Student learning outcomes with hybrid computer simulations and hands-on labs

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Real-Time Interferometric Monitoring System for Exposure Controlled Projection Lithography

Stereolithography is an additive manufacturing process in which liquid photopolymer resin is cross-linked and converted to solid polymer with an ultraviolet light source. Exposure Controlled Projection Lithography (ECPL) is a stereolithographic process in which incident radiation, patterned by a dynamic mask, passes through a transparent substrate to cure a photopolymer layer that grows progressively from the substrate surface. In contrast to existing stereolithography techniques, this technique uses a gray-scale projected image, or alternatively a series of binary bit-map images, to produce a three-dimensional polymer object with the desired shape, and it can be used on either flat or curved substrates. Like most stereolithographic technologies, ECPL works in a unidirectional fashion. Calibration constants derived experimentally are fed to the software used to control the system. This unidirectional fabrication method does not, by itself, allow the system to compensate for minor variations, thereby limiting the overall accuracy of the process. We present here a simple, real-time monitoring system based on interferometry, which can be used to provide feedback control to the ECPL process, thus making it more robust and increasing system accuracy. The results obtained from this monitoring system provide a means to better visualize and understand the various phenomena occurring during the photopolymerization of transparent photopolymers.Mechanical Engineerin

On the Typical and Average Contributions to the Persistent Current in Mesoscopic Rings

Low-temperature measurements of the magnetic response of one or more electrically-isolated, micron-sized metallic rings yield an unexpected yet unequivocal result: the presence of equilibrium persistent currents, with nanoampere-sized amplitudes and either h/e- or h/2e-periodicity in the applied magnetic flux. This effect follows from the extended phase coherence of the conduction electrons in this disordered mesoscopic system. As with transport phenomena, this thermodynamic effect demonstrates sample-specific as well as ensemble-averaging qualities common to mesoscopic physics. With few exceptions, however, there is strong disagreement between the different theoretical calculations and the few successful experiments to date. For this thesis work, we have designed and executed a unique and unprecedented new experiment: the measurement of the sign, amplitude, and temperature dependences of both the typical and average current contributions to the h/e- and h/2e-periodic magnetic response of the same sample of thirty mesoscopic Au rings. Of particular interest here is the innovative design of our custom SQUID-based detector as well as the unusually long phase coherence of electrons in our lithographically-patterned Au sample. Remarkably, both the typical and average contributions are diamagnetic in sign near zero field, over multiple cooldowns, and comparable in magnitude per ring to the Thouless scale Ec of energy level correlations. Taken in conjunction with earlier experiments, the new data strongly challenge conventional theories of the persistent current

Diamagnetic Persistent Current in Diffusive Normal-Metal Rings

We have measured a diamagnetic persistent current with flux periodicities of both h/e and h/2e in an array of thirty diffusive mesoscopic gold rings. At the lowest temperatures, the magnitudes of the currents per ring corresponding to the h/e- and h/2e-periodic responses are both comparable to the Thouless energy Ec≡ħ/τD, where τD is the diffusion time. Taken in conjunction with earlier experiments, our results strongly challenge the conventional theories of persistent current. We consider a new approach associated with the saturation of the phase coherence time τϕ

Diamagnetic Persistent Current in Diffusive Normal-Metal Rings

We have measured a diamagnetic persistent current with flux periodicities of both h/e and h/2e in an array of thirty diffusive mesoscopic gold rings. At the lowest temperatures, the magnitudes of the currents per ring corresponding to the h/e- and h/2e-periodic responses are both comparable to the Thouless energy Ec≡ħ/τD, where τD is the diffusion time. Taken in conjunction with earlier experiments, our results strongly challenge the conventional theories of persistent current. We consider a new approach associated with the saturation of the phase coherence time τϕ

Intrinsic Decoherence in Mesoscopic Systems

We present measurements of the phase coherence time $\tau_\phi$ in six quasi-1D Au wires and clearly show that $\tau_\phi$ is temperature independent at low temperatures. We suggest that zero-point fluctuations of the intrinsic electromagnetic environment are responsible for the observed saturation of $\tau_\phi$. We introduce a new functional form for the temperature dependence and present the results of a calculation for the saturation value of $\tau_\phi$. This explains the observed temperature dependence of our samples as well as many 1D and 2D systems reported to date.Comment: 4 pages, 4 figures & 1 tabl

Small molecule inhibitors of Late SV40 Factor (LSF) abrogate hepatocellular carcinoma (HCC): evaluation using an endogenous HCC model

Hepatocellular carcinoma (HCC) is a lethal malignancy with high mortality and poor prognosis. Oncogenic transcription factor Late SV40 Factor (LSF) plays an important role in promoting HCC. A small molecule inhibitor of LSF, Factor Quinolinone Inhibitor 1 (FQI1), significantly inhibited human HCC xenografts in nude mice without harming normal cells. Here we evaluated the efficacy of FQI1 and another inhibitor, FQI2, in inhibiting endogenous hepatocarcinogenesis. HCC was induced in a transgenic mouse with hepatocyte-specific overexpression of c-myc (Alb/c-myc) by injecting N-nitrosodiethylamine (DEN) followed by FQI1 or FQI2 treatment after tumor development. LSF inhibitors markedly decreased tumor burden in Alb/c-myc mice with a corresponding decrease in proliferation and angiogenesis. Interestingly, in vitro treatment of human HCC cells with LSF inhibitors resulted in mitotic arrest with an accompanying increase in CyclinB1. Inhibition of CyclinB1 induction by Cycloheximide or CDK1 activity by Roscovitine significantly prevented FQI-induced mitotic arrest. A significant induction of apoptosis was also observed upon treatment with FQI. These effects of LSF inhibition, mitotic arrest and induction of apoptosis by FQI1s provide multiple avenues by which these inhibitors eliminate HCC cells. LSF inhibitors might be highly potent and effective therapeutics for HCC either alone or in combination with currently existing therapies.The present study was supported in part by grants from The James S. McDonnell Foundation, National Cancer Institute Grant R01 CA138540-01A1 (DS), National Institutes of Health Grant R01 CA134721 (PBF), the Samuel Waxman Cancer Research Foundation (SWCRF) (DS and PBF), National Institutes of Health Grants R01 GM078240 and P50 GM67041 (SES), the Johnson and Johnson Clinical Innovation Award (UH), and the Boston University Ignition Award (UH). JLSW was supported by Alnylam Pharmaceuticals, Inc. DS is the Harrison Endowed Scholar in Cancer Research and Blick scholar. PBF holds the Thelma Newmeyer Corman Chair in Cancer Research. The authors acknowledge Dr. Lauren E. Brown (Dept. Chemistry, Boston University) for the synthesis of FQI1 and FQI2, and Lucy Flynn (Dept. Biology, Boston University) for initially identifying G2/M effects caused by FQI1. (James S. McDonnell Foundation; R01 CA138540-01A1 - National Cancer Institute; R01 CA134721 - National Institutes of Health; R01 GM078240 - National Institutes of Health; P50 GM67041 - National Institutes of Health; Samuel Waxman Cancer Research Foundation (SWCRF); Johnson and Johnson Clinical Innovation Award; Boston University Ignition Award; Alnylam Pharmaceuticals, Inc.)Published versio

Multiple Current States of Two Phase-Coupled Superconducting Rings

The states of two phase-coupled superconducting rings have been investigated. Multiple current states have been revealed in the dependence of the critical current on the magnetic field. The performed calculations of the critical currents and energy states in a magnetic field have made it possible to interpret the experiment as the measurement of energy states into which the system comes with different probabilities because of the equilibrium and non-equilibrium noises upon the transition from the resistive state to the superconducting state during the measurement of the critical currentComment: 5 pages, 5 figure