Current Search:   Yu, Xiaoming (x)

View All Items

  • CSV Spreadsheet
(1 - 3 of 3)
Development of a Tabletop Coherent Soft X-ray Source
Title
Development of a Tabletop Coherent Soft X-ray Source.
Creator
Kong, Hanfu, Chang, Zenghu, Yu, Xiaoming, Neupane, Madhab, University of Central Florida
Abstract / Description
The goal of this thesis is to design a tabletop coherent soft X-ray source for attosecond high resolution imaging. We collect signals from gas cells with different length and lens with different focal length. A spectrometer with a grating and a CCD camera is applied to observe and measure the spectrum of the X-ray attosecond pulses. This thesis first introduces the theory background of ultrafast lasers, then mainly explains high harmonic generation, which is the key method for attosecond...
Show moreThe goal of this thesis is to design a tabletop coherent soft X-ray source for attosecond high resolution imaging. We collect signals from gas cells with different length and lens with different focal length. A spectrometer with a grating and a CCD camera is applied to observe and measure the spectrum of the X-ray attosecond pulses. This thesis first introduces the theory background of ultrafast lasers, then mainly explains high harmonic generation, which is the key method for attosecond pulses generation, subsequently presents the experiment system and analyzes the results from the experiment, also compares different combinations of parameters of the devices.
Show less
Date Issued
2018
Identifier
CFE0007407, ucf:52732
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007407
INTERFACIAL BEHAVIOR IN POLYMER DERIVED CERAMICS AND SALT WATER PURIFICATION VIA 2D MOS2
Title
INTERFACIAL BEHAVIOR IN POLYMER DERIVED CERAMICS AND SALT WATER PURIFICATION VIA 2D MOS2.
Creator
Li, Hao, An, Linan, Jung, YeonWoong, Zhai, Lei, Feng, Xiaofeng, Yu, Xiaoming, University of Central Florida
Abstract / Description
In the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedancespectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150?(&)deg;C, as well as different annealing temperatures (1100-1400 (&)deg;C). All spectra,...
Show moreIn the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedancespectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150?(&)deg;C, as well as different annealing temperatures (1100-1400 (&)deg;C). All spectra, regardless of temperature and bias, consist of two semi-circular arcs,corresponding to the free-carbon phase and the interface, respectively. The impedance of the free-carbon phase is independent of the bias, while that of the interface decreased significantly with increasing dc bias. It is shown that the change of the interfacial capacitance with the bias can be explained using the double Schottky barrier model. The charge-carrier concentration and potential barrier height were estimated by comparing the experimental data and the model.The results revealed that increasing testing temperature led to an increased charge-carrier concentration and a reduced barrier height, both following Arrhenius dependence, whereas the increase in annealing temperature resulted in increased charge-carrier concentration and barrier height. The phenomena were explained in terms of the unique bi-phasic microstructures of the material. The research findings reveal valuable microstructural information of temperaturedependent properties of polymer derived ceramics, and should contribute towards more precise understanding and control of the electrical as well as dielectric properties of polymer derivedceramics. Furthermore, the desalination performances and underlying mechanisms of two-dimensional CVD-grown MoS2 layers membranes have been experimentally assessed. Based on a successful large-area few-layer 2D materials growth, transfer and integration method, the 2D MoS2 layers membranes showed preserved chemical and microstructural integrity after integration. The few-layer 2D MoS2 layers demonstrated superior desalination capability towards various types of seawater salt solutions approaching theoretically-predicted values. Such performances are attributed to the dimensional and geometrical effect, as well as the electrostatic interaction of the inherently-present CVD-induced atomic vacancies for governingboth water permeation and ionic sieving at the solution/2D-layer interfaces.
Show less
Date Issued
2019
Identifier
CFE0007830, ucf:52813
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007830
Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials
Title
Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials.
Creator
Jennings, Jeffrey, Vaidyanathan, Raj, Kar, Aravinda, Coffey, Kevin, Challapalli, Suryanarayana, Brisbois, Elizabeth, Yu, Xiaoming, University of Central Florida
Abstract / Description
Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive...
Show moreInduction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities.An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop.An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.
Show less
Date Issued
2018
Identifier
CFE0007756, ucf:52378
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007756