Statistical Modeling Of Effective Temperature With Cosmic Ray Flux

The increasing frequency of sporadic weather patterns in the last decade, especially major winter storms, demands improvements in current weather forecasting techniques. Recently, there are growing interests in stratospheric forecasting because of its potential enhancements of weather forecasts. The dominating factors of northern hemisphere wintertime variation of the general circulation in the stratosphere is a phenomenon called stratospheric sudden warming (SSW) events. It is shown in multiple studies that SSW and cosmic ray muon flux variations are strongly correlated with the effective atmospheric temperature changes, which suggests that cosmic ray detectors could be potentially used as meteorological applications, especially for monitoring SSW events. A method for determining the effective temperature with cosmic ray flux measurements is studied in this work by using statistical modeling techniques, such as k-fold cross validation and partial least square regression. This method requires the measurement of the vertical profile of the atmospheric temperature, typically measured by radiosonde, for training the model. In this study, cosmic ray flux measured in Atlanta and Yakutsk are chosen for demonstrating this novel technique. The results of this study show the possibility of realtime monitoring on effective temperature by simultaneous measurement of cosmic ray muon and neutron flux. This technique can also be used for studying the historical SSW events using the past world wide cosmic ray data

Cook blind: Enhancing cooking experiences for visually-impaired people

This paper introduces a new method to assist visually-impaired people to find what they need in order to complete cooking. Following the design thinking made by me at the beginning of my research, I started to create a new design based on target users` suggestions and preferences. This study focuses on the demands and user experiences of visually impaired people, the integration of design principles adapted from industrial design, user-centered design, and interaction design. I recorded the daily activities of the visually impaired individuals, and then investigated the most reasonable and effective solutions. My method of recording these individuals’ daily activates was via verbal interview, video recording interview, and online user research. Each method offered particular advantages to identifying the specific demands and needs of the visually impaired. With these methods, I conducted a series of user studies in order to understand the features of each research method including advantages and disadvantages. Then I devised my original design concept through the synthesis of research results. During the last round of the study, I shared my design with visually impaired persons in order to test the effectiveness of the new design by comparing visually impaired people`s activities with and without this new design

Nonlinear Hall effect as a signature of electronic phase separation in the semimetallic ferromagnet EuB6

This work reports a study of the nonlinear Hall Effect (HE) in the semimetallic ferromagnet EuB6. A distinct switch in its Hall resistivity slope is observed in the paramagnetic phase, which occurs at a single critical magnetization over a wide temperature range. The observation is interpreted as the point of percolation for entities of a more conducting and magnetically ordered phase in a less ordered background. With an increasing applied magnetic field, the conducting regions either increase in number or expand beyond the percolation limit, hence increasing the global conductivity and effective carrier density. An empirical two-component model expression provides excellent scaling and a quantitative fit to the HE data and may be applicable to other correlated electron systems.Comment: 15 Pages, 4 Figures. Accepted for publication in Phys. Rev. Let

Enhanced critical current density of MgB2 superconductor synthesized in high magnetic fields

The effect of high magnetic fields on the current carrying properties of both MgB2 bulks and Fe-sheathed tapes was investigated following different thermal sequences. It is found that application of a large magnetic field during processing results in the quite uniform microstructure and the better connectivity between the MgB2 grains. As a result, the Jc of these samples has shown much higher value than that of the MgB2 samples in the absence of magnetic field. The possible mechanism of the Jc enhancement under an external magnetic field is also discussed.Comment: Presented at ISS2005, Tsukuba, 24-26 Oct., 2005; Revised versio

Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6

As an exemplary Kondo insulator, SmB6 has been studied for several decades; however, direct evidence for the development of the Kondo coherent state and the evolution of the electronic structure in the material has not been obtained due to the rather complicated electronic and thermal transport behavior. Recently, these open questions attracted increasing attention as the emergence of a time-reversal invariant topological surface state in the Kondo insulator has been suggested. Here, we use point-contact spectroscopy to reveal the temperature dependence of the electronic states in SmB6. We demonstrate that SmB6 is a model Kondo insulator: below 100 K, the conductance spectra reflect the Kondo hybridization of Sm ions, but below ~ 30 K, signatures of inter-ion correlation effects clearly emerge. Moreover, we find evidence that the low-temperature insulating state of this exemplary Kondo lattice compound harbors conduction states on the surface, in support of predictions of nontrivial topology in Kondo insulators.Comment: Accepted for publication in Physical Review

Understanding and Manipulating the Thermal Conductance of Sin Membranes in Sub-Kelvin Refrigerators and Sensors

In superconducting transition-edge sensors (TES) and superconducting tunnel junction refrigerators, thermal conductance of the silicon nitride membrane is a key design character. Thermal conductance engineering in silicon nitride membrane is still challenging, especially not introducing extra noise to sensors and diminish its mechanical strength. In this thesis, we introduce our new generation of macroscopic general-purpose refrigerator using superconducting tunnel junction. Using the product of the cooled mass and the temperature reduction as a performance metric, this work is a more than tenfold advance over previous efforts. Based on our model, a better understanding of phonon thermal conductance of silicon nitride membrane and a method to reduce it is needed to get a better phonon cooling performance. We present a theory that quantitative and qualitative agree with our measurements of the thermal conductance G of thin silicon nitride beams in various geometries and with various metal patterns as a function of temperature over the range 0.075 to 0.5 K. We demonstrate that the method of deposit metal patterns on top of silicon nitride manipulates the thermal conductance of freestanding SiN membranes without compromising the robustness of the membrane or the noise of a co-located TES sensor. We deposit and pattern an additional metal layer in different geometries on the SiN membrane thereby achieving a maximum of 56% reduction in G and the change in G is precisely controlled by the details of the patterning