Novel bifunctional double-layer catalysts for application in microreactors for direct DME synthesis

This thesis describes experimental research toward the selective and efficient DME production from syngas in microstructured reactors using bifunctional catalysts. Two catalysts, Cu/ZnO/Al2O3 and ZSM-5, catalyze syngas conversion to methanol and methanol conversion to DME, respectively. The catalysts were prepared and successfully introduced in microchannel reactor for direct DME synthesis

Essays on incomplete market and aggregate fluctuation

This thesis consists of three chapters on incomplete markets and aggregate fluctuations. Chapter 1 examines the impact of frictional financial intermediation in a heterogeneous agents new Keynesian (HANK) model. An incentive problem restricts banking sector leverage and gives rise to an equilibrium spread between the returns on savings and debt. The interest rate spread that impacts on the wealth distribution and movements in it subjects borrowers and savers to different intertemporal prices. The model generates a financial accelerator that is larger than in a representative agent setting, derives mainly from consumption rather than investment, and works through a countercyclical interest rate spread. Credit policy can mute this mechanism while stricter regulation of banking sector leverage inhibits households' ability to smooth consumption in response to idiosyncratic risk. Thus, although leverage restrictions stabilize at the aggregate level, we find substantial welfare costs. In Chapter 2, we show that it is optimal to pay more attention to employment stabilization when both a heterogeneity of households and the matching friction exist even though the price adjustment cost is substantial. This implies that the optimal policy needs to strike a balance between price adjustment and employment stability rather than to pursue complete price stabilization in order to make the poor better off. In addition, we study the effect of a time-varying transfer rule on the volatility of inflation and employment with respect to a volatile job separation shock. We find that the Ramsey planner pays less attention to employment stabilization when a countercyclical transfer rule is in operation. Chapter 3 analyzes the transmission mechanism of monetary policy to consumption in New Keynesian models with heterogeneous households. We show that in these models the countercyclical nature of profits, empirically false, plays a large role in amplifying the intertemporal substitution channel. On the other hand, the interest rate exposure channel, empirically large, plays a small role. We suggest expanding the role of the interest rate exposure channel, while dampening the amplification effect of countercyclical profits, is of primary quantitative importance in future work

The Adoption of Collaborative Robots toward Ubiquitous Diffusion: A Research Agenda

This paper proposes a framework to study the adoption of collaborative robots (co-robots or cobots) as an innovation and their diffusion into the larger population. Collaborative robots are only starting to appear in our society, yet challenges such as fear and distrust may impede their further adoption. This paper discusses the foundational work necessary to understand collaborative robot adoption and the core elements to achieve ubiquitous diffusion, with a focus on human users and the communication processes

Minimally Invasive Lumbar Spinal Decompression in Elderly Patients with Magnetic Resonance Imaging Morphological Analysis

Study DesignCase-control study.PurposeIn this study, we aimed to investigate clinical outcomes and morphological features in elderly patients with lumbar spinal stenosis (LSS) who were treated by minimally invasive surgery (MIS) unilateral laminectomy for bilateral decompression (ULBD) using a tubular retractor.Overview of LiteratureNumerous methods using imaging have been attempted to describe the severity of spinal stenosis. But the relationship between clinical symptoms and radiological features remains debatable.ObjectiveIn this study, we aimed to investigate clinical outcomes and morphological features in elderly patients with LSS who were treated by MIS-ULBD.MethodsWe methodically assessed 85 consecutive patients aged >65 years who were treated for LSS. The patients were retrospectively analyzed in two age groups: 66–75 years (group 1) and >75 years (group 2). Clinical outcomes were assessed using the Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and the modified MacNab criteria. Outcome parameters were compared between the groups at the 1-year follow-up. Core radiologic parameters for central and lateral stenosis were analyzed and clinical findings of the groups were compared.ResultsAt the 1-year follow-up, patients in both groups 1 and 2 demonstrated significant improvement in their VAS and ODI scores. All clinical outcomes, except postoperative ODI, were not significantly difference between the groups. In addition, no significant difference was noted in the preoperative radiological parameters between the groups. There was no statistically significant correlation between radiological parameters and clinical symptoms or their outcomes. Moreover, no differences were noted in perioperative adverse events and in the need for repeat surgery at follow-ups between the groups.ConclusionsMIS-ULBD by tubular approach is a safe and effective treatment option for elderly patients with LSS. Clinical outcomes in patients with LSS and aged >75 years were comparable with those in patients with LSS and aged 66–75 years. Moreover, we did not find any correlation between radiological parameters and clinical outcomes in either of the two patient groups

Effects of rotor???rotor interaction on the wake characteristics of twin rotors in axial descent

In this study, the effects of rotor???rotor interaction on wake characteristics were investigated experimentally for a twin-rotor configuration in axial descent. The wake velocities were measured at descent rates (descent speed/induced velocity at the rotor disk during hover) from 0.87 to 1.52, and the rotor???rotor interaction strength was controlled by adjusting the distance between the rotor tips. As the descent rate increased, the wake of the isolated rotor gradually entered the vortex ring state (VRS), where the flow established an extensive recirculation zone. Correlation analysis was performed to distinguish the rotor wake between tubular and VRS topologies. The flow states for the isolated rotor were classified into pre-VRS, incipient VRS, and fully developed VRS, depending on the probability of vortex ring formation. The results reveal that the effects of rotor???rotor interaction on the wake characteristics of twin rotors differ depending on the descent rate, distance between rotor tips, and wake region. In the outer region, the flow state of the rotor wake remains consistent with that of the isolated rotor, irrespective of the distance between rotor tips. Conversely, the strong rotor???rotor interaction changes the flow state in the inner region by disrupting the vortex ring structure, intensifying the wake asymmetry about the rotational axis. The thrust measurements show that under the VRS, as the two rotors get closer, the thrust coefficient increases until vortex ring disruption occurs, and then decreases after the vortex ring is disrupted

Effects of Rotor-Rotor Interaction on the Wake Structure and Thrust Generation of a Quadrotor Unmanned Aerial Vehicle

In this paper, the effects of rotor-rotor interaction on the wake structure and thrust generation of a quadrotor unmanned aerial vehicle (UAV) are experimentally investigated in the rotor tip Reynolds number range of 34000 ??? 54000. The interaction strength is manipulated by varying the number of rotating rotors and the normalized rotor separation distance. A stronger rotor-rotor interaction places the inner tip vortices between rotors closer to each other, forming an upflow region through vortex pairing and intensifying the turbulence intensity between rotors. To comprehensively evaluate the effect of interaction on the wake structure, we propose a modified Landgrebe???s model that accurately describes the wake boundary of UAV, given the number of rotating rotors and the normalized rotor separation distance. The wake analysis based on the model shows that the stronger the rotor-rotor interaction, the less the wake contracts and the closer the vena contracta moves to the rotor-tip path plane. The momentum theory combined with the modified Landgrebe???s model shows that the loss of axial momentum transfer due to the wake inclination is insufficient to account for the thrust loss caused by the rotor-rotor interaction. This paper shows that the shift of the inner tip vortex away from the rotational axis and the corresponding increase of induced axial velocity followed by a decrease in the local effective angle of attack is another important mechanism for the thrust loss