775 research outputs found
Determination of the Objective Reason Condition in the Conclusion and Renewal of Fixed Term Employment Contracts
No full textAn employment contract may be executed for a fixed or indefinite term. An indefinite-term employment contract is the rule of thumb, whereas a fixed-term contract is an exception. According to Article 11 of the Employment Code No 4857, a fixed-term contract may be signed when it is based on an objective reason, such as fixed-term work, the completion of a certain job, or the emergence of a relevant fact. There is no similar provision in other employment codes, which is why concluding a fixed-term employment contract with a worker covered by the Employment Code is more difficult than terminating workers excluded from the said code. This strict structure to conclude a fixed-term employment contract of the Employment Code has been criticized by the doctrine. According to Article 11, paragraphs 2 and 3, of the Employment Code and Article 430 of the Obligation Code No. 6098, to renew a fixed-term employment contract with all workers, an objective reason is required. This article explains what objective reason means and if such a condition is suitable and evaluates the debates in the doctrine and legal studies regarding the objective reason condition in the conclusion of fixed-term employment contracts, regulated in Article 11 of the Employment Code. Further, the author discusses whether an exception should be introduced into the objective cause condition. This article next examines the objective reason condition for the renewal of fixed-term employment contracts. In this framework, in addition to the objective reason condition, the application of a time limit and a number limit will be evaluated to prevent abuse in the renewal of employment contracts by using successive fixed-term employment agreements
Exploitation of homogeneous isotropic turbulence models for optimization of turbulence remote sensing
No full textHomogeneous isotropic turbulence (HIT) models are compared, with respect to optimization of turbulence remote sensing. HIT models have different applications such as load calculation for wind turbines (Mann, 1998) or droplet track modelling (Pinsky and Khain, 2006). Details of vortices seem of less relevance for modelling `realistic measurements', where the single purpose is to retrieve the eddy dissipation rate (EDR). Without the need for modelling the vortices, a faster and simpler approach might be favorable. The cascade turbulence model (CTM) is suggested. The CTM solution is scale invariant and a fast solution for one-dimensional HIT modelling. In this presentation modelled radar measruments for scanning mode (rotating antenna) are compared for different HIT models. The consequences for turbulence remote sensing optimization are discussed
Le complexe universitaire du bassin parisien : un colosse aux pieds d'argile
No full textThe author has been consulting when the renovation of the universities of the Paris Basin took place. This contribution is a call for action. Taking into account the history of the development of the universities in the main cities of the Paris Basin, and the analysis of the recent consultation held in the Basin about the question (1994-1997), the author gives a series of proposals in order to avoid that the universities of the Basin remain "beginners".Alimentée par l'expérience de l'auteur, engagée comme consultant dans le chantier du développement universitaire du Bassin parisien, cette contribution est un appel à l'action. A partir d'un rappel de la problématique du développement universitaire dans les villes de la grande couronne et d'un regard sur la consultation qui s'est déroulée sur la question (1994-97), sont proposées la création d'une structure permanente fédérant les acteurs concernés et des orientations pour éviter que l'enseignement supérieur dans le Bassin ne soit pas qu'un "enseignement de premier cycle".Unal Marion. Le complexe universitaire du bassin parisien : un colosse aux pieds d'argile. In: Travaux de l'Institut Géographique de Reims, vol. 25, n°97-98, 1998. Le bassin parisien : un espace en construction, sous la direction de Anna Geppert-Hebrard . pp. 109-116
Simplified prediction equation for ultimate stress in beams prestressed with hybrid tendons
No full textThe use of unbonded tendons is getting more widespread in post-tensioning industry; especially in rehabilitation and strengthening of existing damaged concrete members. The prediction of the stress at ultimate in unbonded tendon is important in calculating the capacity of structural members. This thesis presents a simplified prediction equation for concrete beams prestressed with hybrid (a combination of bonded and unbonded) tendons. The proposed equation is based on the Generalized Incremental Analysis (GIA) which uses the trussed-beam model developed by Ozkul et al. (2008) and Nassif et al. (2003). The main objective of this research is to develop a simple, but accurate design equation for the prediction of the stress at ultimate in unbonded tendon. Most important parameters such as loading type, effective prestress of unbonded tendon, concrete strength, area of steel reinforcement and span-to-depth ratio are taken into consideration. The equation is applicable to beams prestressed with unbonded or hybrid, FRP or steel, external or internal tendons. For the validation of the proposed simplified equation, test results available in the literature (199 beams) are collected. The results show that the proposed simplified equation exhibited very good accuracy for the calculation of stress at ultimate in unbonded tendon. The simplified equation is easy to use, accurate and applicable to any material type and combination of tendons.M.S.Includes bibliographical referencesby Gonca Una
High-Resolution Raindrop Size Distribution Retrieval Based on the Doppler Spectrum in the Case of Slant Profiling Radar
No full textDoppler spectra from vertically profiling radars are usually considered to retrieve the raindrop size distribution (DSD). However, to exploit both fall velocity spectrum and polarimetric measurements, Doppler spectra acquired in slant profiling mode should be explored. Rain DSD samples are obtained from simultaneously measured vertical and slant profile Doppler spectra and evaluated. In particular, the effect of the horizontal wind and the averaging time are investigated. The Doppler spectrum provides a way to retrieve the DSD, the radial wind, and a spectral broadening factor by means of a nonlinear optimization technique. For slant profiling of light rain when the horizontal wind is strong, the DSD results can be affected. Such an effect is demonstrated on a study case of stratiform light rain. Adding a wind profiler mode to the radar simultaneously supplies the horizontal wind and Doppler spectra. Before the retrieval procedure, the Doppler spectra are shifted in velocity to remove the mean horizontal wind contribution. The DSD results are considerably improved. Generally, averaged Doppler spectra are input into this type of algorithm. Instead, high-resolution, low-averaged Doppler spectra are chosen in order to take into account the small-scale variability of the rainfall. Investigating the linear relations at fixed median volume diameter, measured reflectivity-retrieved rainfall rate, for a slant beam, the consistency of the integrated parameters is established for two averaging periods. Nevertheless, the corresponding DSD parameter distributions reveal differences attributed to the averaging of the Doppler spectra. The new aspects are to obtain the same retrieval quality as vertically profiling and highly averaged spectra in an automated way.Geoscience and Remote SensingCivil Engineering and Geoscience
Multi-beam raindrop size distributions retrievals on the Doppler spectra: Influence of averaging and mean horizontal wind correction
No full textAcquiring the raindrop size distribution (DSD) from radar data is still a challenge. For profiling radar, this distribution can be estimated from the Doppler spectra. However the Doppler spectrum is not a direct measure of the DSD. The radial component of the wind shifts the Doppler spectrum related to the raindrop size distribution along the Doppler velocity interval. Furthermore, the Doppler spectrum may be broadened by turbulence effect. The Doppler spectra of rain are modelled using Rayleigh scattering, the gamma distribution for the raindrop size, a size-shape relationship and a Gaussian kernel for the turbulence. Comparing the measured Doppler spectrum with the modelled one, a non-linear least-square fit technique is employed to obtain the parameters of the raindrop size distribution (D0, ?) and the turbulence broadening factor of the raindrop size spectrum (?0). The intercept parameter (Nw) and the radial wind component (v0) are estimated by scaling the broadened DSD along the spectral reflectivity axis and the Doppler velocity axis respectively. This approach has been proposed in [1]. So far, this technique has not been further developed, exploited and validated. It is our intention to investigate this methodology using the S-band Doppler-polarimetric TARA radar to retrieve raindrop size distribution from drizzle to heavy precipitation with high spatial and time resolution. Since TARA can profile in three directions, three raindrop size distribution profiles are estimated, which can give insight in the microphysical homogeneity of the precipitation. Because TARA can be used as wind profiler, the mean horizontal wind is estimated and a correction to remove the effect of the radial mean horizontal wind is implemented in the retrieval procedure. Comparison with and without correction is done. Another issue is averaging. Should the Doppler spectra be averaged before the non-linear least-square fit? How should they be averaged and how many averages should be carried out? These questions are discussed. High resolution multi-beams raindrop size distribution retrievals are illustrated and discussed.Geoscience & Remote SensingCivil Engineering and Geoscience
Spectral polarimetric radar clutter suppression to enhance atmospheric echoes
No full textThe clutter present in the Doppler spectra of atmospheric targets can be removed by using polarimetry. The purpose is to suppress the Doppler velocity bins where spectral polarimetric parameters have atypical values. This procedure largely improves profiles of moments and polarimetric parameters of atmospheric targets. Several spectral polarimetric clutter-reduction techniques, which are based on thresholding and intended for real-time processing, are discussed in this paper. A new method, the double spectral linear depolarization ratio clutter-suppression technique, is proposed. Very satisfactory performances are obtained with this method, which can be used in the full range of elevations (08–908). Spectral polarimetric clutter-suppression techniques for real-time processing were studied for the S-band high-resolution Transportable Atmospheric Radar (TARA) profiler. For this study, precipitation, cloud, and clear-air scattering are considered examples of atmospheric echoes. After successful testing in 2008, the double spectral linear depolarization ratio filter was implemented in the real-time processing of the X-band scanning drizzle radar (IDRA).Geoscience and Remote SensingCivil Engineering and Geoscience
Multi-beam raindrop size distribution retrievals on the Doppler spectra
No full textAcquiring the raindrop size distribution from radar data is still a challenge. Generally this distribution is retrieved using the reflectivity, Z, and the differential reflectivity, Zdr, at S-band. The specific differential phase, Kdp, provides a third radar observable in the case of heavy precipitation to strengthen the retrieval technique. For S-band profiling radars, Kdp cannot be used, mainly because of the limited number of range bins containing rain. The Zdr measurement cannot be employed when the elevation is near the vertical, or in the case of drizzle and light rain. Therefore retrievals have to be performed on the measured Doppler spectra. For this purpose, the Doppler spectra of rain are modeled using Rayleigh scattering, the gamma distribution for the raindrop size, a size-shape relationship and a Gaussian kernel for the turbulence. Comparing the measured Doppler spectrum with the modeled one, a non-linear least-square fit technique is employed to obtain the parameters of the raindrop size distribution (D0, ?) and the turbulence broadening factor of the raindrop size spectrum (?0). The intercept parameter (Nw) and the radial wind component (v0) are estimated by scaling the broadened drop size distribution (DSD) along the spectral reflectivity axis and the Doppler velocity axis respectively. This approach has been proposed in (Moisseev et al, 2006). So far, this technique has not been further developed, exploited and validated. It is our intention to investigate this methodology using the Doppler-polarimetric TARA radar to retrieve raindrop size distribution from drizzle to heavy precipitation with high spatial and time resolution. Since TARA can profile in three directions, three raindrop size distribution profiles are estimated, which can give insight in the microphysical homogeneity of the precipitationGeoscience & EngineeringCivil Engineering and Geoscience
Object-Orientated Filter Design in Spectral Domain for Polarimetric Weather Radar
No full textAiming at removing stationary and moving clutter while retaining precipitation for dual-polarization weather radar, a new clutter suppression method, named the object-orientated spectral polarimetric (OBSpol) filter, is put forward in this paper. Based on the spectral polarimetric feature and the range-Doppler continuity of precipitation, the OBSpol filter generates a filtering mask implemented on the raw range-Doppler spectrogram to mitigate the clutter and noise. The procedures are as follows. After the spectral polarimetric filtering and the mathematical morphology method, one binary mask where “1” indicates the precipitation is obtained. Then, the contiguous bins of the same value “1” in the range-Doppler domain are grouped in areas termed as objects. Whether the produced objects are precipitation or not will be further judged based on appropriate weather radar observable. Thus, combining all the filtered separate objects, a filtering mask can be obtained. In this paper, data collected by the polarimetric Doppler IRCTR drizzle radar are used to demonstrate and assess the performance of the proposed technique in the case of ground clutter, narrowband moving clutter, and noise. Two precipitation cases are examined: 1) moderate precipitation with large scale and 2) light precipitation with severe clutter contamination. In the range-Doppler spectrogram, both stationary and narrowband moving clutters are mitigated, while maintaining nonoverlapping precipitation signal. This helps to solve the problem when clutter and precipitation overlap in the time domain. In addition, the OBSpol filter is proven to be effective with different Doppler velocity resolutions. This technique can be applied in real-time due to its low computation complexity. Moreover, the spectral polarimetric filtering can be designed using the measurements of dual-polarization radar systems which do not have cross-polar measurements. Hence, the proposed clutter mitigation technique can be implemented for operational dual-polarization weather radar.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Atmospheric Remote SensingGeoscience and Remote Sensin
Dealiasing of radar Doppler velocities to improve wind estimations
No full textWith its three beams in different directions, the Transportable Atmospheric RAdar system (TARA) can provide a wind field estimation. These estimations are inaccurate when the Doppler velocities in one or more of the three beams are aliased. Amongst different approaches to solve aliasing are a continuity check up to four dimensions, staggering PRT (Pulse Repetition Time) technique and a method using polarimetric information. The staggering PRT technique is not applicable, because it requires altering the radar system itself. For the main beam of TARA the method using polarimetric information is used, but for the offset beams nopolarimetric information is available. The research presented in this thesis focuses on the dealiasing of the offset beams using a continuity check in one dimension. The assumed correctly dealiased main beam is used as a reference to compare the offset beams with. The first step towards correct Doppler velocities is unfolding every individual Doppler spectrum. Then, a reference spectrum is searched for in the main beam. The first spectrum in the offset beam that is placed in the right Doppler velocity interval, is the one that is at the same height as the reference spectrum. From there on a continuity check is performed. First away from the radar and then towards the radar. Comparison is done by using the mean Doppler velocities of every Doppler spectrum. The algorithm proposed in this thesis shows significant improvement in performance, compared with the old algorithm. In case of very wide Doppler spectra, a large difference between the reference and the current spectrum and clutter, the algorithm can fail.Geoscience & Remote SensingTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
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