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"Keeler, Alice"
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50 شيئا يمكنك عملها بتطبيق Google classroom
هو الدليل المطلوب لإعادة منصة التعلم الاجتماعي إلى الحياة في بيئة التعلم الخاصة بك في هذا الكتاب، لن تكون قادرا على تجزئة الوظائف الأساسية المتوافرة في الأداة فحسب، لكن المؤلفتين تقدمان لك المشورة التربوية السليمة عن كيفية جعل التقنية أكثر قوة من خلال ربطها بطرق التدريس التقنية بعمق، نشر الكتاب العبيكان للنشر في الرياض، يشتمل الكتاب على مجموعة من الإيضاحيات.
BOOK
Classroom Performance System (CPS)
Keeler reviews eInstruction Corp's Classroom Performance System, a handheld infrared response system.
Book Review
The influence of invariant solutions on the transient behaviour of an air bubble in a Hele-Shaw channel
We hypothesize that dynamical systems concepts used to study the transition to turbulence in shear flows are applicable to other transition phenomena in fluid mechanics. In this paper, we consider a finite air bubble that propagates within a Hele-Shaw channel containing a depth-perturbation. Recent experiments revealed that the bubble shape becomes more complex, quantified by an increasing number of transient bubble tips, with increasing flow rate. Eventually, the bubble changes topology, breaking into multiple distinct entities with non-trivial dynamics. We demonstrate that qualitatively similar behaviour to the experiments is exhibited by a previously established, depth-averaged mathematical model and arises from the model’s intricate solution structure. For the bubble volumes studied, a stable asymmetric bubble exists for all flow rates of interest, while a second stable solution branch develops above a critical flow rate and transitions between symmetric and asymmetric shapes. The region of bistability is bounded by two Hopf bifurcations on the second branch. By developing a method for a numerical weakly nonlinear stability analysis we show that unstable periodic orbits (UPOs) emanate from the first Hopf bifurcation. Moreover, as has been found in shear flows, the UPOs are edge states that influence the transient behaviour of the system.
Journal Article
The life and fate of a bubble in a geometrically perturbed Hele-Shaw channel
Motivated by the desire to understand complex transient behaviour in fluid flows, we study the dynamics of an air bubble driven by the steady motion of a suspending viscous fluid within a Hele-Shaw channel with a centred depth perturbation. Using both experiments and numerical simulations of a depth-averaged model, we investigate the evolution of an initially centred bubble of prescribed volume as a function of flow rate and initial shape. The experiments exhibit a rich variety of organised transient dynamics, involving bubble breakup as well as aggregation and coalescence of interacting neighbouring bubbles. The long-term outcome is either a single bubble or multiple separating bubbles, positioned along the channel in order of increasing velocity. Up to moderate flow rates, the life and fate of the bubble are reproducible and can be categorised by a small number of characteristic behaviours that occur in simply connected regions of the parameter plane. Increasing the flow rate leads to less reproducible time evolutions with increasing sensitivity to initial conditions and perturbations in the channel. Time-dependent numerical simulations that allow for breakup and coalescence are found to reproduce most of the dynamical behaviour observed experimentally, including enhanced sensitivity at high flow rate. An unusual feature of this system is that the set of steady and periodic solutions can change during temporal evolution because both the number of bubbles and their size distribution evolve due to breakup and coalescence events. Calculation of stable and unstable solutions in the single- and two-bubble cases reveals that the transient dynamics is orchestrated by weakly unstable solutions of the system that can appear and disappear as the number of bubbles changes.
Journal Article
The influence of invariant solutions on the transient behaviour of an air bubble in a Hele-Shaw channel
We hypothesize that dynamical systems concepts used to study the transition to turbulence in shear flows are applicable to other transition phenomena in fluid mechanics. In this paper, we consider a finite air bubble that propagates within a Hele-Shaw channel containing a depth-perturbation. Recent experiments revealed that the bubble shape becomes more complex, quantified by an increasing number of transient bubble tips, with increasing flow rate. Eventually, the bubble changes topology, breaking into multiple distinct entities with non-trivial dynamics. We demonstrate that qualitatively similar behaviour to the experiments is exhibited by a previously established, depth-averaged mathematical model and arises from the model’s intricate solution structure. For the bubble volumes studied, a stable asymmetric bubble exists for all flow rates of interest, while a second stable solution branch develops above a critical flow rate and transitions between symmetric and asymmetric shapes. The region of bistability is bounded by two Hopf bifurcations on the second branch. By developing a method for a numerical weakly nonlinear stability analysis we show that unstable periodic orbits (UPOs) emanate from the first Hopf bifurcation. Moreover, as has been found in shear flows, the UPOs are edge states that influence the transient behaviour of the system.
Journal Article
Impact of Diabetes Mellitus on Percutaneous Revascularization (CAVEAT-I)
We examined the relation between diabetes mellitus and outcomes in patients undergoing percutaneous coronary revascularization in the Coronary Angioplasty Versus Excisional Atherectomy Trial (CAVEAT-I), a randomized trial comparing treatment with either percutaneous transluminal coronary angioplasty or directional atherectomy for de novo lesions in native coronary arteries. Acute success and complication rates, 6-month angiographic restenosis rates, and 1-year clinical outcomes were compared between diabetic and nondiabetic patients undergoing each procedure. Acute success rates between diabetic (n = 191) and nondiabetic (n = 821) patients were similar for both revascularization techniques. Except for the need for dialysis, complication rates were also similar. Six months after atherectomy, diabetic patients had significantly more angiographic restenosis than nondiabetics (59.7% vs 47.4%) and significantly smaller minimum luminal diameters (1.20 vs 1.40 mm). Diabetics undergoing atherectomy required more frequent bypass surgery (12.8% vs 8.5%) and more repeat percutaneous revascularizations (36.5% vs 28.1%) than nondiabetics undergoing atherectomy. Restenosis rates, minimum luminal diameters and repeat revascularizations between diabetics and nondiabetics undergoing angioplasty were similar. The higher restenosis and repeat revascularization rates and the smaller minimum luminal diameter at follow-up in diabetic patients suggest that atherectomy may provide only modest benefit for these patients. The increased restenosis rate in diabetics undergoing atherectomy (but not angioplasty) requires further evaluation.
Journal Article
The life and fate of a bubble in a geometrically-perturbed Hele-Shaw channel
Motivated by the desire to understand complex transient behaviour in fluid flows, we study the dynamics of an air bubble driven by the steady motion of a suspending viscous fluid within a Hele-Shaw channel with a centred depth perturbation. Using both experiments and numerical simulations of a depth-averaged model, we investigate the evolution of an initially centred bubble of prescribed volume as a function of flow rate and initial shape. The experiments exhibit a rich variety of organised transient dynamics, involving bubble break up as well as aggregation and coalescence of interacting neighbouring bubbles. The long-term outcome is either a single bubble or multiple separating bubbles, positioned along the channel in order of increasing velocity. Up to moderate flow rates, the life and fate of the bubble are reproducible and can be categorised by a small number of characteristic behaviours that occur in simply-connected regions of the parameter plane. Increasing the flow rate leads to less reproducible time evolutions with increasing sensitivity to initial conditions and perturbations in the channel. Time-dependent numerical simulations that allow for break up and coalescence are found to reproduce most of the dynamical behaviour observed experimentally including enhanced sensitivity at high flow rate. An unusual feature of this system is that the set of steady and periodic solutions can change during temporal evolution because both the number of bubbles and their size distribution evolve due to break up and coalescence events. Calculation of stable and unstable solutions in the single- and two-bubble cases reveals that the transient dynamics are orchestrated by weakly-unstable solutions of the system termed edge states that can appear and disappear as the number of bubbles changes.
Paper