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

Non-Equilibrium Dynamics and Superfluid Ring Excitations in Binary Bose-Einstein Condensates

We revisit a classic study [D. S. Hall {\it et al.}, Phys. Rev. Lett. {\bf 81}, 1539 (1998)] of interpenetrating Bose-Einstein condensates in the hyperfine states $\ket{F = 1, m_f = -1}\equiv\ket{1}$ and $\ket{F = 2, m_f = +1}\equiv\ket{2}$ of ${}^{87}$Rb and observe striking new non-equilibrium component separation dynamics in the form of oscillating ring-like structures. The process of component separation is not significantly damped, a finding that also contrasts sharply with earlier experimental work, allowing a clean first look at a collective excitation of a binary superfluid. We further demonstrate extraordinary quantitative agreement between theoretical and experimental results using a multi-component mean-field model with key additional features: the inclusion of atomic losses and the careful characterization of trap potentials (at the level of a fraction of a percent).Comment: 4 pages, 3 figures (low res.), to appear in PR

Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)

Two different single particle mass spectrometers were operated in parallel at the Swiss High Alpine Research Station Jungfraujoch (JFJ, 3580 m a.s.l.) during the Cloud and Aerosol Characterization Experiment (CLACE 6) in February and March 2007. During mixed phase cloud events ice crystals from 5–20 micro m were separated from larger ice aggregates, non-activated, interstitial aerosol particles and supercooled droplets using an Ice-Counterflow Virtual Impactor (Ice-CVI). During one cloud period supercooled droplets were additionally sampled and analyzed by changing the Ice-CVI setup. The small ice particles and droplets were evaporated by injection into dry air inside the Ice-CVI. The resulting ice and droplet residues (IR and DR) were analyzed for size and composition by the two single particle mass spectrometers: a custom-built Single Particle Laser-Ablation Time-of-Flight Mass Spectrometer (SPLAT) and a commercial Aerosol Time-of-Flight Mass Spectrometer (ATOFMS, TSI Model 3800). During CLACE 6 the SPLAT instrument characterized 355 individual IR that produced a mass spectrum for at least one polarity and the ATOFMS measured 152 IR. The mass spectra were binned in classes, based on the combination of dominating substances, such as mineral dust, sulfate, potassium and elemental carbon or organic material. The derived chemical information from the ice residues is compared to the JFJ ambient aerosol that was sampled while the measurement station was out of clouds (several thousand particles analyzed by SPLAT and ATOFMS) and to the composition of the residues of supercooled cloud droplets (SPLAT: 162 cloud droplet residues analyzed, ATOFMS: 1094). The measurements showed that mineral dust was strongly enhanced in the ice particle residues. Close to all of the SPLAT spectra from ice residues did contain signatures from mineral compounds, albeit connected with varying amounts of soluble compounds. Similarly, close to all of the ATOFMS IR spectra show a mineral or metallic component. Pure sulfate and nitrate containing particles were depleted in the ice residues. Sulfate and nitrate was found to dominate the droplet residues (~90% of the particles). The results from the two different single particle mass spectrometers were generally in agreement. Differences in the results originate from several causes, such as the different wavelength of the desorption and ionisation lasers and different size-dependent particle detection efficiencies

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

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

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

Mode of Action of the Natural Product Allicin in a Plant Model:Influence on the Cytoskeleton and Subsequent Shift in Auxin Localization

Allicin is a defense substance produced by garlic cells when they are injured. It is a redox-active thiosulfinate showing redox-activity with a broad range of dose-dependent antimicrobial and biocidal activity. It is known that allicin efficiently oxidizes thiol-groups, and it has been described as a redox toxin because it alters the redox homeostasis in cells and triggers oxidative stress responses. Allicin can therefore be used as a model substance to investigate the action of thiol-specific prooxidants. In order to learn more about the effect of allicin on plants, we used pure synthetized allicin, and studied the influence of allicin on organelle movement in Tradescantia fluminensis as a cytoskeleton-dependent process. Furthermore, we investigated cytoplasmic streaming in sterile filaments of Tradescantia fluminensis, organelle movement using transgenic Arabidopsis with organelle-specifics GFP-tags, and effects on actin and tubulin in the cytoskeleton using GFP-tagged lines. Tubulin and actin were visualized by GFP-tagging in transgenic lines of Arabidopsis thaliana to visualize the influence of allicin on the cytoskeleton. Since auxin transport depends on recycling and turnover of the PIN protein involving cytoskeletal transport to and from the membrane localization sites, auxin distribution in roots was investigated using of transgenic PIN1–GFP, PIN3–GFP, DR5–GFP and DII–VENUS Arabidopsis reporter lines. Allicin inhibited cytoplasmic streaming in T. fluminensis, organelle movement of peroxi-somesperoxisomes, and the Golgi apparatus in a concentration-dependent manner. It also destroyed the correct root tip distribution of auxin, which probably contributed to the observed inhibition of root growth. These observations of the disruption of cytoskeleton-dependent transport processes in plant cells add a new facet to the mechanism of action of allicin as a redox toxin in cells

In-plane magnetic field-induced spin polarization and transition to insulating behavior in two-dimensional hole systems

Using a novel technique, we make quantitative measurements of the spin polarization of dilute (3.4 to 6.8*10^{10} cm^{-2}) GaAs (311)A two-dimensional holes as a function of an in-plane magnetic field. As the field is increased the system gradually becomes spin polarized, with the degree of spin polarization depending on the orientation of the field relative to the crystal axes. Moreover, the behavior of the system turns from metallic to insulating \textit{before} it is fully spin polarized. The minority-spin population at the transition is ~8*10^{9} cm^{-2}, close to the density below which the system makes a transition to an insulating state in the absence of a magnetic field.Comment: 4 pages with figure

Stimulating fertility awareness: the importance of getting the language right

While education about fertility is not intrinsically controversial, finding the right language to communicate the topic can be challenging, as there are several risks of unintended negative effects such as dissonance, anxiety, culpability, and stigma due to social norming. In this article, we share some of our learnings from promoting fertility awareness in the hope that they will inspire further debate and research on this topic. Starting from the ethical principles of respect for reproductive autonomy, avoiding harm (in terms of stigma or anxiety) and inclusivity, we have formulated five recommendations: (i) frame fertility awareness messages with (reproductive) autonomy in mind and aim to be inclusive of those who do not represent the traditional nuclear family; (ii) be empathetic and steer clear of blame; (iii) avoid scaremongering and offer a positive angle; (iv) give due consideration to both women and men in fertility health messaging; and (v) tailor the messages to particular contexts and audiences and develop resources in close collaboration with the target groups