Numerical study of the optical nonlinearity of doped and gapped graphene: From weak to strong field excitation

Numerically solving the semiconductor Bloch equations within a phenomenological relaxation time approximation, we extract both the linear and nonlinear optical conductivities of doped graphene and gapped graphene under excitation by a laser pulse. We discuss in detail the dependence of second harmonic generation, third harmonic generation, and the Kerr effects on the doping level, the gap, and the electric field amplitude. The numerical results for weak electric fields agree with those calculated from available analytic perturbation formulas. For strong electric fields when saturation effects are important, all the effective third order nonlinear response coefficients show a strong field dependence.Comment: 12 pages with 9 figure

Third order nonlinearity of graphene: effects of phenomenological relaxation and finite temperature

We investigate the effect of phenomenological relaxation parameters on the third order optical nonlinearity of doped graphene by perturbatively solving the semiconductor Bloch equation around the Dirac points. An analytic expression for the nonlinear conductivity at zero temperature is obtained under the linear dispersion approximation. With this analytic formula as starting point, we construct the conductivity at finite temperature and study the optical response to a laser pulse of finite duration. We illustrate the dependence of several nonlinear optical effects, such as third harmonic generation, Kerr effects and two photon absorption, parametric frequency conversion, and two color coherent current injection, on the relaxation parameters, temperature, and pulse duration. In the special case where one of the electric fields is taken as a dc field, we investigate the dc-current and dc-field induced second order nonlinearities, including dc-current induced second harmonic generation and difference frequency generation.Comment: 23+ pages, 10 figures. In this version we correct a sign typo in Eq. (25), for which we thank the discussion in the work http://arxiv.org/abs/1506.00534v

The logic of organizational markets: thinking through resource partitioning theory

Resource partitioning theory claims that Increasing concentration enhances the life chances of specialist organizations. We systemati- cally think through this theory,specify implicit background assump- tions,sharpen concepts,and rigorously check the theory s logic.As a result,we increase the theory s explanatory power,and claim contrary to received opinion that under certain eneral conditions, resource partitioning and the proliferation of specialists can take place independently of organizational mass and relative size effects, size localized competition,diversifying consumer tastes, increasing number of dimensions of the resource space,and changing niche widths. Our analysis makes furthermore clear that specialist and generalist strategies are asymmetric, and shows that not concentration enhances the life chances of specialists but economies of scale instead.Under the conditions explicated,we argue that if scale economies come to dominate,the number of organizations in the population increases, regardless of the incumbents sizes.

The Belgian migration to SEPA (Single Euro Payments Area)

The main aim of SEPA (Single European Payment Area) is to promote financial integration in Europe, more particularly in the field of cashless payment services and payment systems. It is intended to enable all economic players (businesses, consumers and public authorities) to effect payments anywhere in the SEPA zone (the 27 EU countries plus Iceland, Liechtenstein, Norway and Switzerland) as easily, securely and efficiently as domestic payments. It must also be possible to execute these payments in accordance with a single regulatory framework within which all players have the same rights and obligations. To that end, the European Parliament and the Council adopted a directive on payment services in the internal market, which has to be transposed into national law by 1 November 2009. The SEPA migration is a process whereby the current national payment instruments are gradually replaced by standardised European instruments. More precisely, European instruments have been developed for credit transfers and direct debits, while a general framework has been set up for payment cards. The development of standards for these payment instruments and the organisation of the migration to SEPA were largely decided by the banking sector. For that purpose, interbank consultation bodies were set up at national and European level, and special structures were created to encourage societal dialogue concerning SEPA and its implementation. In Belgium, the organisational structures behind the SEPA migration are the “Steering Committee on the future of means of payment” and the SEPA interbank Forum. SEPA is being created in phases. The signal for the operational launch was given just over a year ago : since 28 January 2008 it has been possible to use the European transfer to effect payments anywhere in the SEPA area. The banking sector set the launch date for the European direct debit at European level : it will coincide with the date on which the payment services directive has to be transposed into national law, namely 1 November 2009. The success of the launch of the European direct debit on that date will depend mainly on a number of legal aspects, its adoption by the market, and the time taken to implement it in banks and businesses. The SEPA Card Framework is ready and has applied since 1 January 2008, but that has had little or no practical impact on the Belgian market in bank cards. Although the original plan for switching to a new payment card scheme in a single operation was abandoned, the Belgian market is technically ready for the introduction of new card payment schemes.SEPA (Single European Payment Area), payments instruments, financial integration, Payment Services Directive, banking standards

Housing supply and the interaction of regional population and employment

Housing markets may significantly affect the relationship between regional population and employment, if housing supply is not fully accommodative to demand. We analyse the relationships between housing supply, regional population and employment empirically in a three-equation dynamic model. Annual regional panel data are used for the Netherlands, where a strong tradition of spatial planning exists. We find that net internal migration is strongly determined by housing supply, whereas employment growth has no statistically significant impact. Growth of the housing stock is only moderately affected by population and employment, possibly as a result of restrictive spatial policies. Employment adjusts substantially towards a long-run relationship with the regional population. The analysis further indicates that labour markets drive this long-run adjustment more than local consumer demand. Hence, people follow houses rather than jobs, and jobs follow people in the long run.

Compensation of regional unemployment in housing markets

Why are regional unemployment differentials in Europe so persistent if, as the wage curve literature demonstrates, there is no compensation in labour markets? We hypothesise that workers in high-unemployment regions are compensated in housing markets. Modelling regional unemployment differentials as a consequence of centralised wage bargaining, we show that clearing of land markets may undo the incentive for workers to migrate to low-unemployment regions in general equilibrium. The compensating differentials hypothesis is tested on city-level data for several countries. Controlling for variation in income and amenities, housing is found to be about 3 percent less expensive on average in cities where unemployment is 10 percent up. An analysis of housing demand survey data, which takes account of housing heterogeneity, yields a similar negative relationship. The magnitude of the income effect generated by this compensating differential is consistent with a -0.10 wage curve elasticity. Workers in regions with high unemployment and low per capita income are therefore not necessarily worse off, and regional support programs should take this into account.

Relaxation phenomena in CsCoCl3·2 H2O

Dynamic susceptibility measurements have been performed on a single crystal of CsCoCl3·2H2O at liquid temperatures by means of a Hartshorn mutual inductance bridge. At the magnetic phase transition a maximum in τabs(H) has been observed. A jump in τabs(T) has been found at the λ-point of liquid helium

Crystallographic and magnetic structure of RbCoCl3 · 2 D2O

The crystallographic and magnetic structure of RbCoCl3 · 2 D2O were determined mainly by means of neutron diffraction measurements. Below TN = 2.79 K the magnetic moments are ordered in a canted antiferromagnetic pattern. A meta-magnetic phase transition is observed at unusually small field values (H = 18 Oe at T = 2 K)

Changements climatiques, sécurité alimentaire et petits producteurs

La présente note d’information donne un aperçu du point de vue de l’AR5 concernant les impacts des changements climatiques sur l’alimentation et l’agriculture – en particulier l’alimentation et l’agriculture du demi-milliard de petits exploitants agricoles, éleveurs et pêcheurs qui sont les plus tributaires, dans l’immédiat, des systèmes agricoles pour leurs moyens d’existence. La note d’information commence par faire l’état des lieux en ce qui concerne les changements climatiques dans les années 2010, jette ensuite un regard prospectif sur les 15 prochaines années eu égard aux impacts et à l’adaptation dans les années 2030, avant de se pencher enfin sur les années 2050 et au-delà