Ultrahigh-repetition-rate bound-soliton harmonic passive mode-locked fiber lasers

On the basis of numerical simulation results, we put forward a way to realize harmonic passive mode locking of fiber lasers with an ultrahigh-repetition-rate pulse train. The equidistant distribution of ultrashort pulses filling the total laser cavity is due to bound-soliton mechanisms. In the case of large bound energy, such long soliton trains are very stable and have the ideal periodic structure as a soliton crystal.     

Measurements of CP-violating asymmetries in the decay B0-->K+K-K0

We analyze the decay B0-->K+K-K0 using 383 x 10(6) BB events collected by the BABAR detector at SLAC to extract CP violation parameter values over the Dalitz plot. Combining all K+K-K0 events, we find ACP=-0.015+/-0.077+/-0.053 and beta eff = 0.352+/-0.076+/-0.026 rad, corresponding to a CP violation significance of 4.8 sigma. A second solution near pi/2-beta eff is disfavored with a significance of 4.5 sigma. We also report ACP and beta eff separately for decays to phi(1020)K0, f0(980)K0, and K+K-K0 with mK+K- > 1.1 GeV/c2.     

Spectral beam combining of a broad-stripe diode laser array in an external cavity

The outputs from an 11-element, linear diode laser array with broad stripes have been beam combined into a single beam with a beam quality of ~20x diffraction limited in the plane of the junction. This beam combining was achieved by use of a common external cavity containing a grating, which simultaneously forces each array element to operate at a different, but controlled, wavelength and forces the beams from all the elements to overlap and propagate in the same direction. The power in the combined beam was 50% of the output from the bare laser array.     

A variational approach to some boundary value problems in the half-line

We study the existence of solutions for two kinds of boundary value problem in the interval [0,[. The problems are suggested by models in Mathematical Physics. In the first kind of problem the condition at the left endpoint is u(0) = while in the second kind a homogeneous Neumann condition u = 0 is imposed. In both cases solutions should satisfy u(+) = 0. Our approach is variational, solutions being obtained as minimizers or mountain pass critical points of some functional.Received: October 21, 2003; revised: June 2, 2004Supported by Fundção para a Ciência e a Tecnologia, program POCTI (Portugal/FEDER-EU).     

Insight into ortho-boronoaldehyde conjugation via a FRET-based reporter assay

Ortho-boronoaldehydes react with amine-based nucleophiles with dramatically increased rates and product stabilities, relative to unfunctionalised benzaldehydes, leading to exciting applications across biological and material chemistry. We have developed a novel Förster resonance energy transfer (FRET)-based assay to provide key new insights into the reactivity of these boronoaldehydes, allowing us to track conjugation with unprecedented sensitivity and accuracy under standardised conditions. Our results highlight the key role played by reaction pH, buffer additives, and boronoaldehyde structure in controlling conjugation speed and stability, providing design criteria for further innovations and applications in the field.

A FRET-based platform has been developed to allow the rapid reactions between ortho-boronoaldehydes and amine-based nucleophiles to be precisely studied.

Reactions between ortho-boronoaldehydes (oBAs) and amine-based nucleophiles have emerged as powerful tools for bioconjugation and materials chemistry over the last decade, due to a combination of rapid reaction rates and tunable product stability. The ortho-boronoimines, and related derivatives (collectively oBIDs), that form have shown high potential in drug delivery,¹in vivo labelling,² and responsive materials.³ To allow further evolution of these technologies and drive innovative new applications, there is a pressing need for increased understanding of the formation of oBIDs and their responsive behaviour. In this work, we deliver a sensitive and versatile platform to realise such understanding, through a Förster resonance energy transfer (FRET) reporter assay of oBID formation. This assay allows us to probe the rapid kinetics of oBID formation in detail, under complex and biomedically relevant conditions.The ortho-boronic acid accelerates the rate of oBID formation (k₁), relative to unfunctionalised benzaldehyde, by both activating the aldehyde to nucleophilic attack and accelerating the rate-determining dehydration step. Though the rate of hydrolysis (k₋₁) is also accelerated, stabilising B–N interactions lead to a significant overall shift in equilibrium towards product formation (decrease in dissociation constant, K_d). For example, while benzaldehyde reacts with alkyl amines with k₁ ∼ 0.1 M⁻¹ s⁻¹ and K_d ∼ 300 M,⁴ the ortho-borono analogue ortho-formylphenylboronic acid (FBPA) forms analogous iminoboronates with a k₁ ∼ 1000 M⁻¹ s⁻¹ and K_d ∼ 10 mM (Fig. 1a).⁵ This 5-order of magnitude increase in reaction rate, and 4-order of magnitude decrease in dissociation constant, typifies the unique reactivity of oBAs.Open in a separate windowFig. 1(a) Comparison of benzaldehyde and ortho-boronoaldehyde reactivity, with the ortho-borono group both accelerating and stabilising imine formation; (b) schematic overview of the FRET platform developed in this work, allowing sensitive monitoring of rapid oBID formation (k₁ > 10⁵ M⁻¹ s⁻¹).Through variation of the oBA and nucleophile coupling partners, K_ds spanning 10⁻²–10⁻⁹ M have been reported.⁶ When coupled with high biocompatibility and potential for stimuli-responsive behaviour, this tunability greatly enhances the potential for biomedical applications of oBIDs. Despite this potential, much of our understanding of oBID chemistry comes from simple, unsubstituted model compounds such as FPBA, which poorly reflect the stereo-electronic characteristics of the functionalised oBAs necessary for translational applications.Moreover, much of this understanding is pieced together from a large number of independent studies, performed and analysed under varying conditions, making comparison challenging. This is particularly important given the highly dynamic nature of oBID linkages, leading to a high sensitivity to environmental conditions and choice of analytical technique. Ultimately, this leads to significant discrepancies in reported rates of formation and stabilities of oBIDs, due to subtle differences in substrate choice, reaction conditions, or analysis method.^7,8To address this, we herein describe a versatile and sensitive FRET-assay for studying oBID formation, stability, and cleavage. This assay is highly tolerant of environmental conditions, allowing us to provide critical new insights into the effects of pH, additives, media, and oBA structure on conjugation. We therefore anticipate that this assay will find future use for the high-throughput screening of novel oBIDs and their stimuli-responsive behaviour.     

Gold Nanoelectrode Arrays and their Evaluation by Impedance Spectroscopy and Cyclic Voltammetry

A sol–gel strategy is developed to fabricate highly regular Au nanoelectrode arrays (NEAs) consisting of a nanoperforated ultrathin membrane of ZrO₂, which exhibits a well‐ordered array of pores (65±5) nm in diameter with a mean center‐to‐center distance of (110±10) nm, on a polycrystalline gold surface. The structural properties are investigated by field‐emission scanning electron microscopy (FE‐SEM), while grazing incidence small‐angle X‐ray scattering (GISAXS) is used to assess the thickness homogeneity and the period of the array of electrodes. In addition, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are carried out to describe quantitatively the accessibility, electrochemical behavior, and diffusion processes of the gold NEA. A model applying parameters obtained from FE‐SEM, CV, and EIS analyses is proposed to simulate the experimental results. A fairly good agreement between the experimental and the simulated data is obtained, thus allowing the deconvolution of the different diffusion regimes at the NEA.     

Search for lepton flavor violating decays tau(+/-) --> l(+/-)pi0, l(+/-)eta, l(+/-)eta'

A search for lepton flavor violating decays of the tau lepton to a lighter mass lepton and a pseudoscalar meson has been performed using 339 fb;{-1} of e;{+}e;{-} annihilation data collected at a center-of-mass energy near 10.58 GeV by the BABAR detector at the SLAC PEP-II storage ring. No evidence of a signal has been found, and upper limits on the branching fractions are set at the 10;{-7} level.     

A Voltammetric Approach for the Simultaneous Determination of Cd and Pb in Water Applying Carbon Paste Electrode Modified with Bismuth Film

Journal of Analytical Chemistry - This study reports the simultaneous voltammetric determination of Cd and Pb by square wave voltammetry (SWV) using carbon paste electrode modified with bismuth...