460 research outputs found
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
Effect of centralization and regionalization of pancreatic surgery on resection rates and survival
Contains fulltext :
236824.pdf (Publisherâs version ) (Closed access
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
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/
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 2012â2018 were identified from the Netherlands Cancer Registry. OS was studied with KaplanâMeier 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 0.55â0.69) and DC (HR = 0.69; 95% CI 0.48â0.98), but not AC (HR = 0.87; 95% CI 0.62â1.22) and DA (HR = 0.85; 95% CI 0.48â1.50). 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
Conversation analysis and online interaction
At the same time as Harvey Sacks was developing conversation analysis (CA), at the same institution a young graduate student attempted to type the word âloginâ into a computer; this message would then be sent to another computer in a different lab. Unfortunately the system crashed after the letters âLâ and âOâ were sent, and so the first word to be sent via the internet (or at least the pre-cursor to it) was âLOâ or perhaps, if we want to read it as such, âhelloâ. The fact that the first message sent via the âinternetâ was, somewhat accidentally, a standard greeting is a foreshadowing of the fact that the internet has become a predominantly interactional medium. Online communication has grown exponentially since that first message. There are currently an estimated 269 billion e-mails, 55 billion Whatsapp messages, over 9.5 billion Instagram photos and videos, and around 500 million tweets sent per day. Online interaction is a worldwide phenomenon, with users of Chinese social media site, Weibo, sending over 100 million messages each day and about 38 billion messages sent every day on WeChat, the Chinese instant messaging service. As conversation analysts are interested in interaction as the primordial site of sociality, the internet is an enormous and ever-growing site of interaction, and as such should be a clear focus for exploring social life.
This review provides an overview of what we already know from studies of CA and online interaction. It will argue that going forward there should be more impetus to explore this area of interaction, not only in its own right but also for what it tells us about human interaction more generally. This paper will show how CA can offer real insight into the organization of online interaction, particularly in relation to the potential affordances and constraints of the interaction
Beyond the Fokker-Planck equation: Pathwise control of noisy bistable systems
We introduce a new method, allowing to describe slowly time-dependent
Langevin equations through the behaviour of individual paths. This approach
yields considerably more information than the computation of the probability
density. The main idea is to show that for sufficiently small noise intensity
and slow time dependence, the vast majority of paths remain in small space-time
sets, typically in the neighbourhood of potential wells. The size of these sets
often has a power-law dependence on the small parameters, with universal
exponents. The overall probability of exceptional paths is exponentially small,
with an exponent also showing power-law behaviour. The results cover time spans
up to the maximal Kramers time of the system. We apply our method to three
phenomena characteristic for bistable systems: stochastic resonance, dynamical
hysteresis and bifurcation delay, where it yields precise bounds on transition
probabilities, and the distribution of hysteresis areas and first-exit times.
We also discuss the effect of coloured noise.Comment: 37 pages, 11 figure
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
Effects of chemotherapy on contralateral breast cancer risk in BRCA1 and BRCA2 mutation carriers:A nationwide cohort study
AIM: BRCA1/2 mutation carriers with primary breast cancer (PBC) are at high risk of contralateral breast cancer (CBC). In a nationwide cohort, we investigated the effects of chemotherapeutic agents given for PBC on CBC risk separately in BRCA1 and BRCA2 mutation carriers. PATIENTS AND METHODS: BRCA1 or BRCA2 mutation carriers with an invasive PBC diagnosis from 1990 to 2017 were selected from a Dutch cohort. We estimated cumulative CBC incidence using competing risks analysis. Hazard ratios (HR) for the effect of neo-adjuvant or adjuvant chemotherapy and different chemotherapeutic agents on CBC risk were estimated using Cox regression. RESULTS: We included 1090 BRCA1 and 568 BRCA2 mutation carriers; median follow-up was 8.9 and 8.4 years, respectively. Ten-year cumulative CBC incidence for treatment with and without chemotherapy was 6.7% [95%CI: 5.1â8.6] and 16.7% [95%CI: 10.8â23.7] in BRCA1 and 4.8% [95%CI: 2.7â7.8] and 16.0% [95%CI: 9.3â24.4] in BRCA2 mutation carriers, respectively. Chemotherapy was associated with reduced CBC risk in BRCA1 (multivariable HR: 0.46, 95%CI: 0.29â0.74); a similar trend was observed in BRCA2 mutation carriers (HR: 0.63, 95%CI: 0.29â1.39). In BRCA1, risk reduction was most pronounced in the first 5 years (HR: 0.32, 95%CI: 0.17â0.61). Anthracyclines and the combination of anthracyclines with taxanes were associated with substantial CBC risk reduction in BRCA1 carriers (HR: 0.34, 95%CI: 0.17â0.68 and HR: 0.22, 95%CI: 0.08â0.62, respectively). CONCLUSION: Risk-reducing effects of chemotherapy are substantial for at least 5 years and may be used in personalised CBC risk prediction in any case for BRCA1 mutation carriers
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