More Evidence for a Distribution of Tunnel Splittings in Mn12_{12}-acetate

In magnetic fields applied parallel to the anisotropy axis, the magnetization of Mn$_{12}$ has been measured in response to a field that is swept back and forth across the resonances corresponding to steps $N=4,5,...9$. The fraction of molecules remaining in the metastable well after each sweep through the resonance is inconsistent with expectations for an ensemble of identical molecules. The data are consistent instead with the presence of a broad distribution of tunnel splittings. A very good fit is obtained for a Gaussian distribution of the second-order anisotropy tunneling parameter $X_E=-\ln(\mid E\mid/2D)$. We show that dipolar shuffling is a negligible effect which cannot explain our data.Comment: minor corrections (PACS nos, signs in Fig. 2

Creation and application of immortalized bait libraries for targeted enrichment and next-generation sequencing

Since the introduction of next-generation sequencing, several techniques have been developed to selectively enrich and sequence specific parts of the genome at high coverage. These techniques include enzymatic methods employing molecular inversion probes, PCR based approaches, hybrid capture, and in-solution capture. In-solution capture employs RNA probes transcribed from a pool of DNA template oligos designed to match regions of interest to specifically bind and enrich genomic DNA fragments. This method is highly efficient, especially if genomic target regions are large in size or quantity. Diverse in-solution capture kits are available, but are costly when large sample numbers need to be analyzed. Here we present a cost-effective strategy for the design of custom DNA libraries, their transcription into RNA libraries, and application for in-solution capture. We show the efficacy by comparing the method to a commercial kit and further demonstrate that emulsion PCR can be used for bias free amplification and virtual immortalization of DNA template libraries

Experimental Upper Bound on Superradiance Emission from Mn12 Acetate

We used a Josephson junction as a radiation detector to look for evidence of the emission of electromagnetic radiation during magnetization avalanches in a crystal assembly of Mn_12-Acetate. The crystal assembly exhibits avalanches at several magnetic fields in the temperature range from 1.8 to 2.6 K with durations of the order of 1 ms. Although a recent study shows evidence of electromagnetic radiation bursts during these avalanches [J. Tejada, et al., Appl. Phys. Lett. {\bf 84}, 2373 (2004)], we were unable to detect any significant radiation at well-defined frequencies. A control experiment with external radiation pulses allows us to determine that the energy released as radiation during an avalanche is less than 1 part in 10^4 of the total energy released. In addition, our avalanche data indicates that the magnetization reversal process does not occur uniformly throughout the sample.Comment: 4 RevTeX pages, 3 eps figure

Parallel magnetic field induced giant magnetoresistance in low density {\it quasi}-two dimensional layers

We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density {\it quasi}-two dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the {\it orbital} motion arising from the {\it finite} layer thickness and the large Fermi wavelength of the {\it quasi}-two dimensional system at low carrier densities.Comment: 4 pages with 4 figures. Accepted for Publication in Physical Review Letter

Hall Coefficient of a Dilute 2D Electron System in Parallel Magnetic Field

Measurements in magnetic fields applied at a small angle with respect to the 2D plane of the electrons of a low-density silicon MOSFET indicate that the Hall coefficient is independent of parallel field from H=0 to $H>H_{sat}$, the field above which the longitudinal resistance saturates and the electrons have reached full spin-polarization. This implies that the mobilities of the spin-up and spin-down electrons remain comparable at all magnetic fields, and suggests there is strong mixing of spin-up and spin-down electron states.Comment: 4 pages, 2 figure

Abrupt Transition between Thermally-Activated Relaxation and Quantum Tunneling in a Molecular Magnet

We report Hall sensor measurements of the magnetic relaxation of Mn$_{12}$ acetate as a function of magnetic field applied along the easy axis of magnetization. Data taken at a series of closely-spaced temperatures between 0.24 K and 1.4 K provide strong new evidence for an abrupt ``first-order'' transition between thermally-assisted relaxation and magnetic decay via quantum tunneling.Comment: 4 pages, including 7 figure

Enhanced Magnetic Anisotropy of Mn12-acetate

Thin films of the Single Molecule Magnet (Mn12-acetate) have been fabricated on a Si-substrate by the Dip-and-Dry method, a simple and robust technique. Atomic force microscopy and X-ray photoelectron spectroscopy characterizations reveal that homogeneous, thin films of a few molecular layers with smoothness at the molecular level are deposited. Significant changes in magnetic properties of Mn12-acetate exposed to the same solvent were observed in zero-field-cooled and field-cooled magnetization, as well as ac-susceptibility measurements. The blocking temperature was found to increase to TB > 10 K at low magnetic fields, indicating an enhanced magnetic anisotropy.Comment: 14 pages, 4 figure

The influence of clouds on radical concentrations: Observations and modelling studies of HOx during the Hill Cap Cloud Thuringia (HCCT) campaign in 2010

The potential for chemistry occurring in cloud droplets to impact atmospheric composition has been known for some time. However, the lack of direct observations and uncertainty in the magnitude of these reactions led to this area being overlooked in most chemistry transport models. Here we present observations from Mt Schmücke, Germany, of the HO2 radical made alongside a suite of cloud measurements. HO2 concentrations were depleted in-cloud by up to 90% with the rate of heterogeneous loss of HO2 to clouds necessary to bring model and measurements into agreement, demonstrating a dependence on droplet surface area and pH. This provides the first observationally derived assessment for the uptake coefficient of HO2 to cloud droplets and was found to be in good agreement with theoretically derived parameterisations. Global model simulations, including this cloud uptake, showed impacts on the oxidising capacity of the troposphere that depended critically on whether the HO2 uptake leads to production of H2O2 or H2O