Anisotropic optical properties of arrays of gold nanorods embedded in alumina

A series of thin films comprising gold nanorods embedded in an alumina matrix have been fabricated with lengths ranging from 75 to 330 nm. Their optical properties, expressed in terms of extinction - In(T), where T is optical transmittance, have been measured as a function of wavelength, rod length, angle of incidence, and incident polarization state. The results are compared to a Maxwell-Garnett based theory modified to take into account the strongly anisotropic nature of the medium. Transverse and longitudinal plasmon resonances are observed. The interaction between the nanorods leads to the splitting of the longitudinal resonance with the longer-wavelength resonance being forbidden for direct optical observations. The shorter-wavelength resonance related to the symmetric coupling between longitudinal plasma excitations in the nanorods depends on rod length, polarization state, and angle of incidence of the probing light. The impact of electron confinement on the optical properties of the gold rods is also seen and may be incorporated into the Maxwell-Garnett theory by restricting the mean free path of the conduction electrons to produce excellent agreement between observations and the complete theory. Annealing experiments that modify the physical structure of the gold confirm this conclusion.

Enhancement of dielectric constant and associated coupling of polarization behavior in thin film relaxor superlattices

Thin film capacitor structures in which the dielectric is composed of superlattices of the relaxors [0.2Pb(Zn1/3Nb2/3)O- 3-0.8BaTiO(3)] and Pb(Mg1/3Nb2/3)O-3 have been fabricated by pulsed laser deposition. Superlattice wavelength (Lambda) was varied between similar to3 and similar to 600 nm, and dielectric properties were investigated as a function of Lambda. Progressive enhancement of the dielectric constant was observed on decreasing Lambda, and, in contrast to previous work, this was not associated with the onset of Maxwell-Wagner behavior. Polarization measurements as a function of temperature suggested that the observed enhancement in dielectric constant was associated with the onset of a coupled response. The superlattice wavelength (Lambda =20 nm) at which coupled functional behavior became apparent is comparable to that found in literature for the onset of coupled structural behavior (between Lambda =5 nm and Lambda =10 nm). (C) 2001 American Institute of Physics.

Effect of Target Polarization in Electron-Ion Recombination

We present results of a study of the effect of target polarization on electron-ion recombination, and show that coherent radiation by the target electrons gives a large contribution to the recombination rate. It significantly modifies the nonresonant photorecombination background. A procedure has been devised whereby this contribution can be evaluated together with the conventional radiative recombination, independently of the dielectronic recombination component. Numerical results are presented for Zn2+, Cd2+, Sn4+, and Xe8+, showing up to an order-of-magnitude enhancement.

The role of target polarization in electron-ion recombination

We investigate the role of dynamic polarization of the target electrons in the process of recombination of electrons with multicharged ions (polarizational recombination). Numerical calculations carried out for a number of Ni- and Ne-like ions demonstrate that the inclusion of polarizational recombination leads to a noticeable increase (up to 30%) in the cross sections for incident electron energies outside the regions of dielectronic resonances. We also present a critical analysis of theoretical approaches used by other authors to describe the phenomenon of polarizational recombination.

Interplay between proton ordering and ferroelectric polarization in H-bonded KDP-type crystals

The origin of ferroelectricity in KH2PO4 (KDP) is studied by first-principles electronic structure calculations. In the low-temperature phase, the collective off-centre ordering of the protons is accompanied by an electronic charge delocalization from the near and localization at the far oxygen within the O-H...O bonds. Electrostatic forces. then, push the K+ ions towards off-centre positions, and induce a macroscopic polarization. The analysis of the correlation between different geometrical and electronic quantities, in connection with experimental data. supports the idea that the role of tunnelling in isotopic effects is irrelevant. Instead, geometrical quantum effects appear to play a central role. (C) 2001 Elsevier Science B.V. All rights reserved.

Polarization Relaxation in an Ionic Liquid Confined between Electrified Walls

The response of a room temperature molten salt to an external electric field when it is confined to a nanoslit is studied by molecular dynamics simulations. The fluid is confined between two parallel and oppositely charged walls, emulating two electrified solid-liquid interfaces. Attention is focused on structural, electrostatic, and dynamical properties, which are compared with those of the nonpolarized fluid. It is found that the relaxation of the electrostatic potential, after switching the electric field off, occurs in two stages. A first, subpicosecond process accounts for 80% of the decay and is followed by a second subdiffusive process with a time constant of 8 ps. Diffusion is not involved in the relaxation, which is mostly driven by small anion translations. The relaxation of the polarization in the confined system is discussed in terms of the spectrum of charge density fluctuations in the bulk.

On the low-frequency electrical polarization of bacterial cells in sands

We performed electrical measurements on sands flushed with bacterial suspensions of varying concentration. The first experiment was conducted with Shewanella putrefaciens (biomass 0â??0.5 mg/L) and the second with Escherichia coli (biomass 0â??42 mg/L). We measured a biomass-dependent low-frequency (10 Hz) polarization. At cell density 12 mg/L polarization increased (up to 15%). We attribute the decrease in polarization at low cell density to alteration of the mineral-fluid interface due to mineral-cell interactions. The polarization enhancement at higher cell density is possibly a pore throat mechanism resulting from decreased ionic mobility and/or electron transfer due to cell accumulation in pores.

Drug use amongst young people attending emotional and behavioural difficulty units during adolescence: A longitudinal anlaysis

This paper reports on the findings from a longitudinal survey of the drug use behaviours of young people who were attending Emotional and Behavioural Difficulty (EBD) units from the age of 11-16 years. It forms part of the Belfast Youth Development Study, a longitudinal study of adolescent drug use. This paper presents a follow-up report to a cross-sectional paper that reported on drug use behaviours of a sample of young people attending EBD units when aged 12/13 years at school year 9 (McCrystal et al 2005a). In the present paper reported drug use and behaviours associated with increased risk of its use between the ages of 11-16 years were examined. The findings show that those attending EBD Units consistently reported higher levels of licit and illicit drug use throughout adolescence. Compared with young people in mainstream school, higher levels of behaviours associated with drug use including antisocial behaviour, disaffection with school, and poor communication with their parents/guardians were noted. These findings have implications for the development and timing of targeted prevention initiatives for young people attending EBD units at all stages of adolescent development.

Substance Use Behaviours of Young People with A Moderate Learning Disability: A longitudinal analysis

Substance use behaviours of young people attending a special school are reported over a four year period from the age of 12-16 years. The paper investigated these behaviours by surveying a cohort of young people with a statement for moderate learning disabilities annually during the last four years of compulsory schooling. The findings show that these young people consistently reported lower levels of tobacco, alcohol and cannabis use compared with those attending mainstream school. No other illicit drug use was reported. The potential implications of these findings are discussed in relation to the context and timing of targeted substance education and prevention initiatives for young people with moderate learning disability attending a special school.

Plasma levels of the immunomodulatory cytokine interleukin-10 during normal human pregnancy: a longitudinal study.

Pregnancy is proposed to be a Th2 phenomenon, where Th2 cytokines inhibit Th1 responses to improve fetal survival. The importance of interleukin-10 (IL-10), an immunomodulatory cytokine produced by Th2 cells, in the maintenance of normal pregnancy is becoming increasingly apparent. In a longitudinal case-control study, the physiological effect of pregnancy on plasma IL-10 was investigated. The plasma concentration of IL-10 was determined using an ELISA technique in 99 pregnant women sampled at 12, 20 and 35 weeks of gestation, 38 non-pregnant control subjects sampled in parallel and in a subgroup of women sampled at 3 days post-partum (n, pregnant 21, non-pregnant 21). Plasma IL-10 was significantly higher in pregnant women at 12, 20 and 35 weeks of gestation (p

Soluble P-selectin levels during normal pregnancy: a longitudinal study.

Objective: To investigate soluble P-selectin (sP-selectin) levels and platelet parameters in normal pregnant women compared with non-pregnant control subjects. Design: A longitudinal case-control study. Setting: Obstetric outpatient clinic in the Jubilee Maternity Hospital, Belfast. Population: One hundred and twenty normal pregnant women and 41 non-pregnant age matched control subjects. Main outcome measures Plasma sP-selectin as a measure of platelet activation in normal pregnancy. Methods: The plasma concentration of sP-selectin in pregnant women sampled at 12, 20 and 35 weeks of gestation, and, in a subgroup at 3 days post-partum, and non-pregnant controls sampled in parallel, was determined using a commercial quantitative sandwich immunoassay kit. Platelet parameters on each blood sample were also recorded using a SYSMEX SE 9500 analyser. Main outcome measures: Plasma sP-selectin as a measure of platelet activation in normal pregnancy. Results: Soluble P-selectin was significantly higher in pregnant women than in non-pregnant control subjects at 20 and 35 weeks of gestation, (p

Electrically switchable nonreciprocal transmission of plasmonic nanorods with liquid crystal

The electro-optic response of a cell consisting of a thin layer of liquid crystal deposited onto gold nanorods embedded in thin film alumina with a transparent top electrode has been investigated. For p-polarized light incident from the liquid crystal side, the extinction peak associated with the nanorod longitudinal plasmon resonance is completely suppressed. The peak could be recovered by applying an external electric field parallel to the long axis of the nanorods. No extinction peak suppression is observed when the light was incident from the nanorod side of the cell. The effect is explained by polarization properties of liquid crystal.

A longitudinal study of infant feeding and obesity throughout the life course

Background: The Centers for Disease Control and Prevention and the US Department of Health and Human Services promote breastfeeding as a strategy for reducing childhood overweight. We evaluated the relation between infant feeding and the development of overweight and obesity throughout life course. Methods: We investigated the association between infant feeding and obesity among 35 526 participants in the Nurses' Health Study II who were followed prospectively from 1989 to 2001. Mothers of participants provided information by mailed questionnaires on the duration of breast- and bottle-feeding, as well as the type of milk or milk substitute in the bottle. Information on body shape at ages 5 and 10, weight at age 18, current weight between 1989 and 2001, and height was reported by the participants. Results: The duration of breastfeeding, including exclusive breastfeeding, was not related to being overweight (25 body mass index (BMI)