The tuneable complexation of gold nanoparticles

Mixed monolayer protected gold nanoparticles have been fabricated incorporating 1,5-dialkyloxynaphthalene moieties that are capable of forming complexes with the tetracationic cyclophane cyclobis(paraquat-p-phenylene); electrochemical reduction of the cyclophane or the addition of tetrathiafulvalene results in disassembly of the complexes.     

Synthesis of chromophores combining second harmonic generation and two photon induced fluorescence properties

The design of new chromophores presenting simultaneous SHG and TPEF properties is reported.     

Polarizable contributions to the surface tension of liquid water

Surface tension, gamma, strongly affects interfacial properties in fluids. The degree to which polarizability affects gamma in water is thus far not well established. To address this situation, we carry out molecular dynamics simulations to study the interfacial forces acting on a slab of liquid water surrounded by vacuum using the Gaussian charge polarizable (GCP) model at 298.15 K. The GCP model incorporates both a fixed dipole due to Gaussian distributed charges and a polarizable dipole. We find a well-defined bulklike region forms with a width of approximately 31 A. The average density of the bulklike region agrees with the experimental value of 0.997 g/cm3. However, we find that the orientation of the molecules in the bulklike region is strongly influenced by the interfaces, even at a distance five molecular diameters from the interface. Specifically, the orientations of both the permanent and induced dipoles show a preferred orientation parallel to the interface. Near the interface, the preferred orientation of the dipoles becomes more pronounced and the average magnitude of the induced dipoles decreases monotonically. To quantify the degree to which molecular orientation affects gamma, we calculate the contributions to gamma from permanent dipolar interactions, induced dipolar interactions, and dispersion forces. We find that the induced dipole interactions and the permanent dipole interactions, as well as the cross interactions, have positive contributions to gamma, and therefore contribute stability to the interface. The repulsive core interactions result in a negative contribution to gamma, which nearly cancels the positive contributions from the dipoles. The large negative core contributions to gamma are the result of small oxygen-oxygen separation between molecules. These small separations occur due to the strong attractions between hydrogen and oxygen atoms. The final predicted value for gamma (68.65 m/Nm) shows a deviation of approximately 4% of the experimental value of 71.972 m/Nm. The inclusion of polarization is critical for this model to produce an accurate value.     

Selective immunoclean-up followed by liquid chromatography for the monitoring of a biomarker of exposure to polycyclic aromatic hydrocarbons in urine at the ng l-1 level

A selective clean-up procedure using an immunosorbent (IS) was developed for the trace-level determination, in water and urine samples, of 3-benzo(a)pyrene-glucuronide (3-BP-G), a biomarker of exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs). First, three sorbents used for the immobilization of antibodies were evaluated for their ability to limit the risk of non-specific interactions and to provide a high bonding density. The best sorbent, i.e. sepharose, was used for the immobilization of two different monoclonal antibodies. The most specific antibody for 3-BP-G was applied to the selective extraction from urine providing a clean extract, an easy and reliable quantification by comparison with a classical SPE process. The sensitivity of the fluorescence associated with the selectivity of the IS provides a limit of detection up to 1.2 ng l(-1) in urine for 3-BP-G.     

Extreme values statistics for Markov chains via the (pseudo-) regenerative method

This paper is devoted to the study of specific statistical methods for extremal events in the markovian setup, based on the regenerative method and the Nummelin technique. Exploiting ideas developed in Rootzén (Adv Appl Probab 20:371–390, 1988), the principle underlying our methodology consists of first generating a random number l of approximate pseudo-renewal times τ ₁, τ ₂, ..., τ _l for a sample path X ₁, ..., X _n drawn from a Harris chain X with state space E, from the parameters of a minorization condition fulfilled by its transition kernel, and then computing submaxima over the approximate cycles thus obtained: $\max_{1+\tau_1\leq i \leq \tau_2}f(X_i),\;\ldots ,\;\max_{1+\tau_{l-1}\leq i \leq \tau_l}f(X_i)This paper is devoted to the study of specific statistical methods for extremal events in the markovian setup, based on the regenerative method and the Nummelin technique. Exploiting ideas developed in Rootzén (Adv Appl Probab 20:371–390, 1988), the principle underlying our methodology consists of first generating a random number l of approximate pseudo-renewal times τ ₁, τ ₂, ..., τ _l for a sample path X ₁, ..., X _n drawn from a Harris chain X with state space E, from the parameters of a minorization condition fulfilled by its transition kernel, and then computing submaxima over the approximate cycles thus obtained: max_{1+t1 ￡ i ￡ t2}f(X_i),  ?,  max_{1+tl-1 ￡ i ￡ tl}f(X_i)\max_{1+\tau_1\leq i \leq \tau_2}f(X_i),\;\ldots ,\;\max_{1+\tau_{l-1}\leq i \leq \tau_l}f(X_i) for any measurable function f:E→ℝ. Estimators of tail features of the sample maximum max_{1 ≤ i ≤ n} f(X _i ) are then constructed by applying standard statistical methods, tailored for the i.i.d. setting, to the submaxima as if they were independent and identically distributed. In particular, the asymptotic properties of extensions of popular inference procedures based on the conditional maximum likelihood theory, such as Hill’s method for the index of regular variation, are thoroughly investigated. Using the same approach, we also consider the problem of estimating the extremal index of the sequence {f(X _n )} _{n ∈ ℕ} under suitable assumptions. Eventually, practical issues related to the application of the methodology we propose are discussed and preliminary simulation results are displayed.     

Active vibration control on a quarter-car for cancellation of road noise disturbance

In this paper, a methodology is presented for the cancellation of road noise, from the analysis of vibration transmission paths for an automotive suspension to the design of an active control system using inertial actuators on a suspension to reduce the vibrations transmitted to the chassis. First, experiments were conducted on a Chevrolet Epica LS automobile on a concrete test track to measure accelerations induced on the suspension by the road. These measurements were combined with experimental Frequency Response Functions (FRFs) measured on a quarter-car test bench to reconstruct an equivalent three dimensional force applied on the wheel hub. Second, FRFs measured on the test bench between the three-dimensional driving force and forces at each suspension/chassis linkage were used to characterize the different transmission paths of vibration energy to the chassis. Third, an experimental model of the suspension was constructed to simulate the configuration of the active control system, using the primary (disturbance) FRFs and secondary (control) FRFs also measured on the test bench. This model was used to optimize the configuration of the control actuators and to evaluate the required forces. Finally, a prototype of an active suspension was implemented and measurements were performed in order to assess the performance of the control approach. A 4.6 dB attenuation on transmitted forces was obtained in the 50–250 Hz range.     

Experimental demonstration of a passive all-fiber Q-switched erbium- and samarium-doped laser

Self-Q-switched operation of the all-fiber laser using erbium and samarium fibers in the cavity is realized experimentally. This passively Q-switched all-fiber laser produces very stable pulses with energy of 142 nJ and duration of 450 ns. The experimental results were well reproduced by the results obtained through the numerical integration of a rate-equations model.     

Conditions ensuring the applicability of cutting-plane methods for solving variational inequalities

Let VIP(F,C) denote the variational inequality problem associated with the mapping F and the closed convex set C. In this paper we introduce weak conditions on the mapping F that allow the development of a convergent cutting-plane framework for solving VIP(F,C). In the process we introduce, in a natural way, new and useful notions of generalized monotonicity for which first order characterizations are presented. Received: September 25, 1997 / Accepted: March 2, 1999?Published online July 20, 2000     

Role of Nuclear Factor-KB in Colon Cancer Cell Apoptosis Mediated by Aminopyropheophorbide Photosensitization

Aminopyropheophorbide (APP) is a second generation of photosensitizer for photodynamic therapy (PDT). We demonstrated that APP strongly absorbed red light and, after being taken up by colon cancer cells (HCT-116 cells), was localized in cytoplasmic and internal membranes but not in mitochondria. The APP-mediated photosensitization was cytotoxic for HCT-116 cells through an induction of apoptosis. Indeed, DNA fragmentation (DNA laddering and terminal deoxyuridine nick-end labeling) and chromatin condensation (4',6-diamidine-2'-phenylindole staining) could be visualized soon after photosensitization. Because nuclear factor (NF)-kappa B is involved in the response to many photosensitizers, we also demonstrated its nuclear translocation in two waves: a rapid and transient one, followed by a slow and sustained phase. The NF-kappa B turned out to be involved in an antiapoptotic response to APP-mediated photosensitization because the HCT-116 cell line expressing the dominant negative mutant of inhibitor-kappa B alpha was more sensitive to apoptosis as measured by DNA fragmentation and caspase activation. These data unambiguously show that a membrane-located photosensitizer can lead to effective apoptosis, reinforcing the idea that PDT can be an effective means to eradicate colon cancer cells.     

Determination of Fluorescence Yields, Singlet Lifetimes and Singlet Oxygen Yields of Water-Insoluble Porphyrins and Metalloporphyrins in Organic Solvents and in Aqueous Media

Abstract— Fluorescence quantum yields and singlet lifetimes for a wide range of hydrophilic to hydrophobic porphyrins and metalloporphyrins have been determined in toluene, methanol or acetone. Photosensitized singlet oxygen yields have been determined in the same solvents. For some porphyrins, the same quantities were determined in an aqueous medium, through use of an amphiphilic polymer to solubilize the porphyrin sensitizer and target molecule, 1, 3-diphenylisobenzofuran. Because rate constants for the deactivation of singlet oxygen ( k _d) and for its reaction with a target molecule (k _a ) are unknown in such aqueous polymer systems, a new method was developed for evaluating yields of singlet oxygen formation that also provides a value for the ratio k_d/k_a. A variation observed in quantum yield of singlet oxygen production for the aqueous polymer system with variation in initial concentration of the target molecule is discussed.