Structural Changes in the BODIPY Dye PM567 Enhancing the Laser Action in Liquid and Solid Media

In the search for more efficient and photostable solid‐state dye lasers, newly synthesized analogs of the borondipyrromethene (BODIPY) dye PM567, bearing the polymerizable methacryloyloxypropyl group at position 2 (PMoMA) or at positions 2 and 6 (PDiMA), have been studied in the form of solid copolymers with methyl methacrylate (MMA). The parent dye PM567, as well as the model analogs bearing the acetoxypropyl group in the same positions, PMoAc and PDiAc, respectively, have been also studied both in liquid solvents and in solid poly(MMA) (PMMA) solution. Although in liquid solution PMoAc and PDiAc have the same photophysical properties as PM567, PDiAc exhibited a photostability up to 10 times higher than that of PM567 in ethanol under 310 nm‐irradiation. The possible stabilization factors of PDiAc have been analyzed and discussed on the basis of the redox potentials, the ability for singlet molecular oxygen [O₂(¹Δ_g)] generation, the reactivity with O₂(¹Δ_g), and quantum mechanical calculations. Both PMoAc and PDiAc, pumped transversally at 532 nm, lased in liquid solution with a high (up to 58 %), near solvent‐independent efficiency. This enhanced photostabilization has been also observed in solid polymeric and copolymeric media. While the solid solution of the model dye PDiAc in PMMA showed a lasing efficiency of 33 %, with a decrease in the laser output of ca. 50 % after 60 000 pump pulses (10 Hz repetition rate) in the same position of the sample, the solid copolymer with the double bonded chromophore, COP(PDiMA‐MMA), showed lasing efficiencies of up to 37 %, and no sign of degradation in the laser output after 100 000 similar pump pulses. Even under the more demanding repetition rate of 30 Hz, the laser emission from this material remained at 67 % of its initial laser output after 400 000 pump pulses, which is the highest laser photostability achieved to date for solid‐state lasers based on organic polymeric materials doped with laser dyes. This result indicates that the double covalent linkage of the BODIPY chromophore to a PMMA polymeric matrix is even more efficient than the simple linkage, for its photostabilization under laser operation.     

3D Printing of a Thermo‐ and Solvatochromic Composite Material Based on a Cu(II)–Thymine Coordination Polymer with Moisture Sensing Capabilities

This work presents the fabrication of 3D‐printed composite objects based on copper(II) 1D coordination polymer ( CP1 ) decorated with thymine along its chains with potential utility as an environmental humidity sensor and as a water sensor in organic solvents. This new composite object has a remarkable sensitivity, ranging from 0.3% to 4% of water in organic solvents. The sensing capacity is related to the structural transformation due to the loss of water molecules that CP1 undergoes with temperature or by solvent molecules' competition, which induces significant change in color simultaneously. The CP1 and 3D printed materials are stable in air over 1 year and also at biological pHs (5–7), therefore suggesting potential applications as robust colorimetric sensors. These results open the door to generate a family of new 3D printed materials based on the integration of multifunctional coordination polymers with organic polymers.     

Measurement distance effects on /spl Phi/-symmetric shaped patterns generated by circular continuous apertures

Sidelobe-level and ripple behaviors of /spl Phi/-symmetric shaped patterns, generated by circular, real and complex, continuous Taylor distributions, is analyzed as a function of measurement distances. This paper reveals that real distributions suffer less-significant power pattern degradation than complex distributions at near-field distances.     

Dye‐Doped Polyhedral Oligomeric Silsesquioxane (POSS)‐Modified Polymeric Matrices for Highly Efficient and Photostable Solid‐State Lasers

Here, the design, synthesis, and characterization of laser nanomaterials based on dye‐doped methyl methacrylate (MMA) crosslinked with octa(propyl‐methacrylate) polyhedral oligomeric silsesquioxane (8MMAPOSS) is reported in relation to their composition and structure. The influence of the silicon content on the laser action of the dye pyrromethene 567 (PM567) is analyzed in a systematic way by increasing the weight proportion of POSS from 1 to 50%. The influence of the inorganic network structure is studied by replacing the 8MMAPOSS comonomer by both the monofunctionalized heptaisobutyl‐methacryl‐POSS (1MMAPOSS), which defines the nanostructured linear network with the POSS cages appearing as pendant groups of the polymeric chains, and also by a new 8‐hydrogenated POSS incorporated as additive to the polymeric matrices. The new materials exhibit enhanced thermal, optical, and mechanical properties with respect to the pure organic polymers. The organization of the molecular units in these nanomaterials is studied through a structural analysis by solid‐state NMR. The domain size of the dispersed phase assures a homogeneous distribution of POSS into the polymer, thus, a continuous phase corresponding to the organic matrix incorporates these nanometer‐sized POSS crosslinkers at a molecular level, in agreement with the transparency of the samples. The silicon–oxygen core framework has to be covalently bonded into the polymer backbone instead of being a simple additive and both the silica content and crosslinked degree exhibit a critical influence on the laser action.     

Toward the Optimized Spintronic Response of Sn‐Doped IrO2 Thin Films

Amorphous and polycrystalline Sn‐doped IrO₂ thin films, Ir_1‐xSn_xO₂, are grown for the first time. Their electrical response and strength of the spin–orbit coupling are studied in order to better understand and tailor its performance as spin current detector material. These experiments prove that the resistivity of IrO₂ can be tuned over several orders of magnitude by controlling the doping content in both the amorphous and the polycrystalline state. In addition, growing amorphous samples increase the resistivity, thus improving the spin current to charge current conversion. As far as the spin–orbit coupling is concerned, the system not only remains in a strong spin–orbit coupling regime but it seems to undergo a slight enhancement in the amorphous state as well as in the Sn‐doped samples.     

Exploring How to Increase the Brightness of Surface‐Enhanced Raman Spectroscopy Nanolabels: The Effect of the Raman‐Active Molecules and of the Label Size

Due to the surface‐enhanced Raman scattering (SERS) effect, SERS labels based on noble‐metal nanoparticles loaded with Raman‐active molecules are good candidates for ultrasensitive multiplexed assays and in vitro/in vivo imaging. However, understanding how to maximize the brightness of such labels is of paramount importance for their widespread application. The effective differential Raman scattering cross‐section (dσ_R/dΩ) of SERS labels made of pegylated gold nanoparticles loaded with various Raman active molecules (Raman reporters) is studied. It is found that proper choice of the Raman reporter and of nanoparticle size can enhance the dσ_R/dΩ by several orders of magnitude. The experimental results are understood by considering the molecular cross‐section for resonant Raman scattering and the local electromagnetic enhancement factor (G_SERS) in the nearby of gold nanoparticles. These results are useful to guide the design of SERS labels with improved performances and to provide a reference for the comparison of the absolute value of the dσ_R/dΩ of SERS labels based on metal nanoparticles.     

A new family of frequency-hop codes

We give an algebraic construction for a new family of frequency-hop codes. The construction is based on properties of finite fields: it is shown that for each field GF(p^m), there exists a large number of codes of length p^m. The codes are also shown to possess the best possible simultaneous two-dimensional autocorrelation and cross-correlation properties. Moreover, they include a family of codes: with a code length of a power of 2, which are ideally suitable for applications in digital communication systems     

SDN-based architecture for providing quality of service to high-performance distributed applications

The specification of quality of service (QoS) requirements in most of the existing networks is still challenging. In part, traditional network environments are limited by their high administrative cost, although software-defined networks (SDNs), a newer network paradigm, simplify the management of the whole network infrastructure. In fact, SDN provides a simple way to effectively develop QoS provisioning mechanisms. In this sense, we explore the SDN model and its flexibility to develop a QoS provisioning architecture. Through the use of our new architecture, network operators are able to specify QoS levels in a simple way. Each individual data flow can be addressed, and the architecture we propose also negotiates the QoS requirements between the network controller and applications. On the other hand, the network controller continuously monitors the network environment. Then, it allocates network elements resources and prioritizes traffic, adjusting the network performance. We evaluate the feasibility of our QoS provisioning mechanism by presenting three experimental setups under realistic scenarios. For example, for a given scenario where we evaluate file transfers, our results indicate that the additional SDN modules present negligible overhead. Moreover, for a given setup, we observe a reduction of up to 82% in the file transfer times.     

Application of genetic algorithms and simulated annealing techniquein optimising the aperture distributions of antenna array patterns

Simulated annealing and genetic algorithms are used for finding optimum excitations for patterns with null-filling. These methods have the advantage that the optimum aperture distribution with a minimal variation between excitations of adjacent elements is found without searching the entire solution space. A comparison between the performance of both methods shows that genetic algorithms are faster than simulated annealing, for this problem