Optical and Magnetic Properties of Conjugate Structures of PbSe Quantum Dots and γ‐Fe2O3 Nanoparticles

An investigation of the optical and magnetic properties of a unique hydrogen‐linked conjugate nanostructure, comprised of superparamagnetic γ‐Fe₂O₃ nanoparticles (NPs) and near‐infrared PbSe nanocrystal quantum dot (NQD) chromophores, is reported. The results show retention of the NQDs’ emission quantum efficiency and radiative lifetime, and only a small red shift of its band energy, upon conjugation to the dielectric surroundings of γ‐Fe₂O₃ NPs. The study also shows the sustainability of the superparamagnetism of the NPs after conjugation, with only a slight decrease of the ferromagnetic–superparamagnetic transition temperature with respect to that of the individual NPs. Thus, the conjugate nanostructure can be considered as a useful medical platform when PbSe NQDs act as fluorescent tags, while the γ‐Fe₂O₃ NPs are used as a vehicle driven by an external magnetic field for targeted delivery of tags or drugs.     

The application of ultrasound radiation to the synthesis of nanocrystalline metal oxide in a non-aqueous solvent

Highly crystalline metal oxide nanoparticles of TiO₂, WO₃, and V₂O₅ were synthesized in just a few minutes by reacting transition metal chloride with benzyl alcohol using ultrasonic irradiation under argon atmosphere in a non-aqueous solvent. The sonochemical process was conducted at a relatively low temperature, 363 K. A unique crystallization process of these nanoparticles has been observed and characterized by powder X-ray diffraction (PXRD), high resolution scanning electron microscopy (HRSEM), and BET. The particles’ size and shape measured from HRSEM reveal “quasi” zero-dimensional, spherical TiO₂ particles in the range of 3–7 nm. The V₂O₅ particles have a “quasi” one-dimensional ellipsoidal morphology, with lengths in the range of 150–200 nm and widths varying between 40 and 60 nm. The WO₃ particles were obtained as “quasi” two-dimensional platelets with square shapes having facets ranging from 30 to 50 nm. The thickness of these platelets was between 2 and 7 nm. The mechanism of the reactions leading to these three metal oxide nanoparticles in a non-aqueous system is substantiated by Nuclear Magnetic Resonance (NMR), and Electron Spin Resonance (ESR).     

Small maximal pro-p Galois groups

For an odd primep we classify the pro-p groups of rank ≤4 which are realizable as the maximal pro-p Galois group of a field containing a primitive root of unity of orderp.     

Finding a Guard that Sees Most and a Shop that Sells Most

We present a near-quadratic time algorithm that computes a point inside a simple polygon P in the plane having approximately the largest visibility polygon inside P, and a near-linear time algorithm for finding the point that will have approximately the largest Voronoi region when added to an n-point set in the plane. We apply the same technique to find the translation that approximately maximizes the area of intersection of two polygonal regions in near-quadratic time, and the rigid motion doing so in near-cubic time.     

Dielectric behavior of thin films of unsaturated polyester‐resin/carbon nanotube semiconductor composites

Since the discovery of carbon nanotubes (CNT), numerous studies have focused on the development of materials combining CNT with polymer composites to exploit both CNT's remarkable characteristics and the complimentary properties of polymer thin films. In particular, unsaturated polyester resin (UPR) and CNT composite materials have not been studied before. Here we develop and characterize a UPR/CNT‐based capacity resistor gas sensor and apply it on THF vapor. The CNT's high aspect ratio provides the composite with better electrical and mechanical performance than other realizations, such as carbon black. We identify and quantify THF in a wide range of operation frequencies, under SATP conditions, as functions of the vertical distance, sample volume and operation frequency. High sensitivity, reversibility and fast response to the dielectric vapor exposure in microliter volumes are achieved. The results are also analyzed in terms of the possible mechanisms relating to THF/sensor interactions, with good correspondence between the model and measured data.     

Matching planar maps

The subject of this paper are algorithms for measuring the similarity of patterns of line segments in the plane, a standard problem in, e.g., computer vision, geographic information systems, etc. More precisely, we define feasible distance measures that reflect how close a given pattern H is to some part of a larger pattern G. These distance measures are generalizations of the well-known Fréchet distance for curves. We first give an efficient algorithm for the case that H is a polygonal curve and G is a geometric graph. Then, slightly relaxing the definition of distance measure, we give an algorithm for the general case where both, H and G, are geometric graphs.     

New Similarity Measures between Polylines with Applications to Morphing and Polygon Sweeping

   Abstract. We introduce two new related metrics, the geodesic width and the link width , for measuring the ``distance' between two nonintersecting polylines in the plane. If the two polylines have n vertices in total, we present algorithms to compute the geodesic width of the two polylines in O(n <sup>2</sup> log n) time using O(n <sup>2</sup> ) space and the link width in O(n <sup>3</sup> log n) time using O(n <sup>2</sup> ) working space where n is the total number of edges of the polylines. Our computation of these metrics relies on two closely related combinatorial strutures: the shortest-path diagram and the link diagram of a simple polygon. The shortest-path (resp., link) diagram encodes the Euclidean (resp., link) shortest path distance between all pairs of points on the boundary of the polygon. We use these algorithms to solve two problems: • Compute a continuous transformation that ``morphs' one polyline into another polyline. Our morphing strategies ensure that each point on a polyline moves as little as necessary during the morphing, that every intermediate polyline is also simple and disjoint to any other intermediate polyline, and that no portion of the polylines to be morphed is stretched or compressed by more than a user-defined parameter during the entire morphing. We present an algorithm that computes the geodesic width of the two polylines and utilizes it to construct a corresponding morphing strategy in O(n ² log ² n) time using O(n ² ) space. We also give an O(nlog n) time algorithm to compute a 2-approximation of the geodesic width and a corresponding morphing scheme. • Locate a continuously moving target using a group of guards moving inside a simple polygon. The guards always determine a simple polygonal chain within the polygon, with consecutive guards along the chain being mutually visible. We compute a strategy that sweeps such a chain of guards through the polygon in order to locate a target. We compute in O(n ³ ) time and O(n ² ) working space the minimum number r ^* of guards needed to sweep an n -vertex polygon. We also give an approximation algorithm, using O(n log n) time and O(n) space, to compute an integer r such that max(r - 16, 2)≤ r ^* ≤ r and P can be swept with a chain of r guards.     

Argon ion stimulated conversion between CFx (x = 0–3) chemical states and fluorine depletion in fluorocarbon films studied by X-ray photoelectron spectroscopy

Surface chemical composition of fluorocarbon films deposited onto indium-tin-oxide (ITO) substrates was modified by 2.0 keV Ar⁺ irradiation with doses of up to 2.6×10¹³ ions/cm². The effect of ion irradiation on the chemical composition and bonding configuration of the upper-surface and sub-surface regions were monitored by high-resolution angle-resolved X-ray photoelectron spectroscopy (AR-XPS). It was found that the as-deposited films compose of a distribution of CF, CF₂, CF₃ and C–C chemical states. C 1s line-shape analysis of XPS spectra measured at grazing and normal emission angles shows that as a result of the irradiation, the population of the CF₃ and CF₂ chemical states were preferentially depleted from the film’s surface resulting in an increased population of the CF and C–C chemical states in the upper-surface region of the film. It is suggested that low energy ion irradiation can be used to chemically modify the surface of fluorocarbon films.