Coulomb gap in a model with finite charge transfer energy

The Coulomb gap in a donor-acceptor model with finite charge transfer energy $\Delta$ describing the electronic system on the dielectric side of the metal-insulator transition is investigated by means of computer simulations on two- and three-dimensional finite samples with a random distribution of equal amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry of the model presented with respect to the exchange of donors and acceptors are derived. In the immediate neighborhood of the Fermi energy $\mu$ the the density of one-electron excitations $g(\epsilon)$ is determined solely by finite size effects and $g(\epsilon)$ further away from $\mu$ is described by an asymmetric power law with a non-universal exponent, depending on the parameter $\Delta$.Comment: 10 pages, 6 figures, submitted to Phys. Rev.

Patient factors associated with titration of medical therapy in patients with heart failure with reduced ejection fraction: data from the QUALIFY international registry

Aims Failure to prescribe key medicines at evidence-based doses is associated with increased mortality and hospitalization for patients with Heart Failure with reduced Ejection Fraction (HFrEF). We assessed titration patterns of guideline-recommended HFrEF medicines internationally and explored associations with patient characteristics in the global, prospective, observational, longitudinal registry. Methods and results Data were collected from September 2013 through December 2014, with 7095 patients from 36 countries [>18 years, previous HF hospitalization within 1–15 months, left ventricular ejection fraction (LVEF) ≤ 40%] enrolled, with dosage data at baseline and up to 18 months from 4368 patients. In 4368 patients (mean age 63 ± 17 years, 75% male) ≥ 100% target doses at baseline: 30.6% (ACEIs), 2.9% (ARBs), 13.9% (BBs), 53.8% (MRAs), 26.2% (ivabradine). At final follow-up, ≥100% target doses achieved in more patients for ACEI (34.8%), BB (18.0%), and ivabradine (30.5%) but unchanged for ARBs (3.2%) and MRAs (53.7%). Adjusting for baseline dosage, uptitration during follow-up was more likely with younger age, higher systolic blood pressure, and in absence of chronic kidney disease or diabetes for ACEIs/ARBs; younger age, higher body mass index, higher heart rate, lower LVEF, and absence of coronary artery disease for BBs. For ivabradine, uptitration was more likely with higher resting heart rate. Conclusions The international QUALIFY Registry suggests that few patients with HFrEF achieve target doses of disease-modifying medication, especially older patients and those with co-morbidity. Quality improvement initiatives are urgently required

Contextual and Granular Policy Enforcement in Database-backed Applications

Database-backed applications rely on inlined policy checks to process users' private and confidential data in a policy-compliant manner as traditional database access control mechanisms cannot enforce complex policies. However, application bugs due to missed checks are common in such applications, which result in data breaches. While separating policy from code is a natural solution, many data protection policies specify restrictions based on the context in which data is accessed and how the data is used. Enforcing these restrictions automatically presents significant challenges, as the information needed to determine context requires a tight coupling between policy enforcement and an application's implementation. We present Estrela, a framework for enforcing contextual and granular data access policies. Working from the observation that API endpoints can be associated with salient contextual information in most database-backed applications, Estrela allows developers to specify API-specific restrictions on data access and use. Estrela provides a clean separation between policy specification and the application's implementation, which facilitates easier auditing and maintenance of policies. Policies in Estrela consist of pre-evaluation and post-evaluation conditions, which provide the means to modulate database access before a query is issued, and to impose finer-grained constraints on information release after the evaluation of query, respectively. We build a prototype of Estrela and apply it to retrofit several real world applications (from 1000-80k LOC) to enforce different contextual policies. Our evaluation shows that Estrela can enforce policies with minimal overheads

High-θ polyacetylene: DC conductivity between 14 mK and 300 K

Highly stretch-oriented polyacetylene (6.5:1) yields conductivities σ of typically 20 000–100 000 Ω−1cm−1 at room temperature when highly doped with iodine. Between T = 300 K and T = 14 mK, σ decreases monotonically by about a factor of 5 for fresh samples. Above 400 mK the temperature dependence for fresh samples is fitted by the SHENG formula and can be interpreted within a phenomenological model. On fresh samples, MONTGOMERY measurements of the conductivities parallel (σı) and perpendicular (σσ) to the stretching axis show a temperature independent anisotropy A=σı/σσ of about 25 indicating a common limiting mechanism for both, σı and σσ. Deliberate oxygen ageing drastically changes σ(T) and results in a temperature dependence of A

Positive ion mobility in normal and superfluid 3He

We report the first measurements of negative ion motion in the superfluid phases of 3He and in the normal phase below 17 mK. Refrigeration was achieved with nuclear demagnetization of copper and we used a pulsed NMR platinum powder thermometer immersed in the liquid. In the A phase the longitudinal resonance frequency provided an additional high-resolution thermometer. In the normal phase we observed a strictly temperature-independent mobility. In the superfluid phases we found two velocity regimes. For small applied electric fields the velocity is a linear function of the field and the corresponding mobility increases monotonically toward lower temperatures. At high electric fields the velocity is a nonlinear function of the field as a result of the pair-breaking effect of the moving ion. Available theoretical calculations are only in partial agreement with our results

On the statistical analysis of single vortex nucleation events in superflud 4He

We investigate the statistical properties of single phase slip events observed in vortex nucleation experiments in 4He by the groups in Berkeley and Paris. From the cumulative distribution function of the events we calculate the sliprate as a function of flow velocity. The critical velocity is defned as the mean velocity and its statistical width as the standard deviation. From the slip rate and from the observed linear temperature dependence of the critical velocitywe obtain the energy barrier for vortex nucleation which is a quadratic function of the flow velocity. A comparison with the statistical properties of the laminar to turbulent transition in the flow around an oscillating sphere shows strikingly different behaviour

Stability of Laminar and Turbulent Flow of Superfluid ⁴He at mK Temperatures around an Oscillating Microsphere

The flow of superfluid helium around a vibrating microsphere is investigated at temperatures between 1 K and 25 mK. At small oscillation amplitudes pure potential flow is observed, the linear drag force on the sphere being determined only by ballistic quasiparticle scattering below 0.7 K with phonons contributing exclusively below 0.5 K. At larger oscillation amplitudes a strongly nonlinear drag force gives evidence of stable turbulent flow if at least 0.6 pW are transferred from the sphere to the turbulent superfluid. In an intermediate range of amplitudes (or driving forces) both flow patterns are unstable and intermittent switching between both is observed below 0.5 K. We have recorded time series of this switching phenomenon at constant drives and temperatures lasting up to 36 hours. We have made a statistical analysis of the times series by means of reliability theory. The lifetime of the turbulent phases grows with increasing drive and diverges at a critical value (or at least becomes unmeasurably long). Stability of the laminar phases in the intermediate regime depends on the excess velocity of the sphere above the critical velocity. Metastable laminar phases are observed above the critical velocity having a mean lifetime limited to 25 minutes by natural background radioactivity which occasionally produces local vorticity due to ionization of the liquid. Finally, it is suggested that the breakdown of potential flow belongs to the class of “system failure” experiments which is well known in reliability testing and whose statistical properties are described by extreme-value theory