Integrated Mach-Zehnder micro-interferometer on LiNbO3

This work presents a scanning micro-interferometer, without moving parts, based on the well-known Mach-Zehnder geometry. The micro-system was obtained by using non-standard processes of planar technology on lithium niobate crystals, in particular the waveguide fabrication was obtained by using high energy ion implantation of medium light mass elements. The scanning effect without moving parts has been obtained by changing the refractive index of the optical waveguides by using electric field. The whole device is 60 mm long with a 0.5×1 mm² cross section, weights only few grams and its power consumption lies in the milliwatt range. The performances were preliminary tested in the spectral window ranging from 0.4 to 1.0 μm. By using standard radiation sources, this micro-system demonstrated a spectral resolution suitable for detecting the characteristic spectral lines of a Xe-arc lamp on a 400 nm wide spectral window. In a further experiment we tested the performances of the microinterferometer for gas trace detection by using a calibrated NO₂ optical gas cell. A sensitivity of about 10 ppb for NO₂ detection, when suitable optical paths are used, was evaluated.     

Bose-Einstein condensation in complex networks.

The evolution of many complex systems, including the World Wide Web, business, and citation networks, is encoded in the dynamic web describing the interactions between the system's constituents. Despite their irreversible and nonequilibrium nature these networks follow Bose statistics and can undergo Bose-Einstein condensation. Addressing the dynamical properties of these nonequilibrium systems within the framework of equilibrium quantum gases predicts that the "first-mover-advantage," "fit-get-rich," and "winner-takes-all" phenomena observed in competitive systems are thermodynamically distinct phases of the underlying evolving networks.     

Temperature dependent local Cu-O displacements from underdoped to overdoped La-Sr-Cu-O superconductor

We have studied doping evolution of the temperature dependent local Cu-O displacements in the La_2-x Sr _x CuO₄ superconductor by polarized Cu K-edge extended X-ray absorption fine structure (EXAFS) measurements. While temperature dependent Debye-Waller factor of the Cu-O bonds, measuring the local Cu-O displacements, shows an anomalous increase at low temperature for the underdoped single crystals, we do not find such a dependence for the case of the overdoped system. The results, which are discussed in the light of recent angle resolved photoemission measurements, provide an evidence for some important correlation between the doping dependent electron-lattice interaction, the charge inhomogeneities and the local Cu-O displacements in the copper oxide superconductors.Received: 9 July 2003, Published online: 19 November 2003PACS: 74.72.Dn La-based cuprates - 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. - 74.81.-g Inhomogeneous superconductors and superconducting systems     

Lattice vibrational property in the transition-metal diboride ZrB2

Lattice vibrational property has been determined in ZrB(2) system using the temperature-dependent extended X-ray-absorption fine-structure (EXAFS) technique from room temperature to 28K. The smooth behavior of Debye-Waller factor curve with temperature is slightly abnormal for the first pair Zr-B. In order to reproduce this curve, an improved Einstein mode with two Einstein frequencies has been used. The quantitative analysis of temperature-dependent Debye-Waller factor of Zr-B pair shows one Einstein frequency is very high and the other is small. These frequencies correspond to the vibration of boron layer atoms and transition-metal layer atoms, respectively. Based on the Einstein mode with one frequency, the vibrational frequency for Zr-Zr pair has been also obtained. Zirconium diboride has two types of Zr-Zr interaction. One is in-plane and the other is out-of-plane along the high symmetry axis. Our analysis shows there is a little difference between in-plane Zr-Zr vibration and out-of-plane one. And the smaller Einstein vibrational frequency for the Zr-B shell is just between the two ones of the Zr-Zr shells. Our results show that the lattice vibrational behavior in ZrB(2) presents obvious particularity and anisotropy.     

A Daniell integral approach to nonstandard Kurzweil-Henstock integral

A workable nonstandard definition of the Kurzweil-Henstock integral is given via a Daniell integral approach. This allows us to study the HL class of functions from [9]. The theory is recovered together with a few new results.     

Grand Canonical Ensembles of Sparse Networks and Bayesian Inference

Maximum entropy network ensembles have been very successful in modelling sparse network topologies and in solving challenging inference problems. However the sparse maximum entropy network models proposed so far have fixed number of nodes and are typically not exchangeable. Here we consider hierarchical models for exchangeable networks in the sparse limit, i.e., with the total number of links scaling linearly with the total number of nodes. The approach is grand canonical, i.e., the number of nodes of the network is not fixed a priori: it is finite but can be arbitrarily large. In this way the grand canonical network ensembles circumvent the difficulties in treating infinite sparse exchangeable networks which according to the Aldous-Hoover theorem must vanish. The approach can treat networks with given degree distribution or networks with given distribution of latent variables. When only a subgraph induced by a subset of nodes is known, this model allows a Bayesian estimation of the network size and the degree sequence (or the sequence of latent variables) of the entire network which can be used for network reconstruction.     

Combining Solid-State NMR with Structural and Biophysical Techniques to Design Challenging Protein-Drug Conjugates

Several protein-drug conjugates are currently being used in cancer therapy. These conjugates rely on cytotoxic organic compounds that are covalently attached to the carrier proteins or that interact with them via non-covalent interactions. Human transthyretin (TTR), a physiological protein, has already been identified as a possible carrier protein for the delivery of cytotoxic drugs. Here we show the structure-guided development of a new stable cytotoxic molecule based on a known strong binder of TTR and a well-established anticancer drug. This example is used to demonstrate the importance of the integration of multiple biophysical and structural techniques, encompassing microscale thermophoresis, X-ray crystallography and NMR. In particular, we show that solid-state NMR has the ability to reveal effects caused by ligand binding which are more easily relatable to structural and dynamical alterations that impact the stability of macromolecular complexes.