Outcomes Teacher Mentoring Has on Professional Learning and Delivery of Instruction

A qualitative study using grounded theory was conducted to discover how educational mentoring was transferred to subsequently transform instructional delivery in the second year of teaching for novice secondary school teachers. The study was conducted in a Deep South Texas public school district during the 2017–2018 academic year. After concluding a year of mentoring, interviews were conducted to reveal how the mentoring phenomena helped transform their present day delivery of instruction. Data was gathered through face-to-face interviews with seven participants. During this second year, the novice teachers primarily relied on both what was learned through their mentoring experiences and networking with experienced colleagues. The novice teachers’ mentoring undertakings revealed a greater need to apply newly acquired learning experiences during the initial year of instruction. In addition, fidelity of implementation in the mentoring process played a crucial role in the viable success of the program. Teachers (mentees) were primarily motivated by individual didactic observations during their mentoring experience. Through constant comparative analysis and the use of memoing five key themes revealed how the effectiveness of the mentoring process was interrelated to the novice teachers’ professional learning, development, and instructional delivery. Emerged themes from the data included: mentoring experiences, classroom management and curriculum, instructional practices, professional development, and student learning progress

Simulation of an absorption based solar cooling facility using a geothermal sink for heat rejection

An important issue of solar cooling facilities based on absorption cycles and sometimes not given the necessary attention is the recooling process of the absorber and condenser. This is critical in the overall behaviour of the facility because the condensation and absorption temperatures will affect the COP and cooling capacity of the chiller. Most of the time the recooling process is made by using a wet cooling tower in a closed loop through the absorber and condenser. The use of a wet cooling tower gives good results in terms of cooling capacity and COP, but presents some health risk, like legionella, and its use is restricted to the industrial sector and places where water scarcity is not present. This paper presents the modification of the already validated TRNSYS simulation of a solar cooling facility, implementing a geothermal heat sink instead of the wet cooling tower in order to dissipate the heat generated internally in the absorption chiller. Simulation results shows that a geothermal heat sink composed of 6 boreholes of 100 meters of depth should be sufficient in order to substitute the wet cooling tower, for a typical Spanish single family dwelling.Universidad Carlos III de Madrid - ITEA Research GroupPublicad

An experimental route to spatiotemporal chaos in an extended 1D oscillators array

We report experimental evidence of the route to spatiotemporal chaos in a large 1D-array of hotspots in a thermoconvective system. Increasing the driving force, a stationary cellular pattern becomes unstable towards a mixed pattern of irregular clusters which consist of time-dependent localized patterns of variable spatiotemporal coherence. These irregular clusters coexist with the basic cellular pattern. The Fourier spectra corresponding to this synchronization transition reveals the weak coupling of a resonant triad. This pattern saturates with the formation of a unique domain of great spatiotemporal coherence. As we further increase the driving force, a supercritical bifurcation to a spatiotemporal beating regime takes place. The new pattern is characterized by the presence of two stationary clusters with a characteristic zig-zag geometry. The Fourier analysis reveals a stronger coupling and enables to find out that this beating phenomena is produced by the splitting of the fundamental spatiotemporal frequencies in a narrow band. Both secondary instabilities are phase-like synchronization transitions with global and absolute character. Far beyond this threshold, a new instability takes place when the system is not able to sustain the spatial frequency splitting, although the temporal beating remains inside these domains. These experimental results may support the understanding of other systems in nature undergoing similar clustering processes.Comment: 12 pages, 13 figure

Slow dynamics in a turbulent von K\'arm\'an swirling flow

We present an experimental study of a turbulent von K\'arm\'an flow produced in a cylindrical container using two propellers. The mean flow is stationary up to $Re = 10^4$, where a bifurcation takes place. The new regime breaks some symmetries of the problem, and is time-dependent. The axisymmetry is broken by the presence of equatorial vortices with a precession movement, being the velocity of the vortices proportional to the Reynolds number. The reflection symmetry through the equatorial plane is broken, and the shear layer of the mean flow appears displaced from the equator. These two facts appear simultaneously. In the exact counterrotating case, a bistable regime appears between both mirrored solutions and spontaneous reversals of the azimuthal velocity are registered. This evolution can be explained using a three-well potential model with additive noise. A regime of forced periodic response is observed when a very weak input signal is applied.Comment: Improved model, additional results and figures, accepted in PR

Subcritical instabilities in a convective fluid layer under a quasi-one-dimensional heating.

The study and characterization of the diversity of spatiotemporal patterns generated when a rectangular layer of fluid is locally heated beneath its free surface is presented. We focus on the instability of a stationary cellular pattern of wave number ks which undergoes a globally subcritical transition to traveling waves by paritybreaking symmetry. The experimental results show how the emerging traveling mode 2ks /3 switches on a resonant triad ks ,ks /2,2ks /3 within the cellular pattern yielding a “mixed” pattern. The nature of this transition is described quantitatively in terms of the evolution of the fundamental modes by complex demodulation techniques. The Bénard-Marangoni convection accounts for the different dynamics depending on the depth of the fluid layer and on the vertical temperature difference. The existence of a hysteresis cycle has been evaluated quantitatively. When the bifurcation to traveling waves is measured in the vicinity of the codimension-2 bifurcation point, we measure a decrease of the subcritical interval in which the traveling mode becomes unstable. From the traveling wave state the system undergoes a global secondary bifurcation to an alternating pattern which doubles the wavelength ks /2 of the primary cellular pattern; this result compares well with theoretical predictions P. Coullet and G. Iooss, Phys. Rev. Lett. 64, 866 1990 . In this cascade of bifurcations towards a defect dynamics, bistability due to the subcritical behavior of our system is the reason for the coexistence of two different modulated patterns connected by a front. These fronts are stationary for a finite interval of the control parameters

Instabilities of conducting fluid layers in cylindrical cells under the external forcing of weak magnetic fluids

In this work, we analyze recent results concerning the instabilities created in a layer of liquid metal by the action of time-dependent magnetic fields. The experimental setup allows the characterization of different patterns very close to the threshold. For very low frequencies of the forcing field, the axisymmetric fluid layer destabilizes with different azimuthal wavenumbers. An improved analysis allows the characterization of different patterns for interaction parameter values as low as 5 · 10 −3

Impact of time-dependent nonaxisymmetric velocity perturbations on dynamo action of von Kármán-like flows

We present numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von K´arm´an–like flow subject to time-dependent nonaxisymmetric velocity perturbations. The numerical model is based on the setup of the French von K´arm´an-sodium dynamo (VKS) and on the flow measurements from a water experiment conducted at the University of Navarra in Pamplona, Spain. The principal experimental observations that are modeled in our simulations are nonaxisymmetric vortexlike structures which perform an azimuthal drift motion in the equatorial plane. Our simulations show that the interactions of these periodic flow perturbations with the fundamental drift of the magnetic eigenmode (including the special case of nondrifting fields) essentially determine the temporal behavior of the dynamo state.We find two distinct regimes of dynamo action that depend on the (prescribed) drift frequency of an (m = 2) vortexlike flow perturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth rates and a drift of the magnetic eigenmode that is synchronized with the perturbation drift. The resonance-like enhancement of the growth rates takes place when the vortex drift frequency roughly equals the drift frequency of the magnetic eigenmode in the unperturbed system. Outside of this small window, the field generation is hampered compared to the unperturbed case, and the field amplitude of the magnetic eigenmode is modulated with approximately twice the vortex drift frequency. The abrupt transition between the resonant regime and the modulated regime is identified as a spectral exceptional point where eigenvalues (growth rates and frequencies) and eigenfunctions of two previously independent modes collapse. In the actual configuration the drift frequencies of the velocity perturbations that are observed in the water experiment are much larger than the fundamental drift frequency of the magnetic eigenmode that is obtained from our numerical simulations. Hence, we conclude that the fulfillment of the resonance condition might be unlikely in present day dynamo experiments. However, a possibility to increase the dynamo efficiency in the VKS experiment might be realized by an application of holes or fingers on the outer boundary in the equatorial plane. These mechanical distortions provoke an anchorage of the vortices at fixed positions thus allowing an adjustment of the temporal behavior of the nonaxisymmetric flow perturbations

HYSTERESIS AND VORTICES DYNAMICS IN A TURBULENT FLOW

Recent results about the slow dynamics present in a fully developed turbulent flow are reported. In a previous paper [de la Torre & Burguete, 2007] we showed that the mean velocity field in a turbulent flow bifurcates subcritically breaking some symmetries of the problem and becomes time-dependent because of equatorial vortices moving with a precession movement. This subcriticality produces a bistable regime, whose main characteristics were successfully reproduced using a three-well potential model with additive noise. In this paper we present the characterization of the hysteresis region, not previously observed, in this bifurcation. This hysteresis appears only for an extremely small range of parameters