Progress Towards Modeling the Ablation Response of NuSil-Coated PICA

The Mars Science Laboratory (MSL) Entry, Descent and Landing Instrumentation (MEDLI) collected in-flight data largely used by the ablation community to verify and validate physics-based models for the response of the Phenolic Impregnated Carbon Ablator (PICA) material [1-4]. MEDLI data were recently used to guide the development of NASAs high-fidelity material response models for PICA, implemented in the Porous material Analysis Toolbox based on OpenFOAM (PATO) software [5-6]. A follow-up instrumentation suite, MEDLI2, is planned for the upcoming Mars 2020 mission [7] after the large scientific impact of MEDLI. Recent analyses performed as part of MEDLI2 development draw the attention to significant effects of a protective coating to the aerothermal response of PICA. NuSil, a silicone-based overcoat sprayed onto the MSL heatshield as contamination control, is currently neglected in PICA ablation models. To mitigate the spread of phenolic dust from PICA, NuSil was applied to the entire MSL heatshield, including the MEDLI plugs. NuSil is a space grade designation of the siloxane copolymer, primarily used to protect against atomic oxygen erosion in the Low Earth Orbit environment. Ground testing of PICA-NuSil (PICA-N) models all exhibited surface temperature jumps of the order of 200 K due to oxide scale formation and subsequent NuSil burn-off. It is therefore critical to include a model for the aerothermal response of the coating in ongoing code development and validation efforts

Superconformal Primary Fields on a Graded Riemann Sphere

Primary superfields for a two dimensional Euclidean superconformal field theory are constructed as sections of a sheaf over a graded Riemann sphere. The construction is then applied to the N=3 Neveu-Schwarz case. Various quantities in the N=3 theory are calculated and discussed, such as formal elements of the super-Mobius group, and the two-point function.Comment: LaTeX2e, 23 pages; fixed typos, sorted references, modified definition of primary superfield on page

Resilience as a communal concept: Understanding adolescent resilience in the context of the Syrian refugee crisis in Bar Elias, Lebanon

Background: The conflict in Syria has led to the displacement of 1.5 million refugees into the neighboring country of Lebanon, with a majority that have yet to return to their homeland. Syrian adolescents in the town of Bar Elias in the Bekaa Valley, Lebanon have lived and grown in the face of resource-limited environments, restricted movement, and a longing for return. Resilience is manifested in the adaptation to such circumstances through close supportive relationships, social engagement, employment, and religion. There is a communal aspect to resilience that is important to the adolescent refugee experience and to the efforts supporting these communities. / Methods: Fifteen one-to-one interviews and two focus groups, with a total of eighteen Syrian adolescents, were analyzed using an inductive thematic analysis informed by grounded theory principles. Participants were recruited through partnering non-governmental organizations (NGOs) in the area, and ethical approval was granted through UCL and the American University in Beirut (AUB). / Results: Syrian adolescents highlighted supportive relationships, communal activities and spaces, memories of home, employment, and shared environments as integral elements to their personal adaptation. Methods of resilience involved social cohesion and establishing stability for one's family and close community. Adaptation to the present is intertwined with facing the consequences of displacement in this new context and maintaining aspirations for a bright future. Engaging with the environments they share and help create is an important facet of resilience and occurs through group gatherings , hobbies, and online communication. Additionally, inner strength can be derived from religious activities and empowers individual processing. / Conclusion: This study illuminates the elements and mechanisms embodied in these adolescents’ communities and relationships that allow for adaptation to life in Bar Elias. These factors strengthen their approach to overcome social barriers and practice resilience. These communal aspects of the adolescents’ lives also connect to their memories of home, current environment, and future aspirations

Investigation of the asymptotic state of rotating turbulence using large-eddy simulation

Study of turbulent flows in rotating reference frames has long been an area of considerable scientific and engineering interest. Because of its importance, the subject of turbulence in rotating reference frames has motivated over the years a large number of theoretical, experimental, and computational studies. The bulk of these previous works has served to demonstrate that the effect of system rotation on turbulence is subtle and remains exceedingly difficult to predict. A rotating flow of particular interest in many studies, including the present work, is examination of the effect of solid-body rotation on an initially isotropic turbulent flow. One of the principal reasons for the interest in this flow is that it represents the most basic turbulent flow whose structure is altered by system rotation but without the complicating effects introduced by mean strains or flow inhomogeneities. The assumption of statistical homogeneity considerably simplifies analysis and computation. The principal objective of the present study has been to examine the asymptotic state of solid-body rotation applied to an initially isotropic, high Reynolds number turbulent flow. Of particular interest has been to determine the degree of two-dimensionalization and the existence of asymptotic self-similar states in homogeneous rotating turbulence

Direct Numerical Simulation of Incompressible Pipe Flow Using a B-Spline Spectral Method

A numerical method based on b-spline polynomials was developed to study incompressible flows in cylindrical geometries. A b-spline method has the advantages of possessing spectral accuracy and the flexibility of standard finite element methods. Using this method it was possible to ensure regularity of the solution near the origin, i.e. smoothness and boundedness. Because b-splines have compact support, it is also possible to remove b-splines near the center to alleviate the constraint placed on the time step by an overly fine grid. Using the natural periodicity in the azimuthal direction and approximating the streamwise direction as periodic, so-called time evolving flow, greatly reduced the cost and complexity of the computations. A direct numerical simulation of pipe flow was carried out using the method described above at a Reynolds number of 5600 based on diameter and bulk velocity. General knowledge of pipe flow and the availability of experimental measurements make pipe flow the ideal test case with which to validate the numerical method. Results indicated that high flatness levels of the radial component of velocity in the near wall region are physical; regions of high radial velocity were detected and appear to be related to high speed streaks in the boundary layer. Budgets of Reynolds stress transport equations showed close similarity with those of channel flow. However contrary to channel flow, the log layer of pipe flow is not homogeneous for the present Reynolds number. A topological method based on a classification of the invariants of the velocity gradient tensor was used. Plotting iso-surfaces of the discriminant of the invariants proved to be a good method for identifying vortical eddies in the flow field

Endoscopic Nasobiliary Drainage in the Management of Acute Cholangitis: An Experience in 143 Patients

Acute cholangitis is associated with a high mortality and morbidity and often requires drainage of the obstructed biliary system. The purpose of this study was to evaluate the usefulness and safety of endoscopic nasobiliary drainage in the treatment and prevention of acute cholangitis due to diverse etiology. During a 32-month period, 143 patients (67 males, 76 females) with age range of 15 to 84 years underwent urgent fluoroscopy guided endoscopic nasobiliary drainage using a 7 Fr catheter either to treat acute cholangitis not responding to antibiotics (group A, n = 116) or to prevent its development following endoscopic retrograde cholangiography performed in an obstructed biliary system (group B, n = 27). Underlying etiology included bile duct stones (92), malignant biliary obstruction (34), choledochal cyst (4), chronic pancreatitis (4), ruptured hydatid cyst (3), portal hypertensive cholangiopathy (3) and liver abscess (3). Endoscopic nasobiliary drainage was performed successfully in 129 patients (90.2%). Cholangitis improved within 1 to 3 days (in group A) or did not develop (in Group B) in 125 patients (96.7%) with successful endoscopic nasobiliary drainage. Two patients however required additional drainage by percutaneous transhepatic route, while two died inspite of effective endoscopic drainage. Of the 14 patients (9.8%) with failed endoscopic drainage, 9 were managed by surgical decompression or percutaneous transhepatic drainage, 3 died of septicemia. Endoscopic nasobiliary drainage is a safe and effective method to treat patients with acute cholangitis as well as to prevent its development following cholangiography performed in an obstructed biliary system

Role of Endoscopic Retrograde Cholangiography and Nasobiliary Drainage in the Management of Postoperative Biliary Leak

In order to assess the role of endoscopic retrograde cholangiography in evaluating the patients with post-operative biliary leak and of endoscopic nasobiliary drainage in its management, 36 patients with biliary leak seen over a period of 9 years were studied. Thirty-two had biliary leak following cholecystectomy, 3 following repair of liver trauma and 1 following choledochoduodenostomy. Patients presented at an interval of 4 days to 210 days (mean ± SEM, 32.4 ± 6.7 days) following laparotomy. Hyperbilirubinemia was noticed in only 13 patients (36.1%), while abdominal ultrasonogram showed ascites or biloma in 24 (66.7%). Endoscopic retrograde cholangiography showed the leak to involve the common bile duct in 55.6%, cystic duct in 33.3% and intrahepatic biliary radicles in 8.3%. Associated lesions included bile duct obstruction due to stricture or accidental ligature in 20%, bile duct stone in 20% and liver abscess in 2.8%

Role of anisotropic impurity scattering in anisotropic superconductors

A theory of nonmagnetic impurities in an anisotropic superconductor including the effect of anisotropic (momentum-dependent) impurity scattering is given. It is shown that for a strongly anisotropic scattering the reduction of the pair-breaking effect of the impurities is large. For a significant overlap between the anisotropy functions of the scattering potential and that of the pair potential and for a large amount of anisotropic scattering rate in impurity potential the superconductivity becomes robust vis a vis impurity concentration. The implications of our result for YBCO high-temperature superconductor are discussed.Comment: 14 pages, RevTeX, 5 PostScript figures, to be published in Phys. Rev. B (December 1, 1996