Measuring two-photon orbital angular momentum entanglement

We put forward an approach to estimate the amount of bipartite spatial entanglement of down-converted photon states correlated in orbital angular momentum and the magnitude of the transverse (radial) wave vectors. Both degrees of freedom are properly considered in our framework, which only requires azimuthal local linear optical transformations and mode selection analysis with two fiber detectors. The coincidence distributions predicted by our approach give an excellent fit to the distributions measured in a recent experiment aimed to show the very high-dimensional transverse entanglement of twin photons from a down-conversion source. Our estimate for the Schmidt number is substantially lower but still confirms the presence of high-dimensional entanglement.Comment: Extended paper of a published version in PRA, with some extra appendice

Occupational choice, number of entrepreneurs and output: theory and empirical evidence with Spanish data

This paper extends the (Lucas, Bell J Econ 9:508–523,1978) model of occupational choices by individuals with different skills, beyond the simple options of self-employment or wage-employment, by including a second choice for the self-employed. That is, an option to hire employees and so become self-employed with employees (SEWEs), or to be self-employed without employees (SEWNEs). We solve for the market equilibrium and examine the sensitivity of relative sizes of occupational groups, and of the level of productivity, to changes in the exogenous parameters. The results show that the positive (negative) association between number of SEWEs (SEWNEs) and productivity, observed in the Spanish data, can be explained, under certain conditions, as the result of cross-region and time differences in average skills. These findings point to the importance of distinguishing between SEWEs and SEWNEs in drawing valid conclusions concerning any link between entrepreneurship and economic development

Earnings distribution, corporate governance and CEO pay

We investigate the relationship between earnings differentials and the pay of CEOs of 190 British companies between 1970 and 1990. We find that (i) changes in the differential between the 90th and 50th weekly earnings percentiles for non-manual adult male workers [90:50] explain changes in the level of real CEO salary and bonus in our sample of companies; (ii) changes in this differential also account for changes in the elasticity of CEO pay to firm size; (iii) a broader measure of earnings inequality does far worse than 90:50 at explaining changes in both the level and the firm size elasticity of CEO pay; (iv) fitting the model on data for 1970-1983 and predicting pay levels for the period starting with the widespread adoption of executive share option schemes in 1984, we find a structural break in the relationship between lower management pay differentials and the pay of the CEO. We conclude first that top executive pay prior to 1984 was a stable function of both firm size and earnings differentials lower on the administrative ladder, consistent with a hypothesis advanced by Herbert Simon in 1957; and second that the use of share options from 1984 onward represents not simply a change in the mode of top executive compensation, but a de -linking of the pay of top executives and that of their subordinates

Exchange Monte Carlo for Molecular Simulations with Monoelectronic Hamiltonians

We introduce a general Monte Carlo scheme for achieving atomistic simulations with monoelectronic Hamiltonians including the thermalization of both nuclear and electronic degrees of freedom. The kinetic Monte Carlo algorithm is used to obtain the exact occupation numbers of the electronic levels at canonical equilibrium, and comparison is made with Fermi-Dirac statistics in infinite and finite systems. The effects of a nonzero electronic temperature on the thermodynamic properties of liquid silver and sodium clusters are presented

Phase-Induced (In)-Stability in Coupled Parametric Oscillators

We report results on a model of two coupled oscillators that undergo periodic parametric modulations with a phase difference $\theta$. Being to a large extent analytically solvable, the model reveals a rich $\theta$ dependence of the regions of parametric resonance. In particular, the intuitive notion that anti-phase modulations are less prone to parametric resonance is confirmed for sufficiently large coupling and damping. We also compare our results to a recently reported mean field model of collective parametric instability, showing that the two-oscillator model can capture much of the qualitative behavior of the infinite system.Comment: 19 pages, 8 figures; a version with better quality figures can be found in http://hypatia.ucsd.edu/~mauro/English/publications.htm

Adsorption of hydrogen sulphide on Metal-Organic Frameworks

Three new sets of interatomic potentials to model hydrogen sulphide (H2S) have been fitted. One of them is a 3-sites potential (which we named 3S) and the other two are 5-sites potentials (which we named 5S and 5Sd). The molecular dipole of the 3S and 5S potentials is 1.43 D, which is the value usually employed for H2S potentials, while the dipole of the 5Sd is the dipole measured experimentally for the H2S molecule, circa 0.974 D. The interatomic potentials parameters were obtained by fitting the experimental vapour-liquid equilibrium, vapour pressure and liquid density curves. The potential parameters fitted so far for H2S have been obtained applying long-range corrections to the Lennard-Jones energy. For that reason, when a cut and shift of the Lennard-Jones potentials is applied they do not yield the correct results. We employed a cut and shift of the Lennard-Jones potentials in the fitting procedure, which facilitates the use of the new potentials to model H2S adsorption on systems such as Metal-Organics Frameworks (MOFs). We have employed the newly developed potentials to study the adsorption of H2S on Cu-BTC, MIL-47 and IRMOF-1 and the results agree with the available electronic structures calculations. All calculations (both quantum and interatomic potential-based) predict that H2S does not bind to the Cu atoms in Cu-BTC

Modifying the hydrophobic nature of MAF-6

Using a combination of molecular simulations techniques, we evaluate the structural tunability of the metal azolate framework with zeolitic RHO topology, MAF-6. Two mechanisms are explored to induce hydrophilicity to this hydrophobic material. The study at a molecular level of water adsorption takes place under a variety of conditions. On a first step, we consider water mixtures containing benzene or alcohols, paying special attention to the effect of the size of the alcohol molecules. On a second approach, we analyse the effect of small weight percentages of salt into the MAF-6 on the water adsorption. We first validate the accuracy of the host–guest interactions by reproducing experimental data. A new set of Lennard-Jones parameters for the interaction water- MAF-6 is also provided. The water adsorption behaviour of MAF-6 is studied in terms of adsorption isotherms, heats of adsorption, radial distribution functions, hydrogen bonds formation, and water distribution inside the material. We found that the presence of long molecules of alcohols favours the water adsorption at low values of pressure by smoothing the phase transition of water withing the MAF-6. On the other hand the addition of salt to the structure creates additional adsorption sites for water enhancing its adsorption, while reducing the saturation capacity of the material since the presence of salt reduces the accessible pore volume

Novel peritoneopericardial diaphragmatic hernia in a dog

A 23-month-old German shepherd dog (GSD) with chronic intermittent gastrointestinal signs presented following acute deterioration compatible with gastrointestinal obstruction and suspected peritoneopericardial diaphragmatic hernia (PPDH). Physical examination revealed depression, abdominal pain, decreased pulse quality, reduced heart sounds and tachypnoea with a shallow breathing pattern. Radiography confirmed PPDH and a granular, 1.3 cm mineral opacity cranial to the cardiac silhouette within the cranioventral thorax. Coeliotomy and median sternotomy revealed strangulated jejunum within the cranial mediastinum, cranial to the pericardium. This was resected and herniorrhaphy was performed. Postoperatively the dog became normal. Midline fusion defects, including the pericardium, can be associated with PPDH and in such cases sternotomy may be required. This is the first report of surgical management of strangulated intestine secondary to an initially conservatively managed PPDH. Mineral opacity on radiography associated with PPDH may represent chronic partial obstruction. This possibly represents a second GSD with Cantrell’s pentalogy