Burdens of Proof Blanchette, Jean-François
2012, 20120427, 2012-04-27
eBook
An examination of the challenges of establishing the authenticity of electronic documents--in particular the design of a cryptographic equivalent to handwritten signatures.
We use numerical simulations and analytical modeling to describe the long-term effects of settling particles on a temperature-stratified fluid. In particular, we examine the final state of the ...stratification and determine under what circumstances a stratification can be mixed by settling particles. We use a two-dimensional model, for computational efficiency, and find a criterion describing when fluid motions around settling particles result in significant mixing. Taking into account the potential of particles to act as heat carriers, we also find that if the particles carry sufficient heat to the bottom of the container, a stable stratification may be destabilized as the heat released by deposited particles triggers convective motions.
Film evolution of a spherical soap bubble Martin, David W.; Blanchette, François
Journal of engineering mathematics,
12/2022, Letnik:
137, Številka:
1
Journal Article
Recenzirano
We present a theoretical and numerical study of the time evolution of the film of a soap bubble. Bubbles are assumed to remain approximately spherical with axisymmetric evolution. Inertia is ...neglected, and the surfactant is assumed insoluble. Applying lubrication theory, we simplify the equations governing the film thickness evolution, surfactant concentration, and tangential fluid velocity. Solving the simplified equations numerically, we examine the long-term behavior of the film and find that most features follow a power law of the form
α
T
β
where
T
is a dimensionless time parameter. We also predict the location (angle from the top) at which the film is thinnest and thus most likely to initiate bursting and present a similarity solution that predicts the decay rate of the minimum film thickness near the pinch-off location.
•A new method for estimating erosion based on local fluid velocity is presented.•The interface separating the fluid from the porous media is mobile as erosion occurs.•A convex combination of Brinkman ...and Navier–Stokes equations is used.•Simulations of erosion in two different applications are presented.•Erosion predictions are compared to a classical stress-based erosion model.
We simulate flows involving porous media and homogenous fluid using a single-domain finite-difference numerical method. The porous medium and unimpeded fluid are separated by a sharp interface where a stress jump boundary condition is implemented using a forcing term. The interface is constructed by connecting Lagrangian markers with cubic splines, allowing for any possible porous media geometry. This model is particularly flexible as it can easily account for a mobile interface. We apply our method to simulate erosion and suspension of particles from a fixed or erodible particulate deposit. The flux of particles entrained from the porous media is obtained from the computed velocity at the interface, in contrast to more common approaches that assume a flux proportional to the viscous stress at the interface.
When two separate masses of the same fluid are brought gently into contact, they are expected to fully merge into a single larger mass to minimize surface energy. However, when a stationary drop ...coalesces with an underlying reservoir of identical fluid, merging does not always proceed to completion. Occasionally, a drop in the process of merging apparently defies surface tension by 'pinching off' before total coalescence occurs, leaving behind a smaller daughter droplet. Moreover, this process can repeat itself for subsequent generations of daughter droplets, resulting in a cascade of self-similar events. Such partial coalescence behaviour has implications for the dynamics of a variety of systems, including the droplets in clouds, ocean mist and airborne salt particles, emulsions, and the generation of vortices near an interface. Although it was first observed almost half a century ago, little is known about its precise mechanism. Here, we combine high-speed video imaging with numerical simulations to determine the conditions under which partial coalescence occurs, and to reveal a dynamic pinch-off mechanism. This mechanism is critically dependent on the ability of capillary waves to vertically stretch the drop by focusing energy on its summit.
Modeling huddling penguins Waters, Aaron; Blanchette, François; Kim, Arnold D
PloS one,
11/2012, Letnik:
7, Številka:
11
Journal Article
Recenzirano
Odprti dostop
We present a systematic and quantitative model of huddling penguins. In this mathematical model, each individual penguin in the huddle seeks only to reduce its own heat loss. Consequently, penguins ...on the boundary of the huddle that are most exposed to the wind move downwind to more sheltered locations along the boundary. In contrast, penguins in the interior of the huddle neither have the space to move nor experience a significant heat loss, and they therefore remain stationary. Through these individual movements, the entire huddle experiences a robust cumulative effect that we identify, describe, and quantify. This mathematical model requires a calculation of the wind flowing around the huddle and of the resulting temperature distribution. Both of these must be recomputed each time an individual penguin moves since the huddle shape changes. Using our simulation results, we find that the key parameters affecting the huddle dynamics are the number of penguins in the huddle, the wind strength, and the amount of uncertainty in the movement of the penguins. Moreover, we find that the lone assumption of individual penguins minimizing their own heat loss results in all penguins having approximately equal access to the warmth of the huddle.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Glatiramer Acetate Blanchette, François; Neuhaus, Oliver
Journal of neurology,
03/2008, Letnik:
255, Številka:
Suppl 1
Journal Article, Conference Proceeding
Recenzirano
Glatiramer acetate is a disease-modifying drug approved for the treatment of relapsing-remitting multiple sclerosis. Since its discovery almost four decades ago, and in particular since the ...observation of its beneficial clinical effects in the late 1980s and early 1990s, numerous data have been generated and contribute pieces of a puzzle to help explain the mechanism of action of glatiramer acetate. Two major themes have emerged, namely (i) the induction of glatiramer acetate-reactive TH2 immunoregulatory cells, and (ii) the stimulation of neurotrophin secretion in the central nervous system that may promote neuronal repair.
Significant advances have been made in the diagnosis and treatment of multiple sclerosis in recent years yet challenges remain. The current classification of MS phenotypes according to disease ...activity and progression, for example, does not adequately reflect the underlying pathophysiological mechanisms that may be acting in an individual with MS at different time points. Thus, there is a need for clinicians to transition to a management approach based on the underlying pathophysiological mechanisms that drive disability in MS. A Canadian expert panel convened in January 2023 to discuss priorities for clinical discovery and scientific exploration that would help advance the field. Five key areas of focus included: identifying a mechanism-based disease classification system; developing biomarkers (imaging, fluid, digital) to identify pathologic processes; implementing a data-driven approach to integrate genetic/environmental risk factors, clinical findings, imaging and biomarker data, and patient-reported outcomes to better characterize the many factors associated with disability progression; utilizing precision-based treatment strategies to target different disease processes; and potentially preventing disease through Epstein-Barr virus (EBV) vaccination, counselling about environmental risk factors (e.g. obesity, exercise, vitamin D/sun exposure, smoking) and other measures. Many of the tools needed to meet these needs are currently available. Further work is required to validate emerging biomarkers and tailor treatment strategies to the needs of individual patients. The hope is that a more complete view of the individual's pathobiology will enable clinicians to usher in an era of truly personalized medicine, in which more informed treatment decisions throughout the disease course achieve better long-term outcomes.
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