The symmetry of the spin Hamiltonian in herbertsmithite, a spin-1/2 kagom\'{e} lattice

We present magnetization measurements on oriented powder of ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ along and perpendicular to the orienting field. We find a dramatic difference in the magnetization between the two directions. It is biggest at low measurement fields $H$ or high temperatures. We show that the difference at high temperatures must emerge from Ising-like exchange anisotropy. This allows us to explain muon spin rotation data at $T\to 0$ in terms of an exotic ferromagnetic ground state.Comment: 5 pages, 5 figure

Design and Fabrication of Rear Suspension and Drivetrain for Union College\u27s SAE Baja Car

My senior project is to design and fabricate the rear suspension and drivetrain for Union College’s SAE Baja car. This project started with the determination of the optimum style of suspension and drivetrain for use on the vehicle. I worked with a company to obtain a custom-built transmission, and I successfully designed the drivetrain to use this transmission. I also designed the frame of the Baja car required to mount these elements. Finally, I designed the rear suspension of the car. The drivetrain design incorporates a 5-speed sequential transmission with a reverse. This transmission is driven by a centrifugal clutch which prevents the engine from stalling. The drivetrain is capable of a top speed of 27mph in fifth gear and puts out a maximum of 440 ft-lbs in first gear. The suspension is a semi-trailing arm design that is fully independent and allows twelve inches of travel for each wheel. At this point the framing and drivetrain are fabricated. Next term I will continue to work with the machine shop to fabricate the suspension components needed to complete the project

Pattern formation in a ring cavity with temporally incoherent feedback

We present a theoretical and experimental study of modulation instability and pattern formation in a passive nonlinear optical cavity that is longer than the coherence length of the light circulating in it. Pattern formation in this cavity exhibits various features of a second-order phase transition, closely resembling laser action

The incoherent feedforward loop can provide fold-change detection in gene regulation

Many sensory systems (e.g., vision and hearing) show a response that is proportional to the fold-change in the stimulus relative to the background, a feature related to Weber's Law. Recent experiments suggest such a fold-change detection feature in signaling systems in cells: a response that depends on the fold-change in the input signal, and not on its absolute level. It is therefore of interest to find molecular mechanisms of gene regulation that can provide such fold-change detection. Here, we demonstrate theoretically that fold-change detection can be generated by one of the most common network motifs in transcription networks, the incoherent feedforward loop (I1-FFL), in which an activator regulates both a gene and a repressor of the gene. The fold-change detection feature of the I1-FFL applies to the entire shape of the response, including its amplitude and duration, and is valid for a wide range of biochemical parameters