Master of Science

thesisNanopore-based devices have emerged as a single-molecule detection and analysis tool for a wide range of applications. Through electrophoretically driving DNA molecules across a nanosized pore, a lot of information can be received, including unfolding kinetics and DNA-protein interactions. This single-molecule method has the potential to sequence kilobase length DNA polymers without amplification or labeling, approaching "the third generation" genome sequencing for around $1000 within 24 hours. α-Hemolysin biological nanopores have the advantages of excellent stability, low-noise level, and precise site-directed mutagenesis for engineering this protein nanopore. The first work presented in this thesis established the current signal of the thymidine glycol lesion in DNA oligomers through an immobilization experiment. The thymidine glycol enantiomers were differentiated from each other by different current blockage levels. Also, the effect of bulky hydrophobic adducts to the current blockage was investigated. Secondly, the α-hemolysin nanopore was used to study the human telomere imotif and RET oncogene i-motif at a single-molecule level. In Chapter 3, it was demonstrated that the α-hemolysin nanopore can differentiate an i-motif form and single-strand DNA form at different pH values based on the same sequence. In addition, it shows potential to differentiate the folding topologies generated from the same DNA sequence

Experimental study of IERSFDs for vibration reduction of gear transmissions

Integral elastic ring squeeze film damper (IERSFD) is proposed to reduce and isolate the vibration of the gear transmissions. IERSFD offers the performance of a low radial stiffness and high squeeze film damping. This paper presents a mechanical model of an IERSFD elastic damping support and a single-degree-of-freedom vibration isolation system for the gear system. An open single-stage spur gear system was built to experimentally study the vibration characteristics of gear transmissions with rigid supports and with IERSFD elastic damping supports filled with damping fluids of different viscosities. The experimental results show that the IERSFD can effectively reduce the peak vibration acceleration of the gear shafts and can guarantee the smooth operation of the gear assembly over a range of speeds. This work shows that an IERSFD can reduce the shock and vibration of the gears’ meshing. It effectively attenuates vibration for most of the gears’ frequency components. Within a limited viscosity range, the vibration reduction is more effective with the higher-viscosity IERSFD damping fluids tested

Research on vibration reduction of multiple parallel gear shafts with ISFD

The vibration reduction methods for reducing the complexly coupled vibrations in multiple parallel gear shafts using integral squeeze film damper (ISFD) is studied in this paper. A multiple parallel gear system with three involute spur gears is built, and experiments are carried out to compare the vibrational characteristics of the gear system with rigid support and ISFD elastic damping support. The experimental results show that the ISFD support can reduce the shock vibrations of the multiple parallel gear shafts with excellent vibration attenuation characteristics due to damping. ISFD elastic damping support can inhibit the vibrations in a wide frequency range during the gear transmission, which can guarantee a smooth transition between multiple parallel gear shafts over a range of operating speeds

A Differential Private Method for Distributed Optimization in Directed Networks via State Decomposition

In this paper, we study the problem of consensus-based distributed optimization where a network of agents, abstracted as a directed graph, aims to minimize the sum of all agents' cost functions collaboratively. In existing distributed optimization approaches (Push-Pull/AB) for directed graphs, all agents exchange their states with neighbors to achieve the optimal solution with a constant stepsize, which may lead to the disclosure of sensitive and private information. For privacy preservation, we propose a novel state-decomposition based gradient tracking approach (SD-Push-Pull) for distributed optimzation over directed networks that preserves differential privacy, which is a strong notion that protects agents' privacy against an adversary with arbitrary auxiliary information. The main idea of the proposed approach is to decompose the gradient state of each agent into two sub-states. Only one substate is exchanged by the agent with its neighbours over time, and the other one is kept private. That is to say, only one substate is visible to an adversary, protecting the privacy from being leaked. It is proved that under certain decomposition principles, a bound for the sub-optimality of the proposed algorithm can be derived and the differential privacy is achieved simultaneously. Moreover, the trade-off between differential privacy and the optimization accuracy is also characterized. Finally, a numerical simulation is provided to illustrate the effectiveness of the proposed approach

Self-absorption in the solar transition region

Transient brightenings in the transition region of the Sun have been studied for decades and are usually related to magnetic reconnection. Recently, absorption features due to chromospheric lines have been identified in transition region emission lines raising the question of the thermal stratification during such reconnection events. We analyse data from the Interface Region Imaging Spectrograph (IRIS) in an emerging active region. Here the spectral profiles show clear self-absorption features in the transition region lines of Si\,{\sc{iv}}. While some indications existed that opacity effects might play some role in strong transition region lines, self-absorption has not been observed before. We show why previous instruments could not observe such self-absorption features, and discuss some implications of this observation for the corresponding structure of reconnection events in the atmosphere. Based on this we speculate that a range of phenomena, such as explosive events, blinkers or Ellerman bombs, are just different aspects of the same reconnection event occurring at different heights in the atmosphere.Comment: Accepted for publication in Ap

Experimental Study on Vibration Reduction Characteristics of Gear Shafts Based on ISFD Installation Position

A novel type of integral squeeze film damper (ISFD) is proposed to reduce and isolate vibration excitations of the gear system through bearing to the foundation. Four ISFD designs were tested experimentally with an open first-grade spur gear system. Vibration reduction characteristics were experimentally studied at different speeds for cases where ISFD elastic damping supports were simultaneously installed on the driving and driven shafts, installed on the driven shaft, or only installed on the driving shaft. Experimental results show that the ISFD elastic damping support can effectively reduce shock vibration of the gear system. Additionally, resonant modulation in gear shafts caused by meshing impact was significantly reduced. Different vibration amplitudes of gear shafts with ISFD installed only on driven or driving shafts were compared. Results indicated that vibration reduction is better when ISFD is only installed on the driven shaft than on the driving shaft

Some New Progress in the Experimental Measurements on Electrical Property of Main Minerals in the Upper Mantle at High Temperatures and High Pressures

In this chapter, we present the recent progress in the experimental studies of the electrical conductivity of dominant nominally anhydrous minerals in the upper mantle of the deep Earth interior, namely, olivine, pyroxene, and garnet. The influences from pressure, oxygen partial pressure, and anisotropic orientation on hydrous and anhydrous electrical conductivities of minerals and rocks have been already explored detailedly. There are two main electric conduction mechanisms in Fe-bearing mantle minerals, for example, small proton and proton hopping conditions, which are well distinguished by the magnitude of activation enthalpy at high temperature and high pressure. Likewise, the conduction mechanisms are efficiently characterized by these obtained positive and negative effects from the oxygen fugacity on electrical conductivities of corresponding dry and wet Fe-bearing silicate minerals at the regions of the upper mantle under conditions of different oxygen partial pressures. On the base of high-pressure laboratory-based conductivity measurements for these nominally anhydrous minerals (e.g., olivine, pyroxene, and garnet), the water content will be estimated within the depth range of the upper mantle. In comprehensive considerations of filed geophysical magnetotelluric results, the electrical conductivity measurements of dominant upper-mantle minerals can thoroughly disclose the distribution, storage state, and migration conduction in the deep Earth interior

Principle, Design and Future of Inchworm Type Piezoelectric Actuators

The inchworm type piezoelectric actuator is one novel actuator to ensure a large working stroke with high resolution which has attracted the continuous attentions from researchers all over the world. In this study, the motion principle of the inchworm type piezoelectric is discussed: the “walker” pattern, the “pusher” pattern and hybrid “walker-pusher” pattern. The classification (linear, rotary and multi-DOF) and development are introduced in details, some significant researches are illustrated. Finally, the future direction of inchworm type piezoelectric actuators is pointed out according the development of inchworm type piezoelectric actuators. This study shows the clear principle, design and future of inchworm type piezoelectric actuators which is meaningful for the development of piezoelectric actuators