We study, using simulated experiments inspired by thin-film magnetic domain patterns, the feasibility of phase retrieval in x-ray diffractive imaging in the presence of intrinsic charge scattering given only photon-shot-noise limited diffraction data. We detail a reconstruction algorithm to recover the sample's magnetization distribution under such conditions and compare its performance with that of Fourier transform holography.

We study a theoretical model of virtual scanning tunneling microscopy (VSTM): a proposed application of interlayer tunneling in a bilayer system to locally probe a two-dimensional electron system (2DES) in a semiconductor heterostructure. We consider tunneling for the case where transport in the 2DESs is ballistic and show that the zero-bias anomaly is suppressed by extremely efficient screening. Since such an anomaly would complicate the interpretation of data from VSTM, this result is encouraging for efforts to implement such a microscopy technique.

Rare earth doping is the key strategy to increase the Curie temperature (TC) of the ferromagnetic semiconductor EuO. The interplay between doping and charge carrier density (n), and the limit of the TC increase, however, are yet to be understood. We report measurements of n and TC of Gd-doped EuO over a wide range of doping levels. The results show a direct correlation between n and TC, with both exhibiting a maximum at high doping. On average, less than 35% of the dopants act as donors, raising the question about the limit to increasing TC. © 2010 The American Physical Society.

We study the electronic states of graphene in piecewise constant potentials using the continuum Dirac equation appropriate at low energies and a transfer matrix method. For superlattice potentials, we identify patterns of induced Dirac points that are present throughout the band structure and verify for the special case of a particle-hole symmetric potential their presence at zero energy. We also consider the cases of a single trench and a p-n junction embedded in neutral graphene, which are shown to support confined states.

We fabricated large arrays of suspended, single-layer graphene membrane resonators using chemical vapor deposition (CVD) growth followed by patterning and transfer. We measure the resonators using both optical and electrical actuation and detection techniques. We find that the resonators can be modeled as flat membranes under tension, and that clamping the membranes on all sides improves agreement with our model and reduces the variation in frequency between identical resonators.

The detection of mechanical vibrations near the quantum limit is a formidable challenge since the displacement becomes vanishingly small when the number of phonon quanta tends toward zero. An interesting setup for on-chip nanomechanical resonators is that of coupling them to electrical microwave cavities for detection and manipulation. Here we show how to achieve a large cavity coupling energy of up to (2Ï€) 1 MHz/nm for metallic beam resonators at tens of megahertz.

Two recent theoretical models, Bai et al (2004, 2007) and Tadigotla et al (2006), formulated thermodynamic explanations of sequence-dependent transcription pausing by RNA polymerase (RNAP). The two models differ in some basic assumptions and therefore make different yet overlapping predictions for pause locations, and different predictions on pause kinetics and mechanisms. Here we present a comprehensive comparison of the two models.

A pixel array detector (PAD) module has been developed at Cornell University for the collection of diffuse diffraction data in anticipation of coherent X-ray imaging experiments that will be conducted at the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. The detector is designed to collect X-rays scattered from monochromatic femtosecond pulses produced by the LCLS X-ray laser at framing rates up to 120 Hz.

Eukaryotic cell flattening is valuable for improving microscopic observations, ranging from bright field (BF) to total internal reflection fluorescence (TIRF) microscopy. Fundamental processes, such as mitosis and in vivo actin polymerization, have been investigated using these techniques. Here, we review the well known agar overlayer protocol and the oil overlay method. In addition, we present more elaborate microfluidics-based techniques that provide us with a greater level of control.

Background context: Needle puncture of the intervertebral disc (IVD) is required for delivery of therapeutic agents to the nucleus pulposus and for some diagnostic procedures. Needle puncture has also been implicated as an initiator of disc degeneration. It is hypothesized that needle puncture may initiate IVD degeneration by altering microscale mechanical behavior in the annulus fibrosus (AF). Purpose: Quantify the changes in AF microscale strain behavior resulting from puncture with a hypodermic needle. Study design: Cadaveric IVD tissue explant study.