abroad to study EM. CONCLUSIONS: A survey of international EM is challenging to achieve because of difficulty in both identifying and in contacting potential respondents. Based on sparse data, population density (urban, rural) appears to be related to both the location to which acutely ill patients are taken for their care and to the level of technology available. The specialty of EM is now recognised internationally and education in EM is common.

Detection of hemizygosity in Hermansky-Pudlak syndrome by quantitative real-time PCR.

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by oculocutaneous albinism, a bleeding diathesis and, in some patients, pulmonary fibrosis or granulomatous colitis. HPS is associated with biosynthesis defects of melanosomes, platelet-dense bodies, and lysosomes. There are seven genetic HPS subtypes; HPS-1 is the most common. We used a real-time quantitative PCR (qPCR) approach to investigate six HPS-1 patients, previously assigned as having homozygous mutations in the HPS1 gene. HPS1 gene copy numbers, calculated by use of a comparative Ct method, revealed that one patient was in fact hemizygous for her c.1189delC (S396delC) HPS1 mutation. The causative deletion/insertion was 13,966 bp in size, with defined breakpoints, and involved an adjacent gene (C10orf33). A mechanism of formation is proposed for the deletion/insertion, and both multiplex and qPCR indicated that the deletion/insertion was present in the patient, her brother, and her father. qPCR amplification is valuable for detecting deletions too small to be identified by fluorescence in situ hybridization. This demonstration of hemizygosity, performed using genomic DNA, can eliminate concerns about non-paternity and can verify the diagnosis of an autosomal recessive disorder when a DNA alteration appears to be homozygous by standard PCR and sequencing methods, and its pathogenicity is in doubt.

[The practice guideline: 'Treatment of tobacco dependence']. / Richtlijn 'Behandeling van tabaksverslaving'.

The interdisciplinary guideline 'Treatment of tobacco dependence' discusses the approach to smoking patients. The point of departure is the concept that smoking is an addiction and that its treatment should be based on this fact. The effectiveness of treatment depends on the patient's motivation to stop smoking and on the intensity of the intervention. Pharmacotherapy may be of added value here, particularly for persistent smokers. The guideline aims at reaching as many smoking patients as possible, regardless of whether there is a relationship between their symptoms or ill health and smoking. Practitioners should ask about smoking habits regularly and smokers should be advised at least once to stop. Further treatment and guidance aims in particular to increase the motivation to quit and at those who are prepared to stop on the basis of the stages-of-change model. More intensive possibilities for treatment, by both general practitioners and specialists, are needed for persistent smokers. Such facilities are hardly available at all in The Netherlands at present, but will have to be developed to make the cost-effective treatment of tobacco addiction possible on a large scale.

Catheter-less Cohen transtrigonal ureteric reimplantation.

OBJECTIVE: To review the profile and outcome of patients in whom it was elected not to insert a bladder catheter as part of the management of Cohen transtrigonal ureteric reimplantation surgery. PATIENTS AND METHODS: Between April 2000 and April 2001, 37 patients underwent ureteric reimplantation by the senior author, using the Cohen transtrigonal technique. The use of the catheter-less protocol began after the blockage of a suprapubic catheter soon after surgery; the catheter was removed with no adverse event. Subsequently, 27 of those undergoing ureteric reimplantation were selected not to have a bladder catheter. Later in the study a greater proportion of patients had no catheter inserted, as confidence with the catheter-less technique increased. Caudal anaesthetic, oral analgesia and a single dose of intravesical bupivacaine were used for pain relief. The children were monitored closely after surgery and a urethral catheter inserted in the one patient who had not voided after 6 h. RESULTS: The patients generally tolerated the lack of a bladder catheter well. Of the 27 patients who did not have a catheter inserted at surgery, one required catheterization (a girl with bilateral duplex systems and large ureteroceles). Two children stayed in hospital for 2 days after surgery, one was discharged on the day of surgery, and the remainder went home on oral analgesia on the first day after surgery. Since starting the catheter-less approach, 10 patients have had a suprapubic catheter because they had more complex surgery, were older or because the approach had not developed sufficiently at the time of surgery. CONCLUSIONS: Intravesical ureteric reimplantation is not only safe when omitting a bladder catheter but, if used selectively, there appears to be a significant decrease in the hospital stay and discomfort after surgery.

Trans-pyeloureteric anastomosis in the management of pelviureteric junction obstruction.

BACKGROUND: The application of pyeloureteric anastomoses in the management of pelviureteric junction obstruction is described. METHODS: Two patients, one requiring a ureterocystoplasty for bladder augmentation but with a coexistent contralateral pelviureteric junction (PUJ) obstruction and the other with gross hydronephrosis but an atretic ipsilateral ureter, underwent trans-pyeloureteric anastomosis to relieve the obstruction. RESULTS: Both patients demonstrated satisfactory drainage of the upper tracts on postoperative imaging. CONCLUSIONS: Transureteropyeloplasty represents a novel and valid technique of urinary tract reconstruction in complex cases of PUJ obstruction.

A lower motor neuron disease in newborn Romney lambs.

AIM: To determine the cause and nature of a disease in newborn New Zealand Romney lambs characterised by progressive weakness and premature death. METHODS: Affected lambs were examined clinically, humanely killed and submitted to necropsy. Selected fonmalin-fixed tissues were examined histologically. Data on the parentage of the lambs were collected. RESULTS: The principle lesions found were degeneration and loss of neurons in ventral horns of the spinal cord and brain stem and Wallerian degeneration of motor nerves and denervation atrophy of skeletal muscles fibres. CONCLUSION: The lesions are those of a lower motor neuron disease which appeared to have a genetic cause.

Seasonal variation of gas exchange and pigmentation in branches of three grafted clones of mature ponderosa pine exposed to ozone and acid rain.

Gas exchange and pigmentation responses of mature ponderosa pine (Pinus ponderosa Laws.) branches to ozone and acid rain exposure were investigated using three grafted clones growing in a managed seed orchard. Exposure of one-year-old foliage to twice ambient ozone (2 x AMB) resulted in significant decreases in net photosynthesis (Pn), stomatal conductance (gsw) and pigmentation relative to charcoal-filtered (CF) and ambient (AMB) ozone treatments. Ozone effects on gas exchange and pigmentation were most pronounced during late-season and differed significantly among clones. Environmental parameters (e.g. light, vapor pressure deficit, and temperature) accounted for more variation in Pn than did cumulative ozone exposure. Minimal differences in gsw and Pn among ozone treatments occurred during seasonal periods of high temperature and evaporative demand. Negative effects of 2 x AMB ozone on gsw and pigmentation were greatest for the clones having highest and lowest phenotypic vigor under ambient conditions; the clone of moderate phenotypic vigor under ambient conditions was least sensitive to ozone. Application of simulated acid rain of pH 3.0, pH 5.1 or no rain (NR) had little impact on gas exchange or pigmentation.

Biopolymer synthesis on polypropylene supports: oligonucleotide arrays.

High-density oligonucleotide arrays have been constructed on clear, aminated polypropylene film using conventional phosphoramidite-based synthesis chemistries. A semiautomated 64-channel fluidic chemical delivery system is used to prepare the 64 x 64 array containing 4096 oligonucleotide elements. The completed array has been successfully used in the hybridization and fluorescence (Streptavidin-FITC) detection of a biotinylated 18-mer oligonucleotide target complementary to the F508 codon region of the cystic fibrosis transmembrane conductance regulator gene. A hybridization simulation model based upon Nearest Neighbor approximations is used to predict the outcome of the array hybridization experiment.