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Publication Metadata only “O/F shift” in hybrid rockets(American Institute of Aeronautics and Astronautics, 2014) Toson, Elena; Evans, Brian; Department of Mechanical Engineering; Karabeyoğlu, Mustafa Arif; Faculty Member; Department of Mechanical Engineering; College of Engineering; 114595For most hybrid rocket systems, oxidizer to fuel ratio (O/F) changes over time due to 1) natural growth of the fuel port diameter and 2) oxidizer flow rate variations, if throttling is employed. This phenomenon, which is referred to as “O/F shift”, leads to a reduction in motor performance. Note that liquid or solid rocket motors are not subject to temporal O/F variations, which is wrongfully considered as one of the most critical disadvantages of hybrid rockets. In this paper, the effect of “O/F shift” is quantified for hybrid rocket motors. Analytical formulas for the temporal O/F variation and the overall c* efficiency drop associated with the variation has been derived for single circular port motors. It has been shown that for a typical motor, c* efficiency drop due to O/F variation is well below 0.2%, a value which is too small to be measured in an actual motor test. It is also shown that for a wagon wheel type multiport configuration (with triangular ports), efficiency drop is significantly worse than the single circular port case. Even for the multiport systems, the shift does not have a controlling effect on the overall efficiency of the motor. A number of strategies have been outlined to control the adverse effects of O/F variation in a hybrid rocket. For a single circular port design with limited throttling, no mitigation is required. For systems with deep throttling requirements, aft oxidizer injection seems like a viable strategy to retain a high level of overall efficiency.Publication Metadata only “Tell Me Your Story, I’ll Tell You What Makes It Meaningful’’: characterization of meaningful social interactions between intercultural strangers and design considerations for promoting them(Springer Science and Business Media Deutschland GmbH, 2021) N/A; Department of Sociology; Department of Media and Visual Arts; Department of Media and Visual Arts; Ramirez Galleguillos, María Laura; Eloiriachi, Aya; Serdar, Büşra; Coşkun, Aykut; PhD Student; Undergraduate Student; Master Student; Faculty Member; Department of Sociology; Department of Media and Visual Arts; Graduate School of Social Sciences and Humanities; College of Social Sciences and Humanities; College of Social Sciences and Humanities; College of Social Sciences and Humanities; N/A; N/A; N/A; 165306Positive meaningful interactions are encounters that promote positive attitudes and learning about others, which are needed to develop healthy social fabrics and cultural diversity. However, individuals tend to interact more with people like themselves often avoiding encounters with others that seem to be different, for example, with intercultural strangers. Though previous HCI work has been concerned with exploring meaningful experiences with products and technologies as a way of promoting product attachment, the field lacks studies exploring how design could facilitate intercultural MSI. Designing interventions to support intercultural MSI requires i) understanding what characteristics make these interactions meaningful and ii) how these characteristics can be addressed through design. In this study, we contribute to the literature by producing knowledge on these aspects. Based on an analysis of 56 real-life stories about intercultural MSI and an idea generation session with designers, we characterize intercultural MSI with four dimensions (outcomes, feelings, context, and elements) and we identify four design considerations to be taken into account when designing interventions to support intercultural MSI. Hence, our contribution is to formulate this knowledge while highlighting how the characteristics and perceptions of intercultural MSI can be applied to design new technologies that promote this kind of interaction. © 2021, Springer Nature Switzerland AG.Publication Metadata only “Working from home”: government initiatives to promote returning to Latvia amidst the Covid-19 pandemic(Springer, 2021) N/A; Lace, Agnese; PhD Student; Graduate School of Social Sciences; N/ADuring the early stages of the Covid-19 pandemic, the government of Latvia not only implemented a rather successful evidence-based approach to policy making regarding limiting the effects of the spread of the disease, but also designed a communication campaign ‘Ahead of the Curve’ to highlight this success and encourage diaspora members and others to consider Latvia as the place to settle down while ‘working from home’. In parallel, a return migrant organization initiated a debate in the Diaspora Consultative Council on the need for a clear approach to attracting digital nomads. This paper discusses the implications of these policy developments on the nature of Latvia's diaspora policy and return migration policy. The analysis explores the content of the campaign and policy debates to find the frames used to describe this new reality. It highlights the dependency of diaspora and return migration policy making on perceived economic growth or stability by policymakers.Publication Metadata only 10-NJ multipass-cavity femtosecond CR3+: LiCAF laser pumped by low-power single-mode diodes(Optical Society of America, 2009) Kärtner, Franz X.; Fujimoto, James G.; Demirbaş, Ümit; Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851We report on the generation of 9.9-nJ, 95-fs pulses at a repetition rate of 9.58 MHz from a multipass-cavity Cr3+:LiCAF laser pumped by single-mode diodes with a total absorbed pump power of only 540 mW.Publication Metadata only 16.4: the optics of an autostereoscopic multiview display(SID, 2010) Baghsiahi, Hadi; Selviah, David R.; Willman, Eero; Fernández, Anibal; Day, Sally E.; Surman, Phil A.; N/A; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Erden, Erdem; Chellappan, Kishore Velichappattu; Ürey, Hakan; Master Student; Researcher; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 8579An autostereoscopic head-tracked back projection display that uses an RGB laser illumination source and a fast light engine is described. Images are horizontally scanned columns controlled by a spatial light modulator that directs two or more images in the directions of the apposite viewers 'eyes.Publication Open Access 2D hybrid meshes for direct simulation Monte Carlo solvers(Institute of Physics (IOP) Publishing, 2013) Şengil, Nevsan; Department of Mathematics; Şengil, Uluç; Master Student; Department of Mathematics; College of SciencesThe efficiency of the direct simulation Monte Carlo (DSMC) method decreases considerably if gas is not rarefied. In order to extend the application range of the DSMC method towards non-rarefied gas regimes, the computational efficiency of the DSMC method should be increased further. One of the most time consuming parts of the DSMC method is to determine which DSMC molecules are in close proximity. If this information is calculated quickly, the efficiency of the DSMC method will be increased. Although some meshless methods are proposed, mostly structured or non-structured meshes are used to obtain this information. The simplest DSMC solvers are limited with the structured meshes. In these types of solvers, molecule indexing according to the positions can be handled very fast using simple arithmetic operations. But structured meshes are geometry dependent. Complicated geometries require the use of unstructured meshes. In this case, DSMC molecules are traced cell-by-cell. Different cell-by-cell tracing techniques exist. But, these techniques require complicated trigonometric operations or search algorithms. Both techniques are computationally expensive. In this study, a hybrid mesh structure is proposed. Hybrid meshes are both less dependent on the geometry like unstructured meshes and computationally efficient like structured meshes.Publication Metadata only 2D scanning MEMS stage integrated with microlens arrays for high-resolution beam steering(IEEE, 2009) Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; Ürey, Hakan; Gökçe, Sertan Kutal; Holmstrom, Sven; Arslan, Aslıhan; Ataman, Çağlar; Seren, Hüseyin Rahmi; Faculty Member; Master Student; Researcher; Master Student; PhD Student; Master Student; Other; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; 8579; N/A; N/A; N/A; N/A; N/A; N/AA novel MEMS stage using one set of comb fingers, capable of 2-axis motion is designed and developed. With an integrated 1.1mm square microlens-array it deflects 40um in-plane at 60V and 95um out-of-plane at 100V.Publication Metadata only 300 GHz broadband transceiver design for low-THz band wireless communications in indoor internet of things(Ieee, 2017) N/A; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Khalid, Nabil; Abbasi, Naveed Ahmed; Akan, Özgür Barış; Researcher; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 6647This paper presents the architectural design of a 300 GHz transceiver system that can be used to explore the high speed communication opportunities offered by the Terahertz (THz) band for advanced applications of Internet-of-Things (IoT). We use low cost industry ready components to prepare a fully customizable THz band communication system that provides a bandwidth of 20 GHz that is easily extendable up to 40 GHz. Component parameters arc carefully observed and used in simulations to predict the system performance while the compatibility of different components is ensured to produce a reliable design. Our results show that the receiver provides a conversion gain of 51 dB with a noise figure (NE) of 9.56 dB to achieve a data rate of 90.31 Gbps at an operation range of 2 meters, which is suitable for high speed indoor IoT nodes. The flexible design of the transceiver provides groundwork for further research efforts in 5G IoT applications and pushing boundaries of throughputs to the order of terabits per second (Tbps).Publication Metadata only 3D articulated shape segmentation using motion information(Institute of Electrical and Electronics Engineers (IEEE), 2010) Department of Computer Engineering; N/A; Yemez, Yücel; Kalafatlar, Emre; Faculty Member; Master Student; Department of Computer Engineering; College of Engineering; Graduate School of Sciences and Engineering; 107907; N/AWe present a method for segmentation of articulated 3D shapes by incorporating the motion information obtained from time-varying models. We assume that the articulated shape is given in the form of a mesh sequence with fixed connectivity so that the inter-frame vertex correspondences, hence the vertex movements, are known a priori. We use different postures of an articulated shape in multiple frames to constitute an affinity matrix which encodes both temporal and spatial similarities between surface points. The shape is then decomposed into segments in spectral domain based on the affinity matrix using a standard K-means clustering algorithm. The performance of the proposed segmentation method is demonstrated on the mesh sequence of a human actor.Publication Metadata only 3D display dependent quality evaluation and rate allocation using scalable video coding(Ieee, 2009) N/A; N/A; Department of Electrical and Electronics Engineering; Saygılı, Görkem; Gürler, Cihat Göktuğ; Tekalp, Ahmet Murat; Master Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 26207It is well known that the human visual system can perceive high frequency content in 3D, even if that information is present in only one of the views. Then, the best 3D perception quality may be achieved by allocating the rates of the reference (right) and auxiliary (left) views asymmetrically. However the question of whether the rate reduction for the auxiliary view should be achieved by spatial resolution reduction (coding a downsampled version of the video followed by upsampling after decoding) or quality (QP) reduction is an open issue. This paper shows that which approach should be preferred depends on the 3D display technology used at the receiver. Subjective tests indicate that users prefer lower quality (larger QP) coding of the auxiliary view over lower resolution coding if a "full spatial resolution" 3D display technology (such as polarized projection) is employed. On the other hand, users prefer lower resolution coding of the auxiliary view over lower quality coding if a "reduced spatial resolution" 3D display technology (such as parallax barrier - autostereoscopic) is used. Therefore, we conclude that for 3D IPTV services, while receiving full quality/resolution reference view, users should subscribe to differently scaled versions of the auxiliary view depending on their 3D display technology. We also propose an objective 3D video quality measure that takes the 3D display technology into account.