The adequacy of the present practice in dynamic aggregated modelling of wind farm systems

Large offshore wind farms are usually composed of several hundred individual wind turbines, each turbine having its own complex set of dynamics. The analysis of the dynamic interaction between wind turbine generators (WTG), interconnecting ac cables, and voltage source converter (VSC) based High Voltage DC (HVDC) system is difficult because of the complexity and the scale of the entire system. The detailed modelling and modal analysis of a representative wind farm system reveal the presence of several critical resonant modes within the system. Several of these modes have frequencies close to harmonics of the power system frequency with poor damping. From a computational perspective the aggregation of the physical model is necessary in order to reduce the degree of complexity to a practical level. This paper focuses on the present practices of the aggregation of the WTGs and the collection system, and their influence on the damping and frequency characteristics of the critical oscillatory modes. The effect of aggregation on the critical modes are discussed using modal analysis and dynamic simulation. The adequacy of aggregation method is discussed

Climate or rural development policy?

Being heavily energy dependent, it is not much of a surprise that Europe pays special attention to reducing the use of fossil fuels. Each one of the ten new member states is characterized by relatively low per capita energy consumption and relatively low energy efficiency, and the share of renewables in their energy mix tends to be low, too. The paper examines the problem when policy measures create a decrease in environmental capital instead of an increase. In this case it hardly seems justified to talk about environmental protection. The authors describe a case of a Hungarian rapeseed oil mill which would not be of too much interest on its own but given that almost all similar plants went bankrupt, there are some important lessons to learn from its survival. The enterprise the authors examined aimed at establishing a micro-regional network. They completed a brown-field development to establish a small plant on the premises of a former large agricultural cooperative. By partnering with the former employees and suppliers of the sometime cooperative, they enjoyed some benefits which all the other green-field businesses focusing on fuel production could not. The project improved food security, energy security and population retention as well

Quenched Narrow-Line Laser Cooling of 40Ca to Near the Photon Recoil Limit

We present a cooling method that should be generally applicable to atoms with narrow optical transitions. This technique uses velocity-selective pulses to drive atoms towards a zero-velocity dark state and then quenches the excited state to increase the cooling rate. We demonstrate this technique of quenched narrow-line cooling by reducing the 1-D temperature of a sample of neutral 40Ca atoms. We velocity select and cool with the 1S0(4s2) to 3P1(4s4p) 657 nm intercombination line and quench with the 3P1(4s4p) to 1S0(4s5s) intercombination line at 553 nm, which increases the cooling rate eight-fold. Limited only by available quenching laser power, we have transferred 18 % of the atoms from our initial 2 mK velocity distribution and achieved temperatures as low as 4 microK, corresponding to a vrms of 2.8 cm/s or 2 recoils at 657 nm. This cooling technique, which is closely related to Raman cooling, can be extended to three dimensions.Comment: 5 pages, 4 figures; Submitted to PRA Rapid Communication

An atomic clock with 10−1810^{-18} instability

Atomic clocks have been transformational in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Next-generation optical atomic clocks can extend the capability of these timekeepers, where researchers have long aspired toward measurement precision at 1 part in $\bm{10^{18}}$. This milestone will enable a second revolution of new timing applications such as relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests on physics beyond the Standard Model. Here, we describe the development and operation of two optical lattice clocks, both utilizing spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of $\bm{1.6\times 10^{-18}}$ after only $\bm{7}$ hours of averaging

Reflections on the Ethical Content of the IT Honours Program Project Module

Part 4: Syllabus DesignInternational audienceHonours programs in South African universities must include a research project module. There are external pressures from professional bodies and government that influences the nature of the project module. This paper presents a reflection on the process of managing the project module at a South African university taking into account internal and external demands. The focus for this paper is on the ethical content of the projects. Examples of projects are presented after which the ethical awareness of the students is discussed. Not all projects have ethical, legal or social issues, however ethical aspects need to be reflected upon and awareness of these issues is essential during the planning of the project. The awareness that students have on ethical, social and legal issues is investigated in this paper

The effect of cancer stage and treatment modality on quality of life in oropharyngeal cancer

Objectives/Hypothesis To examine changes in health-related quality of life among oropharyngeal cancer patients by stages and across treatment types among advanced cancer patients. Study Design Individual prospective cohort study. Methods All newly diagnosed patients with oropharyngeal cancer treated with curative intent were routinely assessed. The European Organization for Research and Treatment of Cancer (EORTC) both the Main Module quality-of-life questionnaire (QLQ-C30) and the Head and Neck Cancer (HNC) Module (QLQ-H&N35) were administered at diagnosis and 3, 6, and 12 months thereafter. Complete case analysis was used following assessment of missing data. The proportion of patients with clinically significant deterioration (changes of ≥10 points) from baseline were calculated for each follow-up time point and compared by stage (I/II vs. III/IV) and then treatment type (chemotherapy and radiotherapy [CRT] vs. surgery and postoperative radiotherapy [S&PORT]). Results Deterioration in most domains was most frequent for stage III/IV patients at 3 months (both modules), whereas stage I/II patients experienced this at 6 months (QLQ-C30) and 12 months (H&N35). Among stage III/IV patients, this happened at all time points for S&PORT patients (QLQ-C30) versus 12 months for CRT patients (H&N35). The number of patients reporting deterioration was lower for most domains at 12 months compared to earlier periods, although dry mouth remained a problem for most patients (60%-85% across treatment/stage groups). Conclusions Our preliminary findings suggest that general and disease-specific deterioration is of most concern for stage I/II patients at 6 and 12 months and at 3 months for advanced cancer patients. For stage III/IV patients receiving S&PORT, general deterioration remains a problem after diagnosis, whereas for CRT patients, disease-specific deterioration is of most concern at 12 months. Level of Evidence 4. Laryngoscope, 124:151-158, 201

Object Segmentation and Ground Truth in 3D Embryonic Imaging

Many questions in developmental biology depend on measuring the position and movement of individual cells within developing embryos. Yet, tools that provide this data are often challenged by high cell density and their accuracy is difficult to measure. Here, we present a three-step procedure to address this problem. Step one is a novel segmentation algorithm based on image derivatives that, in combination with selective post-processing, reliably and automatically segments cell nuclei from images of densely packed tissue. Step two is a quantitative validation using synthetic images to ascertain the efficiency of the algorithm with respect to signal-to-noise ratio and object density. Finally, we propose an original method to generate reliable and experimentally faithful ground truth datasets: Sparse-dense dual-labeled embryo chimeras are used to unambiguously measure segmentation errors within experimental data. Together, the three steps outlined here establish a robust, iterative procedure to fine-tune image analysis algorithms and microscopy settings associated with embryonic 3D image data sets