Well-posedness of the spatially homogeneous Landau equation for soft potentials

We consider the spatially homogeneous Landau equation of kinetic theory, and provide a differential inequality for the Wasserstein distance with quadratic cost between two solutions. We deduce some well-posedness results. The main difficulty is that this equation presents a singularity for small relative velocities. Our uniqueness result is the first one in the important case of soft potentials. Furthermore, it is almost optimal for a class of moderately soft potentials, that is for a moderate singularity. Indeed, in such a case, our result applies for initial conditions with finite mass, energy, and entropy. For the other moderatley soft potentials, we assume additionnally some moment conditions on the initial data. For very soft potentials, we obtain only a local (in time) well-posedness result, under some integrability conditions. Our proof is probabilistic, and uses a stochastic version of the Landau equation, in the spirit of Tanaka

Relaxation dynamics in covalently bonded organic monolayers on silicon

We study the dynamic electrical response of a silicon-molecular monolayer-metal junctions and we observe two contributions in the admittance spectroscopy data. These contributions are related to dipolar relaxation and molecular organization in the monolayer in one hand, and the presence of defects at the silicon/molecule interface in the other hand. We propose a small signal equivalent circuit suitable for the simulations of these molecular devices in commercial device simulators. Our results concern monolayers of alkyl chains considered as a model system but can be extended to other molecular monolayers. These results open door to a better control and optimization of molecular devices.Comment: 1 pdf file including text, figures and tables. Phys. Rev. B, in pres

Anomalous photon diffusion in atomic vapors

The multiple scattering of photons in a hot, resonant, atomic vapor is investigated and shown to exhibit a L\'evy Flight-like behavior. Monte Carlo simulations give insights into the frequency redistribution process that originates the long steps characteristic of this class of random walk phenomena

Wigner function negativity and contextuality in quantum computation on rebits

We describe a universal scheme of quantum computation by state injection on rebits (states with real density matrices). For this scheme, we establish contextuality and Wigner function negativity as computational resources, extending results of [M. Howard et al., Nature 510, 351--355 (2014)] to two-level systems. For this purpose, we define a Wigner function suited to systems of $n$ rebits, and prove a corresponding discrete Hudson's theorem. We introduce contextuality witnesses for rebit states, and discuss the compatibility of our result with state-independent contextuality.Comment: 18 + 4 page

A cold-atom random laser

Conventional lasers make use of optical cavities to provide feedback to gain media. Conversely, mirrorless lasers can be built by using disordered structures to induce multiple scattering, which increases the effective path length in the gain medium and thus provides the necessary feedback. These so-called random lasers potentially offer a new and simple mean to address applications such as lighting. To date, they are all based on condensed-matter media. Interestingly, light or microwave amplification by stimulated emission occurs also naturally in stellar gases and planetary atmospheres. The possibility of additional scattering-induced feedback (that is, random lasing) has been discussed and could explain unusual properties of some space masers. Here, we report the experimental observation of random lasing in a controlled, cold atomic vapour, taking advantage of Raman gain. By tuning the gain frequency in the vicinity of a scattering resonance, we observe an enhancement of the light emission of the cloud due to random lasing. The unique possibility to both control the experimental parameters and to model the microscopic response of our system provides an ideal test bench for better understanding natural lasing sources, in particular the role of resonant scattering feedback in astrophysical lasers

Business angels and Agency Costs

This paper examines business angels’ behaviours towards agency costs by studying how business angels reduce conflicts of interests with entrepreneurs. The theoretical framework of this paper is based on the agency theory and the incomplete contract theory. In order to make this study more accurate, corporate governance mechanisms were also used to decipher and understand business angels’ behaviours. Using these theories, the research framework is based on four different areas of interest: contracts and the different rights these involve, informal and formal involvement of business angels in investments, the relationship between the entrepreneurs and the business angels and finally corporate governance mechanisms. This paper is based an analysis of the results of 5 interviews and a questionnaire that was sent to 78 British and French business angels. From these the impact of different factors on the agency costs was determined. The findings show that the business angels’ involvement, the trustworthy relationship between the business angels and the entrepreneurs and certain corporate governance mechanisms can successfully mitigate against agency costs. On the contrary, analysis results showed that using extensive control and monitoring rights or appointing non-executive directors onto the boards increased agency costs. Thus, this paper answers how business angels can mitigate agency costs with entrepreneurs

Threshold of a random laser based on Raman gain in cold atoms

We address the problem of achieving a random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. In this system, the elastic scattering cross-section is related to the complex atomic polarizability. As a consequence, the random laser threshold is expressed as a function of this polarizability, which can be fully determined by spectroscopic measurements. We apply this idea to experimentally evaluate the threshold of a random laser based on Raman gain between non-degenerate Zeeman states and find a critical optical thickness on the order of 200, which is within reach of state-of-the-art cold-atom experiments

0346: Neonatal arterial switch operation: the sooner the better!

ObjectiveTo evaluate the impact of preoperative management on in-hospital post-operative outcomes after an arterial switch operation (ASO) in newborns with transposition of the great arteries (TGA)MethodsIn this retrospective monocentric study, we included all newborns with TGA±ventricular septal defect who underwent an ASO between 2008 and 2014. Collected data included demographics, clinical and anatomic characteristics, and preoperative management (Rashkind, prostaglandin infusion, mechanical ventilation, age at surgery). Univariate and multivariate analyses were performed to study the impact of preoperative characteristics on time to extubation, a surrogate marker of postoperative morbidity.ResultsAmong the 59 included newborns, 47 (79%) had an antenatal diagnosis, 31 (52%) received prostaglandins (median duration: 96 h; range 0-192h), and 38 (65%) underwent a Rashkind procedure. Mean age at surgery was 5±2 days. The mortality rate was 5% (n=3). Younger age at surgery significantly increased the probability to be extubated within 2 days after surgery, both in univariate analysis (Odd ratio 0.64; confidence interval 0.44-0.92) (p=0.01) and after adjustment for preoperative characteristics and management (OR 0.61; CI 0.39-0.95) (p=0.03). The presence of coronary anomalies tended to increase time to extubation, whereas Rashkind procedure and prostaglandin treatment had no impact.ConclusionOur study shows that younger age at surgery is associated with lower postoperative morbidity in newborns undergoing an ASO. These findings suggest that early surgery is preferable to delay with palliative management such as Rashkind and/or Prostaglandins

Meningitis Serogroup W135 Outbreak, Burkina Faso, 2002

In 2002, the largest epidemic of Neisseria meningitidis serogroup W135 occurred in Burkina Faso. The highest attack rate was in children <5 years of age. We describe cases from 1 district and evaluate the performance of the Pastorex test, which had good sensitivity (84%) and specificity (89%) compared with culture or PCR