Turbulence in a free surface

We report an experimental and numerical study of turbulent fluid motion in a free surface. The flow is realized experimentally on the surface of a tank filled with water stirred by a vertically oscillating grid positioned well below the surface. Particles floating on the surface are used to visualize the flow. The effect of surface waves appears to be negligible. The flow is unconventional in that it is confined to two dimensions but does not have squared vorticity as a conservation law, that it is not divergence free and that it inherits scaling features of the mean square velocity differences S_2(R) and the vorticity fluctuations Omega(R) from the bulk 3-d turbulence.Comment: 4 pages, 4 Postscript figure

Sensitivity of the Atlantic meridional overturning circulation to South Atlantic freshwater anomalies

The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin-scale salt-advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic. <br/

Turbulence and passive scalar transport in a free-slip surface

We consider the two-dimensional (2D) flow in a flat free-slip surface that bounds a three-dimensional (3D) volume in which the flow is turbulent. The equations of motion for the two-dimensional flow in the surface are neither compressible nor incompressible but strongly influenced by the 3D flow underneath the surface. The velocity correlation functions in the 2D surface and in the 3D volume scale with the same exponents. In the viscous subrange the amplitudes are the same, but in the inertial subrange the 2D one is reduced to 2/3 of the 3D amplitude. The surface flow is more strongly intermittent than the 3D volume flow. Geometric scaling theory is used to derive a relation between the scaling of the velocity field and the density fluctuations of a passive scalar advected on the surface.Comment: 11 pages, 10 Postscript figure

Effect of centralization and regionalization of pancreatic surgery on resection rates and survival

Contains fulltext : 236824.pdf (Publisher’s version ) (Closed access

Statistical mechanics of Fofonoff flows in an oceanic basin

We study the minimization of potential enstrophy at fixed circulation and energy in an oceanic basin with arbitrary topography. For illustration, we consider a rectangular basin and a linear topography h=by which represents either a real bottom topography or the beta-effect appropriate to oceanic situations. Our minimum enstrophy principle is motivated by different arguments of statistical mechanics reviewed in the article. It leads to steady states of the quasigeostrophic (QG) equations characterized by a linear relationship between potential vorticity q and stream function psi. For low values of the energy, we recover Fofonoff flows [J. Mar. Res. 13, 254 (1954)] that display a strong westward jet. For large values of the energy, we obtain geometry induced phase transitions between monopoles and dipoles similar to those found by Chavanis and Sommeria [J. Fluid Mech. 314, 267 (1996)] in the absence of topography. In the presence of topography, we recover and confirm the results obtained by Venaille and Bouchet [Phys. Rev. Lett. 102, 104501 (2009)] using a different formalism. In addition, we introduce relaxation equations towards minimum potential enstrophy states and perform numerical simulations to illustrate the phase transitions in a rectangular oceanic basin with linear topography (or beta-effect).Comment: 26 pages, 28 figure

Treatment and overall survival of four types of non-metastatic periampullary cancer:nationwide population-based cohort study

Background: Periampullary adenocarcinoma consists of pancreatic adenocarcinoma (PDAC), distal cholangiocarcinoma (DC), ampullary cancer (AC), and duodenal adenocarcinoma (DA). The aim of this study was to assess treatment modalities and overall survival by tumor origin. Methods: Patients diagnosed with non-metastatic periampullary cancer in 2012–2018 were identified from the Netherlands Cancer Registry. OS was studied with Kaplan–Meier analysis and multivariable Cox regression analyses, stratified by origin. Results: Among the 8758 patients included, 68% had PDAC, 13% DC, 12% AC, and 7% DA. Resection was performed in 35% of PDAC, 56% of DC, 70% of AC, and 59% of DA. Neoadjuvant and/or adjuvant therapy was administered in 22% of PDAC, 7% of DC, 7% of AC, and 12% of DA. Three-year OS was highest for AC (37%) and DA (34%), followed by DC (21%) and PDAC (11%). Adjuvant therapy was associated with improved OS among PDAC (HR = 0.62; 95% CI 0.55–0.69) and DC (HR = 0.69; 95% CI 0.48–0.98), but not AC (HR = 0.87; 95% CI 0.62–1.22) and DA (HR = 0.85; 95% CI 0.48–1.50). Conclusion: This retrospective study identified considerable differences in treatment modalities and OS between the four periampullary cancer origins in daily clinical practice. An improved OS after adjuvant chemotherapy could not be demonstrated in patients with AC and DA

Destabilization of the thermohaline circulation by transient perturbations to the hydrological cycle

We reconsider the problem of the stability of the thermohaline circulation as described by a two-dimensional Boussinesq model with mixed boundary conditions. We determine how the stability properties of the system depend on the intensity of the hydrological cycle. We define a two-dimensional parameters' space descriptive of the hydrology of the system and determine, by considering suitable quasi-static perturbations, a bounded region where multiple equilibria of the system are realized. We then focus on how the response of the system to finite-amplitude surface freshwater forcings depends on their rate of increase. We show that it is possible to define a robust separation between slow and fast regimes of forcing. Such separation is obtained by singling out an estimate of the critical growth rate for the anomalous forcing, which can be related to the characteristic advective time scale of the system.Comment: 37 pages, 8 figures, submitted to Clim. Dy

β relaxation and low-temperature aging in a Au-based bulk metallic glass: From elastic properties to atomic-scale structure

The slow β relaxation is understood to be a universal feature of glassy dynamics. Its presence in bulk metallic glasses (BMGs) is evidence of a broad relaxation time spectrum that extends to deep within the glassy state. Despite the breadth of research devoted to this phenomenon, its microscopic origin is still not fully understood. The low-temperature aging behavior and atomic structural rearrangements of a Au₄₉Cu₂₆.₉Si₁₆.₃Ag₅.₅Pd₂.₃ BMG are investigated in the regime of the slow β relaxation by employing an ensemble of experimental techniques such as high-intensity synchrotron x-ray scattering, modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA), impulse excitation, and dilatometry. Evidence of a distinct slow β-relaxation regime is seen in the form of (1) an excess wing of the DMA loss modulus beginning at ∼50 °C, (2) a crossover effect of elastic modulus with isothermal aging at 50 °C, and (3) a broad, nonreversing and largely irreversible sub-Tg endotherm in theMDSC results. Atomic rearrangements occurring at the onset of the measured slow β-relaxation temperature regime were found to be confined mainly to the short-range order length scale while no significant atomic rearrangements occur on the length scale of the medium-range order. Furthermore, evidence is presented that suggests the crossover effect in Young’s modulus is due to the evolution of chemical short-range order. These results support the emergent picture of a dynamically heterogeneous glassy structure, in which low-temperature relaxation occurs through atomic rearrangements confined mostly to the short-range order length scale

Nationwide Outcome of Tailored Surgery for Symptomatic Chronic Pancreatitis based on Pancreatic Morphology:Validation of the International guidelines

OBJECTIVE: To determine the nationwide use and outcome of tailored surgical treatment for symptomatic chronic pancreatitis (CP) as advised by recent guidelines.SUMMARY BACKGROUND DATA: Randomized trials have shown that surgery is superior to endoscopy in patients with symptomatic CP, although endoscopy remains popular Recent guidelines advice to "tailor surgery" based on pancreatic morphology meaning that the least extensive procedure should be selected based on pancreatic morphology. However, nationwide, and multicenter studies On tailored surgery for symptomatic CP are lacking.METHODS: Nationwide multicenter retrospective analysis of consecutive patients undergoing surgical treatment for symptomatic CP in all seven Dutch university medical centers (2010-2020). Outcomes included volume trend, major complications, 90-day mortality, postoperative opioid use and clinically relevant pain relief. Surgical treatment was tailored based on the size of the main pancreatic duct and pancreatic head (e.g. surgical drainage for a dilated pancreatic duct, and normal size pancreatic head).RESULTS: Overall, 381 patients underwent surgery for CP: 127 surgical drainage procedures ( 33%; mostly extended lateral pancreaticojejunostomy), 129 duodenum-preserving pancreatic head resections (DPPHR, 34%, mostly Frey), and 125 formal pancreatic resections (33%, mostly distal pancreatectomy). The annual surgical volume increased slightly (Pearson r=0.744). Mortality (90-day) occurred in 6 patients (2%), and was non-significantly lower after surgical drainage (0%, 3%, 2%; P =0.139). Major complications (12%, 24%, 26%; P =0.012), postoperative pancreatic fistula grade B/C (0%, 3%, 22%; P =0.038), surgical reintervention (4%, 16%, 12%; P =0.006), and endocrine insufficiency ( 14%, 21%, 43%; P &lt;0.001) occurred less often after surgical drainage. After a median follow-up of 11 months [IQR 3-23] good rates of clinically relevant pain relief ( 83%, 69%, 80%; P =0.082) were observed and 81% of opioid users had stopped using (83%, 78%, 84%, P =0.496).CONCLUSION: The use of surgery for symptomatic CP increased over the study period. Drainage procedures were associated with the best safety profile and excellent functional outcome, highlighting the importance of tailoring surgery based on pancreatic morphology.</p

Nationwide Outcome of Tailored Surgery for Symptomatic Chronic Pancreatitis based on Pancreatic Morphology:Validation of the International guidelines

OBJECTIVE: To determine the nationwide use and outcome of tailored surgical treatment for symptomatic chronic pancreatitis (CP) as advised by recent guidelines.SUMMARY BACKGROUND DATA: Randomized trials have shown that surgery is superior to endoscopy in patients with symptomatic CP, although endoscopy remains popular Recent guidelines advice to "tailor surgery" based on pancreatic morphology meaning that the least extensive procedure should be selected based on pancreatic morphology. However, nationwide, and multicenter studies On tailored surgery for symptomatic CP are lacking.METHODS: Nationwide multicenter retrospective analysis of consecutive patients undergoing surgical treatment for symptomatic CP in all seven Dutch university medical centers (2010-2020). Outcomes included volume trend, major complications, 90-day mortality, postoperative opioid use and clinically relevant pain relief. Surgical treatment was tailored based on the size of the main pancreatic duct and pancreatic head (e.g. surgical drainage for a dilated pancreatic duct, and normal size pancreatic head).RESULTS: Overall, 381 patients underwent surgery for CP: 127 surgical drainage procedures ( 33%; mostly extended lateral pancreaticojejunostomy), 129 duodenum-preserving pancreatic head resections (DPPHR, 34%, mostly Frey), and 125 formal pancreatic resections (33%, mostly distal pancreatectomy). The annual surgical volume increased slightly (Pearson r=0.744). Mortality (90-day) occurred in 6 patients (2%), and was non-significantly lower after surgical drainage (0%, 3%, 2%; P =0.139). Major complications (12%, 24%, 26%; P =0.012), postoperative pancreatic fistula grade B/C (0%, 3%, 22%; P =0.038), surgical reintervention (4%, 16%, 12%; P =0.006), and endocrine insufficiency ( 14%, 21%, 43%; P &lt;0.001) occurred less often after surgical drainage. After a median follow-up of 11 months [IQR 3-23] good rates of clinically relevant pain relief ( 83%, 69%, 80%; P =0.082) were observed and 81% of opioid users had stopped using (83%, 78%, 84%, P =0.496).CONCLUSION: The use of surgery for symptomatic CP increased over the study period. Drainage procedures were associated with the best safety profile and excellent functional outcome, highlighting the importance of tailoring surgery based on pancreatic morphology.</p