Passive equalization of nonuniform EDFA gain by optical filteringfor megameter transmission of 20 WDM channels through a cascade ofEDFA's

Through the incorporation of optical filters in a cascade of erbium-doped fiber amplifiers (EDFA's), with each amplifier exhibiting nonuniform gain, we determine the optimal conditions for passively equalizing many wavelength division multiplexed (WDM) channels while maintaining a high SNR. For 20 WDM channels spaced 0.5 nm apart, it is found that 3-dB, 2-nm-wide notch filters with center wavelength at 1.560 μm will provide sufficient SNR equalization for potential megameter transmission when located after every 20 EDFA's. This performance is achieved with no a priori knowledge of the input or output signals     

All-optical address recognition for optically-assisted routing in next-generation optical networks

Optical fiber communication technology enabled high-speed, long-distance capacity in today's networks. The packet switching functions such as address recognition and routing are performed in the electrical domain after optical-to-electrical conversion. As more real-time applications come online, demand for bandwidth increases, and electronic processing may potentially become a bottleneck at the intermediate nodes along the network. We introduce some optical address recognition schemes for optically-assisted routing that may decrease the processing delay at these nodes.     

ATP‐Responsive Aptamer‐Based Metal–Organic Framework Nanoparticles (NMOFs) for the Controlled Release of Loads and Drugs

Nanoparticles consisting of metal–organic frameworks (NMOFs) modified with nucleic acid binding strands are synthesized. The NMOFs are loaded with a fluorescent agent or with the anticancer drug doxorubicin, and the loaded NMOFs are capped by hybridization with a complementary nucleic acid that includes the ATP‐aptamer or the ATP‐AS1411 hybrid aptamer in caged configurations. The NMOFs are unlocked in the presence of ATP via the formation of ATP‐aptamer complexes, resulting in the release of the loads. As ATP is overexpressed in cancer cells, and since the AS1411 aptamer recognizes the nucleolin receptor sites on the cancer cell membrane, the doxorubicin‐loaded NMOFs provide functional carriers for targeting and treatment of cancer cells. Preliminary cell experiments reveal impressive selective permeation of the NMOFs into MDA‐MB‐231 breast cancer cells as compared to MCF‐10A normal epithelial breast cells. High cytotoxic efficacy and targeted drug release are observed with the ATP‐AS1411‐functionalized doxorubicin‐loaded NMOFs.     

Synthesis and Applications of Stimuli‐Responsive DNA‐Based Nano‐ and Micro‐Sized Capsules

Stimuli‐responsive, drug‐loaded, DNA‐based nano‐ and micro‐capsules attract scientific interest as signal‐triggered carriers for controlled drug release. The methods to construct the nano‐/micro‐capsules involve i) the layer‐by‐layer deposition of signal‐reconfigurable DNA shells on drug‐loaded microparticles acting as templates, followed by dissolution of the core templates; ii) the assembly of three‐dimensional capsules composed of reconfigurable DNA origami units; and iii) the synthesis of stimuli‐responsive drug‐loaded capsules stabilized by DNA?polymer hydrogels. Triggers to unlock the nano‐/micro‐capsules include enzymes, pH, light, aptamer?ligand complexes, and redox agents. The capsules are loaded with fluorescent polymers, metal nanoparticles, proteins or semiconductor quantum dots as drug models, with anti‐cancer drugs, e.g., doxorubicin, or with antibodies inhibiting cellular networks or enzymes over‐expressed in cancer cells. The mechanisms for unlocking the nano‐/micro‐capsules and releasing the drugs are discussed, and the applications of the stimuli‐responsive nano‐/micro‐capsules as sense‐and‐treat systems are addressed. The scientific challenges and future perspectives of nano‐capsules and micro‐capsules in nanomedicine are highlighted.     

Application of polyethyleneimine-quinone modified electrodes for voltammetric measurements of pH

A modified polymer, ie benzylated polyethyleneimine (PEI), coated on a glassy carbon electrode in which negatively charged quinones have been incorporated, has been used for voltammetric measurement of pH. A linear dependence of the average of the peak potentials as a function of pH was observed. The system has been successfully applied also to ultramicroelectrodes.     

Photochemically Induced Oxidative and Reductive Regeneration of NAD(P)+/NAD(P)H Cofactors: Applications in Biotransformations

Photosensitized regeneration of NAD(P)H cofactors is accomplished by biocatalyzed and artificially catalyzed transformations in photochemical assemblies. Photogenerated N,N'-dimethyl-4,4′-bipyridinium radical cation, MV^+., acts as electron carrier for the reduction of NADPH in the presence of the enzyme ferredoxin reductase and for the reduction of NADH in the presence of lipoamide dehydrogenase. For the photogeneration of MV^+. and subsequent NADPH formation, three different photosensitizers are applied: Ru(bpz)²₃⁺, Ru(bpy)²₃⁺, and Zn—TMPyP⁴⁺. The highest quantum yield for NADPH formation is observed with Ru(bpz)₃²⁺ and is ϕ = 1.7 × 10⁻¹. For NADH regeneration only Zn-TMPyP⁴⁺ can be applied. Ru(bpy)₃²⁺ and Ru(bpz)²⁺₃ interact with NADH in their excited or oxidized forms and therefore cannot be used as light-active compounds in the system. The NADPH regeneration cycle has been coupled to the biocatalyzed synthesis of glutamic acid. Although Ru(bpz)₃²⁺ is 42.5-fold more efficient than Ru(bpy)₃²⁺ in the regeneration of NADPH, the synthesis of glutamic acid is improved only by a factor of 2 in the presence of Ru(bpz)₃²⁺, implying that the coupled process is rate limiting. Oxidative regeneration of the NAD⁺ cofactor is accomplished in a photosystem that includes Ru(bpy)₃²⁺ as photosensitizer. The photoprocess is coupled to dehydrogenation of ethanol, propanol, lactic acid, and alanine with concomitant H₂ evolution. A photosystem that includes Ru(bpy)₃²⁺ as photosensitizer, ascorbate as electron donor, and chloro-tris-(3-diphenylphosphinobenzene sulfonate)Rh(I), RhCl(dpm)₃^3-, is catalytically active in the photoinduced regeneration of NAD(P)H cofactors. Mechanistic investigations show that photogenerated Ru(bpy)₃⁺ mediates the generation of a hydrido-rhodium complex that acts as a charge relay for the production of NAD(P)H.     

PCF-based polarization splitters with simplified structures

We propose novel polarization splitters based on photonic crystal fibers (PCFs), in which the cores of the splitters are nearly nonbirefringent. Different from conventional fiber-based polarization splitters, the birefringence in the new splitters results mainly from narrow silica regions physically connecting the two cores. This means that polarization splitting can be achieved without employing highly birefringent cores, which provides a possibility to greatly simplify the structures of the PCF-based polarization splitters and make them more practical. A 5-mm-long splitter with an extinction ratio of 20 dB has been obtained. We also discuss how the silica regions influence coupling characteristics of the dual-core PCFs and present a design guidance for the polarization splitters based on polarization-dependent coupling.     

Surface-stiffened elastic halfspace under the action of a horizontally directed Mindlin force

This paper presents an analytical solution to the problem of the interaction between a thin plate that is adhesively bonded to the surface of an isotropic elastic halfspace and a concentrated Mindlin-type force that acts parallel to the bonded surface. The model is an idealization of a surface-stiffened region that has potential applications ranging from mechanics of thin films, thermal barrier coatings, layering created by attrition and wear of surfaces and functionally graded materials. The solution also illustrates the influence of the flexural plate model in mitigating the development of unbounded displacements during the application of localized loading directly at the bonded plate.