A systematic study of the initial state in heavy ion collisions based on the quark participant assumption

We investigate the initial state geometric quantities of heavy ion collisions based on the quark participant assumption in the Glauber multiple scattering approach. A systematic comparison to the nucleon participant assumption has been presented and confronted with the charged multiplicity measurements in various collision systems. It is found that the quark participant based assumption can be important to understand the data in multiplicity production and the initial spatial eccentricity in small systems.Comment: 7 pages, 10 figure

Correlation Decay up to Uniqueness in Spin Systems

We give a complete characterization of the two-state anti-ferromagnetic spin systems which are of strong spatial mixing on general graphs. We show that a two-state anti-ferromagnetic spin system is of strong spatial mixing on all graphs of maximum degree at most \Delta if and only if the system has a unique Gibbs measure on infinite regular trees of degree up to \Delta, where \Delta can be either bounded or unbounded. As a consequence, there exists an FPTAS for the partition function of a two-state anti-ferromagnetic spin system on graphs of maximum degree at most \Delta when the uniqueness condition is satisfied on infinite regular trees of degree up to \Delta. In particular, an FPTAS exists for arbitrary graphs if the uniqueness is satisfied on all infinite regular trees. This covers as special cases all previous algorithmic results for two-state anti-ferromagnetic systems on general-structure graphs. Combining with the FPRAS for two-state ferromagnetic spin systems of Jerrum-Sinclair and Goldberg-Jerrum-Paterson, and the very recent hardness results of Sly-Sun and independently of Galanis-Stefankovic-Vigoda, this gives a complete classification, except at the phase transition boundary, of the approximability of all two-state spin systems, on either degree-bounded families of graphs or family of all graphs.Comment: 27 pages, submitted for publicatio

Content Creation in the Digital Economy: A Comprehensive Exploration and Investigation of Work Environment and Content Creators’ Behaviours

With the emergence and rapid spread of digital technologies, the world is undergoing a profound transformation. The digital economy that has evolved as a result has fundamentally changed and impacted every aspect of society and business, and it will undoubtedly change and reshape employment and work from various perspectives as well. Flexibility and autonomy have always been the strong attraction that the digital economy provides to workers, but behind this hidden truth is the strict control of platforms and algorithms. This thesis seeks to further deepen the understanding of working in the digital economy through a series of studies ranging from the broad to the specific, especially on the work of a particular group of content creators. This thesis contains four studies. Study 1 is a review paper that attempts to clarify the distinction between different concepts from the digital economy on a macro level. Studies 2-4 turn the perspective to a particular group of workers in the digital economy, the content creators. Study 2 uses two quantitative studies to theorise the characteristics of working on content creative platforms by developing a typology of these platforms. The third study was a systematic review to explore the power imbalance between platform algorithms and creators in content creative platforms. The fourth study employs a quantitative study that explores the impact of the platform work environment on the creators' behaviour from an individual perspective. This series of studies makes important theoretical contributions to the field related to employment relations in the digital economy context, especially content creative platforms, from both macro and micro perspectives. In addition, this series of studies provides practical implications for content creators, platforms and policymakers

Characterization of laser-produced plasmas as light sources for extreme ultraviolet lithography and beyond

2019 Fall.Includes bibliographical references.Lithography is a critical process in the fabrication of integrated circuits. The continuous increase in computing power for more than half a century has depended in the ability to print smaller and smaller features, which has required the use of light sources operating at increasingly shorter wavelengths. There is keen interest in the development of high-power light sources for extreme ultraviolet (EUV) lithography at λ=13.5 nm and future beyond extreme ultraviolet (BEUV) lithography near λ=6.7 nm. The work conducted in this dissertation has characterized aspects of laser-produced plasmas (LPPs) that serve as light sources for EUV / BEUV lithography. The laser pulse shape dependence of the conversion efficiency of λ=1.03 μm laser into in-band 13.5 nm EUV emission in a Sn LPP was studied as a function of laser pulse shape and durations. Laser pulses of arbitrary temporal shape with variable energy and pulse widths were generated using a programmable pulse synthesizer based on a diode-pumped chirped pulse amplification Yb: YAG laser. The pulse synthesizer is based on wave front splitting and pulse stacking for the generation of arbitrary shape laser pulses of Joule-level energy. Pulses ranging from hundreds of ps to several ns were generated with a single laser. The measurements showed the CE favors the use of nearly square pulses of duration longer than 2 ns, in agreement with hydrodynamic/atomic physics simulations. A significant increase in CE was observed when Q-switched pulses were substituted by square pulses of similar duration. Conditions were observed at which the EUV pulse duration significantly outlasts the laser pulse in the direction normal to the target surface, in contrast at grazing angles the measured EUV pulse duration is shorter and similar to the laser pulse duration. The physics leading to this angular anisotropy is discussed, along with the spectroscopic characterization of EUV emission and at-wavelength images that characterize the source size. Another aspect of this dissertation includes a comprehensive study of the emission from Gd and Tb LPPs in the λ=6.5 - 6.7 nm region. BEUV emission spectra were measured as a function of laser pulse duration (120 ps - 4 ns), emission angle, and spatial location within the plasma. At-wavelength images of the BEUV emitting plasma region were obtained as a function of irradiation parameters. The peak of the emission spectrum was observed to broaden and to shift to longer wavelengths as the laser pulses are shortened from ns to hundreds of ps. Transient self-consistent hydrodynamic/atomic physics simulations show that the picosecond irradiation creates significantly hotter plasmas in which the dominant emission originates from more highly ionized species. Gd LPP emission driven by nanosecond laser pulses best matched the reflectivity band of our La/B4C mirrors. Spatially resolved spectra of the Gd LPP were acquired for different laser parameters and were compared to simulations. The CE into in-band BEUV emission was determined by integrating angularly resolved measurements obtained using an array of calibrated energy monitors. A maximum CE of 0.47% / 0.45% for the Gd / Tb LPPs was obtained within a 0.6% bandwidth. The results are of potential interest BEUV lithography