A scaling-limit approach to the theory of laser transition

The conditions for the appearance of a sharp laser transition are formulated in terms of a scaling limit, involving vanishing cavity loss and light-matter coupling, $\kappa \to 0$, $g \to 0$, such that $g^2/\kappa$ stays finite. It is shown analytically that in this asymptotic parameter domain, and for pump rates above the threshold value, the photon output becomes large in a sense that is specified, and the photon statistics becomes strictly Poissonian. Numerical examples for the case of a two-level and a three-level emitter are presented and discussed in relation to the analytic result.Comment: Intended as contribution to "Photonics Europe 2012" Brussels, Belgiu

Global Public Goods and Global Health

The repair rate on electron beam welded diaphragm hasn’t been at the desired level at Siemens SIT for several years. An improvement program the past five years has reduce the repair rate from 60% to 12-15% but the goal of 5% repair rate hasn’t been met. Collection of diaphragm weld and repair data started in the fall 2011 and in this thesis the material composition of the materials used for the production will be analysed from a statistical perspective. The thesis includes a comprehensive research of the nonparametric statistical methods suitable for non normally distributed, highly kurtotic and skewed data. Unfortunately a lot of statistical tests loose their power to correctly reject a false hypothesis with this kind of data. All of the elements in the material composition and the mechanical properties were analysed individually. In some of the cases it was possible to use statistical methods but in other it was not possible to conclude anything with statistics. Every case of outliers was evaluated individually. The main conclusions are that in all of the four materials there are some elements and mechanical properties outside of the material specifications. A number of cases also had outliers inside of the material specification and in most cases those were causing the variability in the data and had higher repair rates than the overall repair rate. Some trends were found, for example the weld quality was better for lower yield strength in all materials and higher chromium content in material A produced better quality. The first steps to improvement for Siemens are to find out why materials outside of the material specifications are getting all the way to the production without anyone noticing. A simple material process control chart could visually notify if a material is outside of the specification limits or even just outside of the usual. Knowing exactly how the material is before starting the production will give time and space for preventive measures if they are necessary and could improve lead times and decrease costs.För några år har Siemens hatt kvalitetsproblem med Electron Beam svetsing av mellanväggar. Förbättringsprojekt har reducerat reparationer intensivt men fortfarande finns det problemer med svetsningen. Inga mellanväggar lämnar produktionen utan att ha bra kvalitet så att förbättringarna ska fokusera på att reducera produktionskostnader och ledtider. Hösten 2011 började Siemens att samla reparation data för mellanväggarna och i det examens arbetet blir materialsamansättningen analyserad med statistiska metoder. Arbetet innehåller övergripande analysis på non-parametriska statistiska metoder och hur dom funkerar på skevat data med hög kurtosis. Tyvärr finns det inte många metoder som har hög chans att förkasta falska hypoteser när man jobbar med sånt data. Alla elementer och mekaniska egenskaper av materialet blev analyserade, men tyvärr inte alltid med statistiska metoder. Alla extremvärden blev analyserade individuellt. I alla fyra materialer finns det elementer och mekaniska egenskaper utan förmaterialets specifikationer. I vissa fall finns det outliers inom materialets specifikationer men som har högre reparation procent än det vanliga och orsakar variationen i datat. Vissa tendenser kunne hittas, till exempel att det går bättre att svetsa materialer med lägre sträckgräns och högre kromhalt går bättre för material A. Simpelt processstyrningdiagram skulle kunna visa om material är utanför material specifikationen men också om materialet är utanför det ”vanliga”. Att veta exact hur materialet är innan produktion kan sjunka ledtider och produktionskostnader

Nonlinear plastic modes in disordered solids

We propose a framework within which a robust mechanical definition of precursors to plastic instabilities, often termed `soft-spots', naturally emerges. They are shown to be collective displacements (modes) $\hat{z}_0$ that correspond to local minima of the `barrier function' $b(\hat{z})$. The latter is derived from the cubic approximation of the variation $\delta U_{\hat{z}}(s)$ of the potential energy upon displacing particles a distance $s$ along $\hat{z}$. We show that modes $\hat{z}_0$ corresponding to low-lying minima of $b(\hat{z})$ lead to transitions over energy barriers in the glass, and are therefore associated with highly asymmetric variations $\delta U_{\hat{z}}(s)$ with $s$. We further demonstrate how a heuristic search for local minima of $b(\hat{z})$ can a-priori detect the locus and geometry of imminent plastic instabilities with remarkable accuracy, at strains as large as $\gamma_c-\gamma \sim 10^{-2}$ away from the instability strain $\gamma_c$, where the non-affine displacements under shear are still largely delocalized. Our findings suggest that the a-priori detection of plastic instabilities can be effectively carried out by the investigation of the landscape of $b(\hat{z})$.Comment: 8 pages, 8 figure

Analyzing the changing gender wage gap based on multiply imputed right censored wages

"In order to analyze the gender wage gap with the German IAB-employment sample we have to solve the problem of censored wages at the upper limit of the social security system. We treat this problem as a missing data problem. We regard the missingness mechanism as not missing at random (NMAR, according to Little and Rubin, 1987, 2002) as well as missing by design. The censored wages are multiply imputed by draws of a random variable from a truncated distribution. The multiple imputation is based on Markov chain Monte Carlo (MCMC) technique. We complete the dataset with this technique in order to apply a Juhn-Murphy-Pierce-decomposition. As the main sources for the narrowing gender wage gap from 1991 to 2001 we identify an improvement of women's position within the wage distribution." (Author's abstract, IAB-Doku) ((en))Lohnunterschied, Lohnhöhe, geschlechtsspezifische Faktoren, IAB-Beschäftigtenstichprobe, Datenaufbereitung, Datenanalyse, angewandte Statistik, Imputationsverfahren

Specific Plateaus of the Quantum Hall Effect Induced by an Applied Bias

The spectrum and the eigenstates of a finite 2D tight-binding electronic system, with Dirichlet boundary conditions, in magnetic field and external linear potential are studied. The eigenstates show an equipotential character and may cross the plaquette in the direction perpendicular to the electric field. When leads are added to the plaquette, the channels carrying the current may be shortcut by equipotentials, resulting in additional plateaus situated inbetween the usual IQHE plateaus. This idea is confirmed by a numerical calculation within the four-terminal Landauer-B\"{u}ttiker approach.Comment: 9 pages, revtex, 2 gif figures and 5 postscript figure

Wage subsidies for needy job-seekers and their effect on individual labour market outcomes after the German reforms

"In Germany, since 2005 needy job-seekers without access to earnings-related and insurance-paid 'unemployment benefit I' are entitled to means-tested and tax-funded 'unemployment benefit II'. Several active labour market programmes support the integration of these needy job-seekers into the labour market. Our paper estimates the average effect of targeted wage subsidies - paid to employers for a limited period of time - on the subsequent labour market prospects of participating needy job-seekers. We apply propensity score matching to compare participants with a group of similar non-participants. The results show that wage subsidies had in fact large and significant favourable effects: 20 months after taking up a subsidised job, the share of persons in regular employment is nearly 40 percentage points higher across participants. Estimated effects on the shares not unemployed and the share no longer receiving 'unemployment benefit II' are slightly smaller." (Author's abstract, IAB-Doku) ((en))Arbeitslosengeld II-Empfänger, Eingliederungszuschuss - Erfolgskontrolle, Arbeitsmarktchancen