Effect of Surface Nanopatterning on Slip: The Case of Couette Flow of Long-Chain Polyethylene Melt Flowing Past Gold Surfaces.

The manifestation of slip during flow of a polymer melt past a solid surface depends on several parameters, such as film thickness, the strength of polymer-solid interactions compared to the cohesive energy of the polymer, and the roughness of the surface. Understanding the role of these molecular aspects for slip is crucial in microfluidics, friction-tuning, polymer extrusion, and nanocomposites applications. The present article investigates the effect of surface nanopatterning on slip, via Couette-flow simulations of long chain polyethylene melts past nanopatterned gold surfaces. Slip is quantified in terms of the true and effective slip velocity, and the slip length. When polymer chains are adsorbed to surfaces with periodic features (e.g., crystal planes), they develop preferential ordering in a way that enables them to minimize their free energy. The orientation of a chain is affected by that of its neighbors; thus, when several chains come together, they are prone to form regions with crystal-like orientation. We show that, in some cases, the introduction of nanopatterns on the surface can perturb and induce reorganization of these regions, and in turn affect slip. The nanopatterns are realized as periodic defect stripes of variable width, depth, areal density, and orientation angle. In situations in which the width of the defects becomes comparable to the diameter of individual chain backbones, slip is minimized (stick conditions). Cutting the nanopatterns in low symmetry directions can affect the quality of their edges and lead to enhanced friction. To characterize these edges we have devised a scheme for the quantification of the mean square roughness and mean position of the surface, which is general and applicable in 2 and 3 dimensions for any kind of material, either crystalline of amorphous. Applying the patterns on the opposing solid surfaces in a symmetric or antisymmetric manner has a profound effect on flow. We show that the application of nanopatterns in symmetric configurations generates zero net flow and induces additional shear along directions normal to the direction of the flow. The application of symmetry-breaking configurations can guide flow toward preferential directions, a result with possible applications in microfluidic devices.

Esophageal melanoma: a systematic review and exploratory recurrence and survival analysis.

Esophageal melanoma is a rare and poorly described malignancy. We sought to review all available data on the clinicopathological features, management options, and outcomes of patients with esophageal melanoma to guide clinicians working to treat these uncommon tumors. A systematic literature search of the PubMed, Embase, and Cochrane databases was performed. Exploratory recurrence and survival analyses were performed using previously-validated pooled Cox and logistic regression techniques for case reports and case series. Quality assessment of included studies was performed using the tools developed by the Joanna Briggs and the National Heart, Lung, and Blood Institutes. Fifty-nine studies were reviewed. A total of 93 patients with esophageal melanoma were identified. The mean patient age was 61.2 ± 10.6 years. Esophageal melanoma usually developed at the lower esophagus (48.4%). 90.3% of the patients were symptomatic at presentation, with dysphagia being the most common symptom (72%). Esophagectomy was performed in 91.4% of the patients. Postoperatively, 14 patients (15.1%) received adjuvant chemotherapy. Tumor recurrence was seen in 37 patients (39.8%). The median time to recurrence was 6 months. Disease-specific mortality was 43%. All-cause mortality was 46.1%. On multivariable Cox regression, older patient age (hazard ratio [HR] = 0.91, P = 0.008) and higher Melan-A expression (HR = 0.21; P = 0.029) were associated with a significantly lower risk of mortality. Higher S100 levels (HR = 37.4; P = 0.001) were predictive of poor survival. On logistic regression, large, ulcerated, lower esophageal tumors were significantly more likely to recur (P = 0.018, P = 0.013, and P = 0.027 respectively). Esophageal melanoma is a rare malignancy that tends to present with dysphagia. Most surgically-treated patients undergo esophagectomy. Large, ulcerated, lower esophageal lesions recur more frequently. Immunohistochemistry provides prognostic information regarding survival.

Multiscale simulations of PS-SiO2 nanocomposites: from melt to glassy state.

The interaction energetics, molecular packing, entanglement network properties, segmental dynamics, and elastic constants of atactic polystyrene-amorphous silica nanocomposites in the molten and the glassy state are studied via molecular simulations using two interconnected levels of representation: (a) a coarse-grained one, wherein each polystyrene repeat unit is mapped onto a single "superatom" and the silica nanoparticle is viewed as a solid sphere. Equilibration at all length scales at this level is achieved via connectivity-altering Monte Carlo simulations. (b) A united-atom (UA) level, wherein the polymer chains are represented in terms of a united-atom forcefield and the silica nanoparticle is represented in terms of a simplified, fully atomistic model. Initial configurations for UA molecular dynamics (MD) simulations are obtained by reverse mapping well-equilibrated coarse-grained configurations. By analysing microcanonical UA MD trajectories, the polymer density profile is studied and the polymer is found to exhibit layering in the vicinity of the nanoparticle surface. An estimate of the enthalpy of mixing between polymer and nanoparticles, derived from the UA simulations, compares favourably against available experimental values. The dynamical behaviour of polystyrene (in neat and filled melt systems) is characterized in terms of bond orientation and dihedral angle time autocorrelation functions. At low concentration in the molten polymer matrix, silica nanoparticles are found to cause a slight deceleration of the segmental dynamics close to their surface compared to the bulk polymer. Well-equilibrated coarse-grained long-chain configurations are reduced to entanglement networks via topological analysis with the CReTA algorithm, yielding a slightly lower density of entanglements in the filled than in the neat systems. UA melt configurations are glassified by MD cooling. The elastic moduli of the resulting glassy nanocomposites are computed through an analysis of strain fluctuations in the undeformed state and through explicit mechanical deformation by MD, showing a stiffening of the polymer in the presence of nanoparticles. UA simulation results for the elastic constants are compared to continuum micromechanical calculations invoked in homogenization models of the overall mechanical behaviour of heterogeneous materials. They can be interpreted in terms of the presence of an "interphase" of approximate thickness 2 nm around the nanoparticles, with elastic constants intermediate between those of the filler and the matrix.

Skeletal muscle disease: patterns of MRI appearances.

Although the presumptive diagnosis of skeletal muscle disease (myopathy) may be made on the basis of clinical-radiological correlation in many cases, muscle biopsy remains the cornerstone of diagnosis. Myopathy is suspected when patients complain that the involved muscle is painful and tender, when they experience difficulty performing tasks that require muscle strength or when they develop various systemic manifestations. Because the cause of musculoskeletal pain may be difficult to determine clinically in many cases, MRI is increasingly utilised to assess the anatomical location, extent and severity of several pathological conditions affecting muscle. Infectious, inflammatory, traumatic, neurological, neoplastic and iatrogenic conditions can cause abnormal signal intensity on MRI. Although diverse, some diseases have similar MRI appearances, whereas others present distinct patterns of signal intensity abnormality. In general, alterations in muscle signal intensity fall into one of three cardinal patterns: muscle oedema, fatty infiltration and mass lesion. Because some of the muscular disorders may require medical or surgical treatment, correct diagnosis is essential. In this regard, MRI features, when correlated with clinical and laboratory findings as well as findings from other methods such as electromyography, may facilitate correct diagnosis. This article will review and illustrate the spectrum of MRI appearances in several primary and systemic disorders affecting muscle, both common and uncommon. The aim of this article is to provide radiologists and clinicians with a collective, yet succinct and useful, guide to a wide array of myopathies.

pERK activation in esophageal carcinomas: clinicopathological associations.

MAPK (mitogen-activated protein kinase) pathway is considered a control regulator in various malignant tumors but its role in esophageal carcinomas remains elusive. In our study, we examined the possible prognostic significance of MAPK pathway in human esophageal cancer. We searched for mutations in exons 18-21 of EGFR gene, codons 12 and 13 of K-RAS gene and exon 15 of B-RAF gene by high resolution melting analysis (HRMA) and pyrosequencing in 44 esophageal carcinomas. Immunohistochemistry was performed in 29 cases in order to evaluate expression levels of pERK (extracellular-signal regulated kinase). In one laser microdissected squamous cell carcinoma, a somatic K-RAS mutation at codon 12 was detected, whereas none of the cases displayed mutations in EGFR and B-RAF genes. Elevated nuclear as well as cytoplasmic pERK expression (100% and 62% of cases respectively) was observed independently of EGFR and B-RAF mutational status. Increasing pERK nuclear and cytoplasmic expression as well as the intensity of nuclear staining was found to be significantly correlated with tumor grade in univariate and multivariate statistical analysis. Our findings depict the presence of activated ERK despite the low frequency of upstream alterations, implicating ERK activation in the acquisition of a more aggressive phenotype in esophageal cancer.

Bougie insertion: A common practice with underestimated dangers.

INTRODUCTION: Esophageal perforation after bariatric operations is rare. We report two cases of esophageal perforation after bariatric operations indicating the dangers of a common practice - like insertion of esophageal tubes - and we describe our management of that complication. PRESENTATION OF CASE: A 56 year old woman who underwent laparoscopic sleeve gastrectomy and a 41 year old woman who underwent laparoscopic adjustable gastric banding respectively. In both operations a bougie has been used and led to esophageal perforation. DISCUSSION: The insertion of bougie and especially of inflated bougie is a common practice. It is an invasive procedure that in most cases is performed by the anesthesiologist team. CONCLUSION: Bougie insertion is an invasive procedure with risks and should always be attempted under direct supervision of surgical team or should be inserted by a surgeon.

Wegener granulomatosis masquerading as pneumonia.

We report a case of an elderly patient with a limited form of Wegener granulomatosis, which simulated the clinical and imaging features of organizing pneumonia. Here we call attention to this atypical case presentation that eloquently illustrates the many faces of Wegener granulomatosis.

Preoperative levosimendan in heart failure patients undergoing noncardiac surgery.

BACKGROUND: Heart failure (HF) is a major cause of perioperative morbidity and mortality in noncardiac surgery. Preoperative optimisation of these patients is, thus, of utmost importance. Levosimendan seems promising for patients undergoing cardiac surgery; however, its safety and efficacy in HF patients undergoing noncardiac surgery have not been evaluated. OBJECTIVE: To evaluate the effects of prophylactic preoperative levosimendan administration on left ventricular function in HF patients undergoing noncardiac surgery. METHODS: HF patients with ejection fraction <30%undergoing elective noncardiac surgery in 2005 were included in this prospective study. Patients were admitted to our surgical intensive care unit one day preoperatively. Under continuous haemodynamic monitoring, the treatment protocol consisted of an initial loading dose (24 microg/kg) for ten minutes followed by a continuous 24-hour infusion (0.1 microg/kg/min) at the end of which patients underwent surgery. Echocardiography was performed before infusion (day 0) and on the 7th postinfusion day (day 7). Measurements included left ventricular ejection fraction (LVEF), velocity time integral(VTI), pre-ejection period (PEP), ejection time (ET),maximum (Pmax) and minimum P(min) transvalvular aortic pressure gradient, and maximum (Vmax) and minimum V(min) aortic velocity. RESULTS: Twelve consecutive patients were enrolled. Levosimendan resulted in a significant increase in LVEF,VTI, P(max), P(min), V(max), and V(min) (p<0.01) and, moreover, a significant reduction in PEP, ET, and PEP/ET (p=0.04) on day 7 compared with day 0 values. No adverse reactions,complications or mortality occurred during 30-day follow-up. CONCLUSION: Prophylactic preoperative levosimendan treatment may be safe and efficient for perioperative optimisation of heart failure patients undergoing noncardiac surgery.

Intrahepatic venous continuation associated with inferior vena cava hypoplasia: evaluation with sonography, MR imaging and MR angiography.

A 17-year-old Asian girl was admitted to our hospital because of acute onset of abdominal pain. Abdominal imaging work-up revealed an unusual pattern of congenital vascular anomalies, including a hypoplastic IVC and large intrahepatic venous collaterals along with an atypical, accessory hepatic vein. Congenital or acquired abnormalities of the inferior vena cava (IVC) can lead to formation of collateral pathways that help bypass the blood flow obstacle.

Formation of rodlike structures of water between oppositely charged ions in decane and polyethylene.

The Gibbs ensemble Monte Carlo method has been combined with the connectivity altering osmotic Gibbs ensemble to study water solubility and clustering in decane and polyethylene. We show that the presence of oppositely charged ion pairs that have fixed positions in the hydrocarbon matrices leads to an order of magnitude increase in the water solubility. This is important to a wide range of technical applications, since the uptake of the water leads to an increase in volume--or expansion--of the hydrocarbon phase which, in the case of polyethylene, may change the polymer properties and lead to water treeing. The increase in solubility is largest when the ions are sufficiently close so that rod-shaped clusters of water molecules form between the ions.

A simplified technique for translaryngeal tracheostomy (TLT). A preliminary report.

OBJECTIVE: In this prospective observational study we present preliminary results of a modification of the translaryngeal tracheostomy technique that was introduced by Fantoni in 1997. The study was conducted in a five-bed surgical intensive care unit of a university teaching hospital. PATIENTS AND METHODS: The study included 14 consecutive surgical patients (8 men, 6 women) who underwent a modified translaryngeal tracheostomy in a 6-month period. In our modification of the technique, we keep the basic principle of the inside-to-outside approach of the Fantoni technique, and combine it with a blind needle insertion, as reported in the classic subcricoid retrograde intubation technique. The technique that we use involves two medical doctors and a nurse. RESULTS: Mean patient age was 68.9 years (range: 31-85 years) and mean APACHE II score was 15.8 (range: 6-31). Mean operative time for the procedure was 15.2 min (range: 11.5-22 min). Eight of the patients died during the postoperative course in the ICU from causes relevant to their surgical pathology. One patient survived to be discharged from the ICU but died of an acute myocardial infraction later in the same hospital stay. Five patients survived to be discharged from the hospital. CONCLUSIONS: The modified translaryngeal tracheostomy seems to be as reliable and safe as the original technique. In addition, the modified technique is faster and can be performed without the use of an endoscope.

Monte Carlo simulations of equilibrium solubilities and structure of water in n-alkanes and polyethylene.

Gibbs ensemble Monte Carlo methods based on a force field that combines the simple point charge [Berendsen et al., in Intermolecular Forces, edited by Pullman (Reidel, Dordrecht, 1981), p. 331] and transferable potentials for phase equilibria [Martin and Siepmann, J. Phys. Chem. B 102, 2659 (1998)] models were used to study the equilibrium properties of binary systems consisting of water and n-alkanes with chain lengths from hexane to hexadecane. In addition, systems where extended linear alkane chains (up to 300 carbon units long) were used to represent amorphous polyethylene were simulated in the presence of water using a connectivity altering osmotic Gibbs ensemble. In these simulations the equilibrium between a liquid water phase and a polymer phase into which water was inserted was studied. The predicted solubilities, which were determined between 350 and 550 K, are in good agreement with experiment, where experimental results are available, and the density of water molecules in the hydrocarbons is approximately 63% as high as in saturated water vapor under the same conditions. At the lower temperatures most of the water exists as monomers; increasing the temperature leads to an increase in the density of water in the alkane phase and hence in the fraction of molecules that participate in clusters. Dimers are the most prevalent clusters in all hydrocarbons and at all temperatures studied, and the fraction of clusters of given size decrease with increasing cluster size. A large fraction of trimers, tetramers, and pentamers, which are the cluster sizes for which topologies have been studied, are cyclic at low temperatures, but at higher temperatures linear structures predominate. The same properties are observed for pure water vapor clusters in equilibrium with the liquid phase, showing that the cluster topologies are not significantly affected by the surrounding hydrocarbon.

Refractory septic shock: efficacy and safety of very high doses of norepinephrine.

The aim of this study was to evaluate the safety, efficacy, and effects of administration of very high doses of norepinephrine (> 4 microg kg(-1) min(-1)) in catecholamine-resistant septic shock. We reviewed the charts of all patients with nonresponding to commonly used norepinephrine doses (< or = 4 microg kg(-1) min(-1)) septic shock from January 1999 to December 2002 in our Surgical Intensive Care Unit. All patients were treated with high norepinephrine doses (> 4 microg kg(-1) min(-1)), after initial resuscitation, so as to achieve a mean arterial pressure higher than or equal to 65 mmHg. During this 4-year period, 12 consecutive patients with catecholamine-resistant septic shock were included in our study. When compared with the values obtained prior to the administration of very high norepinephrine doses, the values of mean arterial pressure (p = 0.003) and systemic vascular resistance (p = 0.002) significantly increased after the administration of such doses, and additionally, lactate concentrations (p = 0.003) decreased. In contrast, no significant changes were observed regarding mean central venous pressure, pulmonary capillary wedge pressure, and pulmonary arterial pressure. Administration of high norepinephrine doses in our patients resulted in a survival rate of 33.4%. Management of catecholamine-resistant septic shock patients poses a challenging problem. Administration of very high norepinephrine doses is safe and effective and may improve survival of these patients with otherwise extremely high mortality rates.

Imaging findings in symptomatic patients with femoral diaphyseal stress injuries.

PURPOSE: To assess the imaging findings seen in symptomatic patients with stress injuries of the femoral diaphysis. MATERIAL AND METHODS: Seven patients (5 F, 2 M, age range 16 to 56 years, mean 38 years) underwent imaging evaluation of the symptomatic lower extremity due to an insidious onset of thigh or groin pain unrelated to trauma. Imaging studies included radiography and magnetic resonance imaging (MRI) in seven patients, bone scintigraphy in five, and computed tomography (CT) in three. RESULTS: Radiographs depicted three frank fractures in two patients, and revealed findings of stress injury in six patients. Available scintigraphic and CT findings were abnormal. On MR images, a solitary fracture was seen in two patients; two patients presented with bilateral stress fractures of the femoral diaphysis; and all seven patients had the imaging features of stress injury. Femoral diaphyseal stress fractures (n = 6) appeared as linear regions of T1- and T2-weighted low signal intensity, surrounded by diffuse bone marrow edema. Three of the six frank fractures, with an evident fracture line, were longitudinal and parallel to the cortical surface. CONCLUSION: Femoral diaphyseal stress fractures are often inconspicuous with conventional radiography. MRI depicts the changes of stress injury in the femoral diaphysis, and is particularly useful in documenting the presence, morphology, and extent of fracture(s), information valuable for definitive diagnosis and appropriate management.

Magnetic resonance imaging of para-acetabular insufficiency fractures in patients with malignancy.

AIM: To describe the characteristic magnetic resonance imaging (MRI) findings of para-acetabular insufficiency fractures in patients with malignancy, and compare the MRI appearance of these fractures with that of metastatic bone disease. MATERIALS AND METHODS: MRI examinations were reviewed in 16 patients with a known malignant tumour and severe hip pain that raised the possibility of local recurrence or metastatic disease. Six patients had received pelvic irradiation, and three patients were receiving steroid medication. RESULTS: The total number of fractures detected was 21: a solitary fracture was present in 11 patients and five patients had bilateral para-acetabular fractures. Two patients had associated sacral insufficiency fractures, and one of them had stress fractures involving both acetabular columns. Conventional radiography allowed the diagnosis of 14 (67%) fractures; six (28%) radiographic examinations were negative; and one (5%) examination was equivocal for fracture. Available scintigraphic and computed tomography (CT) studies revealed typical findings of fracture. Using MRI, insufficiency fractures appeared as linear regions of low signal intensity on T1- and T2-weighted images. Marked marrow oedema was evident in all cases. Fractures characteristically were parallel to the superior acetabulum in a curvilinear fashion in 18 (86%) instances, and were oblique in three (14%) instances. The fractures demonstrated considerable enhancement after intravenous gadolinium administration. No associated soft tissue masses were documented. CONCLUSION: Para-acetabular insufficiency fractures are a cause of hip pain, which may mimic skeletal metastasis in the patient with malignancy and pelvic irradiation. Recognition of the characteristic MRI findings of these fractures can preclude misdiagnosis and unnecessary bone biopsy.