Effect of Graphene Characteristics on Morphology and Performance of Composite Noble Metal-Reduced Graphene Oxide SERS Substrate

Graphene/noble metal substrates for surface enhanced RAMAN scattering (SERS) possess synergistically improved performance, due to the strong chemical enhancement mechanism accounted to graphene and the electromagnetic mechanism raised from the metal nanoparticles. However, only the effect of noble metal nanoparticles characteristics on the SERS performance was studied so far. In attempts to bring a light to the effect of quality of graphene, in this work, two different graphene oxides were selected, slightly oxidized GOS (20%) with low aspect ratio (1000) and highly oxidized (50%) GOG with high aspect ratio (14,000). GO and precursors for noble metal nanoparticles (NP) simultaneous were reduced, resulting in rGO decorated with AgNPs and AuNPs. The graphene characteristics affected the size, shape, and packing of nanoparticles. The oxygen functionalities actuated as nucleation sites for AgNPs, thus GOG was decorated with higher number and smaller size AgNPs than GOS. Oppositely, AuNPs preferred bare graphene surface, thus GOS was covered with smaller size, densely packed nanoparticles, resulting in the best SERS performance. Fluorescein in concentration of 10⁻⁷ M was detected with enhancement factor of 82 × 10⁴. This work demonstrates that selection of graphene is additional tool toward powerful SERS substrates.     

Exact X-wave solutions of the hyperbolic nonlinear Schrödinger equation with a supporting potential

We find exact solutions of the two- and three-dimensional nonlinear Schrödinger equation with a supporting potential. We focus in the case where the diffraction operator is of the hyperbolic type and both the potential and the solution have the form of an X-wave. Following similar arguments, several additional families of exact solutions can also can be found irrespectively of the type of the diffraction operator (hyperbolic or elliptic) or the dimensionality of the problem. In particular we present two such examples: The one-dimensional nonlinear Schrödinger equation with a stationary and a “breathing” potential and the two-dimensional nonlinear Schrödinger with a Bessel potential.     

Formation of alkane‐phosphonic acid self‐assembled monolayers on alumina: an in situ SPR study

The formation process of n‐alkane phosphonic acid CH₃ (CH₂)_n?1 PO(OH)₂ (n = 10,12,14,18) self‐assembled monolayers (SAMs), deposited from ethanol solutions on aluminum oxide, has been monitored in situ using surface plasmon resonance (SPR) spectroscopy. In addition, the two‐solvent approach is used to obtain both film thickness and refractive index of the fully formed adsorbed layers. A densely packed adsorbed layer is formed only for the longest molecules with n = 18. The chain length and solution concentration dependence of formation kinetics are studied, and the existence of two distinct kinetic steps is revealed. Fittings of the experimental results with various kinetic models are performed. Our analysis suggests that during the first kinetic step, a transition from a lying‐down to a standing‐up phase takes place, and the growth of this standing‐up phase is governed by second‐order kinetics. The second slow kinetic step is described by a modified first‐order Langmuir law. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of anaesthetics and analgesics in human urine by headspace SPME and GC

The determination of widely used anaesthetic and analgesic drugs in biological fluids is of major clinical importance. Typical methods used for sample preparation employ liquid–liquid extraction protocols which are complex, costly, not handy and not amenable to automation. In the present communication, we report the development of a methodology that employs headspace solid‐phase microextraction (HS‐SPME) for the determination of four anaesthetic (lidocaine, midazolam, diazepam and ketamine) and three analgesic drugs (fentanyl, remifentanyl and codeine) in human urine. Important parameters controlling SPME were studied: selection of SPME fibre, type and amount of salt added, preheating and extraction time, extraction temperature, sample volume and desorption time. GC with nitrogen phosphorus detection (GC‐NPD) facilitates sensitive and selective detection of the anaesthetics. The developed method renders an efficient tool for the precise and sensitive determination of the anaesthetics and analgesics in human urine (RSDs ranged from 7.7 to 12.6%, whereas LODs ranged from 0.01 to 1.5 ng/mL). The method was applied to the determination of the anaesthetics and analgesics in human urine from patients that had undergone coronary by‐pass surgery operations. The proposed protocol can function as an attractive alternative for clinical acute intoxications and medico‐legal cases.     

Existence of a pair of positive solutions for a class of nonlinear eigenvalue problems

In this paper, we consider a nonlinear elliptic equation driven by the p-Laplacian and with a parameter λ > 0. Using a combination of variational and degree theoretic methods, we show that there exists λ^* > 0 such that, if λ > λ^*, then the problem has two positive smooth solutions. Our result extends earlier ones by Rabinowitz (semilinear equations) and Guo (nonlinear equations).      

A genetic approach for strategic resource allocation planning

Enterprises often implement a measurement system to monitor their march towards their strategic goals. Although this way it is possible to assess the progress of each goal, there is no structured way to reconsider resource allocation to those goals and to plan an optimal (or near optimal) allocation scheme. In this study we propose a genetic approach to match each goal with an autonomous entity (agent) with a specific resource sharing behavior. The overall performance is evaluated through a set of functions and genetic algorithms are used to eventuate in approximate optimal behavior’s schemes. To outline the strategic goals of the enterprise we used the balanced scorecard method. Letting agents deploy their sharing behavior over simulation time, we measure the scorecard’s performance and detect distinguished behaviors, namely recommendations for resource allocation.     

Development of recombinant protein-based influenza vaccine. Expression and affinity purification of H1N1 influenza virus neuraminidase

The influenza virus surface glycoprotein antigen neuraminidase (NA) is a crucial viral enzyme with many potential medical applications; therefore, the development of efficient upstream and downstream processing strategy for the expression and purification of NA is of high importance. In the present work the NA gene from the H1N1 influenza virus strain A/Beijing/262/95 was cloned from viral RNA and expressed in expresSF+ insect cells using the baculovirus expression vector system (BVES). A limited affinity-ligand library was synthesized and evaluated for its ability to bind and purify the recombinant H1N1 neuraminidase. Affinity-ligand design was based on mimicking the interactions of the lock-and-key (LAK) motif (Phe-Gly-Gln), a common structural moiety found in the subunit interface of glutathione S-transferase I (GST I), and plays an important structural role in subunit-subunit recognition. Solid-phase combinatorial chemistry was used to synthesize 13 variants of the lock-and-key lead ligand (Phe-Trz-X, where X was selected alpha-amino acid) using the 1,3,5-triazine moiety (Trz) as the scaffold for assembly. One immobilized ligand, bearing phenylalanine and isoleucine linked on the chlorotriazine ring (Phe-Trz-Ile), displayed high affinity for NA. Absorption equilibrium and molecular modeling studies were carried out to provide a detailed picture of Phe-Trz-Ile interaction with NA. This LAK-mimetic affinity adsorbent was exploited in the development of a facile purification protocol for NA, which led to 335-fold purification in a single-step. The present purification procedure is the most efficient reported so far for recombinant NA.     

Magnetic resonance spectroscopy: a noninvasive diagnosis of gliomatosis cerebri

Gliomatosis cerebri (GC) is characterized by a diffuse infiltration of neoplastic glial cells with preservation of neuronal architecture. It can be very difficult to diagnose during life because the clinical manifestations are protean and tests are often nondiagnostic. The diagnosis of GC needs to be based on radiological, clinical and pathological criteria. We present a patient with GC, which initially presented as acute stroke attack. We discuss the usefulness of noninvasive methods, such a MR spectroscopy, in the diagnosis, grading and management of GC.     

A LOW-FREQUENCY ELECTROMAGNETIC NEAR-FIELD INVERSE PROBLEM FOR A SPHERICAL SCATTERER

The interior low-frequency electromagnetic dipole excitation of a dielectric sphere is uti- lized as a simplified but realistic model in various biomedical applications. Motivated by these considerations, in this paper, we investigate analytically a near-field inverse scatter- ing problem for the electromagnetic interior dipole excitation of a dielectric sphere. First, we obtain, under the low-frequency assumption, a closed-form approximation of the series of the secondary electric field at the dipole＇s location. Then, we utilize this derived approx- imation in the development of a simple inverse medium scattering algorithm determining the sphere＇s dielectric permittivity. Finally, we present numerical results for a human head model, which demonstrate the accurate determination of the complex permittivity by the developed algorithm.     

An EEG study of brain connectivity dynamics at the resting state

We investigated the dynamical behavior of resting state functional connectivity using EEG signals. Employing a recently introduced methodology that considers the time variations of phase coupling among signals from different channels, a sequence of functional connectivity graphs (FCGs) was constructed for different frequency bands and analyzed based on graph theoretic tools. In the first stage of analysis, hubs were detected in the FCGs based on local and global efficiency. The probability of each node to be identified as a hub was estimated. This defined a topographic function that showed widespread distribution with prominence over the frontal brain regions for both local and global efficiency. Hubs consistent across time were identified via a summarization technique and found to locate over forehead. In the second stage of analysis, the modular structure of each single FCG was delineated. The derived time-dependent signatures of functional structure were compared in a systematic way revealing fluctuations modulated by frequency. Interestingly, the evolution of functional connectivity can be described via abrupt transitions between states, best described as short-lasting bimodal functional segregations. Based on a distance function that compares clusterings, we discovered that these segregations are recurrent. Entropic measures further revealed that the apparent fluctuations are subject to intrinsic constraints and that order emerges from spatially extended interactions.