Lumped-parameter models for low-temperature geothermal fields and their application

The behavior of low-temperature geothermal reservoirs under exploitation is simulated using analytical lumped-parameter models. These models consider the effects of fluid production and reinjection, as well as natural recharge, on the pressures (or water levels) of low-temperature, liquid-dominated geothermal systems. The computed responses for constant production/injection flow rates are given in the form of analytical expressions. Variable flow rate cases are modeled, based on the Duhamel's principle. Reservoir parameters are obtained by applying a weighted nonlinear least-squares estimation technique in which measured field data are history matched to the corresponding model response. By using history-matched models, the future performance of the reservoir can be predicted for different production/injection scenarios in order to optimize the management of a given geothermal system.We demonstrate the applicability of the models by simulating measured data from the Laugarnes geothermal field in Iceland, and the Balcova–Narlidere field in Turkey.     

Drilling thick fabric woven CFRP laminates with double point angle drills

Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates.     

Highly-Directional,Highly-Efficient Solution-Processed Light-Emitting Diodes of All-Face-Down Oriented Colloidal Quantum Well Self-Assembly

Semiconductor colloidal quantum wells (CQWs) provide anisotropic emission behavior originating from their anisotropic optical transition dipole moments (TDMs). Here, solution-processed colloidal quantum well light-emitting diodes (CQW-LEDs) of a single all-face-down oriented self-assembled monolayer (SAM) film of CQWs that collectively enable a supreme level of IP TDMs at 92% in the ensemble emission are shown. This significantly enhances the outcoupling efficiency from 22% (of standard randomly-oriented emitters) to 34% (of face-down oriented emitters) in the LED. As a result, the external quantum efficiency reaches a record high level of 18.1% for the solution-processed type of CQW-LEDs, putting their efficiency performance on par with the hybrid organic-inorganic evaporation-based CQW-LEDs and all other best solution-processed LEDs. This SAM-CQW-LED architecture allows for a high maximum brightness of 19,800 cd m⁻² with a long operational lifetime of 247 h at 100 cd m⁻² as well as a stable saturated deep-red emission (651 nm) with a low turn-on voltage of 1.7 eV at a current density of 1 mA cm⁻² and a high J₉₀ of 99.58 mA cm⁻². These findings indicate the effectiveness of oriented self-assembly of CQWs as an electrically-driven emissive layer in improving outcoupling and external quantum efficiencies in the CQW-LEDs.     

Melt Electrospinning Writing of Highly Ordered Large Volume Scaffold Architectures

The additive manufacturing of highly ordered, micrometer‐scale scaffolds is at the forefront of tissue engineering and regenerative medicine research. The fabrication of scaffolds for the regeneration of larger tissue volumes, in particular, remains a major challenge. A technology at the convergence of additive manufacturing and electrospinning–melt electrospinning writing (MEW)–is also limited in thickness/volume due to the accumulation of excess charge from the deposited material repelling and hence, distorting scaffold architectures. The underlying physical principles are studied that constrain MEW of thick, large volume scaffolds. Through computational modeling, numerical values variable working distances are established respectively, which maintain the electrostatic force at a constant level during the printing process. Based on the computational simulations, three voltage profiles are applied to determine the maximum height (exceeding 7 mm) of a highly ordered large volume scaffold. These thick MEW scaffolds have fully interconnected pores and allow cells to migrate and proliferate. To the best of the authors knowledge, this is the first study to report that z‐axis adjustment and increasing the voltage during the MEW process allows for the fabrication of high‐volume scaffolds with uniform morphologies and fiber diameters.     

An experimental study on the conversion between IFPUG and COSMIC functional size measurement units

The adoption of functional size measurement (FSM) methods in software organizations is growing. In particular, special attention is being paid to the COSMIC method, because of its novelties against 1st generation FSM methods such as IFPUG FPA. One of the main problems facing organizations wanting to use COSMIC is how to properly convert the software functional size of the projects in their portfolio measured by the previously adopted FSM method to the size measured by the new method.The objective of this paper is to find a sound mathematical basis for converting an IFPUG measurement to a COSMIC measurement.In the light of previously published researches, parallel measurements were performed to establish three new datasets (respectively composed by 21, 14 and 35 data points) and verified by an expert measurer, certified on both techniques. In order to obtain a more precise solution, the search for a mathematical relationship has been run using new nonlinear equation types.Results from the analysis confirmed an approximated conversion factor of 1:1, within a range between 0.9 and 1.1, but moving from a larger number of data points analyzed then in past studies.These results can be very useful for those companies starting to use their benchmarking databases populated in IFPUG FP units to projects measured in COSMIC FP.     

Realization of a VCO for WLAN applications using 0.35 μm‐siGe BICMOS technology

In this article, a 4.5–5.8 GHz, ?G_m LC voltage controlled oscillator (VCO) for IEEE 802.11a standard is presented. The circuit is designed with Austria MicroSystems 0.35 μm SiGe BiCMOS process that includes high‐speed SiGe heterojunction bipolar transistors (HBTs). According to measurement results, phase noise is ?102.3 dBc/Hz at 1 MHz offset from 5 GHz carrier frequency. A linear, 1300 MHz tuning range is obtained utilizing accumulation‐mode varactors. Phase noise is relatively low because of the advantage of differential tuning concept. Output power of the fundamental frequency changes between ?1.6 and 0.9 dBm depending on the tuning voltage. Average second and third harmonic levels are ?25 and ?41 dBm, respectively. The circuit draws 14 mA DC current from 3.3 V supply including buffer circuits leading to a total power dissipation of 46.2 mW. The prototype VCO occupies an area of 0.6 mm² on Si substrate, including DC and RF pads. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Shortest hop multipath algorithm for wireless sensor networks

Shortest hop or distance path is one of the most common methods used for relaying messages in a wide variety of networks. It provides an efficient message relaying to destination in terms of energy and time. There are many algorithms for constructing shortest hop or distance path. However, according to our knowledge, no algorithm for constructing a shortest hop multipath for wireless sensor networks (WSNs) has yet been proposed in the literature. In this paper, we propose a novel distributed shortest hop multipath algorithm for WSNs in order to generate energy efficient paths for data dissemination or routing. The proposed algorithm generates shortest hop braided multipath to be used for fault-tolerance or load-balancing. It guarantees the BFS tree and generates near optimal paths in O(V.D+V) message complexity and O(D²) time complexity regarding the communication costs towards the sink after termination of algorithm.