Field-Assisted DC-Pulsed Cathodes for next generation light sources and accelerators

International audienceThe scope of that contribution is to present the challenges of the next particle sources for accelerators. It is admitted that emittance near Interaction Point (IP) is strongly dominated by the emittance of the low power source. To minimize theBremstrahlung effects in the Interaction Point (IP), we also need extremely low emittance bunches, ultra high brillance, very low charges sub fC, near depopulated attosecond electronic bunches. These produced bunches should fit the entrances of Dielectric Laser Accelerators (DLA) and Laser Plasma Accelerators (LPA).A 20kV DC pulsed sub nanosecond Field Emission Array source with extremely low emittance is considered in order to obtain such results. Firstly, we will describe the DC-pulsed experimental source by blocks. Following that, we will raise more general problems induced by DC-pulsed configuration: thermal transient behaviour of nanostructures, enhancement of plasmons coupling in relation to nanostructured networks, then fast prototyping of cathode geometry will be undertaken using different models. These cathodes are to be fabricated at Orsay.We present the method of curvilinear coordinate calculus, adapted to major classes of nanostructured tips. We define 3 major classes of 3D analytical profiles to emulate experimental conditions (multi-segment, quadratic and exponential one) and apply curvilinear analytical Maxwellsolving to find electrostatic potential around the profile. Our method is concurrent to T-splines for instance, but it is expected to converge faster. Cathode physics will be modelled integrating different phenomenons: photo/thermal/field/emission... Results will be compared to electromagnetic simulations with CST and Astra tools. To conclude, we shall then evaluate the emittance performances planned for a 20keV cathodic source, and its acceptance to the next stages, with the help of some electrostatic focusing. Numerous experimental and theoretical aspects are to be solved

RF Coaxial Resonator for Investigating Multipactor Discharges on Metal and Dielectric Surfaces

http://accelconf.web.cern.ch/AccelConf/LINAC2014/html/auth0693.htmTHPP096International audienceMultipactor discharge is a phenomenon in which electrons impact one or more material surfaces in resonance with an alternating electric field. The discharge can occur for a wide range of frequencies, from the MHz range to tens of GHz, and in wide array of geometries if the impacted surface has a secondary electron emission (SEE) yield larger than one. The discharge can take place on a single surface or between two surfaces. A novel coaxial resonator to investigate two-surface multipactor discharges on metal and dielectric surfaces in the gap region under vacuum conditions has been designed and tested. The resonator is ~ 100 mm in length with an outer diameter of ~ 60 mm (internal dimensions). A pulsed RF source delivers up to 30 W average power over a wide frequency range 650-900 MHz to the RF resonator. The incident and reflected RF signals are monitored by calibrated RF diodes. An electron probe provides temporal measurements of the multipacting electron current with respect to the RF power. These experiments were successful in identifying multipacting and allowed us the evaluation of a home made sputtered titanium nitride (TiN) thin layers as a Multipactor suppressor

An exploratory study of Palestinian science teachers' views of the nature of science

This mixed methods study investigates Palestinian science teachers' views of the nature of science (NOS), with an in-depth exploration of the nature, causes and context of these views, and the possible reasons why teachers hold such views. The research provides suggestions of possible ways to improve Palestinian science teachers' views of NOS, and the factors within the Palestinian context that might either facilitate or hamper efforts to promote teachers' understanding of NOS. Quantitative data were collected during the first phase of the study from a sample of 277 teachers working in three areas in Palestine. Twelve teachers were randomly selected for the second qualitative phase. In line with the regional and global literature, the results of the closed NOS survey, the open-ended questionnaire and the individual semi-structured interviews revealed that Palestinian science teachers hold relatively naive, traditional views of most of the main tenets of NOS. During the qualitative phase, a series of semi-structured interviews was also carried out with ten Palestinian academics to explore in depth their views and suggestions concerning the nature, causes and context of teachers' views of NOS. They identified possible factors responsible for this apparent naivete in teachers' views and suggested ways to improve their understanding of NOS. The analysis of academics' responses revealed eight main factors that might explain the naivete of teachers' views of NOS: Palestinian socio-cultural background, education policy, teachers' own personal values, teaching approaches at school and university levels, science textbooks, teacher training programmes, educational supervision and school resources. Possible ways to improve teachers' views of NOS could be grouped in six main areas: tertiary science teaching and teacher preparation programmes, teaching as a well-resourced profession, Palestinian science textbooks, education supervision and in-service teacher training, educational leadership and administration system, and public scientific literacy and critical awareness. Finally, there is a consideration of the possible implications of these findings for teaching and teacher education in Palestine, for policy making bodies in the Ministry of Education and Higher Education, for methodology, and for future research in the area

QUALITE DES MODELES NUMERIQUES DE TERRAIN DERVIES PAR CORRELATION AUTOMATIQUE

Digital Terrain Models are plying an important role as information layer, mainly with the development of geographic information systems, since they describe the topographic surface of the terrain and hence it constitutes a valuable support for the study of variety of geographical and environmental events. With the advent of digital techniques and the advantages they are offering in terms of automation and precision, users are adopting image matching techniques to derive automatically Digital Terrain Models. The quality of these DTM are determined by different factors (photo scale, scanning resolution and software parameterization). This paper is a contribution to evaluate the influence of some of some factors on the final accuracy of DTM derived by correlation. In this respect, different tests were carried out on two photo scales (1/7500 an 1/20000) flown on varying topography. The photos were scanned to 20, 25, 32 and 42 microns pixel sizes and digital terrain models were derived using ViruoZo software from Supresoft. The assessment of the derived DTMs quality was based on qualitative (visual comparisons of contours) and quantitative ( RMS computed from residuals on ground check points) criteria. Results showed that, in rugged terrain, DTM derived from 1/20000 photos are accurate to 32cm, which may enable deriving contours with 1 m interval. The introduction of break lines prior to the correlation seems to have less influence on the accuracy of derived DTM when the generated grid is very dense, but contributes to reduce the editing burden. The high accuracy of automatically derived DTM may contribute to make less tight the map to photo scale ratio. For instance mapping at 1/5000 from 1/20000 photos can preserve the height accuracy, while with conventional methods, height accuracy at 1/5000 map scale is preserved usually for mapping from 1/12000. 1

Geochemical characterization the waters of Foggaras the Continental Intercalary Aquifer of Timinoune region (south west Algeria)

The study of the Continental Intercalary (C.I) groundwater of the region of Timimoune (southwestern Algeria), based on physico-chemical data (major elements), allowed to understand the geochemistry of foggaras water. The aquifer is contained in the formations of the Lower Cretaceous (Albian and Barremian). The waters are strongly mineralized with an average value 2g / l.The waters have a clear predominance of facies chlorinated-sodium. The risk is high to excessive soil salinization, and the risk of medium alkalinity to very high. Statistical analysis led us to reach two conclusions, the first is that, variable electrical conductivity (EC), dry residue (RS), Na+, Ca2+, Cl-, SO4 --, mineralization, are best correlated and responsible the signing of the mineral load of water, the second is that the nitrate ion (NO3-) opposite to the above-mentioned variables mark its anthropogenic origin. Keywords: Continental Intercalary, mineralization, salinity, PCA, Nitrat

Speech Enhancement via EMD

WOSInternational audienceIn this study, two new approaches for speech signal noise reduction based on the empirical mode decomposition (EMD) recently introduced by Huang et al. (1998) are proposed. Based on the EMD, both reduction schemes are fully data-driven approaches. Noisy signal is decomposed adaptively into oscillatory components called intrinsic mode functions (IMFs), using a temporal decomposition called sifting process. Two strategies for noise reduction are proposed: filtering and thresholding. The basic principle of these two methods is the signal reconstruction with IMFs previously filtered, using the minimum mean-squared error (MMSE) filter introduced by I. Y. Soon et al. (1998), or thresholded using a shrinkage function. The performance of these methods is analyzed and compared with those of the MMSE filter and wavelet shrinkage. The study is limited to signals corrupted by additive white Gaussian noise. The obtained results show that the proposed denoising schemes perform better than the MMSE filter and wavelet approach

Performance Evaluation of Beit-Lahia Wastewater Treatment Plant in the Northern Gaza Strip

Wastewater treatment plant at Beit Lahia and its partially treated effluent lake are considered the primary sources of pollution for the ground water and ambient environment. From February to May 2005, Field and laboratory tests were conducted and historical operating data were evaluated to assess the system performance in term of removal efficiency for the hybrid lagoon system. This study attempts to distinguish the factors leading to the inadequate performance of the BLWWTP in removing organic matter and nitrogen. The efficiencies of the different stages of the treatment and the global performance have been compared. Collection and analysis of available historical data revealed a constantly decreasing removal of biochemical oxygen demand (BOD5), chemical oxygen demand (COD), suspended solids (SS), and fecal coliform (FC). Analysis of data showed that the lagoon system removed 87%, 57%, 60 %, 20%, 13%, 16%, and 94.7% of the influent TSS, BOD5, COD, TKN, NH3, PO4-2, and FC respectively with an effluent concentration of 39 mg/L, 178 mg/L, 72 mg/L, 84 mg/L, 72 mg/L, 5.5 mg/L, and 2.04E+05. The decreasing removal of pollutants appeared to be caused by increased hydraulic and organic load that exceeds treatment plant capacity, incorrect design that lead to inefficient hydrodynamics, and inadequate operation. Over hydraulic and organic loadings, limitation of Oxygen supply and unavailability of DO, inadequate design of plant geometry and high facultative and maturation ponds depth are the main factors leading to inadequate treatment system performance. The study present suggestions like repositioning of inlets and outlets and/or adding baffles, micro-screen, and chlorination unit which can be introduced as short and simple solutions to overcome and improve partially the inefficiencies and poor treatment plant performance

An exploratory study of Palestinian science teachers' views of the nature of science

This mixed methods study investigates Palestinian science teachers' views of the nature of science (NOS), with an in-depth exploration of the nature, causes and context of these views, and the possible reasons why teachers hold such views. The research provides suggestions of possible ways to improve Palestinian science teachers' views of NOS, and the factors within the Palestinian context that might either facilitate or hamper efforts to promote teachers' understanding of NOS. Quantitative data were collected during the first phase of the study from a sample of 277 teachers working in three areas in Palestine. Twelve teachers were randomly selected for the second qualitative phase. In line with the regional and global literature, the results of the closed NOS survey, the open-ended questionnaire and the individual semi-structured interviews revealed that Palestinian science teachers hold relatively naive, traditional views of most of the main tenets of NOS. During the qualitative phase, a series of semi-structured interviews was also carried out with ten Palestinian academics to explore in depth their views and suggestions concerning the nature, causes and context of teachers' views of NOS. They identified possible factors responsible for this apparent naivete in teachers' views and suggested ways to improve their understanding of NOS. The analysis of academics' responses revealed eight main factors that might explain the naivete of teachers' views of NOS: Palestinian socio-cultural background, education policy, teachers' own personal values, teaching approaches at school and university levels, science textbooks, teacher training programmes, educational supervision and school resources. Possible ways to improve teachers' views of NOS could be grouped in six main areas: tertiary science teaching and teacher preparation programmes, teaching as a well-resourced profession, Palestinian science textbooks, education supervision and in-service teacher training, educational leadership and administration system, and public scientific literacy and critical awareness. Finally, there is a consideration of the possible implications of these findings for teaching and teacher education in Palestine, for policy making bodies in the Ministry of Education and Higher Education, for methodology, and for future research in the area

Can net photosynthesis and water relations provide a clue on the forest decline of Quercus suber in North Tunisia?

Net photosynthesis, sap flow density (SFD) and water use efficiency (WUE) were measured in a Quercus suber forest in north Tunisia in an attempt to explain the forest decline. In general, sap flow was positively related to light intensity and water loss, indicating that high light intensities can increase the SFD up to the saturation point in the cork oak. CO2 assimilation of cork oak in this region was light intensity-dependent. Cork oak showed a general increase in photosynthetic rates with increasing light intensity up to the light saturation point. Increased radiation probably increased the photosynthesis and growth above ground in this area, whereas the below-ground soil had insufficient moisture for uptake through the roots because the high light intensity and temperature induced high evapotranspiration.Key words: Decline, evaportranspiration, light intensity, Quercus suber, sap flow density, water use efficiency