An insight into polarization states of solid-state organic lasers

The polarization states of lasers are crucial issues both for practical applications and fundamental research. In general, they depend in a combined manner on the properties of the gain material and on the structure of the electromagnetic modes. In this paper, we address this issue in the case of solid-state organic lasers, a technology which enables to vary independently gain and mode properties. Different kinds of resonators are investigated: in-plane micro-resonators with Fabry-Perot, square, pentagon, stadium, disk, and kite shapes, and external vertical resonators. The degree of polarization P is measured in each case. It is shown that although TE modes prevail generally (P>0), kite-shaped micro-laser generates negative values for P, i.e. a flip of the dominant polarization which becomes mostly TM polarized. We at last investigated two degrees of freedom that are available to tailor the polarization of organic lasers, in addition to the pump polarization and the resonator geometry: upon using resonant energy transfer (RET) or upon pumping the laser dye to an higher excited state. We then demonstrate that significantly lower P factors can be obtained.Comment: 12 pages, 12 figure

Synthetic Data Generation and Defense in Depth Measurement of Web Applications

Measuring security controls across multiple layers of defense requires realistic data sets and repeatable experiments. However, data sets that are collected from real users often cannot be freely exchanged due to privacy and regulatory concerns. Synthetic datasets, which can be shared, have in the past had critical flaws or at best been one time collections of data focusing on a single layer or type of data. We present a framework for generating synthetic datasets with normal and attack data for web applications across multiple layers simultaneously. The framework is modular and designed for data to be easily recreated in order to vary parameters and allow for inline testing. We build a prototype data generator using the framework to generate nine datasets with data logged on four layers: network, file accesses, system calls, and database simultaneously. We then test nineteen security controls spanning all four layers to determine their sensitivity to dataset changes, compare performance even across layers, compare synthetic data to real production data, and calculate combined defense in depth performance of sets of controls

Evaluation of alternative solvents in common amide coupling reactions : replacement of dichloromethane and N,N-dimethylformamide

A range of alternative solvents have been evaluated within amidation reactions employing common coupling reagents with a view to identifying suitable replacements for dichloromethane and N,N-dimethylformamid

Laser-controlled fluorescence in two-level systems

The ability to modify the character of fluorescent emission by a laser-controlled, optically nonlinear process has recently been shown theoretically feasible, and several possible applications have already been identified. In operation, a pulse of off-resonant probe laser beam, of sufficient intensity, is applied to a system exhibiting fluorescence, during the interval of excited- state decay following the initial excitation. The result is a rate of decay that can be controllably modified, the associated changes in fluorescence behavior affording new, chemically specific information. In this paper, a two-level emission model is employed in the further analysis of this all-optical process; the results should prove especially relevant to the analysis and imaging of physical systems employing fluorescent markers, these ranging from quantum dots to green fluorescence protein. Expressions are presented for the laser-controlled fluorescence anisotropy exhibited by samples in which the fluorophores are randomly oriented. It is also shown that, in systems with suitably configured electronic levels and symmetry properties, fluorescence emission can be produced from energy levels that would normally decay nonradiatively. © 2010 American Chemical Society

Fluorescence studies on new potential antitumoral benzothienopyran-1-ones in solution and in liposomes

Fluorescence properties of four new potential antitumoral compounds, 3-arylbenzothieno[2,3-c]pyran-1-ones, were studied in solution and in lipid membranes of dipalmitoyl phosphatidylcholine (DPPC), egg yolk phosphatidylcholine (Egg-PC) and dioctadecyldimethylammonium bromide (DODAB). The 3-(4-methoxyphenyl)benzothieno[2,3-c]pyran-1-one (1c) exhibits the higher fluorescence quantum yields in all solvents studied. All compounds present a solvent sensitive emission, with significant red shifts in polar solvents for the methoxylated compounds. The results point to an ICT character of the excited state, more pronounced for compound 1c. Fluorescence (steady-state) anisotropy measurements of the compounds incorporated in liposomes of DPPC, DODAB and Egg-PC indicate that all compounds have two different locations, one due to a deep penetration in the lipid membrane and another corresponding to a more hydrated environment. In general, the methoxylated compounds prefer hydrated environments inside the liposomes. The 3-(4- fluorophenyl)benzothieno[2,3-c]pyran-1-one (1a) clearly prefers a hydrated environment, with some molecules located at the outer part of the liposome interface. On the contrary, the preferential location of 3-(2-fluorophenyl)benzothieno[2,3-c]pyran-1-one (1b) is in the region of lipid hydrophobic tails. Compounds with a planar geometry (1a and 1c) have higher mobility in the lipid membranes when phase transition occurs.Portugal and FEDER (Fundo Europeu de Desenvolvimento Regional), for financial support through Centro de Física (CFUM) and Centro de Química (CQ-UM) of University of Minho and through the Project PTDC/QUI/81238/2006. M.S.D. Carvalho and R.C. Calhelha acknowledge FCT for their PhD grants SFRH/BD/47052/2008 and SFRH/BD/29274/2006, respectively.Fundação para a Ciência e a Tecnologia (FCT