Systolic Array Implementations With Reduced Compute Time.

The goal of the research is the establishment of a formal methodology to develop computational structures more suitable for the changing nature of real-time signal processing and control applications. A major effort is devoted to the following question: Given a systolic array designed to execute a particular algorithm, what other algorithms can be executed on the same array? One approach for answering this question is based on a general model of array operations using graph-theoretic techniques. As a result, a systematic procedure is introduced that models array operations as a function of the compute cycle. As a consequence of the analysis, the dissertation develops the concept of fast algorithm realizations. This concept characterizes specific realizations that can be evaluated in a reduced number of cycles. It restricts the operations to remain in the same class but with reduced execution time. The concept takes advantage of the data dependencies of the algorithm at hand. This feature allows the modification of existing structures by reordering the input data. Applications of the principle allows optimum time band and triangular matrix product on arrays designed for dense matrices. A second approach for analyzing the families of algorithms implementable in an array, is based on the concept of array time constrained operation. The principle uses the number of compute cycle as an additional degree of freedom to expand the class of transformations generated by a single array. A mathematical approach, based on concepts from multilinear algebra, is introduced to model the recursive transformations implemented in linear arrays at each compute cycle. The proposed representation is general enough to encompass a large class of signal processing and control applications. A complete analytical model of the linear maps implementable by the array at each compute cycle is developed. The proposed methodology results in arrays that are more adaptable to the changing nature of operations. Lessons learned from analyzing existing arrays are used to design smart arrays for special algorithm realizations. Applications of the methodology include the design of flexible time structures and the ability to decompose a full size array into subarrays implementing smaller size problems

Experimental diagnostics and modeling of inductive phenomena at low frequencies in impedance spectra of proton exchange membrane fuel cells

Representation of fuel cell processes by equivalent circuit models, involving resistance and capacitance elements representing activation losses on both anode and cathode in series with resistance representing ohmic losses, cannot capture and explain the inductive loop that may show up at low frequencies in Nyquist diagram representation of the electrochemical impedance spectra. In an attempt to explain the cause of the low-frequency inductive loop and correlate it with the processes within the fuel cell electrodes, a novel equivalent circuit model of a Proton Exchange Membrane (PEM) fuel cell has been proposed and experimentally verified here in detail. The model takes into account both the anode and the cathode, and has an additional resonant loop on each side, comprising of a resistance, capacitance and inductance in parallel representing the processes within the catalyst layer. Using these additional circuit elements, more accurate and better fits to experimental impedance data in the wide frequency range at different current densities, cell temperatures, humidity of gases, air flow stoichiometries and backpressures were obtained

Numerical study on the formability of metallic bipolar plates for Proton Exchange Membrane (PEM) fuel cells

Thin stamped bipolar plates (BPPs) are viewed as promising alternatives to traditional graphite BPPs in proton exchange membrane fuel cells. Metallic BPPs provide good thermal/electrical conductivity and exhibit high mechanical strength, to support the loads within the stack. However, BPPs manufactured by stamping processes are prone to defects. In this study, the effect of the tool’s geometry on the thin sheet formability is investigated through finite element simulation. Despite the broad variety of flow field designs, most of BPPs comprise two representative zones. Hence, in order to reduce the computational cost, the finite element analysis is restricted to these two zones, where the deformation induced by the stamping tools is investigated. The channel/rib width, the punch/die fillet radii, and the channel depth are the parameters studied. The analysis is conducted for a stainless steel SS304 with a thickness of 0.15 mm. The results show that the maximum value of thinning occurs always in the U-bend channel section, specifically in the fillet radius of the die closest to the axis of revolution.This research was funded by the Portuguese Foundation for Science and Technology (FCT) under projects PTDC/EMS-TEC/0702/2014 (POCI-01-0145-FEDER-016779) and PTDC/EMS-TEC/6400/2014 (POCI-01-0145-FEDER-016876) by UE/FEDER through the program COMPETE 2020. The support under the project MATIS (CENTRO-01-0145-FEDER-000014) is also acknowledged

Evaluation of leaching behavior and immobilization of zinc in cement-based solidified products

This study has examined leaching behavior of monolithic stabilized/solidified products contaminated with zinc by performing modified dynamic leaching test. The effectiveness of cement-based stabilization/solidification treatment was evaluated by determining the cumulative release of Zn and diffusion coefficients, De. The experimental results indicated that the cumulative release of Zn decreases as the addition of binder increases. The values of the Zn diffusion coefficients for all samples ranged from 1.210-8 to 1.1610-12 cm2 s-1. The samples with higher amounts of binder had lower De values. The test results showed that cement-based stabilization/solidification treatment was effective in immobilization of electroplating sludge and waste zeolite. A model developed by de Groot and van der Sloot was used to clarify the controlling mechanisms. The controlling leaching mechanism was found to be diffusion for samples with small amounts of waste material, and dissolution for higher waste contents

Techno-economic analysis of PEM fuel cells role in photovoltaic-based systems for the remote base stations

Expansion of telecommunication networks even to the most remote areas where connection to the utility grid could never be justified, especially in touristic regions, has led to the increasing need for stand-alone power systems. In Adriatic coastal area employment of hybrid photovoltaic-based systems is straightforward due to high sun potential. Inherent intermittent nature of renewable sources is especially not compatible with telecommunication system who require uninterrupted power supply. This leads to the need of not only energy storage, but also a "back up" solution in the case of primary system failure. Emphasis is put on the system reliability and simplicity while system price is not necessarily top priority. Usual approach of using diesel generators as a "back up" has been challenged by the introduction of PEM fuel cells. Even with hydrogen technologies market development still lagging behind some comparable advantages such as high energy conversion efficiency, silent operation and no emissions make PEM fuel cells a legitimate candidate for replacing traditional oil burning generators. Technoeconomic analysis of various stand-alone power systems for the remote base station on an Adriatic island is made. At the moment, levelized cost of electricity point of view still gives slight advantage to the diesel generators. Long term reliability of PEM fuel cells system still needs to be examined in practice, as this combined with pro-environmental characteristics of fuel cells can make the difference especially in pristine and protected areas. Furthermore, uncertain petroleum market and fast developing hydrogen technology market could reverse this trend in the near future.Peer ReviewedPostprint (author’s final draft

Effects of Mud from a Zinc-plating Plant and Zeolite Saturated with Zinc on Portland Cement Hydration and Properties of Hardened Cement Pastes

This work investigates the impact of mud from a zinc-plating plant and zeolite saturated with zinc on early hydration processes of ordinary Portland cement. During the first 48 hours of hydration, the addition of mud significantly affects the cement hydration kinetics. The partial replacement of cement with zeolite saturated with zinc ions, reduces the negative impact of mud on the hydration processes. Samples with the additions showed lower compressive strength than the sample without additions. With regard to the standard limits for this type of cement, mud shares are eligible up to 5 wt. % and a mixture of mud and saturated zeolite up to 10 wt. %

Optimalno korištenje energije sa socijalnog aspekta (Osvrt na esej Ivana Illicha Energy and Equity)

U eseju Energy and Equity Ivan Illich razrađuje tezu da svaki sustav, proces ili ljudska aktivnost raste ili se odvija do određenog praga nakon kojeg daljnji rast ili daljnje aktivnosti postaju kontraproduktivne. Illich ilustrira svoju tezu na primjeru transporta. Razvoj tehnike omogućuje sve veće brzine transportnih sredstava, no ljudi u prosjeku provode više vremena u transportu nego nekad. Dakle, brzina ne mora nužno značiti uštedu na vremenu. Upravo je brzina, a s tim povezana i potrošnja energije, ključan čimbenik koji čini transport socijalno destruktivnim jer izaziva društveno raslojavanje na one koji je mogu i ne mogu priuštiti. Budući da je stalan rast potrošnje energije nemoguć iz fizičkih, ekoloških i socijalnih razloga, Ivan Illich vidi budućnost čovječanstva u postindustrijskom društvu tehnološke zrelosti, oslobođenom obilja i ovisnosti o potrošnji

Primjena elektrokemijskog kompresora za recirkulaciju vodika u gorivnom članku

Elektrokemijski kompresor vodika, po dizajnu i izvedbi identičan gorivnom članku, se može koristiti za recirkulaciju neiskorištenog vodika s izlaza sklopa (svežnja) gorivnog članka natrag na njegov ulaz. Može se inkorporirati u sklop (svežanj) gorivnih članaka ili se može koristiti kao zasebna jedinica

Postharvest procedures and preservation technology of kiwifruit

Cilj ovog istraživanja je na temelju prikupljene relevantne literature proučiti postupke poslije berbe i tehnologiju čuvanja kivija. Odnosi se na skladištenje, bolesti, fiziološke poremećaje, transport, tretmane i sve ostale čimbenike koji utječu na kvalitetu ploda kivija nakon berbe i neposredno prije berbe, a mogu utjecati na kvalitetu tijekom skladištenja.Utvrđeno je kako je čuvanje na niskim temperaturama imalo značajan utjecaj na fizikalno-kemijska i nutritivna svojstva kivija čime se poboljšala kvaliteta, pojačala se čvrstoća, škrob i sadržaj topljive suhe tvari uslijed nižeg disanja i proizvodnje etilena, produžen je sami rok trajanja ploda bez ikakvih ozljeda ili promjene boje. Ustanovljeno je kako je antioksidativno djelovanje znatno smanjeno nakon četiri mjeseca hladnog skladištenja i kako hladno skladištenje ima negativan učinak na antioksidativno djelovanje u plodu kivija. Zaključeno je kako tretman kalcijem i HRW tretman čine plod prihvatljivijim zbog smanjenja brzine promjene boje i smanjenja truleži. Ustanovljeno je da salicilna kiselina ima pozitivan utjecaj na postotak gubitka težine ploda kivija i njegovo propadanje. Također je ustanovljeno kako tretman etilenom ubrzava proces zrenja, na što je kivi izrazito osjetljiv.The aim of this study is to investigate post-harvest procedures and kiwi fruit preservation techniques based on relevant literature collected. It relates to storage, diseases, physiological disorders, transport, treatments and all other factors affecting the quality of kiwi fruit after harvesting and just before harvesting that may affect the quality during storage. It was established that low temperature storage had a significant impact on the physico-chemical and nutritional properties of the kiwi fruit, which improved the quality, strengthened starch and starch content of dry solids due to lower breathing and ethylene production, extended the shelf-life itself without any injury or color change. It has been found that antioxidant activity has been significantly reduced after four months of cold storage and how cold storage has a negative effect on antioxidant activity in kiwi fruit. It was concluded that calcium treatment and HRW treatment make the fruit more acceptable by reducing the rate of change in color and decreasing rot. It has been found that salicylic acid has a positive effect on the percentage of loss of kiwi weight and its degradation. It has also been found that treating with ethylene accelerates the ripening process, which makes the kiwi extremely sensitive