Relationship between incoherent excitation energy migration processes and molecular structures in zinc(II) porphyrin dendrimers

Multiporphyrin dendrimers are among the most promising architectures to mimic the oxygenic light-harvesting complex because of their structural similarities and synthetic convenience. The overall geometries of dendrimers are determined by the core structure, the type of dendron, and the number of generations of interior repeating units. The rigid core and bulky volume of exterior porphyrin units in multiporphyrin dendrimers give rise to well-ordered three-dimensional structures. As the number of generations of interior repeating units increases, however, the overall structures of dendrimers become disordered and randomized due to the flexibility of the repeating units. To reveal the relationship between molecular structure and processes of excitation-energy migration in multiporphyrin dendrimers, we calculated the molecular structure and measured the time-resolved transient absorption and fluorescence anisotropy decays for various hexaarylbenzene-anchored polyester zinc(II) porphyrin dendrimers along with three types of porphyrin dendrons as references. We found that the congested two-branched type dendrimers exhibit more efficient energy migration processes than one- or three-branched type dendrimers because of multiple energy migration pathways, and the three-dimensional packing efficiency of dendrimers strongly depends on the type of dendrons.     

Search for the Higgs boson in H --> WW(*) decays in pp collisions at square root of 1.96 TeV

We present a search for the standard model Higgs boson in H --> WW(*) decays with e+e-, e+/-mu-/+, and mu+mu- final states in pp collisions at a center-of-mass energy of square root of s = 1.96 TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300-325 pb(-1), depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs boson production cross section times branching ratio sigma x BR(H --> WW(*) are presented.     

Isolated single quantum dot emitters in all-epitaxial microcavities

Data are presented on a fabrication approach that places an isolated single quantum dot at the center of a semiconductor microcavity. The microcavity is based on an all-epitaxial mesa-confined design that is mechanically robust and provides the thermal dissipation needed for a single photon source device technology. Microphotoluminescence is used to reveal single quantum dot emission with the essential optical properties of single quantum emitters.     

Search for the standard model Higgs Boson in the pp[over]-->ZH-->nunu[over]bb[over] channel

We report a search for the standard model (SM) Higgs boson based on data collected by the D0 experiment at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 260 pb(-1). We study events with missing transverse energy and two acoplanar b jets, which provide sensitivity to the ZH production cross section in the nunu[over]bb[over] channel, and to WH production when the lepton from the W-->lnu decay is undetected. The data are consistent with the SM background expectation, and we set 95% C.L. upper limits on sigma(pp[over]-->ZH/WH)xB(H-->bb[over]) from 3.4/8.3 to 2.5/6.3 pb, for Higgs-boson masses between 105 and 135 GeV.     

Search for neutral Higgs bosons decaying to tau pairs in pp[over ] collisions at sqrt[s]=1.96 TeV

A search for the production of neutral Higgs bosons Phi decaying into tau(+)tau(-) final states in pp[over ] collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of approximately 325 pb(-1), were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for Phib(b[over ])-->bb[over ]b(b[over ]) and are interpreted in the minimal supersymmetric standard model.     

Effects of temperature and carrier gas flow amount on the formation of GaN nanorods by the HVPE method

We fabricated one-dimensional GaN nanorods on AlN/Si (1 1 1) substrates at various temperatures, and carrier gas flow amount, using the hydride vapor phase epitaxy (HVPE) method. An AlN buffer layer of 50 nm thickness was deposited by RF sputtering for 25 min. Stalagmite-like GaN nanorods formed at a growth temperature of 650 °C. The diameters and lengths of GaN nanorods increase with growth time, whereas the density of nanorods decreases. And we performed the experiments by changing the carrier gas flow amount at a growth temperature of 650 °C and HCl:NH₃ flow ratio of 1:40. GaN nanorods, with an average diameter of 50 nm, were obtained at a carrier gas flow amount of 1340 sccm. The shape, structures, and optical characteristics of the nanorods were investigated by field-emission scanning electron microscopy, X-ray diffraction, and photoluminescence.     

Parameterized OWA operator weights: An extreme point approach

Since Yager first presented the ordered weighted averaging (OWA) operator to aggregate multiple input arguments, it has received much attention from the fields of decision science and computer science. A critical issue when selecting an OWA operator is the determination of the associated weights. For this reason, numerous weight generating methods, including rogramming-based approaches, have appeared in the literature. In this paper, we develop a general method for obtaining OWA operator weights via an extreme point approach. The extreme points are represented by the intersection of an attitudinal character constraint and a fundamental ordered weight simplex. The extreme points are completely identified using the proposed formula, and the OWA operator weights can then be expressed by a convex combination of the identified extreme points. With those identified extreme points, some new OWA operator weights can be generated by a centroid or a user-directed method, which reflects the decision-maker’s incomplete preferences. This line of reasoning is further extended to encompass situations in which the attitudinal character is specified in the form of interval with an aim to relieve the burden of specifying the precise attitudinal character, thus obtaining less-specific expressions that render human judgments readily available. All extreme points corresponding to the uncertain attitudinal character are also obtained by a proposed formula and then used to prioritize the multitude of alternatives. Meanwhile, two dominance rules are effectively used for prioritization of alternatives.     

Particle size dependence of electro-optical switching in ZrP nano colloid

Aqueous colloid of 2-dimensional (2D) α-ZrP nanoparticles can serve as an excellent material for Kerr devices. We investigate the influence of the particle size on the electro-optical switching for isotropic and biphasic α-ZrP colloids that exhibit stable Kerr effect. Smaller sized α-ZrP colloid has wider range of isotropic and biphasic phases, but since the anisotropic polarizability is approximately proportional to square diameter of particles, the larger sized α-ZrP colloid has higher birefringence at a given concentration. The dynamic response time is also dramatically influenced by the particle size. Smaller sized particle has lower viscosity, and the fall time monotonically increases with increasing particle size. However, the rise time has the minimum at around 0.6 μm owing to the competitive contributions of the anisotropic polarizability and the rotational viscosity. Thus, the particle size in α-ZrP colloid is an important factor to determine the electro-optical performance of a Kerr device based on 2D α-ZrP colloids. These findings will be important in developing electro-optical devices using lyotropic liquid crystal colloids.     

Devices and architectures for photonic chip-scale integration

Silicon nanophotonics holds the promise of dramatically advancing the state of the art in computing by enabling parallel architectures that combine unprecedented performance and ease of use with affordable power consumption. This paper presents a design study for a many-core architecture called Corona which utilizes dense wavelength division multiplexing (DWDM) for on- and off-chip communication together with the devices which will be needed to implement such a communication infrastructure.