bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology development of PC/PE blends during compounding in a twin‐screw extruder
Authors: Yin Bo , Zhao Yin , Yu Run‐Ze , An Hai‐Ning , Yang Ming‐Bo
Published: December 2006

The morphological development of a polycarbonate/polyethylene (PC/PE) blend in a twin‐screw extruder was studied using a scanning electron microscope (SEM). The effects of extrusion temperature, viscosity ratio (the ratio of the viscosity of the dispersed phase to that of the matrix), and the screw configuration on the morphology of the PC/PE blend during the extrusion were discussed in detail. It was found that the morphology of the dispersed particles and the interfacial adhesion between the dispersed phase and matrix were both influenced by the extrusion temperature. The dispersed phase had a spheroidal shape and a small size during the high temperature processing, and an irregular shape and a large size when it was processed at low temperature. The PC phase with a lower viscosity was easier to disperse and also to coalesce. Therefore, the deformation of the low‐viscosity dispersed phase during the processing was more intense than that of the high‐viscosity dispersed phase. By comparing the effects of the different screw configurations on the morphology development of the PC/PE blend, it was found that the melting and breaking up of the dispersed phase were mainly affected in the initial blending stages by the number of the kneading blocks. While a kneading block with a 90 degree staggering angle was used, the size of the dispersed particles decreased and the long fibers were shortened, the large particles were drawn by the additional kneading zone. Finally, all of these structures were completely changed to the short fibers. POLYM. ENG. SCI., 47:14–25, 2007. © 2006 Society of Plastics Engineers
Efficient dispersion of multi‐walled carbon nanotubes by in situ polymerization
Authors: Hu Nantao , Zhou Hongwei , Dang Guodong , Rao Xianhua , Chen Chunhai , Zhang Wanjin
Published: December 2006

Multi‐walled carbon nanotube (MWNT)‐reinforced polyimide nanocomposites were synthesized by in situ polymerization of monomers in the presence of acylated MWNTs. The acyl groups associated with the MWNTs participated in the reaction through the formation of amide bonds. This process enabled uniform dispersion of MWNT bundles in the polymer matrix. The resultant MWNT–polyimide nanocomposite films were optically transparent with significant mechanical enhancement at a very low loading (0.5 wt%). Evidence has been obtained for improved interactions between the nanotubes and the matrix polymer. Copyright © 2006 Society of Chemical Industry
Preparation of superabsorbent slow release nitrogen fertilizer by inverse suspension polymerization
Authors: Liu Mingzhu , Liang Rui , Zhan Falu , Liu Zhen , Niu Aizhen
Published: December 2006

A superabsorbent, slow release nitrogen fertilizer (SSRNF) was prepared by inverse suspension polymerization of partially neutralized acrylic acid using N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of urea. The polymer was characterized using infrared spectral analysis, and network structural parameters such as molecular weight between crosslinks (Mc) and crosslink density (q) were calculated. The effects of reaction conditions, such as reaction time, reaction temperature, initiator, crosslinker and the degree of neutralization of acrylic acid, on water absorbency were investigated. The nitrogen content of SSRNF synthesized under optimal conditions was 22.7%, and the water absorbencies were about 965 g g−1 in distilled water and 185 g g−1 in tap water. The nitrogen slow release behaviors of the SSRNF in water and water retention capacity of soil with the SSRNF were also investigated. A possible slow release mechanism was proposed and the release rate constant K and the diffusion coefficient D of urea in the hydrogel was calculated. The results showed that the product not only had good slow release properties but also excellent soil moisture preservation capacity, which could effectively improve the utilization of fertilizer and water resources simultaneously. Therefore, the SSRNF is a multifunctional water managing material, which would find application in agriculture and horticulture, especially in drought‐prone areas where the availability of water is limited. Copyright © 2006 Society of Chemical Industry
Effect of cationic surfactant on homogenization and polymerization of methyl methacrylate miniemulsion modified by chitosan
Authors: Jeng Jauder , Dai Chi‐An , Chiu Wen‐Yen , Young Pin‐Yen
Published: December 2006

Homogenization of monomer droplets and polymerization of methyl methacrylate (MMA) miniemulsion, stabilized by a combination of cationic surfactants including different amounts of n‐hexadecyltrimethylammonium chloride (HTMA) and chitosan 100, were investigated. With increasing HTMA concentration or decreasing concentration of chitosan 100, the required ultrasonication time for the miniemulsion to reach a critically stabilized state is reduced. After polymerization, for higher HTMA concentrations, droplet nucleation dominates because of higher surface coverage of HTMA on the droplets. However, for lower HTMA concentrations, the size distributions (SDs) of final latex particles are different from those of the droplets. Because surface coverage of HTMA on the droplets is lower in this condition, both droplet nucleation and homogeneous and/or micellar nucleation occur simultaneously in the miniemulsion polymerization. On increasing the concentration of chitosan 100 in the system, the SD of the final latex particles is far different from that of the droplets. This is due to a decrease of the effective surface coverage of chitosan 100 and HTMA on the droplets. Consequently, the opportunity of collision coalescence of the droplets increases, and MMA molecules can diffuse out more easily into the aqueous phase. Droplet nucleation is, therefore, no longer the major source for the latex particles. Copyright © 2006 Society of Chemical Industry
Understanding surfaces and buried interfaces of polymer materials at the molecular level using sum frequency generation vibrational spectroscopy
Authors: Chen Zhan
Published: December 2006

This paper reviews recent progress in the studies on polymer surfaces/interfaces using sum frequency generation (SFG) vibrational spectroscopy. SFG theory, technique, and some experimental details have been presented. The review is focused on the SFG studies on buried interfaces involving polymer materials, such as polymer–water interfaces and polymer–polymer interfaces. Molecular interactions between polymer surfaces and adhesion promoters as well as biological molecules such as proteins and peptides have also been elucidated using SFG. This review demonstrates that SFG is a powerful technique to characterize molecular level structural information of complicated polymer surfaces and interfaces in situ. Copyright © 2006 Society of Chemical Industry
Thermomechanical properties and shape memory effect of epoxidized natural rubber crosslinked by 3‐amino‐1,2,4‐triazole
Authors: Chang Young‐Wook , Mishra Joy K , Cheong Jong‐Hoon , Kim Dong‐Kook
Published: December 2006

A thermally induced shape memory polymer based on epoxidized natural rubber (ENR) was produced by curing the ENR with 3‐amino‐1,2,4‐triazole as a crosslinker in the presence of bisphenol‐A as a catalyst. Dynamic mechanical and tensile analysis was conducted to examine the variation of glass transition temperature, stiffness, and extensibility of the vulcanizates with the amount of curatives. Shape memory properties of the ENR vulcanizates were characterized by shape retention and shape recovery. It was revealed that the glass transition temperature of the ENR vulcanizates could be tuned well above room temperature by increasing the amount of curing agents. Also, ENR vulcanizates with Tg higher than ambient temperature showed good shape memory effects under 100% elongation, and the response temperatures of the recovery were well matched with Tg of the samples. Copyright © 2006 Society of Chemical Industry
Copolymers of N‐methylpyrrole and 3,4‐ethylenedioxythiophene: structural, physical and electronic properties
Authors: Ocampo Cintia , Alemán Carlos , Oliver Ramón , Arnedillo M Luisa , Ruiz Oriol , Estrany Francesc
Published: December 2006

The structural, electric and electronic properties of copolymers derived from mixtures of N‐methylpyrrole and 3,4‐ethylenedioxythiophene (EDOT) with various concentration ratios have been investigated and, additionally, compared with those of the corresponding homopolymers. The electropolymerization kinetics of all the generated copolymers and the homopolymers was examined in terms of current productivity using chronoamperometry. The chemical structure of the linkages between adjacent monomers and the microstructure of the chains were investigated using Fourier transform infrared spectroscopy and quantum mechanical calculations, respectively. The results indicate that the linkages between monomeric units formed during the anodic copolymerization are of the α–α type, while the microstructure of the copolymers depends on the EDOT content. Theoretical calculations were also used to examine the electronic properties of the systems under study, while the conductivity and the electrical stability were studied using the sheet‐resistance method. Interestingly, the electric properties are consistent with the random and block microstructures predicted for the copolymers with low and high EDOT content, respectively. Copyright © 2006 Society of Chemical Industry
The Decomposition of some RDX and HMX Based Materials in the One‐Dimensional Time to Explosion Apparatus. Part 1. Time to Explosion and Apparent Activation Energy
Authors: Williams Michael Robert , Matei Mariana Violetta
Published: December 2006

A One‐Dimensional Time to Explosion (ODTX) apparatus has been used to study the times to explosion of a number of compositions based on RDX and HMX over a range of contact temperatures. The times to explosion at any given temperature tend to increase from RDX to HMX and with the proportion of HMX in the composition. Thermal ignition theory has been applied to time to explosion data to calculate kinetic parameters. The apparent activation energy for all of the compositions lay between 127 kJ mol−1 and 146 kJ mol−1. There were big differences in the pre‐exponential factor and this controlled the time to explosion rather than the activation energy for the process.
Preparation of Cu/CNT Composite Particles and Catalytic Performance on Thermal Decomposition of Ammonium Perchlorate
Authors: Ping Cui , Li Fengsheng , Jian Zhou , Wei Jiang
Published: December 2006

Composite particles of carbon nanotubes (CNTs) and Cu were prepared by a chemical reduction method. Characterization of Cu/CNT composite particles was performed by TEM, SEM, FT‐IR, XRD, XPS, AAS, DTA and EDS. The results show that the surface of CNTs is covered by Cu particles, and that the diameter of Cu/CNT composite particles gets larger than that of CNTs. Furthermore, in the presence of Cu/CNT composite particles, the peak temperature of the high‐temperature decomposition of ammonium perchlorate (AP) decreased by 126.3 °C, and the peak of the low‐temperature decomposition disappeared. Compared with a sample of simply mixed Cu and CNTs, the peak temperature of the high‐temperature decomposition of AP‐Cu/CNTs composite particles decreased by 11.4 °C. Compared with Cu, the peak temperature of the high‐temperature decomposition of AP‐Cu/CNT composite particles decreased by 20.9 °C. This work shows that the catalytic performance of Cu on the thermal decomposition of AP can be improved by compounding with CNTs.
Effects of Twin‐Screw Extrusion Processing on the Burning Rate of Composite Propellants
Authors: Gallant Frederick M. , Bruck Hugh A. , Prickett Suzanne E.
Published: December 2006

A new process for continuous manufacturing of composite propellants has been developed using Twin Screw Extrusion (TSE). The effects of TSE‐processing on the burning rates of an ammonium perchlorate (AP)‐based composite propellant have been characterized over a wide composition range (79 to 87 wt. % AP) and a wide range of screw speeds (45 to 85 RPM) using a quadratic model for an experimental Response Surface Analysis (RSA) based on the Kowalski, Cornell, and Vining (KCV) algorithm. Using Student‘s T‐test, it was determined that burning rates obtained from strand‐burning rate tests at 3.5 MPa, 7.0 MPa, and 10.5 MPa are affected only by the individual ingredients, the interaction between the coarse AP particles and the binder, and the screw speed. Measured burning rates were found to be 40% to 100% higher than Petite Ensemble Model (PEM) predictions, which was accounted for by modifying the PEM through a power law relationship with pressure that includes a rule‐of‐mixtures dependence of the exponent and coefficient on the weight fraction of coarse and fine AP particles. The resulting modified PEM reduced differences between the predictions and experimental data by 79% at 3.5 MPa, 83% at 7.0 MPa, and 78% at 10.5 MPa.
Antibody array profiling reveals serum TSP‐1 as a marker to distinguish benign from malignant prostatic disease
Authors: Shafer Michael W. , Mangold Leslie , Partin Alan W. , Haab Brian B.
Published: December 2006

BACKGROUND

Blood protein markers that provide more accurate or earlier diagnosis of prostate cancer should have a positive impact on prostate cancer treatment and management.

METHODS

Serum samples from control subjects and patients with benign or malignant prostatic disease were analyzed on antibody arrays targeting multiple candidate prostate cancer markers and detected with two‐color, rolling‐circle amplification (TC‐RCA). The measurements of certain antibodies were validated using immunoblots, immunoprecipitation/mass spectrometry, and sandwich immunoassays.

RESULTS

Several potential disease‐associated protein alterations were uncovered. The most significant was thrombospondin‐1, which was strongly elevated in patients with benign prostatic disease and repressed in patients with prostate cancer. Thrombospondin‐1 levels did not correlate with prostate‐specific antigen (PSA) levels and differentiated benign from malignant disease with 79% sensitivity and 81% specificity.

CONCLUSIONS

The measurement of thrombospondin‐1 could be used to assist the decision to obtain a biopsy in men with suspected prostate cancer, which could lead to a reduction in the number of unnecessary prostatic biopsies. Prostate 67:255–267, 2007. © 2006 Wiley‐Liss, Inc.
Changes in steroid receptors and proteoglycan expression in the guinea pig prostate stroma during puberty and hormone manipulation
Authors: Sakko Andrew J. , Ricciardelli Carmela , Mayne Keiko , Dours‐Zimmermann Maria T. , Zimmermann Dieter R. , Neufing Petra , Tilley Wayne D. , Marshall Villis R. , Horsfall David J.
Published: December 2006

Background

Proteoglycans are structural and informational molecules important during embryogenesis and organ maturation. Maturation of the prostate is influenced by androgens and estrogens, but changes in the relative spatiotemporal expression of steroid receptors and proteoglycans during hormonal change are unexplored.

Methods

Guinea pig prostate was used to define hormone‐induced changes in the expression of androgen (AR) and estrogen (ERα) receptors, chondroitin sulfate (CS) glycosaminoglycan and core proteins of versican and syndecan‐1. Tissue locations of AR, ERα, CS and the proteoglycans versican and syndecan‐1 were determined by immunohistochemistry. Cellular content of ERα and syndecan‐1 was assessed visually. Versican, CS56 epitope, and AR were quantified by image analysis.

Results

AR expression within prostate epithelial and stromal cell nuclei decreased following castration and increased following treatment of castrate animals with dihydrotestosterone (DHT). ERα expression was restricted to prostate stromal cell nuclei and decreased during puberty, and following treatment of castrate animals with DHT. Versican was present in periacinar stroma immediately peripheral to basal epithelial cells, fibromuscular stromal tissue bands surrounding acinar units, and loose fibrovascular connective tissue interspersed between individual acini. Versican and native CS expression decreased (>10‐fold) in periacinar stroma during puberty and following administration of DHT to castrated animals. Expression of syndecan‐1 was restricted to fibromuscular cells of prostate stroma, and remained constant during puberty and hormone manipulation.

Conclusions

ERα, versican core protein and CS side chain epitopes are negatively regulated in prostate stromal tissue by DHT, whilst AR levels are positively regulated. Prostate 67:288–300, 2007. © 2006 Wiley‐Liss, Inc.
Allelopathy in crop/weed interactions — an update
Authors: Belz Regina G
Published: December 2006

Since varietal differences in allelopathy of crops against weeds were discovered in the 1970s, much research has documented the potential that allelopathic crops offer for integrated weed management with substantially reduced herbicide rates. Research groups worldwide have identified several crop species possessing potent allelopathic interference mediated by root exudation of allelochemicals. Rice, wheat, barley and sorghum have attracted most attention. Past research focused on germplasm screening for elite allelopathic cultivars and the identification of the allelochemicals involved. Based on this, traditional breeding efforts were initiated in rice and wheat to breed agronomically acceptable, weed‐suppressive cultivars with improved allelopathic interference. Promising suppressive crosses are under investigation. Molecular approaches have elucidated the genetics of allelopathy by QTL mapping which associated the trait in rice and wheat with several chromosomes and suggested the involvement of several allelochemicals. Potentially important compounds that are constitutively secreted from roots have been identified in all crop species under investigation. Biosynthesis and exudation of these metabolites follow a distinct temporal pattern and can be induced by biotic and abiotic factors. The current state of knowledge suggests that allelopathy involves fluctuating mixtures of allelochemicals and their metabolites as regulated by genotype and developmental stage of the producing plant, environment, cultivation and signalling effects, as well as the chemical or microbial turnover of compounds in the rhizosphere. Functional genomics is being applied to identify genes involved in biosynthesis of several identified allelochemicals, providing the potential to improve allelopathy by molecular breeding. The dynamics of crop allelopathy, inducible processes and plant signalling is gaining growing attention; however, future research should also consider allelochemical release mechanisms, persistence, selectivity and modes of action, as well as consequences of improved crop allelopathy on plant physiology, the environment and management strategies. Creation of weed‐suppressive cultivars with improved allelopathic interference is still a challenge, but traditional breeding or biotechnology should pave the way. Copyright © 2006 Society of Chemical Industry
Equation of state of nanocrystalline BaTiO3 up to 52 GPa at room temperature
Authors: Kumar Ravhi S. , Cornelius Andrew L. , Nicol Malcolm F.
Published: December 2006

We have performed in situ high pressure X‐ray powder diffraction experiments on nanocrystalline BaTiO3 (average particle size 40 nm) up to 52 GPa using synchrotron X‐rays in the angle dispersive geometry with a diamond anvil cell. In order to understand the grain size effect on the tetragonal (P4mm) to cubic (Pm3m) phase transition and the compressibility, experiments were also carried out on bulkBaTiO3 up to 36 GPa. The results show nanoBaTiO3 is less compressible than the bulkBaTiO3 and the phase transition pressure is found to be 1.9 GPa higher for nanoBaTiO3. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature and pressure dependence of the recombination mechanisms in 1.3 μm and 1.5 μm GaInNAs lasers
Authors: McConville Daniel G. , Sweeney Stephen J. , Adams Alfred R. , Tomic Stanko , Riechert Henning
Published: December 2006

We have studied the pressure and temperature dependence of the threshold current density, J th, in 1.3 μm and 1.5 μm GaInNAs edge‐emitting lasers. We find that J th is more temperature sensitive for the 1.5 μm devices. From analysis of the spontaneous emission from these devices we find that J th for the 1.3 μm devices is comprised of 50% non‐radiative monomolecular recombination, 25% radiative recombination and 25% non‐radiative Auger recombination at room temperature. In the 1.5 μm devices however it is composed of 30% monomolecular recombination, 10% radiative recombination and 60% Auger recombination. It is clear that the major difference in J th between the devices is caused by the increased Auger recombination in the 1.5 μm devices. Previously, we found that J th for 1.3 µm GaInNAs lasers increases with pressure due to the increase in Auger recombination brought about by a large increase in the cubed threshold carrier density (n 3th). However, for the 1.5 µm devices, we find no significant change in J th with pressures up to 8 kbar. We suggest that this is due to the higher Auger coefficient for the 1.5 µm devices, which compensates for the increase in n 3th with pressure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibrational properties of single walled carbon nanotubes under pressure from Raman scattering experiments and molecular dynamics simulations
Authors: Choi In‐Hwan , Yu Peter Y. , Tangney Paul , Louie Steven G.
Published: December 2006

We have investigated theoretically and experimentally the pressure dependent structural and vibrational properties of single‐walled carbon nanotubes (SWNT). Bundles of SWNTs are studied inside a diamond anvil high pressure cell with micro‐Raman scattering. The tube diameter and size distribution are determined from the radial breathing modes (RBM) of the tubes. The pressure coefficient and linewidth of one of the high frequency C–C bond stretching modes was found to change suddenly at ∼3 GPa which is well below the structural transformation pressure (P c) for the tubes in our sample. Molecular dynamics simulations were used to calculate the vibrational density of states of SWNTs as a function of pressure. Our simulations suggest that the experimental results can be explained by a softening of a low‐frequency optical mode of the SWNTs – the “squashing” mode – and the dynamical effect of this softening on other phonon modes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calibration of the ruby pressure scale to 150 GPa
Authors: Silvera Isaac F. , Chijioke Akobuije D. , Nellis W. J. , Soldatov A. , Tempere J.
Published: December 2006

For many years the ruby pressure standard has been the so‐called quasi‐hydrostatic scale of Mao, Xu, and Bell published in 1986. The calibration was determined by X‐ray diffraction of metal markers in an argon pressurization medium to 80 GPa, along with simultaneous measurement of the shift of the ruby R lines. We have used data in the literature, as well as our own, mostly for ruby in quasi‐hydrostatic helium, to produce a new ruby scale with calibration data that extends to 150 GPa. The new scale shows that at the highest shifts of the ruby R lines the pressures are substantially higher than on the old scale. To understand small systematic shifts of the pressures as determined from the X‐ray diffraction of metal “markers” used in the calibration, a finite element analysis of quasi‐hydrostatic conditions in a diamond anvil cell has been carried out. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
It's time to celebrate!
Authors: Stutzmann Martin
Published: December 2006

The beginning of the 19th century was a remarkable period for culture and science, indeed. Many of Beethoven's great works were performed for the first time, the first asteroids Ceres and Pallas were discovered, Alessandro Volta informed the Royal Society in London about a new source for electrical current, the industrial revolution began with the invention of punch card controlled weaving machines by Jacquard and the appearance of steam engines as power sources for ships or trains, and Alexander von Humboldt travelled and surveyed the New World. At the same time, also the foundations of modern crystallography and solid state science were laid, with the discovery of many metallic elements and, most notably, the first editions of René Just Haüy's “Traité de Minéralogie” in 1801 and the “Traité de Physique” in 1803.

On this scale of events, the opening of a small printing shop in lower Manhattan by Charles Wiley in 1807 remained practically unnoticed. However, in the following 200 years not only did solid state physics develop into one of the most active fields in modern science, but also the small printing shop did prosper into one of the largest science publishers worldwide. physica status solidi became part of the Wiley family with the acquisition of VCH in 1996 and, since then, has enjoyed the support and stimulating atmosphere as the largest solid state physics unit within Wiley. Thus, all members of the Editorial Office and all Editors of physica status solidi take great pleasure in congratulating Wiley on the occasion of the 2007 Bicentennial and expressing their best wishes for a prosperous future!

Also physica status solidi has continued its growth and positive development under the publishing agreement entered with Wiley in 2002. Thus, the number of submitted and published articles has again increased significantly in the past year, by 20% and 25%, respectively. Among the other notable events in 2006 was the completion of the Physics and Astronomy Backfile Collection, which now provides easy and complete access to more than 300 000 pages published in physica status solidi since the foundation of the journal at www.interscience.wiley.com/backfiles/physics. And last but not least, the Rapid Research Letter section of physica status solidi has just been launched as an independent journal, pss‐RRL, complementing pss (a), pss (b), and pss (c) by providing a special service for the fast publication of important new findings in all areas of solid state physics. Please have a look at the home page of the new journal www.pss‐rapid.com for further details.

As this year comes to an end, I would like to express my sincere thanks to our authors, referees, readers, and everybody involved in editing and producing physica status solidi for their continued interest, valuable contributions, and dedication. Good luck and all the best for 2007! And once again: Happy 200th anniversary, Wiley!

Garching, December 2006
The response of the coupled tropical ocean–atmosphere to westerly wind bursts
Authors: Fedorov Alexey V.
Published: December 2006

Two different perspectives on El Niño are dominant in the literature: it is viewed either as one phase of a continual southern oscillation (SO), or alternatively as the transient response to the sudden onset of westerly wind bursts (WWBs). Occasionally those bursts do indeed have a substantial effect on the SO—the unusual strength of El Niño of 1997/98 appears to be related to a sequence of bursts—but frequently the bursts have little or no impact. What processes cause some bursts to be important, while others remain insignificant? The question is addressed by using a simple coupled tropical ocean–atmosphere model that simulates a continual, possibly attenuating, oscillation to study the response to WWBs. The results show that the impact of WWBs depends crucially on two factors: (i) the background state of the system as described by the mean depth of the thermocline and intensity of the mean winds, and (ii) the timing of the bursts with respect to the phase of the SO. Changes in the background conditions alter the sensitivity of the system, so that the impact of the bursts on El Niño may be larger during some decades than others. Changes in the timing of WWBs affect the magnitude and other characteristics of the SO by modifying the energetics of the ocean–atmosphere interactions. A reasonable analogy is a swinging pendulum subject to modest blows at random times—those blows can either magnify or diminish the amplitude, depending on their timing. It is demonstrated that a WWB can increase the strength of El Niño significantly, if it occurs 6 to 10 months before the peak of warming, or can reduce the intensity of the subsequent El Niño, if it occurs during the cold phase of the continual SO. Copyright © 2002 Royal Meteorological Society.
The dynamically driven long‐term trend in stratospheric ozone over northern middle latitudes
Authors: Hadjinicolaou Panos , Jrrar Amna , Pyle John A. , Bishop Lane
Published: December 2006

The cause of the observed mid‐latitude decline in ozone in a 20‐year integration of a stratospheric chemical transport model forced by European Centre for Medium‐Range Weather Forecasts analyses for the years 1979 to 1998 is investigated. A very simple chemical scheme for ozone is used which includes no interannual variation so that any modelled interannual variability, or trend, must arise from changes in the meteorology. The integration from 1979 to 1998 does show a downward trend in mid‐latitude ozone in which many of the observed features are reproduced, especially between the middle 1980s and the early 1990s. A detailed statistical trend analysis shows that the quantitative comparison between modelled and observed trend is very sensitive to the choice of period considered. However, there is good qualitative agreement in terms of the latitudinal variation of the trend. For the different periods considered, the dynamically driven model trend accounts for at least half of the observed northern mid‐latitude trend averaged over December to February. The vertical variation of the modelled and observed trends agree qualitatively. The modelled total ozone correlates well with the vertical winter EP‐flux at 100 hPa and the North Atlantic Oscillation index, suggesting that long‐term changes in stratospheric circulation are intimately connected to the observed mid‐latitude ozone trend. Copyright © 2002 Royal Meteorological Society.
Nucleation effects on the habit of vapour grown ice crystals from −18 to −42°C
Authors: Bailey M. , Hallett J.
Published: December 2006

Ice crystals have been nucleated and grown by a new method where supersaturation is controlled by combining static diffusion chamber and expansion chamber techniques. Crystals were nucleated and grown on $50\ \mu \hbox{m}$ diameter glass filaments at pressures of 500 to 300 hPa, typical of clouds with temperatures from −18 to −42°C, respectively. Crystals were also nucleated on particles of finely powdered silver iodide and kaolinite adhering to glass filaments, in order to investigate effects on habit due to different nucleating materials. Critical supersaturations for nucleation were measured for each case and were in good agreement with previous nucleation studies. Crystals were grown at ice supersaturations which ranged from less than 1% to just above water saturation. For ice growth below a critical supersaturation, nucleation was achieved by applying a brief adiabatic expansion to the static diffusion chamber with a filament in place and the chamber evacuated to the target pressure for the temperature of interest. Nucleation occurred at a critical supersaturation, followed by growth at a lower value. A review of past laboratory experiments and recent in situ observations reveals good agreement between laboratory and field observations when the effects of nucleating methods and growth times are taken into account. Contrary to studies which report the habit of ice as ‘prism’‐like or columnar below approximately −22°C, the habit is found to be plate‐like for temperatures ranging from −18°C to −40°C at ice supersaturations relevant to the atmosphere. Additionally, the plate‐like‐habit distribution is dominated by polycrystalline forms, which is consistent with aspects of past laboratory studies and recent observations obtained with improved aircraft instrumentation. The habits and habit distributions obtained from glass and kaolinite most closely resemble those observed in the atmosphere, while the results from silver iodide show large differences. Below −40°C, the habit becomes columnar except at low supersaturation, and is still dominated by polycrystals which appear as rosettes for ice supersaturations greater than about 20%. ‘Bullet rosettes’ were observed to nucleate and grow on clean glass threads below −40°C but not on kaolinite which predominantly grew single columns and irregular polycrystals with columnar components; silver iodide produced single columns with few polycrystals. This behaviour indicates that rosettes result from ice nuclei which share few or no crystallographic similarities with ice, and is consistent with that expected from homogeneous nucleation. Critical supersaturation measurements for nucleation were extended down to −70°C, and revealed that below −40°C ice crystals can nucleate on glass at ice supersaturations of 25%, and at values of approximately 15% on kaolinite or silver iodide. Copyright © 2002 Royal Meteorological Society
Insights into cloud parametrization provided by a prognostic approach
Authors: Gregory David , Wilson Damian , Bushell Andrew
Published: December 2006

Starting from an assumption that within an area there is a distribution of temperature and humidity, equations are derived for the prognostic evolution of cloud fraction and area‐mean condensed water under the action of uniform forcing. These are contrasted to alternative equation sets which are based upon consideration of humidity variations alone, and approximations involved in the derivations of these are highlighted. The properties of, and relationships between, current diagnostic and prognostic cloud schemes are examined using the prognostic formulation, and assumptions concerning the nature of the subgrid distribution of thermodynamic variables are discussed. While the approaches of Smith and Tiedtke provide a consistent description of cloud formation, the Sundqvist approach is found to implicitly include changes in the character of the distribution as cloud cover increases, inconsistent with an assumption of uniform forcing. Additional properties of the Tiedtke scheme are explored and extensions suggested to improve the treatment of cloud dissipation. © Crown Copyright 2002.
The axial coherence of Kelvin–Helmholtz billows
Authors: Thorpe S. A.
Published: December 2006

Factors affecting the along‐axis coherence length of Kelvin–Helmholtz billows are reviewed. Little is known of the processes which determine or limit this length. Laboratory experiments show that, as they develop, billows may be irregularly spaced, resulting in pairing along their length, or, more commonly, grow at different rates in patches which subsequently amalgamate. Both processes result in features described as ‘knots’, where neighbouring billows join. The tangling of billow vortices in the knots leads to local turbulence and mixing, often before turbulence develops at a smaller scale within the billows themselves. The axial coherence length of billows is limited to the along‐axis distance between these knots. Such features in the atmosphere and the ocean have received little attention in spite of their possible bearing on clear‐air turbulence and to heat and momentum transport. Observations of atmospheric billows suggest an axial coherence length which is of the same order as that found in the laboratory, about four billow wavelengths. Copyright © 2002 Royal Meteorological Society.
Gravity waves generated by the dry convective boundary layer: Two‐dimensional scale selection and boundary‐layer feedback
Authors: Lane. Todd P. , Clark Terry L.
Published: December 2006

This study examines the generation of gravity waves by the dry convective boundary layer in two dimensions. In particular, a number of cases are considered which range from zero background‐flow conditions to conditions with strong wind shear. These experiments agree with previous studies that identified a distinct horizontal‐scale selection of the gravity waves due to changes in wind speed. Detailed linear analysis is completed which attributes the horizontal‐scale selection to two processes. The first process is the dissipation of downstream‐propagating gravity waves by critical levels, and the second process is the trapping of upstream‐propagating waves. The result is a narrow region of the generated spectrum of gravity waves that are able to propagate vertically. The experiments also agree with previous studies that have observed a resonant interaction between the boundary‐layer thermals and the gravity waves. This resonance is described as a result of the trapped gravity waves, which form a resonant cavity near the top of the mixed layer. Finally, the experiments are used to evaluate the role of shear in the gravitywave generation. In cases with little resonance, shear is shown to play a minor role in the wave generation. In these cases, changes in the wave's amplitude spectrum are mostly due to linear wave refraction and the aforementioned selection mechanism. Copyright © 2002 Royal Meteorological Society.
The role of advection of fluxes in modelling dispersion in convective boundary layers
Authors: Abiodun Babatunde J. , Enger Leif
Published: December 2006

A Eulerian three‐dimensional higher‐order closure dispersion model is presented. The model uses mean wind and turbulence quantities from a second‐order atmospheric boundary‐layer model. The dispersion model is validated against results from tank and field experiments and compared to results from Lagrangian dispersion models. The results show quite good agreement with experiment and Lagrangian modelling results for point source dispersion in a convective boundary layer (CBL). Sensitivity studies with the model help to identify the role played by advection and horizontal transport terms in the equations for the fluxes in simulating the essential features of pollutant dispersion.

Results from the sensitivity tests show that the characteristic features of dispersion from point sources in the CBL—with an ascending plume during ground‐level release and a descending plume from a lifted point source—are caused by an imbalance between the advection and diffusion terms in the equation for the vertical flux. Furthermore, it is shown that there is also a tendency for the plume to split horizontally, which is similarly caused by an imbalance between the advection and diffusion terms in horizontal fluxes. The simulated lateral standard deviations of distance x from a point source, for the vertically integrated concentration, are proportional to x close to the source and to x1/2 far away from the source, if and only if the advection and diffusion terms are included in the equations for the turbulent fluxes of concentration. Copyright © 2002 Royal Meteorological Society.
The impact of time‐averaging on the detectability of nonlinear empirical relations
Authors: Yuval  , Hsieh William W.
Published: December 2006

This paper studies how time‐averaging of observations can affect the detectable nonlinear empirical relations in the data. The example used is the simulation of the precipitation rate as a daily, weekly and monthly variable. The feedforward neural network (NN) model is employed to simulate the precipitation rate. A measure of the nonlinearity of the NN relation is introduced and is used to calculate the nonlinearity of the NNs. It is found that the use of data averaged over periods longer than the inherent time‐scale of the involved variables can result in a dramatic weakening of the detected nonlinearity. A suggested theoretical explanation asserts that averaging of independent samples of the data records yields distributions approaching the multi‐variate normal, in which case the relations among the variables are closer to linear. Copyright © 2002 Royal Meteorological Society.
Diagnosis of systematic forecast errors dependent on flow pattern
Authors: Ferranti L. , Klinker E. , Hollingsworth A. , Hoskins B. J.
Published: December 2006

Singular‐value decomposition (SVD) analysis is employed to study flow‐dependent forecast errors. The results presented are based on ECMWF operational forecasts and verifying analysis of 500 hPa heights for the most recent seven winter periods. Beyond forecast day 3 the flow‐dependent errors are mainly localized over the Atlantic sector and are associated with the North Atlantic Oscillation‐ (NAO)‐like circulation anomalies. The forecasts systematically underestimate the intensity of pressure anomalies centred over Iceland with the effect of reducing the anomalous westerly/easterly flow over the eastern north Atlantic/western Europe. The flowdependent component of the errors explains about 10% of the total forecast‐error variance. However, since it is associated with the NAO mode that dominates the variability of the European weather on longer time‐scales, it is essential to identify the model limitations in predicting this flow anomaly in order to guide future work on improving forecasts over Europe.

The relationship between forecast‐error variability and NAO fluctuations is effectively described by an SVD analysis performed on fields of forecast‐error magnitude and analyses. Regions with large (small) forecast‐error anomalies are located over the maximum of the anomalous westerly (easterly) jet, while on the flanks of the jet the error anomaly is expected to be minimum/maximum. Copyright © 2002 Royal Meteorological Society.
The development and testing of a new two‐time‐level semi‐Lagrangian scheme (SETTLS) in the ECMWF forecast model
Authors: Hortal Mariano
Published: December 2006

A new treatment of the two‐time‐level semi‐Lagrangian scheme is presented which avoids extrapolation in time of the velocities used for the computation of the trajectories and for the nonlinear terms of the evolution equations.

Extrapolation in time is used in the original two‐time‐level scheme in order to make it centred in time and therefore second‐order accurate. This time‐extrapolation can lead to instabilities. In the new scheme the secondorder accuracy is achieved by means of a Taylor series expansion to second order around the departure point of the semi‐Lagrangian trajectory thus avoiding extrapolation of the first‐order term. The estimate of the secondorder term in this expansion is obtained by means of a stable time extrapolation from the previous time step and therefore the scheme is named the ‘Stable Extrapolation Two‐Time‐Level Scheme’ or SETTLS.

Some cases of noise in forecast fields, arising from an instability of the time extrapolation in the version of the two‐time‐level semi‐Lagrangian scheme used operationally at the European Centre for Medium‐Range Weather Forecasts (ECMWF) between December 1996 and April 1998, are diagnosed; it is shown that the noise can be removed by the use of the SETTLS. Copyright © 2002 Royal Meteorological Society.
A study on the optimization of the deployment of targeted observations using adjoint‐based methods
Authors: Bergot Thierry , Doerenbecher Alex
Published: December 2006

A new adjoint‐based method to find the optimal deployment of targeted observations, called Kalman Filter Sensitivity (KFS), is introduced. The major advantage of this adjoint‐based method is that it allows direct computation of the reduction of the forecast‐score error variance that would result from future deployment of targeted observations. This method is applied in a very simple one‐dimensional context, and is then compared to other adjoint‐based products, such as classical gradients and gradients with respect to observations. The major conclusion is that the deployment of targeted observation is strongly constrained by the aspect ratio between the length‐scale of the sensitivity area and the length‐scale of the analysis‐error covariance matrix. This very simple example also clearly illustrates that the reduction of forecast‐error variance is stronger for assimilation schemes which have a smaller characteristic length‐scale. Finally, the KFS technique is applied in a diagnostic way (i.e. once the observations are done) to four FASTEX cases. For these cases, the reduction of the forecasterror variance is in agreement with the efficiency of targeted observations as previously studied. A preliminary step towards an operational use has been performed on FASTEX IOP18, and results seem to validate the KFS approach of targeting. Copyright © 2002 Royal Meteorological Society.
An uncertainty model for Bayesian Monte Carlo retrieval algorithms: Application to the TRMM observing system
Authors: L'ecuyer Tristan S. , Stephens Graeme L.
Published: December 2006

An error model for Bayesian Monte Carlo retrieval algorithms which explicitly accounts for uncertainty introduced by the use of a finite database of realizations, as well as uncertainties associated with the modelling and measurement components of the retrieval is described. The model provides a rigorous estimate of the uncertainty in all retrieved parameters as well as a breakdown of this uncertainty into two components attributable to an imperfect database, and modelling and measurement uncertainties, respectively. This error information is critical for algorithm development, model validation and, in particular, in variational data assimilation where the relative accuracy of the observations and the background forecast determines how much the latter is modified in the assimilation process.

Using the error model, uncertainties in the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) instantaneous surface rainfall product (2A12) are found to range from 40 to 60 percent in rainfall up to 20 mm h−1.. In heavier rain, uncertainties rapidly increase due to heavy attenuation in all TMI channels which requires surface rainfall to be inferred solely from the non‐unique relationship between surface rain rate and the ice‐scattering signature in the strongly coupled 37 and 85 GHz brightness temperatures. In light rain, the fact that the database attempts to approximate nature's infinite cloud probability density function by a finite set of realizations, and the inherent inability of the TMI brightness temperatures to completely distinguish between all cloud profiles in the database, dominate retrieval uncertainties. Between 4 and 10 mm h−1 both error components are comparable while measurement and model uncertainties dominate in heavier rainfall. Preliminary attempts to incorporate radar reflectivity data to reduce profile database uncertainties show promise, but can lead to a compensating increase in the modelling and measurement‐error component.

Results highlight the need for studying sources of systematic error in the cloud database such as errors in cloud microphysical assumptions, beam‐filling errors, or biases in the radiative‐transfer calculations used to simulate brightness temperatures for each profile. In addition, the utility of the error model for estimating uncertainties in any Bayesian Monte Carlo retrieval algorithm is demonstrated. Copyright © 2002 Royal Meteorological Society.
Helicity, superhelicity and weighted relative potential vorticity: Useful diagnostic pseudoscalars?
Authors: Hide Raymond
Published: December 2006

Advances in techniques of data assimilation in meteorology and oceanography and continuing improvements in the scope and reliability of numerical simulations of motions in atmospheres and oceans and other rotating fluid systems offer opportunities for experimenting with novel diagnostic schemes for elucidating basic dynamical processes. Here attention is drawn to the likely diagnostic value of determinations of the fields of certain pseudoscalar quantities, namely helicity, superhelicity and weighted relative potential vorticity. Copyright © 2002 Royal Meteorological Society.