66 research outputs found
KOMPARATIVNA ANALIZA UTJECAJA ZASIĆENJA VODOM NA IZGARANJE NAFTE U LEŽIŠTU
The amount of oil together with the water Originally in Place (OIP), makes up the liquid phase in heavy oil reservoir systems. This amount of liquid present in the pores of the reservoir system is known as liquid saturation, plays a vital role in improving oil recovery through In-Situ Combustion (ISC) process. The oil phase acts as fuel in generating thermal energy required for viscosity reduction and the water phase supports in the formation of an enlarged condensation zone that aids in higher mobility of the low viscous oil. A numerical investigation is carried out to study the role of water saturation on the performance of in-situ combustion in a heavy oil reservoir. A finite-difference based numerical model is developed and validated for water recovery. The model is then used to carry out the impact of liquid saturation on the performance of the ISC, as it plays a vital role in screening criteria for the selection of ISC. The numerical results projected a significant effect on the thermal and production profile during the process. A comparison between the effect of variation in water and oil saturations projected a significant increase in reservoir temperatures with increased water saturation than the oil saturation. The highest reservoir temperatures are observed at the maximum liquid (oil and water together) saturation. Further, the additional water drive provided by increased water saturation is observed to contribute to early production rates.Količina nafte zajedno s ukupnim rezervama vode (engl. originally in place, OIP) čini tekuću fazu ležišta teške nafte. Ova količina tekućine prisutna u porama ležišta poznata je kao zasićenje tekućom fazom, a ima vitalnu ulogu u povećanju iscrpka nafte pomoću procesa izgaranja nafte u ležištu (engl. in situ combustion, ISC). Naftna faza djeluje kao gorivo i stvara toplinsku energiju potrebnu za smanjenje viskoznosti, a vodena faza potiče stvaranje proširene kondenzacijske zone, koja doprinosi većoj mobilnosti nisko viskozne nafte. Provedeno je numeričko istraživanje utjecaja zasićenja vodom na in situ izgaranje u ležištu teške nafte. U sklopu istraživanja razvijen je i vrednovan numerički model za iscrpak vode temeljen na metodi konačnih razlika. Model je korišten za provođenje utjecaja zasićenja tekućinom na izvedbu ISC-a, s obzirom na to da ima vitalnu ulogu u odabiru kriterija za odabir odgovarajućega ISC-a. Dobiveni numerički rezultati upućuju na znatan učinak na toplinski i proizvodni profil tijekom procesa. Usporedba učinka varijacija u zasićenosti vodom i naftom pokazuje znatno povećanje temperature ležišta s povećanjem zasićenosti vodom u odnosu na vodu u slučaju povećanja zasićenosti naftom. Najviše temperature ležišta opažene su pri maksimalnoj zasićenosti tekućinom (nafta i voda zajedno). Nadalje, uočen je dodatni vodonaporni (hidraulični) režim, koji se, zbog povećanja zasićenosti vodom, javlja u ranoj fazi proizvodnje
Hybrid external cavity laser with an amorphous silicon-based photonic crystal cavity mirror
Funding: EU ERC-SG 337508 DANCER, EU H2020 Marie Skłodowska-Curie 713654 and SFI 18/TIDA/6128.The authors present results on the performance of a hybrid external cavity photonic crystal laser-comprising semiconductor optical amplifier, and a 2D photonic crystal cavity fabricated in low-temperature amorphous silicon. The authors demonstrate that lithographic control over amorphous silicon photonic crystal cavity-resonant wavelengths is possible, and that single-mode lasing at optical telecommunications wavelengths is possible on an amorphous silicon platform.Publisher PDFPeer reviewe
Extreme Mid-IR light control with SiC microstructures
In this thesis, we present our original theoretical investigations of SiC microstruc-tures for extreme light control in the Reststrahlen band of Silicon Carbide (SiC),
that occurs in the Mid-IR spectral regime. In this frequency regime, most of the
light will be reflected from bulk SiC, due to the extreme permittivity response of SiC.
However, we demonstrate that it is possible to control light to be absorbed or ultra
refracted within the microstructures constructed from SiC in the Reststrahlen band
of SiC. In particular, we show that this high reflective behaviour of SiC can be over-come via different mechanisms: by achieving a Photonic Crystal (PC) band-edge
reflectionless condition in a SiC terminated one-dimensional (1D)-PC, by tailoring
the effective phonon-polariton gap in SiC-based effective metamaterials, or by cou-pling to cavity modes in SiC structures made of rectangular-cross-section pillars.
Furthermore, we demonstrate that by varying the thickness of SiC layers and filling
ratio throughout SiC 1D-PC structures or by using SiC pillars of different size in a
pyramid arrangement, we can achieve a broad absorption bandwidth with the SiC
microstructures. This absorption control provides insight for the design of efficient
thermal emitters, which can be used in thermal conversion devices. Moreover, us-ing the concept of Bloch impedance, we find that translucent spectral regions can
exist in SiC 1D-PCs. This possibility is highly desirable for constructing optical
components in the Mid-IR spectrum where suitable bulk highly refractive materials
are rare. In addition, we also present a complete theory of propagation in lossy
1D-PCs, by systematically extending the comprehensive theory for lossless 1D-PCs.
Relying on this theory, we report superbending of light, beyond 90
0
in a judiciously
designed superprism constructed with a SiC 1D-PC. Since, the findings reported
in this thesis are in principle applicable to any polar material, we believe that our
work will inspire the design of a variety of absorptive/emissive and ultra-refractive
devices across the THz/Mid-IR spectrum.College of Engineering, Mathematics and
Physical Sciences (CEMPS), University of Exete
Broadband Mid-IR superabsorption with aperiodic polaritonic photonic crystals
We propose an approach for broadband near-perfect absorption with aperiodic-polaritonic photonic crystals (PCs) operating in the phononpolariton gap of the constituent material. In this frequency regime the bulk polaritonic materials are highly reflective due to the extreme permittivity values, and so their absorption capabilities are limited. However, we are able to achieve absorptance of more than 90% almost across the entire phonon-polariton gap of SiC with a SiC-air aperiodic one-dimensional(1D)-PC with angular bandwidth that covers the range of realistic diffraction-limited sources. We explore two types of aperiodic PC schemes, one in which the thickness of the SiC layer increases linearly, and one in which the filling ratio increases linearly throughout the structure. We find that the former scheme performs better in terms of exhibiting smoother spectra and employing less SiC material. On the other hand, the second scheme performs better in terms of the required total structure size. We analyze the principles underpinning the broadband absorption merit of our proposed designs, and determine that the key protagonists are the properties of the entry building block and the adiabaticity of the aperiodic sequencing scheme. Further investigation with derivative lamellar sequences,–resulting by interchanging or random positioning of the original building blocks–, underline the crucial importance of the building block arrangement in an increasing order of thickness. If we relax the requirement of near-perfect absorption, we show that an averaged absorption enhancement across the SiC phonon-polariton gap of ~10 can be achieved with much shorter designs of the order of two free-space wavelengths. Our findings suggest that our aperiodic polaritonic PC route can be promising to design broadband electromagnetic absorbers across the spectrum
Phonon-polaritonics: enabling powerful capabilities for infrared photonics
Here, we review the progress and most recent advances in phonon-polaritonics, an emerging and growing field that has brought about a range of powerful possibilities for mid- to far-infrared (IR) light. These extraordinary capabilities are enabled by the resonant coupling between the impinging light and the vibrations of the material lattice, known as phonon-polaritons (PhPs). These PhPs yield a characteristic optical response in certain materials, occurring within an IR spectral window known as the reststrahlen band. In particular, these materials transition in the reststrahlen band from a high-refractive-index behavior, to a near-perfect metal behavior, to a plasmonic behavior – typical of metals at optical frequencies. When anisotropic they may also possess unconventional photonic constitutive properties thought of as possible only with metamaterials. The recent surge in two-dimensional (2D) material research has also enabled PhP responses with atomically-thin materials. Such vast and extraordinary photonic responses can be utilized for a plethora of unusual effects for IR light. Examples include sub-diffraction surface wave guiding, artificial magnetism, exotic photonic dispersions, thermal emission enhancement, perfect absorption and enhanced near-field heat transfer. Finally, we discuss the tremendous potential impact of these IR functionalities for the advancement of IR sources and sensors, as well as for thermal management and THz-diagnostic imaging
Low-loss, compact, spot-size-converter based vertical couplers for photonic integrated circuits
Funding: (i) European Union Horizon H2020 Programme (H2020-ICT27-2015, COSMICC No. 688516). (ii) European Union Research Council (ERC) starting grant 337508.In recent years, the monolithic integration of new materials such as SiN, Ge and LiNbO3 on silicon (Si) has become important to the Si photonics community due to the possibility of combining the advantages of both material systems. However, efficient coupling between the two different layers is challenging. In this work, we present a spot size converter based on a two-tier taper structure to couple the optical mode adiabatically between Si and SiN. The fabricated devices show a coupling loss as low as 0.058 dB ± 0.01 dB per transition at 1525 nm. The low coupling loss between the Si to SiN, and vice versa, reveals that this interlayer transition occurs adiabatically for short taper lengths (<200 µm). The high refractive index contrast between the Si and SiN is overcome by matching the optical impedance. The proposed two-tier taper structure provides a new platform for optoelectronic integration and a route towards 3D photonic integrated circuits.PostprintPeer reviewe
Compact photonic-crystal superabsorbers from strongly absorbing media
Copyright © 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, Volume 114 (3), article 033504, and may be found at http://dx.doi.org/10.1063/1.4811521We present a route to near-perfect absorption in compact photonic-crystal (PC) structures constructed from strongly absorbing media that are typically highly reflective in bulk form. Our analysis suggests that the key underlying mechanism in such PC superabsorbers is the existence of a PC-band-edge reflectionless condition. Although the latter is by default uncharacteristic in photonic crystals, we propose here a clear recipe on how such condition can be met by tuning the structural characteristics of one-dimensional lossy PC structures. Based on this recipe, we constructed a realizable three-layer SiC- BaF2 -SiC PC operating within the Reststrahlen band of SiC. We demonstrate near-perfect absorption in this prototype of total thickness smaller than λ/3 , where more than 90% of the impinging light is absorbed by the top deep-subwavelength layer of thickness ∼λ/1100 . We believe our study will inspire new photonic-crystal-based designs for extreme absorption harnessing across the electromagnetic spectrum.University of Exete
Wavelet (valić) transformacija
Valić transformacija daje sofisticiranu vremensko-frekvencijsku analizu i koristi se u brojnim algoritmima u raznim područjima znanosti. Nakon teorijske pozadine i usporedbe sa frekvencijskom analizom, bit će prezentirane neke primjene u području sažimanja slike i uklanjanju šuma iz signala. Pojašnjen je i algoritam za prepoznavanje osoba pomoću očnog uzorka
Activated platelets induce MLKL-driven neutrophil necroptosis and release of neutrophil extracellular traps in venous thrombosis
Venous thromboembolic (VIE) disease, often manifesting as deep vein thrombosis or pulmonary embolism, involves clot formation consisting of blood cells and platelets locked in plasma protein and chromatin networks. The latter derives from neutrophil extracellular traps released by dying neutrophils;however, the molecular mechanisms of neutrophil death in VIE remains unknown. We speculated that mixed lineage kinase-like (MLKL)-driven neutrophil necroptosis contributes to VTE. Indeed, human inferior venous cava thrombus material stained positive for phosphorylated MLKL, the activated version of MLKL that executes necroptotic cell death. In mice, MLKL immunostaining showed co-localization of MLKL with citrullinated histone H3, a marker of neutrophil extracellular trap (NET) formation. These data provide indirect support for a role of MLKL-mediated necroptosis. As a functional proof, both the stabilizer of receptor-interacting protein kinase-1 (RIPK1) and necroptosis inhibitor necrostatin-1s as well as genetic deficiency of MLKL partially prevented clot formation upon inferior vena cava ligation in mice. In both experiments terminal deoxynucleotidyl transferase dUTP nick-end labeling, RIPK3, and citrullinated histone H3+ areas were markedly reduced within the remnant thrombus. In vitro, thrombin-activated platelets induced cell death and NET formation in human neutrophils, which was inhibited by necrostatin-1s treatment. Necrostatin-1s and necrosulfonamide also inhibited neutrophil-platelet aggregate formation induced by tumor necrosis factor-a but had no effect on platelet activation itself. We conclude that in VTE, activated platelets, and possibly other triggers, induce neutrophil necroptosis, a process contributing to clot formation by releasing chromatin in the extracellular space
- …