Search results for " wind"
showing 10 items of 403 documents
Over the Cuckoo’s Nest : Towards a Nordic Model of the Responsible University?
2019
AbstractThis concluding chapter takes stock of the major elements, both empirical and conceptual, that underpin the case chapters presented in the book. The chapter is organised in three distinct sections. First, addressing a largely scientific audience, the chapter attempts to make conceptual sense of the findings from an organisational theory perspective. Second, it shifts focus to the wider community of practitioners (policy makers, advisers, university managers and administrators, etc.) by shedding light on the practical implications of the volume’s core findings for both policy and practice. Third, the chapter once again addresses an academic audience by sketching out the road ahead re…
Robust motion control of nonlinear quadrotor model with wind disturbance observer
2021
This paper focuses on robust wind disturbance rejection for nonlinear quadrotor models. By leveraging on nonlinear unknown observer theory, it proposes a nonlinear dynamic filter that, using sensors already on-board the aircraft, can estimate in real-time wind gust signals in the three dimensions. The wind disturbance is then treated as input to the PD controller for a quick and robust flight pathway in presence of disturbances. With this scheme, the wind disturbance can be precisely estimated online and compensated in real-time. Hence, the quadrotor can successfully reach its desired attitude and position. To show the effective and desired performance of the method, simulation results are …
Solar and interplanetary triggers of the largest Dst variations of the solar cycle 23
2012
Abstract We present the results of an investigation from the Sun to the Earth of the sequence of events that caused major Dst decreases (Δ Dst ≤ – 100 nT during 1 h) that occurred during 1996–2005. These events are expected to be better related to geomagnetic induced current (GIC) events than those events where any geomagnetic index is far from its quiet time value. At least one full halo CME with a speed on the plane of sky above 900 km/s participates in every studied event. The seven events were triggered by interplanetary signatures, which arise as a consequence of interaction among different solar ejections. The interaction arises at different stages from the solar surface, between segm…
ARQ Aware Scheduling for the IEEE 802.16 Base Station
2008
The IEEE 802.16 technology defines the ARQ mechanism that enables a connection to resend data at the MAC level if an error is detected. In this paper, we analyze the ARQ aware scheduling for the 802.16 base station. In particular, we consider how the BS scheduler can account for the ARQ block size, absence of the ARQ block rearrangement, and the ARQ transmission window. We propose a set of constraints that can be applied to any base station scheduler algorithm. To test them, we run a number of simulation scenarios. The simulations results confirm that the ARQ aware scheduling can improve the overall performance.
Performance analysis of the ieee 802.16 arq mechanism
2007
The IEEE 802.16 technology defines the ARQ mechanism that enables a connection to resend data at the MAC level if an error is detected. In this paper, we analyze the key features and parameters of the 802.16 ARQ mechanism. In particular, we consider a choice for the ARQ feedback type, an algorithm to build block sequences, a scheduling of the ARQ feedbacks and retransmissions, the ARQ block rearrangement, ARQ transmission window and ARQ block size. We run a number of simulation scenarios to study these parameters and how they impact a performance of application protocols. The simulation results reveal that the ARQ mechanism and its correct configuration play an important role in transmittin…
On ARQ feedback intensity of the IEEE 802.16 ARQ mechanism
2008
The IEEE 802.16 standard defines the ARQ mechanism as a part of the MAC layer. The functioning of the ARQ mechanism depends on a number of parameters. The IEEE 802.16 specification defines them but it does not provide concrete values and solutions. We ran simulation scenarios to study how the ARQ feedback intensity impacts the performance of application protocols. The simulation results reveal that a low ARQ feedback intensity results only in a marginal improvement. Though it is possible to optimize the ARQ feedback intensity, it is reasonable to rely upon more frequent ARQ feedback messages as they do not result in a performance degradation. At the same time, ARQ connections, which work on…
Hotel chain performance: a gravity-DEA approach
2011
Performance in business management can be measured in terms of competitiveness and efficiency. Generally speaking, competitiveness is a comparative concept of the ability of a firm, sub-sector or country to sell and supply goods and/or services in a given market, as measured by its market share. Particularly in competitive markets, efficiency plays a key role in determining this ability but it is not, by itself, sufficient. Indeed, while competitiveness has more to do with “pursuing the correct strategy” towards the conservation and/or increase of the market share, operational efficiency is mainly a measure of how well the firm, sub-sector or country under study processes inputs to achieve …
Spectral Density Estimate for Stable Processes Observed with an Additive Error
2018
International audience; In this paper, a symmetric alpha stable process where its spectral representation has an additive error is considered. The error is supposed to be constant. A periodogram as estimator of the spectral density and its rate of convergence are given. In order to give an asymptotically unbiased and consistent estimate of the spectral density, this periodogram is smoothed by an adapted spectral window. The rate of convergence is given.
On the linear friction welding process of aluminum alloys: Experimental insights through process monitoring
2013
Abstract Linear friction welding is a solid-state joining process for non-axisymmetric components in which joining of materials is obtained through the relative motion of two components under pressure. In the process the heat source is given by the frictional forces work decaying into heat determining a local softening of the material and eventually bonding conditions. A dedicated fixture was equipped with sensors for the in-process acquisition of variables regarding kinematics, dynamics and temperature levels. The results of an experimental campaign aimed to weld AA6082-T6 aluminum alloy parts are presented and a process window is identified for the used alloy.
Improving High Frequency Transformers behavior for DC-DC Converter Used in Electric Vehicles
2018
The paper presents a design procedure for high frequency transformer windings adopted in the DC-DC converter used in electric vehicles. The output of the design procedure is the integration of a 3D printed plastic case in the transformer windings, with the aim to maximize the output power. The proposal design procedure is entirely based on a finite element analysis approach and on a differential evolution algorithm used for the solution of the optimization problem.