Construction of a time-averaged crossed optical dipole trap for ultracold 6Li atoms

The use of ultracold neutral atoms for quantum computing and quantum simulation offers many advantages in terms of scalability. The Fermion Quantum Processor (FermiQP) experiment aims to use ultracold fermionic 6Li atoms to construct a novel combined digital- and analogue quantum processor. In this thesis, a crossed-beam optical dipole trap (ODT), implemented using a 200 W, red detuned (1070 nm) laser, is proposed for use in the experiment. Trap geometries larger than the size of the focused beam are to be achieved through spatial modulation in the MHz regime using an acousto-optic modulator (AOM). The feasibility of the proposal was tested with a proof-of-concept setup built with a lower-power 1064 nm laser. A time-averaged potential with a vertical cross-sectional area approximately three times that of the static beam was attained by modulating the beam position at 3.4 MHz. By dynamically changing the shape of the time-averaged potential, the proposed ODT promises more efficient loading and faster evaporative cooling that would reduce the cycle time of the experiment as compared to a static crossed ODT.Ultrakalte neutrale Atome als Plattform für Quantum Computing und Quantensimulationen stechen aufgrund ihrer Skalierbarkeit hervor. Das Fermion-Quantenprozessor-Experiment (FermiQP) hat sich zum Ziel gesetzt, einen auf ultrakalten neutralen 6Li-Atomen basierenden experimentellen Aufbau zu realisieren, der die Funktionen eines digitalen und eines analogen Quantencomputers vereinigt. In dieser Arbeit wird eine optische Dipolfalle, die mittels eines rot-verstimmten 200 W-Lasers (1070 nm) implementiert werden soll, vorgestellt. Fallengeometrien größer als der Strahldurchmesser im Fokus sollen durch räumliche Modulation im MHz-Regime mittels eines akusto-optischen Modulators ermöglicht werden. Die Durchführbarkeit des Vorhabens wurde mit einem Aufbau, der mit einem 1064 nm-Laser mit niedrigerer Leistung betrieben wurde, getestet. Mittels Modulation der Strahlposition mit 3,4 MHz wurde ein zeitlich gemitteltes Potential mit einer vertikalen Querschnittsfläche erreicht, die ungefähr drei mal so groß wie die ohne Modulation erreichbare Querschnittsfläche ist. Durch dynamische Variation der Form des zeitlich gemittelten Potentials werden ein effizienteres Beladen und ein schnelleres Verdampfungskühlen als mit einer statischen Dipolfalle möglich, wodurch die Zeit eines Experimentdurchlaufs reduziert werden kann

Properties Analysis of Spent Commercial Residue Hydrotreating Catalyst: Surface Property Changes of Spent Catalysts in Commercial Residue Hydrotreating Unit

In this study, the changes of the surface properties of 14 spent catalysts, which were sampled from a commercial residue hydrotreating unit at the end of an operation cycle, were analyzed and compared with the corresponding fresh catalysts. It was found that the changes in the surface properties do not have change laws along the bed height. Furthermore, the pore size, pore volume and surface area of most of the catalysts decreased after reaction and the number of micropores of the spent catalysts increased, due to the fact that the coke and metals deposited in the catalyst to alter the pore distribution. But some catalysts with high coke content, the pore size and pore volume decreased with the increase of surface area, which was a result of the forming of massive micro/mesopores (the pore size is mainly ranged from 3 to 10 nm), when partial soft coke desorbed under the action of the deposited active metals and micro/mesopores were formed in macropores or large mesopores. The surface properties of the spent catalysts were not only related to the deposition amounts, but also to the deposition configurations of the coke and metals on the catalysts

Properties Analysis of Spent Catalyst for Fixed-Bed Residue Hydrotreating Unit: Composition of Deposited Elements Along Catalyst Bed

Element compositions of spent catalyst from a commercial fixed-bed residue hydrotreating unit of Petro-China were analyzed in order to investigate the reasons for the catalyst deactivation. The spent catalysts were sampled from different axial position of the reactor. Depositions of C, H, S, N, Ni and V on the spent catalysts were studied. No necessary relation was observed for the contents of various deposited elements along the bed at the end of a run. The deposition amount of elements was mainly related to local reaction conditions and catalyst loading states in the fixed-bed. The catalysts with high metal depositions have low contents of coke, high contents of sulfur and high H/C, which indicates that residue hydrotreating is an autocatalytic process. Metal sulfides deposited on catalysts have a hydrogenation activity in residue hydrotreating. The coke on residue hydrotreating catalysts mainly comes from some specific condensed ring structures containing nitrogen existed in asphaltene which is difficult to hydrotreat.Key words: Spent catalyst; Residue hydrotreating; Deposited elements; Compositio

Properties Analysis of Spent Catalyst for Fixed-Bed Residue Hydrotreating Unit: Radial Distribution of Deposited Elements in Spent Catalyst Particles

14 spent catalysts, which were sampled from a commercial residue hydrotreating unit at the end of an operation cycle, were analyzed by SEM to describe elements distributions along the radial direction of particles. Different from laboratory equipment, on the whole, V, Ni and S showed U-shaped pattern along the radial direction of spent catalysts. The catalyst bed has been penetrated by deposited metals and deposited massive metals on catalyst, so the pore size of catalyst decreased, diffusion resistance increased and reactants entered internal of the catalysts more difficultly. Most of the organometallic compounds hydrotreated and deposited on outside of the catalyst particles. It is showed that metals deposited on catalyst in forms of metal sulfides because the points of high metal content also have high sulfur contents unexceptionally. The structure of high metal deposition catalyst was destroyed obviously or massive irregular material has deposited on the external surface. It is verified by SEM that there is no any distribution law for deposited elements along the bed height. The change laws of deposited elements along the bed height and radial direction of particles were influenced by various factors in commercial residue hydrotrating.Key words: Residue hydrotreating unit; Spent catalyst; SE

Thermodynamic non-equilibrium effects in bubble coalescence: A discrete Boltzmann study

The Thermodynamic Non-Equilibrium (TNE) effects in the coalescing process of two initially static bubbles under thermal conditions are investigated by a Discrete Boltzmann Model (DBM). The spatial distributions of the typical none-quilibrium quantity, i.e., the Non-Organized Momentum Fluxes (NOMF) during evolutions are investigated in detail. The density-weighted statistical method is used to highlight the relationship between the TNE effects and the morphological or kinetics characteristics of bubble coalescence. It is found that the $xx$-component and $yy$-component of NOMF are anti-symmetrical; the $xy$-component changes from an anti-symmetric internal and external double quadrupole structure to an outer octupole structure during the coalescing process. More importantly, the evolution of the averaged $xx$-component of NOMF provides two characteristic instants, which divide the non-equilibrium process into three stages. The first instant corresponds to the moment when the mean coalescing speed gets the maximum and at this time the ratio of minor and major axes is about $1/2$. The second instant corresponds to the moment when the ratio of minor and major axes gets $1$ for the first time. It is interesting to find that the three quantities, TNE intensity, acceleration of coalescence and negative slope of boundary length, show a high degree of correlation and attain their maxima simultaneously. Surface tension and heat conduction accelerate the process of bubble coalescence while viscosity delays it. Both surface tension and viscosity enhance the global non-equilibrium intensity, whereas heat conduction restrains it. These TNE features and findings present some new insights into the kinetics of bubble coalescence

EFFECTS OF TWO TYPES OF CONTROLLABLE DEFORMATION ON ENERGY EXTRACTION OF A FLEXIBLE HYDROFOIL

Energy extraction capacity of controllably flexible hydrofoil was studied under two identified deformation modes. Deformation modes, flexure parameters (flexure amplitude and flexure coefficient ) and motion parameters (reduced frequency f* and pitching amplitude 0) were investigated to understand the effects of controllably flexible deformation on energy extraction. The results reveal that deformation modes affect the effective angle of attack and vortex structure, which influence hydrodynamic performance. The energy extraction capacity improves from the deformation mode 2 to the rigid hydrofoil and then to the deformation mode 1. Under the deformation mode 1, lift, moment and power coefficients are increased obviously with the increase of , while they increase slightly with . Power coefficients and efficiency are sensitive to , which influences the development of leading-edge vortices. The flexible coefficient affects the wake structure, which has less impact on variation of force coefficient. As the increase in f*, averaged power coefficients firstly increase and then decrease. Further, the optimal f* is subjected to 0. Interestingly, a critical reduced frequency f*s, which is generally increase with increasing 0, was found under three modes. The condition that f* > f*s. is a prerequisite for subsequent adjustments of flexure modes and parameters according to different requirement of power coefficient under different tidal currents. The range of high efficiency () is: deformation mode 1 (36.1% rigid hydrofoils (34.2% deformation mode 2 (26.9%<<30.3%)

Binary Structuring Elements Decomposition Based on an Improved Recursive Dilation-Union Model and RSAPSO Method

This paper proposed an improved approach to decompose structuring elements of an arbitrary shape. For the model of this method, we use an improved dilation-union model, adding a new termination criterion, as the sum of 3-by-3 matrix should be less than 5. Next for the algorithm of this method, we introduced in the restarted simulated annealing particle swarm optimization method. The experiments demonstrate that our method can find better results than Park's method, Anelli's method, Shih's SGA method, and Zhang's MFSGA method. Besides, our method gave the best decomposition tree of different SE shapes including “ship,” “car,” “heart,” “umbrella,” “vase,” “tree,” “cat,” “V,” “bomb,” and “cup.

A Dual Stealthy Backdoor: From Both Spatial and Frequency Perspectives

Backdoor attacks pose serious security threats to deep neural networks (DNNs). Backdoored models make arbitrarily (targeted) incorrect predictions on inputs embedded with well-designed triggers while behaving normally on clean inputs. Many works have explored the invisibility of backdoor triggers to improve attack stealthiness. However, most of them only consider the invisibility in the spatial domain without explicitly accounting for the generation of invisible triggers in the frequency domain, making the generated poisoned images be easily detected by recent defense methods. To address this issue, in this paper, we propose a DUal stealthy BAckdoor attack method named DUBA, which simultaneously considers the invisibility of triggers in both the spatial and frequency domains, to achieve desirable attack performance, while ensuring strong stealthiness. Specifically, we first use Discrete Wavelet Transform to embed the high-frequency information of the trigger image into the clean image to ensure attack effectiveness. Then, to attain strong stealthiness, we incorporate Fourier Transform and Discrete Cosine Transform to mix the poisoned image and clean image in the frequency domain. Moreover, the proposed DUBA adopts a novel attack strategy, in which the model is trained with weak triggers and attacked with strong triggers to further enhance the attack performance and stealthiness. We extensively evaluate DUBA against popular image classifiers on four datasets. The results demonstrate that it significantly outperforms the state-of-the-art backdoor attacks in terms of the attack success rate and stealthinessComment: 10 pages, 7 figures. Submit to ACM MM 202

Collectively optimal routing for congested traffic limited by link capacity

We show that the capacity of a complex network that models a city street grid to support congested traffic can be optimized by using routes that collectively minimize the maximum ratio of betweenness to capacity in any link. Networks with a heterogeneous distribution of link capacities and with a heterogeneous transport load are considered. We find that overall traffic congestion and average travel times can be significantly reduced by a judicious use of slower, smaller capacity links.Comment: 7 pages, 4 figure