bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal distribution of bioclimatic potential for the Codling moth and the Colorado potato beetle in Norway: model predictions versus climate and field data from the 1990s
Authors: Rafoss Trond , Sæthre May‐Guri
Published: August 2003

Abstract 1 Based on climate data from a network of agrometeorological stations in Norway, the effects of current and future climate regimes on the spatial and temporal distribution of the Codling moth (Cydia pomonella) and the establishment potential of the Colorado potato beetle (Leptinotarsa decemlineata) were investigated.

2 The study was accomplished using climex, a dynamic climate matching‐ and climate response estimation model, which predicts potential distribution of an organism based on its known geographical distribution.

3 Validation of the climex model predictions for C. pomonella against field data on spatial distribution of the species in Norway resulted in a refined set of climate response parameters for C. pomonella. Temporal occurrence of C. pomonella seems to be affected by climate (temperature) and insecticide treatment against the Apple fruit moth (Argyresthia conjugella) in the previous season.

4 Climate change scenarios (0.1 °C increase per degree in latitude in daily maximum and minimum temperatures) indicated an extension of the potential geographical range for C. pomonella, and 23 new locations were found favourable for its long‐term survival. The abundance and pest status of C. pomonella could increase dramatically in those locations where the species is already established.

5 Leptinotarsa decemlineata would only temporarily find suitable climate conditions in Norway and hence only be able to establish interim populations in a few regions under current climate conditions. Climate change scenarios for L. decemlineata indicated that the species would be able to establish as far north as 64°N, mainly in the inland of eastern Norway.

6 In general, the methods applied support the process of decreasing the uncertainty both in our knowledge about the pests themselves and about the environment, which are crucial elements in predicting whether a species is able to establish in a new area.
Effects of elevated CO2and temperature on the leaf chemistry of birchBetula pendula(Roth) and the feeding behaviour of the weevilPhyllobius maculicornis
Authors: Kuokkanen Kari , Yan Shanchun , Niemelä Pekka
Published: August 2003

Abstract1 The effect of elevated CO2and temperature on the foliar chemistryBetula pendulaRoth and the feeding performance of polyphagous weevilsPhyllobius maculicornisGerm. was studied. Birch seedlings were grown during one growing season in chamber‐less field conditions and in closed‐top chambers exposed to four different treatments: ambient CO2(350 p.p.m) and temperature, elevated atmospheric CO2(700 p.p.m) and ambient temperature, elevated temperature +3 °C above ambient) and ambient CO2, and a combination of elevated CO2and temperature.

2 In leaves under CO2enrichment, the concentration of nitrogen and some flavonol glycosides significantly decreased, whereas the concentration of total phenolics, condensed tannins and (+)‐catechin significantly increased. The total concentration of cinnamoylquinic acids was significantly increased by CO2and decreased by temperature. The concentration of salidroside increased under elevated temperature.

3 Weevil‐feeding experiments were carried out in a five‐choice arrangement, one leaf from each of the five treatments (chamber‐less field controls and four different treatments in chambers) being placed in random order in a plastic box. The weevils preferred the leaves grown under elevated CO2, which had low nitrogen, high phenolics and the highest condensed tannin concentrations. Whether the reason for this trend is due to the stimulating effect of condensed tannins and/or a change in other secondary compounds, remains unknown. The weevils did not show any obviously different response in feeding performance to temperature and the combination of elevated CO2and temperature.
Detection of Rhopalosiphum insertum (apple‐grass aphid) predation by the predatory mite Anystis baccarum using molecular gut analysis
Authors: Cuthbertson Andrew G. S. , Fleming Colin C. , Murchie Archie K.
Published: August 2003

Abstract  1 A simple, yet sensitive polymerase chain reaction based technique was developed for the detection of the apple‐grass aphid Rhopalosiphum insertum in the gut of Anystis baccarum, a predatory mite.

2 A range of conserved polymerase chain reaction primers for insect mitochondrial and ribosomal DNA were tested in order to amplify R. insertum DNA. The mitochondrial DNA primers LrRNAR2 + N1F1, amplified a region between the ND1 and large subunit RNA genes.

3 DNA sequencing of the R. insertum ND1‐LRNA polymerase chain reaction product allowed aphid‐specific polymerase chain reaction primers to be designed. These amplified a 283‐bp product from individual aphids. No polymerase chain reaction product was amplified from individual A. baccarum.

4 Using the aphid‐specific primers against A. baccarum fed on R. insertum, the diagnostic 283‐bp product was amplified.

5 Two restriction enzymes (RsaI and AluI) produced patterns that allowed unambiguous identification of R. insertum DNA from that of Macrosiphum euphorbiae and Myzus persicae.
Defoliation of Sitka spruce by the European spruce sawfly, Gilpinia hercyniae (Hartig): a retrospective analysis using the needle trace method
Authors: Williams D. T. , Straw N. A. , Day K. R.
Published: August 2003

Abstract 1 During 1968–74, an outbreak of the European spruce sawfly Gilpinia hercyniae, defoliated many stands of Sitka spruce in commercial forests in mid‐Wales. The needle trace method was used to determine retrospectively the temporal pattern and intensity of defoliation in a stand of Sitka spruce in Hafren Forest that had been damaged severely at the time of the sawfly outbreak.

2 An initial calibration experiment, designed to test the reliability of the needle trace method when applied to Sitka spruce, indicated that artificially induced defoliation of up to 75% was detected by the technique with an accuracy of ±7%. Higher rates of defoliation were underestimated by up to 17%.

3 For the main sample of trees, the needle trace method demonstrated that retention of needle sets (average needle retention) was reduced by up to 33–38% over a 10‐year period coincident with the G. hercyniae outbreak and the years immediately afterward when the canopy was recovering.

4 Analysis of needle loss within separate needle cohorts and age‐classes revealed that 1‐year‐old needles were the most severely defoliated. The density of 1‐year‐old needles was reduced by 51–78% in 1970–73.

5 Defoliation at the time of the G. hercyniae outbreak was associated with reductions in annual height, radial, and volume increments of 24–49%, 30–59% and 32–56%, respectively. Radial and volume increments suffered their greatest reductions 1 year later than height increments.

6 The study demonstrates that the needle trace method can be applied successfully to Sitka spruce to quantify defoliation caused by an insect outbreak occurring many years previously, and that the technique can provide data on needle loss that is valuable for interpreting reductions in tree growth.
Field oviposition rates and egg load dynamics of pollen beetles (Meligethes aeneus Fab.) (Colepotera: Nitidulidae)
Authors: Ekbom Barbara , Ferdinand Victoria
Published: August 2003

Abstract 1 Egg loads from field collected pollen beetles (Meligethes aeneus Fab., Coleoptera: Nitidulidae) were determined by dissecting beetles caught at the beginning and end of the putative daily oviposition period. Field collected beetles were offered Brassica napus (L.) plants in cages for 8 (morning and early afternoon), 16 (overnight), and 24 h to ascertain the number of eggs laid during these time periods.

2 Most eggs were laid in the morning and early afternoon. The proportion of gravid females was higher at the beginning of the oviposition period than at the end. Most females in the morning carried two eggs, whereas one egg was more common in the afternoon.

3 We hypothesized that the number of eggs laid during the oviposition period would be equivalent to the difference between egg loads at the beginning and end of oviposition. This was not the case; differences in egg loads were significantly lower than number of eggs laid. However, the number of eggs laid was equivalent to the egg load at the beginning of the oviposition period, suggesting that eggs available in the morning are laid during the following day.

4 Population estimates of daily oviposition rates, approximately 0.7 eggs per beetle and day, were close to estimates from laboratory studies when the proportion of gravid females was taken into consideration.
Feeding by the pine weevil Hylobius abietis in relation to sun exposure and distance to forest edges
Authors: Nordlander Göran , Örlander Göran , Langvall Ola
Published: August 2003

Abstract  1 The intensity of feeding by adult pine weevils Hylobius abietis (L.) on the stem bark of Norway spruce Picea abies (L.) Karst. seedlings planted in rows with a north–south orientation across a clear‐cutting, was measured throughout a growth season. The feeding was then correlated to light interception, soil temperature and distance to the nearest forest edge.

2 Feeding was at least twice as intense on seedlings in the central part of the clear‐cutting compared to those at the edges. The decline began approximatety 15 m from the edge and was of similar proportions on both the sun‐exposed and shaded sides.

3 Measures of global radiation and soil temperature correlated well with consumption on the shaded side. However, on the sun‐exposed side, there were no apparent correlations with global radiation or soil temperature that could explain the decline in consumed bark area.

4 We conclude that the decline in feeding towards the forest edges was mainly due to factors other than the microclimate variables we monitored. We suggest that the presence of roots of living trees along the forest edge may reduce damage to seedlings, since they provide an alternative source of food for the weevils. This alternative‐food hypothesis may also explain why seedlings in shelterwoods usually suffer less damage from pine weevils than seedlings in clear‐cuttings.
Attack dynamics of the pine shoot beetle, Tomicus piniperda (Col.; Scolytinae) in Scots pine stands defoliated by Bupalus piniaria (Lep.; Geometridae)
Authors: Cedervind Jan , Pettersson Mattias , Långström Bo
Published: August 2003

Abstract 1 After a 1‐year, extensive pine looper (Bupalus piniaria) outbreak, plots were laid out to study tree susceptibility to attack, and performance of Tomicus piniperda in pine trees suffering from varying levels of defoliation.

2 Tomicus piniperda was the dominating stem‐attacking species among the primary stem colonizers, and 82% of all trees that died had been colonized by T. piniperda.

3 Beetle attacks primarily struck severely defoliated trees, i.e. trees that suffered from 90% to 100% defoliation.

4 Beetle attacks peaked in the second year after cessation of the outbreak, and suppressed trees were both more frequently attacked and more susceptible to beetle attack than intermediate and dominant trees.

5 Trees surviving beetle attacks carried more foliage than trees that did not survive the attacks.

6 A single year of severe defoliation is enough to render pine trees susceptible to secondary pests, such as T. piniperda.
The immunological basis of psoriasis
Authors: Griffiths C E M
Published: August 2003

Evidence that psoriasis is an immune‐mediated disorder comes from laboratory studies, clinical observation, and use of targeted therapies. Immunohistochemical studies have shown that the majority of T cells in psoriatic plaques are CD45RO+ memory‐effector T cells that migrate into skin in recognition of an as yet undetermined antigen. There is also a predominance of Th1 cytokines, namely interferon gamma, in psoriatic plaques, in contrast to the predominance of Th2 cytokines found in atopic dermatitis. The efficacy of therapeutic agents that target T cells, such as anti‐CD4+ monoclonal antibodies, cyclosporin, and interleukin‐2 fusion toxin, has provided further substantial evidence that psoriasis is a T‐cell‐mediated disease. New T‐cell targeted approaches and cytokine modulation are advancing basic science in providing an understanding of the evidence for the importance of the immune process in the biology of psoriasis.
Species‐specific differences in oak foliage affect preference and performance of gypsy moth caterpillars
Authors: Foss L. K. , Rieske L. K.
Published: July 2003

The gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), is an introduced defoliator that preferentially feeds on oaks, Quercus spp. (Fagaceae) in the north‐eastern USA. As the gypsy moth expands its geographic range, the extensive oak component in forests and urban environments of the USA assure its successful establishment. Given their economic and ecological importance, and the gypsy moth's potential to cause mortality, we evaluated caterpillar preference and performance on various oaks prevalent in the central hardwoods region. Most of the physical and chemical characteristics we measured, from budbreak phenology to foliar chemistry, varied significantly among the oak species tested. Similarly, insect preference and performance varied significantly, though not always in predictable ways. Caterpillar preference was compared for black, Q. velutina Lamarck, burr, Q. macrocarpa Michaux, cherrybark, Q. pagoda Rafinesque, northern red, Q. rubra L., pin, Q. palustris Muenchhausen, swamp white, Q. bicolor Willdenow, white, Q. alba L., and willow, Q. phellos L., oaks. Gypsy moth preference was greatest for black and burr, and least for northern red, pin, and willow oaks. We assessed foliar characteristics and caterpillar performance on foliage from burr, cherrybark, northern red, pin, and willow oaks. Caterpillar preference did not always correlate with performance. Gypsy moth consumption and growth were highest, and development most rapid, on pin oak, which had high nitrogen and tannin levels, and was among the least preferred. Northern red and willow oaks were also among the least preferred and were the least suitable tested, producing caterpillars with moderate to low consumption and growth rates, as well as the longest development. Northern red oak contained the lowest foliar tannins; willow oak foliage was lowest in carbohydrates and nitrogen. Our results suggest that a combination of foliar characteristics may be responsible for gypsy moth preference and performance, and that an optimal combination of foliar components serves to maximize host suitability. These data will provide information useful for planning and managing urban forests in the presence of expanding gypsy moth populations.
Learning of host searching cues by the larval parasitoid Microplitis croceipes
Authors: Takasu Keiji , Lewis W.J.
Published: July 2003

We conducted laboratory experiments using a wind tunnel to determine the effects of prior experience on the learning and retention of learned responses in the larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Although most females that had either antennated host frass or oviposited in a host in the presence of vanilla odor, made oriented flight to the odor from downwind in the wind tunnel at 30 min after experience, only those that had oviposited in a host with the odor responded to the odor at 24 h after experience. Females that had oviposited in the non‐natural host beet armyworm (BAW) larva with or without the odor did not respond to the odor at 30 min after experience. These results indicate that an oviposition in the host in the presence of odors strongly affects associative learning and the persistence of learned response to the odors. When females were allowed to antennate host frass in the presence of vanilla and to subsequently oviposit in a host within an interval of 5 min or less, their learned response to vanilla also persisted for 24 h. Similarly, when females were conditioned to link vanilla with host frass and then allowed to make an ovipositor contact with host hemolymph, their learned response persisted for 24 h. However, antennal contact with hemolymph after such conditioning of vanilla with host frass did not improve the persistence of learned response to the odor. These results indicate that ovipositor contact with host hemolymph during oviposition is partially responsible for an increased retention of learned response. Females responded to vanilla 48% of the time at 30 min after antennating host frass without the odor, but their response to the odor significantly decreased after oviposition in a BAW larva subsequent to the antennation of host frass. This result indicates that oviposition in a BAW larva decreases subsequent response to general odors. Based on the results, we discuss the foraging behavior of M. croceipes dependent on learning and subsequent experiences.
The effects of host weight at parasitism on fitness correlates of the gregarious koinobiont parasitoid Microplitis tristis and consequences for food consumption by its host, Hadena bicruris
Authors: Elzinga Jelmer A. , Harvey Jeffrey A. , Biere Arjen
Published: July 2003

Gregarious koinobiont parasitoids attacking a range of host sizes have evolved several mechanisms to adapt to variable host resources, including the regulation of host growth, flexibility in larval development rate, and adjustment of clutch size. We investigated whether the first two mechanisms are involved in responses of the specialist gregarious parasitoid Microplitis tristis Nees (Hymenoptera: Braconidae) to differences in the larval weight and parasitoid load of its host Hadena bicruris Hufn. (Lepidoptera: Noctuidae). In addition, we examined the effects of parasitism on food consumption by the host. Parasitoids were offered caterpillars of different weight from all five instars, and parasitoid fitness correlates, including survival, development time, and cocoon weight, were recorded. Furthermore, several host growth parameters and food consumption of parasitized and unparasitized hosts were measured. Our results show that M. tristis responds to different host weights by regulating host growth and by adjusting larval development rate. In hosts with small weights, development time was increased, but the increase was insufficient to prevent a reduction in cocoon weight, and as a result parasitoids experienced a lower chance of successful eclosion. Cocoon weight was negatively affected by parasitoid load, even though host growth was positively affected by parasitoid load, especially in hosts with small weights. Later instars were more optimal for growth and development of M. tristis than early instars, which might reflect an adaptation to the life‐history of the host, whose early instars are usually concealed and inaccessible for parasitism on its food plant, Silene latifolia Krause (Caryophyllaceae). Parasitism by M. tristis greatly reduced total host food consumption for all instar stages. Whether plants can benefit directly from the attraction of gregarious koinobiont parasitoids of their herbivores is a subject of current debate. Our results indicate that, in this system, the attraction of a gregarious koinobiont parasitoid can directly benefit the plant by reducing the number of seeds destroyed by the herbivore.
Marking bark beetle parasitoids within the host plant with rubidium for dispersal studies
Authors: Hougardy E. , Pernet P. , Warnau M. , Delisle J. , Grégoire J.‐C.
Published: July 2003

A technique using rubidium chloride (RbCl), a trace element, as internal label is proposed for marking hymenopteran parasitoids attacking a concealed host, Ips typographus L. (Coleoptera: Scolytidae). RbCl was introduced directly into spruce via the vascular system using glass tubing. RbCl passed through the food chain and was detected at the parasitoid level by electrothermal atomic absorption spectroscopy (EAAS) or flame emission spectroscopy (FES). Mark persistency until day 8 after emergence was tested in labelled Rhopalicus tutela (Walker) (Hymenoptera: Pteromalidae). The mark decreased with time only in fed females, probably due to excretion and/or egg resorption. The proportion of marked males did not vary with time or treatment.
Effectiveness of protein‐rich pea flour for the control of stored‐product beetles
Authors: Hou Xingwei , Fields Paul
Published: July 2003

Protein‐rich pea flour is toxic to many stored‐product insects. We investigated several factors that may affect the efficacy of protein‐rich pea flour: insect species, insect population densities, grain species, temperature, and moisture. Adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae) was more susceptible to protein‐rich pea flour than Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae). Protein‐rich pea flour did not increase the mortality of adult Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). However, it reduced the number of offspring of all three species. The toxicity of protein‐rich pea flour was not reduced after 9 months when stored at −15 °C, or at room temperature as flour or mixed with grain. Its toxicity in wheat increased with higher temperature and at lower grain moisture contents. Protein‐rich pea flour was more toxic in wheat and barley than in maize. This difference among grain species was not due to the kernel size of the grain, as ground wheat or maize with the same particle size still had different LD50s.
Effects of mass releases of Trichogramma brassicae on predatory insects in maize
Authors: Babendreier D. , Rostas M. , Höfte M. C. J. , Kuske S. , Bigler F.
Published: July 2003

We investigated whether mass releases of Trichogramma brassicae against the European corn borer will have detrimental effects on populations of other natural enemies in maize. In a tiered approach, experiments investigated the host acceptance of T. brassicae towards eggs of Chrysoperla carnea, Episyrphus balteatus, Adalia bipunctata, and Coccinella septempunctata under laboratory, caged, and field conditions. The factitious host, Ephestia kuehniella, and in one case also Mamestra brassicae were used as control. Under laboratory conditions, 53% of the T. brassicae females parasitised C. carnea eggs, 70% parasitised E. balteatus eggs, while 91% of the females parasitised E. kuehniella eggs, with T. brassicae emerging from C. carnea, E. balteatus, and E. kuehniella at rates higher than 81%. No parasitoid offspring emerged from eggs of A. bipunctata and C. septempunctata. However, we observed significantly increased mortality on A. bipunctata eggs, compared to the control, and also found young instars of T. brassicae inside A. bipunctata eggs. In a second experiment where the host acceptance behaviour of the parasitoid female was directly observed for 10 min, 10% of T. brassicae females were found to oviposit in eggs of A. bipunctata, but the development of parasitoid offspring failed. No C. septempunctata eggs, 13% of E. balteatus eggs, 23% of C. carnea eggs, 33% of E. kuehniella egg clusters, and 83% of M. brassicae eggs were accepted for oviposition. In the greenhouse under caged conditions, the parasitism rate of C. carnea eggs (7%) and E. balteatus eggs (0.4%) were significantly lower than of E. kuehniella eggs (21 and 27%, respectively). In the final tier, 3.1% of C. carnea eggs were parasitised by T. brassicae under field conditions. This was significantly less than the observed parasitism rate of E. kuehniella egg clusters (64%). From direct observations of the parasitoids’ host acceptance behaviour and the low parasitism rates observed under caged and field conditions, we conclude that detrimental effects of the mass release of T. brassicae on populations of natural enemies in maize are unlikely to occur.
Infrared second harmonic generation spectroscopy of Ge(111) interfaces
Authors: Bodlaki D. , Freysz E. , Borguet E.
Published: August 2003

Infrared second harmonic generation (IR-SHG) spectroscopy, an extension of spectroscopic SHG to the IR, is described and applied to the investigation of germanium–dielectric interfaces in the spectral region near the direct and indirect band gap of the bulk semiconductor. The spectrum of the Ge(111)–GeO2 interface, in the 1100–2000 nm fundamental wavelength range, is dominated by a resonance at 590 nm. This feature is assigned to the direct Γ25>Γ2 transition between valence and conduction band states. Polarization and azimuth dependent IR-SHG spectroscopy revealed that the anisotropic contribution, containing bulk quadrupole, ξ, and surface, ∂11, nonlinear susceptibility terms, dominates the 590 nm resonance. S-termination of Ge(111) significantly modifies the interface nonlinear optical response. The IR-SHG spectrum of S–Ge(111) presents a new, possibly surface resonance at ∼565 nm, in addition to the resonance inherent to the bulk Ge at 590 nm, tentatively assigned to an interband transition of Ge atoms associated with the surface.
Bending electrostriction and space-charge distribution in polyurethane films
Authors: Watanabe Masashi , Wakimoto Naoko , Shirai Hirofusa , Hirai Toshihiro
Published: August 2003

Application of an electric field bent a polyurethane single-layer film. The bending direction depended on the chemical structure of the polyurethane. A film made from a polyurethane (N-PU) that had phenylimino groups in its structure bent toward the anode side. On the other hand, another film made from a different kind of polyurethane (Nt-PU) that had nitrophenyl groups bent toward the cathode side. Measurements of the space-charge distributions in the films using a pulsed electroacoustic method revealed contrasting distributions between the films. That is, in the N-PU film, positive space charge accumulated near the cathode. In the Nt-PU film, the negative one accumulated near the anode. These contrasting results between N-PU and Nt-PU both in the bending direction and the space-charge distribution suggested a direct relation of space charge to the bending mechanism.
Surface plasmon broadening for arbitrary shape nanoparticles: A geometrical probability approach
Authors: Coronado Eduardo A. , Schatz George C.
Published: August 2003

A geometrical probability measure is proposed for calculating the effective conduction electron mean free path of an arbitrary shape convex particle. It is shown that the plasmon widths determined from this mean free path are consistent with exact quantum mechanical widths for simple particle shapes. We use the mean free path formula to evaluate size and shape dependent dielectric functions and extinction spectra for silver spheroids, square prisms, truncated tetrahedrons, and cylinders.
Donor–acceptor pair photoluminescence spectra analysis in CdTe:Ag
Authors: Zelaya-Angel O. , Garcia-Rocha M. , Mendoza-Alvarez J. G. , Cardenas M. , Aguilar-Hernandez J.
Published: August 2003

Photoluminescence (PL) spectra of CdTe single crystals and films, undoped and Ag-doped, were studied in the range of the photon energy (hν): 1.5–1.6 eV, at 10 K. Films were doped during the growth process. Thin layers of Ag were vacuum evaporated onto the surface of undoped CdTe crystals, then were submitted to thermal annealing in a N2+2% H2 ambient at 400 °C for 3 h. PL spectra of crystals exhibit a donor–acceptor pair (DAP) emission at hν=1.491 eV (named here DAPAg2) with the highest intensity with respect to other signals. The PL of films is characterized by a peak at 1.5 eV followed by several phonon replicas. In both cases, the DAP emissions are due to the Ag-impurity presence and are accompanied by phonon replicas. Unannealed intrinsic crystals exhibit a unique broad DAPAg1 peak at hν=1.501 eV, and one month aged at room temperature Ag-doped crystals only display a wide DAPAg2 peak at hν=1.491 eV with 65% of its initial intensity, that reflects a reduced density of Ag diffused-doping levels. The origin of DAP lines in a PL spectra of CdTe:Ag has not been completely well defined until now, and we have introduced some explanatory conclusions about and a simple model for electronic transitions. This issue is important because Ag is an everpresent residual impurity in CdTe.
Current limiting mechanisms in indium-tin-oxide/poly3-hexylthiophene/aluminum thin film devices
Authors: Chiguvare Z. , Parisi J. , Dyakonov V.
Published: August 2003

We studied the temperature dependent current-voltage characteristics of regioregular poly (3-hexylthiophene 2.5-diyl) (P3HT) thin films sandwiched between indium tin oxide (ITO) and aluminum (Al) electrodes (ITO/P3HT/Al devices), with the aim of determining the current limiting mechanism(s) in these devices, and the temperature and/or applied electric field range(s) in which these mechanisms are valid. The current-voltage characteristics of the ITO/P3HT/Al devices showed that current flow across the device is limited by hole injection at the Al/P3HT interfaces at temperatures below 240 K, when the device is biased with high potential on Al. Above this temperature, the bulk transport properties control the characteristics. For the reverse bias, the ITO/P3HT contact does not limit the current; instead it is controlled by a space charge that accumulates due to the low charge carrier mobility in the polymer. An expression that provides a criterion to determine the validity of applying either the Richardson–Schottky thermionic emission model or the Fowler–Nordheim field emission model was deduced. It can be employed to determine the electrical field at which the transition from charge injection by thermionic emission to that by field emission for a given temperature and interface potential barrier height takes place. Our experimental data fit to the deduced expression. Theoretical limits of the model are also discussed. By considering the regions of the current-voltage curves where field emission or thermionic emission was applicable, the interface potential barriers were estimated, respectively. Hence, conclusions on whether the current-voltage behavior of the devices was contact limited or bulk limited could be drawn.
(3+1)
-resonantly enhanced multiphoton ionization-photoelectron spectroscopy of the (3d-4s) supercomplex of acetylene: The geometry of the E state revisited through experiment and theory
Authors: Blanchet Valérie , Boyé Séverine , Zamith Sébastien , Campos Andréa , Girard Bertrand , Liévin Jacques , Gauyacq Dolores
Published: August 2003

(3+1) -resonance enhanced multiphoton ionization-photoelectron spectroscopy (REMPI-PES) has been carried out via various low vibrational levels of the D, F, and E states belonging to the (3d-4s) supercomplex of acetylene. The photoelectron analysis takes into account the Renner–Teller coupling occurring in the ion ground state. In the 74 500–76 500 cm−1 energy range, the coupling between the F Rydberg state and E valence state is strongly revealed through the photoelectron spectra. Moreover, the vibrational analysis of the REMPI-PES spectra enlighten the controversial geometry of the E valence state. They strongly indicate a planar trans-bent geometry of the E valence state, quantitatively confirmed by an ab initio study. This study confirms the tentative frequencies for the ν1 stretching mode (3307 cm−1 for C2H2+, 2572 cm−1 for C2D2+), as well as the frequencies for the bending mode: trans-ν4 (694 cm−1 for C2H2+, 586 cm−1 for C2D2+) and cis-ν5 (775 cm−1 for C2H2+, 569 cm−1 for C2D2+) of the cations.
Electromagnetic wave absorption property of carbon microcoils in 12–110 GHz region
Authors: Motojima S. , Noda Y. , Hoshiya S. , Hishikawa Y.
Published: August 2003

The electromagnetic (EM) wave absorption properties in the gigahertz region (12–110 GHz) of carbon microcoils (CMCs) with a three-dimensional-helical/spiral chiral structure (1–10 μm coil diameter and 0.1–10 mm coil length) were examined using the open space method. It was found that the target value of reflection loss, over −20 dB (above 99% absorptivity) necessitated for commercial applications, could be obtained for EM absorption composites of only 1–2 wt % addition of CMCs in a polyurethane matrix for the 30–35, 50–55, 75–80, and 95–100 GHz bands. A CMCs addition of more than 3 wt % resulted in a decrease of the EM wave absorptivity, because of the increase in the reflection of the EM waves. Multilayer absorption composites showed a higher EM absorptivity than that of single-layer composites. The longer the coil length, the higher the absorptivity could be obtained. The absorption mechanism of the EM waves by CMCs is discussed.
Thermal annealing effects on the structural and electrical properties of HfO2/Al2O3 gate dielectric stacks grown by atomic layer deposition on Si substrates
Authors: Cho Moonju , Park Hong Bae , Park Jaehoo , Hwang Cheol Seong , Lee Jong-Cheol , Oh Se-Jung , Jeong Jaehack , Hyun Kwang Soo , Kang Hee-Sung , Kim Young-Wuk , Lee Jong-Ho
Published: August 2003

HfO 2 / Al 2 O 3 gate dielectric thin film stacks were deposited on Si wafers using the atomic layer deposition technique. A 3.3-nm-thick Al2O3 interlayer was grown at 400 °C using Al(CH3)3 and O3, and 2.5–3.5-nm-thick HfO2 films were grown at either 300 or 400 °C using HfCl4 and H2O. Thermal annealing of the dielectric film stack at temperatures ranging from 400 to 1000 °C under pure N2 atmosphere resulted in variation of the equivalent oxide thicknesses. The equivalent oxide thickness of the dielectric film stack showed a minimum after annealing at 650 °C irrespective of the HfO2 film growth temperature. High temperature (>800 °C) annealing induced the formation of SiO2 and intermixing between the HfO2 and Al2O3 layers, which resulted in an increase in the equivalent oxide thickness of the film stack. The structural changes in the stacked films as a function of the annealing temperature were compared with those of HfO2 and Al2O3 single layers. The film stack showed minimal hysteresis (<15 mV) behavior in the capacitance–voltage curve and a shift in flat-band voltage of 0.6–0.9 V by negative fixed charges at the Al2O3/SiO2 interface after annealing at temperature >500 °C. The variation in fixed charge density as a function of the annealing temperature was also investigated. A minimum equivalent oxide thickness of 1.3 nm with leakage current density of 8×10−6 A/cm2 at −1 V was obtained with the poly-Si electrode even after annealing at 1000 °C for 10 s. This leakage current density is seven orders of magnitude smaller than that of SiO2 with similar equivalent oxide thickness.
Molecular dynamics investigation of water permeation through nanopores
Authors: Allen Rosalind , Hansen Jean-Pierre , Melchionna Simone
Published: August 2003

Molecular dynamics (MD) simulations are carried out to investigate the permeation of nanometer-sized cylindrical pores connecting two reservoirs, by water molecules and by a reference Lennard-Jones fluid. Water molecules penetrate a channel of fixed length only beyond a minimum radius. Near threshold, permeation is found to be intermittent and sensitive to other physical parameters, including the polarizability of the medium (e.g., a cell membrane) embedding the channel. Once the molecules fill the pore, the confined water exhibits properties (mean density, diffusivity, hydrogen bonding) surprisingly close to those of the bulk. The intermittent behavior near the threshold is analyzed in terms of a Landau-like grand potential regarded as a function of the pore occupancy. The grand potential, which is determined using a biased sampling technique, generally exhibits two minima, associated with the “empty” and “filled” states, separated by a potential barrier (transition state). No intermittent filling of identical pores is observed in the possible case of the reference Lennard-Jones fluid over a wide range of physical conditions, pointing to the specific role of hydrogen bonding for intermittent behavior. A careful analysis of the MD-generated configurations shows that the filled state nucleates around a chain of hydrogen-bonded molecules spanning the pore.
Channel-facilitated membrane transport: Average lifetimes in the channel
Authors: Berezhkovskii Alexander M. , Pustovoit Mark A. , Bezrukov Sergey M.
Published: August 2003

The transport of many solutes across biological membranes happens with the help of specialized proteins that form water-filled channels traversing the membranes. Recent experimental and theoretical work demonstrates that solute translocation can be facilitated by attractive interactions between the channel and penetrating particle. Here we consider an important aspect of channel-facilitated passive transport, the average lifetimes in the channel for those particles that traverse the channel and those that return, as well as the total average lifetime of the particle in the channel. Exact expressions for the average lifetimes are derived in the framework of a one-dimensional diffusion model. The validity of our one-dimensional analysis is verified by good agreement of the theoretical predictions with the average lifetimes found in three-dimensional Brownian dynamics simulations.
Dipole-bound anions of carbonyl, nitrile, and sulfoxide containing molecules
Authors: Hammer Nathan I. , Diri Kadir , Jordan Kenneth D. , Desfrançois Charles , Compton Robert N.
Published: August 2003

Dipole-bound anions of 27 molecules containing either a carbonyl, nitrile, or sulfoxide group were studied using Rydberg electron transfer (RET) reactions with rubidium atoms excited to ns 2S and nd 2D excited states. The electron affinity of each molecule was obtained from the Rydberg state, nmax*, that gave the largest negative ion yield using the empirical relationship electron affinity=23/nmax*2.8 eV as well as from fitting the charge exchange profile to a theoretical curve crossing model. Electron affinities for the low dipole moment molecules (carbonyls) were also deduced from measurements of the electric field required to detach the electron from the anion. Calculations of the electron affinities for some of the nitriles at the coupled-cluster level of theory were performed. The dependencies of the electron affinity upon dipole moment, polarizability, dispersion interaction, conformation, and geometry of the molecules were investigated. It was found that a higher dipole moment generally results in a higher electron affinity. However, for molecules with similar dipole moments, other factors such as polarizability and the dispersion interaction play an important role. The effect of collision velocity on the creation of these anions is also studied through the use of different carrier gases (H2, He, Ne, Ar, Kr, Xe) in the nozzle jet expansion. Competition between RET and collisional detachment is observed and discussed qualitatively.
Doppler-free laser polarization and optical–optical double resonance polarization labeling spectroscopies of a large molecule: Naphthalene
Authors: Kabir M. H. , Kasahara S. , Demtröder W. , Tatamitani Y. , Doi A. , Katô Hajime , Baba Masaaki
Published: August 2003

Doppler-free laser polarization (DFLP) spectroscopy is successfully applied to a large polyatomic molecule, naphthalene. Rotationally resolved spectra of the 33(b2g)01 vibronic band of the Ã 1B1u←X̃ 1Ag electronic transition of gas phase naphthalene at room temperature have been measured with the technique of DFLP spectroscopy. The typical width of the observed spectral lines was 15 MHz, and the absolute wave numbers were measured with an accuracy of better than ±0.0002 cm−1. In order to assign the dense and complicated parts of the spectra, the technique of Doppler-free optical–optical double resonance polarization labeling spectroscopy was used. Both V-type and Λ-type double resonances were observed, and these signals were found to be very useful for the unambiguous assignment of the complicated lines of DFLP spectrum. Three rotational constants A, B, and C, three symmetric-top quartic centrifugal distortion constants ΔJ, ΔJK, and ΔK, and two asymmetric-top distortion constants δJ and δK were determined by a least-squares fitting of 4632 spectral lines in the range J=4–154 and Ka=0–40 with a standard deviation of 0.0002 cm−1. No appreciable perturbation was observed.
Carrier dynamics in nitride-based light-emitting p-n junction diodes with two active regions emitting at different wavelengths
Authors: Li Y.-L. , Gessmann Th. , Schubert E. F. , Sheu J. K.
Published: August 2003

The carrier transport and recombination dynamics of monolithic InGaN/GaN light-emitting p-n junction structures with two active regions are investigated. Room-temperature and low-temperature photoluminescence and room-temperature electroluminescence measurements show two emission bands originating from the two active regions. In electroluminescence, the intensity ratio of the two emission bands is independent of injection current. In contrast, the intensity ratio depends strongly on the excitation intensity in photoluminescence measurements. The dependency of the emission on excitation is discussed and attributed to carrier transport between the two active regions and to the different carrier injection dynamics in photoluminescence and electroluminescence. The luminous efficacy of a Gaussian dichromatic white-light source is calculated assuming a line broadening ranging from 2kT to 10kT. Luminous efficacies ranging from 380 to 440 lm/W are obtained for broadened dichromatic sources.
A monolayer organic light-emitting diode using an organic dye salt
Authors: Xu Hongguang , Meng Ruiping , Xu Chunxiang , Zhang Junxiang , He Guohua , Cui Yiping
Published: August 2003

Monolayer organic light-emitting diodes (OLEDs) are fabricated with an organic dye salt as an emitting layer. The emission intensity is one order of magnitude stronger and the luminescent efficiency is four times higher than those of the corresponding monolayer tris(8-hydroxyquinolino) aluminum devices. The optical and electrical characteristics demonstrate the organic salt efficiently balances the charge injection from electrodes, which may be interpreted by considering the polarity of the organic ionic salt. These results suggest a class of novel materials for OLEDs.
Disorder effects on the imaging of a negative refractive lens made by arrays of dielectric cylinders
Authors: Gupta Bikash C. , Ye Zhen
Published: August 2003

By a numerical simulation based upon multiple scattering theory, we confirm that, for certain frequencies, crystal structures formed by dielectric cylinders embedded in parallel in a uniform medium can indeed act as a negative refractive lens. Some agreement with and differences from previous studies are elaborated upon. The refractive index is also estimated from ray optics approximation. The tolerance of the lens to positional disorders is then discussed.
Annealing effects on the conduction mechanisms of p+-amorphous- Si0.8C0.2:H/n-crystalline-Si diodes
Authors: Marsal L. F. , Martin I. , Pallares J. , Orpella A. , Alcubilla R.
Published: August 2003

P + -type hydrogenated amorphous silicon–carbon (a-Si1−xCx:H) on n-type crystalline silicon (c-Si) heterojunction diodes were fabricated and characterized electrically. The effects of thermal annealing on the electrical transport properties of a-Si0.8C0.2:H/c-Si diodes were investigated by measuring their current–voltage characteristics. From the dark current–voltage characteristics measured at different temperatures (298–373 K), transport mechanisms were analyzed in detail. Two carrier transport mechanisms were found to be the origin of forward current. At low bias voltage and temperatures above 320 K as-deposited diodes are dominated by recombination currents on the amorphous side of the space charge region whereas annealed diodes are mainly dominated by diffusion mechanisms. In contrast, at temperatures below 320 K, both types of diodes are mainly dominated by multitunneling capture emission. At higher voltages, the current becomes space charge limited for both diodes throughout the temperature range studied.
Characterization of BCl3/N2 plasmas
Authors: Nordheden Karen J. , Sia Joanne F.
Published: August 2003

Optical emission spectroscopy, quadrupole mass spectrometry, and electron density measurements were used to study the effect of the percentage of N2 on the characteristics of BCl3/N2 plasmas and their resulting etch processes. The etch rate of GaAs increased from 80 Å/min in pure BCl3 to over 1000 Å/min in a 40:60 BCl3:N2 mixture (15 mTorr, 50 W, 20 sccm). The optical emission intensities of both molecular and atomic chlorine exhibited maxima near 30% N2, and an argon actinometer indicated a large increase in argon emission as a function of the increase in N2 percentage. Microwave measurements indicated that the average electron density increased only slightly with an increase in nitrogen percentage up to 60% N2. Mass spectrometric analysis of the plasmas showed that both the dissociation of BCl3 and the production of molecular chlorine were significantly enhanced by the addition of N2. These results suggest that an increase in the electron temperature as a result of electron attachment heating (and possibly energy transfer from N2 metastables) is responsible for the increased dissociation and enhanced production of etch species.
Nonlinear absorption temporal dynamics of Fe-doped GaInAs/InP multiple quantum wells
Authors: Guézo M. , Loualiche S. , Even J. , Le Corre A. , Dehaese O. , Pellan Y. , Marceaux A.
Published: August 2003

GaInAs/InP multiple quantum wells (MQWs) are used as saturable absorbers for all-optical signal regeneration at a 1.55-μm wavelength. These MQWs are doped during their growth by molecular-beam epitaxy with Fe to improve their temporal response. The present work develops a theoretical description of the carrier recombination dynamics in these MQWs. Temporal evolution of the populations of excitons, holes, electrons, and iron traps is determined by coupled evolution equations. The model describes the optical temporal nonlinearity of the saturable absorbers near the excitonic peak transition. Furthermore, pump-probe experiments have been performed to measure the recovery time of these structures having different Fe doping concentrations. A good agreement between the experimental measurements and the model predictions of the optical temporal behaviors of the saturable absorbers is obtained. The control of the recovery time (nanoseconds to picoseconds) with the Fe traps in a large concentration range (1015 to 1019 cm−3) is particularly well highlighted by this model. The Fe doping concentration prescribed to reach a targeted fast recovery time is predicted with good accuracy by the model, which leads us to propose an attractive way to design ultra-high-speed, all-optical signal regenerators based on saturable absorbers.
Vibrational spectroscopy of HOD in liquid D2O. VII. Temperature and frequency dependence of the OH stretch lifetime
Authors: Lawrence C. P. , Skinner J. L.
Published: August 2003

Recent experiments have shown that the vibrational lifetime of the OH stretch fundamental of dilute HOD in liquid D2O has fascinating dependences on temperature and excitation frequency. In particular, the lifetime increases with increasing temperature and increases with increasing excitation frequency. Using the theoretical model for vibrational relaxation in this system that we developed previously, we calculate the temperature and frequency dependence of the lifetime, reproducing the observed experimental trends. The physical origins of both effects are similar, and involve the dependence of the energy gap between the OH fundamental and the bend overtone (of HOD) on temperature and frequency. The success of our model in describing the experiments provides some support for the relaxation mechanism it implies, which primarily involves direct excitation of the bend overtone.