bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Asian expression of the PDO
Authors: D'Arrigo Rosanne , Wilson Rob
Published: March 2006

The causes and mechanisms of Pacific Decadal Variability (PDV) are still being investigated. One reason that such variability is not better understood is the scarcity of high‐resolution paleoclimatic records from the Asian side of the North Pacific. Here we present a reconstruction of the boreal spring (March–May) Pacific Decadal Oscillation (PDO) index, spanning A.D. 1565–1988, that is the first to represent the large‐scale Asian expression of this phenomenon using tree‐ring data. Intervention analysis reveals significant (95% level) regime shifts corresponding to those in the instrumental PDO during the mid‐1920s, mid‐1940s and mid‐1970s, the latter period associated with the famed 1976 shift in Pacific climate. Shifts in the preinstrumental period show varying correspondence with those of a North American‐based tree‐ring reconstruction of the North Pacific index (NPI), another indicator of Pacific decadal climate variability. Differences between these two time series hint at modulation of local climate from Asian monsoon, El Niño‐Southern Oscillation (ENSO) and volcanic forcing, which could be partly masked by combining data from these sensitive regions in future PDO reconstructions. Overall, however, comparison of the reconstructions from both Asia and North America (NA) is useful for evaluating the distinct expressions of the PDO on both sides of the North Pacific and their interactions with the tropics. Copyright © 2006 Royal Meteorological Society.
Remediation of a soil contaminated with heavy metals by immobilizing compounds
Authors: Usman Abdul R. A. , Kuzyakov Yakov , Lorenz Klaus , Stahr Karl
Published: March 2006

The labile fraction of heavy metals (HM) in soils is the most important for toxicity for plants and microorganisms. Thus, it is crucial to reduce this fraction in contaminated soils to decrease the negative effect of HM. In a greenhouse experiment, the effects of several additives on the labile fractions of Zn, Cd, Cu, Ni, and Pb were investigated in a soil contaminated during long‐term sewage‐sludge application. The accumulation of HM was studied in the aboveground biomass of wheat (Triticum aestivum L.). The additives used were the clay minerals Na‐bentonite, Ca‐bentonite, and zeolite; the Fe oxides hematite and goethite; the phosphate fertilizers superphosphate and Novaphos. Wheat was planted three times during 5 months, allowed to grow for 7 w, and harvested. Dry matter and HM content of shoots were determined after each harvest. Soil samples were taken after the first and third harvest, and the NH4NO3‐extractable HM contents were determined.

After the addition of 2% Na‐bentonite as well as 2% Ca‐bentonite, a strong reduction of the labile HM soil fraction and shoot HM concentration was observed. At the end of the experiment, the labile fraction was reduced due to the addition of Na‐bentonite and Ca‐bentonite by 24% and 31% for Zn, by 37% and 36% for Cd, by 41% and 43% for Cu, by 54% and 61% for Ni, and by 48% and 41% for Pb, respectively. Furthermore, the shoot HM concentrations with the exception of Zn were reduced below the phytotoxicity range. Accordingly, the shoot dry‐matter production was significantly increased.

The addition of phosphate fertilizers (notably Novaphos) strongly reduced the bioavailability of Pb for wheat plants. By addition of 0.05% Novaphos, the labile fraction and the shoot concentration of Pb were lowered by 39% and 64%, respectively. However, the addition of Fe oxides and zeolite resulted only in a small reduction in HM bioavailability to wheat plants. Among the studied additives, Na‐bentonite and Ca‐bentonite have the most promising potential to reduce the bioavailability for the studied HM.
Soil microbial biomass and activity: the effect of site characteristics in humid temperate forest ecosystems
Authors: Friedel Jürgen K. , Ehrmann Otto , Pfeffer Michael , Stemmer Michael , Vollmer Tobias , Sommer Michael
Published: March 2006

Microbial biomass, respiratory activity, and in‐situ substrate decomposition were studied in soils from humid temperate forest ecosystems in SW Germany. The sites cover a wide range of abiotic soil and climatic properties. Microbial biomass and respiration were related to both soil dry mass in individual horizons and to the soil volume in the top 25 cm. Soil microbial properties covered the following ranges: soil microbial biomass: 20 µg C g–1–8.3 mg C g–1 and 14–249 g C m–2, respectively; microbial C–to–total organic C ratio: 0.1%–3.6%; soil respiration: 109–963 mg CO2‐C m–2 h–1; metabolic quotient (qCO2): 1.4–14.7 mg C (g Cmic)–1 h–1; daily in‐situ substrate decomposition rate: 0.17%–2.3%. The main abiotic properties affecting concentrations of microbial biomass differed between forest‐floor/organic horizons and mineral horizons. Whereas microbial biomass decreased with increasing soil moisture and altitude in the forest‐floor/organic horizons, it increased with increasing Ntot content and pH value in the mineral horizons. Quantities of microbial biomass in forest soils appear to be mainly controlled by the quality of the soil organic matter (SOM), i.e., by its C : N ratio, the quantity of Ntot, the soil pH, and also showed an optimum relationship with increasing soil moisture conditions. The ratio of Cmic to Corg was a good indicator of SOM quality. The quality of the SOM (C : N ratio) and soil pH appear to be crucial for the incorporation of C into microbial tissue. The data and functional relations between microbial and abiotic variables from this study provide the basis for a valuation scheme for the function of soils to serve as a habitat for microorganisms.
Nitrogen fertilization and nitrate leaching into groundwater on arable sandy soils
Authors: Köhler Kai , Duynisveld Wilhelmus H. M. , Böttcher Jürgen
Published: March 2006

Nitrate leaching depending on N fertilization and different crop rotations was studied at two sites with sandy soils in N Germany between 1995 and 2000. The leaching of NO$ _3^- $ was calculated by using a numerical soil‐water and N model and regularly measured Nmin values as input data. Also the variability of Nmin values on the sandy soils was determined along transects. They reveal the high variability of the Nmin values and show that it is not possible to confirm a significant Nmin difference between fertilizer treatments using the normal Nmin‐sampling intensity. Nitrate‐leaching calculations of five leaching periods showed that even strongly reduced N‐fertilizer applications did not result in a substantially lower NO$ _3^- $ leaching into the groundwater. Strong yield reductions of even more than 50%, however, were immediately measured. Mean NO$ _3^- $ concentrations in the groundwater recharge are >50 mg L–1 and are mainly due to mineralization from soil organic matter. Obviously, the adjustment of the N cycle in the soil to a new equilibrium and a reduced NO$ _3^- $‐leaching rate as a consequence of lower N inputs need a much longer time span. Catch crops are the most efficient way to reduce the NO$ _3^- $ concentrations in the groundwater recharge of sandy soils. Their success, however, strongly depends on the site‐specific development possibilities of the catch crop. Even with all possible measures implemented, it will be almost impossible to reach NO$ _3^- $ concentrations <50 mg L–1 in sandy soils. The only way to realize this goal on a regional scale could be by increasing areas with lower nitrate concentrations in the groundwater recharge like grassland and forests.
Anisotropy of pore functions in structured Stagnic Luvisols in the Weichselian moraine region in N Germany
Authors: Dörner José , Horn Rainer
Published: March 2006

In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (kf), and the air permeability (ka) were measured. The air‐filled porosity (ϵa) was determined, and pore‐continuity indices (ka/ϵa, ka/ϵa2, N) and blocked porosities (ϵb) were derived from the relationship between ka and ϵa.

The development of soil structures with defined forms and dimensions (e.g., platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon.
Subglacial bedform evidence for a major palaeo‐ice stream and its retreat phases in Amundsen Gulf, Canadian Arctic Archipelago
Authors: Stokes C. R. , Clark C. D. , Winsborrow M. C. M.
Published: March 2006

Ascertaining the location of palaeo‐ice streams is crucial in order to produce accurate reconstructions of palaeo‐ice sheets and examine interactions with the ocean–climate system. This paper reports evidence for a major ice stream in Amundsen Gulf, Canadian Arctic Archipelago. Mapping from satellite imagery (Landsat ETM+) and digital elevation models, including bathymetric data, is used to reconstruct flow‐patterns on southwestern Victoria Island and the adjacent mainland (Nunavut and Northwest Territories). Several flow‐sets indicative of ice streaming are found feeding into the marine trough and cross‐cutting relationships between these flow‐sets (and utilising previously published radiocarbon dates) reveal several phases of ice stream activity centred in Amundsen Gulf and Dolphin and Union Strait. A large erosional footprint on the continental shelf indicates that the ice stream (ca. 1000 km long and ca. 150 km wide) filled Amundsen Gulf, probably at the Last Glacial Maximum. Subsequent to this, the ice stream reorganised as the margin retreated back along the marine trough, eventually splitting into two separate low‐gradient lobes in Prince Albert Sound and Dolphin and Union Strait. The location of this major ice stream holds important implications for ice sheet–ocean interactions and specifically, the development of Arctic Ocean ice shelves and the delivery of icebergs into the western Arctic Ocean during the late Pleistocene. Copyright © 2006 John Wiley & Sons, Ltd.
Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods
Authors: Wohlfarth B. , Blaauw M. , Davies S. M. , Andersson M. , Wastegård S. , Hormes A. , Possnert G.
Published: March 2006

The sediment sequence from Hässeldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hässeldalen Tephra and the 10‐ka Askja Tephra. Twenty‐eight high‐resolution 14C measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono‐ and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hässeldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and ‘realistic’ age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hässeldala port are large and calendar year estimates differ according to the assumptions of the age‐model. Not only do these results provide a cautionary note for over‐dependence on one age‐model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age–depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright © 2006 John Wiley & Sons, Ltd.
Climatic oscillations in central Italy during the Last Glacial–Holocene transition: the record from Lake Accesa
Authors: Magny Michel , de Beaulieu Jacques‐Louis , Drescher‐Schneider Ruth , Vannière Boris , Walter‐Simonnet Anne‐Véronique , Millet Laurent , Bossuet Gilles , Peyron Odile
Published: March 2006

This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.
Double‐Hydrophilic Polymer Brushes: Synthesis and Application for Crystallization Modification of Calcium Carbonate
Authors: He Lihong , Zhang Yanhong , Ren Lixia , Chen Yongming , Wei Hao , Wang Dujin
Published: March 2006

Summary: A water‐soluble diblock copolymer composed of poly(ethylene glycol) (PEG) and a cylindrical poly(acrylic acid) (PAA) brush is reported. It is prepared by a ‘grafting from’ approach using stepwise atom transfer radical polymerization combined with group transformation. Uniform molecular brushes, PEG113‐b‐P(MA‐g‐PAA26)169, are thus prepared as indicated by atom force microscopy analysis. This PAA densely grafted polymer is used to induce the crystallization of calcium carbonate in aqueous solution. Different experimental conditions, fast mixing reactions and static diffusion methods, are applied to explore the effect of polymer brushes on the crystallization, which is characterized by scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.

AFM image of the polymer brushes on mica and an SEM image of CaCO3 particles prepared in its presence.

magnified image

AFM image of the polymer brushes on mica and an SEM image of CaCO3 particles prepared in its presence.
Some Properties of Nanomaterials prepared through the Encapsulation within Polymer Fibrils of 1‐D Filaments of a Self‐assembled Bicopper Complex
Authors: Guenet Jean‐Michel , Poux Sandrine , Thierry Annette
Published: March 2006

Summary: A new type of nanomaterial prepared from ternary systems polymer/bicopper organic complex/solvent is presented. Each binary system displays differing types of behaviour: The polymer solutions produce thermoreversible gels while the bicopper organic complex forms randomly‐dispersed, self‐assembled threads in organic solvents The nanomaterial results from the encapsulation of the bicopper complex threads into the polymer fibrils through heterogeneous nucleation. The magnetic behaviour and the rheological properties of these materials will be briefly outlined and discussed.
Molecular Recognition and Catalysis: from Macrocyclic Receptors to Molecularly Imprinted Metal Complexes
Authors: Karakhanov Edward A. , Karapetyan Lyusyen M. , Kardasheva Yulia S. , Maksimov Anton L. , Runova Elena A. , Skorkin Vitaliy A. , Terenina Maria V.
Published: March 2006

Summary: The results of studying a number of reactions catalyzed by several types of soluble macromolecular catalytic systems capable of selectively binding organic substrates, namely, modified cyclodextrins, calixarenes and dendrimers are presented. The use of modified cyclodextrins as components of a catalytic system in the phenol and benzene hydroxylation by hydrogen peroxide allows one both to increase the catalytic activity and to change significantly the chemical selectivity. Phosphorilated calixarene – Rh catalytic systems was found to be catalytically active in hydroformylation of linear alkenes C7–C12. The results of experiments on the oxidation of C7–C16 alkenes show that, when the ligand is the dendrimer molecule, the fraction of forming methyl ketones substantially increases for the substrates C7–C9. For the higher alkenes, this effect is not observed.
Solid Polymer Electrolytes Studied by NMR Spectroscopy and DFT Calculations
Authors: Spěváček Jiří , Brus Jiří , Dybal Jiří
Published: March 2006

Summary: Results obtained recently on polymer electrolytes poly(ethylene oxide) (PEO)/LiCF3SO3 and poly(2‐ethyl‐2‐oxazoline) (POZ)/AgCF3SO3 by a combination of solid‐state 13C and 1H NMR spectroscopy and DFT quantum‐chemical calculations are discussed. Essentially the same local structure was found for the amorphous and crystalline phases of semicrystalline PEO/LiCF3SO3 polymer electrolyte. The amorphous POZ/AgCF3SO3 complex has a defined stoichiometry with two POZ monomeric units per one AgCF3SO3. A close contact between the metal salt and polymer was determined for both investigated systems from the Lee‐Goldburg cross‐polarization 1H → 13C dynamics.
Polymeric Quasi‐one‐dimensional Platinum Compounds
Authors: Bremi Juliane , Fontana Margherita , Caseri Walter , Smith Paul
Published: March 2006

Summary: Magnus' green salt, [Pt(NH3)4][PtCl4], is a quasi‐one‐dimensional inorganic semiconductor containing linear arrays of platinum atoms. Its use in materials science is limited since it does not melt prior to decomposition and is largely insoluble in water and organic solvents which makes processing difficult. We have remedied this deficiency by substitution of coordinated ammonia or chloride by monodentate or bidentate ligands, including optically active aminoalkanes, resulting in soluble compounds. Depending on the ligands, the polymeric supramolecular structure in the solid state persisted in solution or decayed to ion pairs. In the solid state, the ligands markedly influenced the Pt‐Pt distances, which on their part directed optical and electrical properties. Thus, high chiral anisotropy factors, cryochromic behavior, or (anisotropic) electric semiconductivity were found. A number of derivatives were processed to oriented films and fibers. Some complexes exhibited the color and electric characteristics of Magnus' green salt and thus can be regarded as soluble equivalents of Magnus' green salt. Oriented films of such a compound were applied as active semiconducting layer in field‐effect transistors (FET). The corresponding devices showed remarkable stability towards air and water which was superior to that of unprotected field‐effect transistors based on typical organic polymers.
Optical Properties of M(II) Schiff‐base Complexes Dispersed in Ethylene based Polymers
Authors: Boccia Massimiliano , Liuzzo Vincenzo , Pucci Andrea , Narducci Piero , Ruggeri Giacomo
Published: March 2006

Summary: Several salicylaldiminate M(II) complexes of Nickel, Copper and Cobalt have been prepared and mixed with ethylene based polymers in order to prepare new composite materials with interesting morphological and optical properties by profiting of the presence of alkyl chains and push‐pull substituents connected to the ligand structure. The phase dispersion behaviour of the binary films has been studied by scanning electron microscopy (SEM) and x‐ray microanalysis, whereas the optical properties of the composite samples have been evaluated by UV‐vis and fluorescence spectroscopy. The results in absorption have been analysed in terms of the anisotropy induced by the mechanical orientation of the polymer matrix and by the role of the metal centre according to the different strength of the complexes transition dipole moment. The luminescence behaviour have been discussed in terms of potential developments aimed at preparing polymeric supported Schiff base ligands for metal ions sensor applications.
Silica Polyamine Composites: New Supramolecular Materials for Cation and Anion Recovery and Remediation
Authors: Hughes Mark , Miranda Paul , Nielsen Dan , Rosenberg Edward , Gobetto Roberto , Viale Alessandra , Burton Sarah
Published: March 2006

Summary: The surface coverage of amorphous silica gels used in the synthesis of silica polyamine composites has been investigated by 29Si NMR. By diluting the polyamine anchor silane, chloropropyl trichlorosilane, with methyl trichlorosilane it was found that surface coverage could be markedly improved for a range of amine polymers after grafting to the silica surface. The commensurate decrease in the number of anchor points and increase in the number of free amines results in an increase in metal capacity and/or an improvement in capture kinetics. Solid state CPMAS‐13C NMR has been employed to investigate the structure and metal ion binding of a series of these composite materials. It is reported that the highly branched polymer, poly(ethyleneimine) (PEI) exhibits much broader 13C NMR resonances than the linear polymers poly(allylamine) (PAA) and poly(vinylamine) (PVA). These results are understood in terms of the low energy conformations calculated from molecular modeling studies. Three new applications of the technology are also presented: 1) separation of lanthanides as a group from ferric ion and all other divalent ions; 2) a multi step process for recovering and concentrating the valuable metals in acid mine drainage; 3) a process for removing low level arsenic and selenium in the presence of sulfate using immobilized cations on the composite materials.
Synthesis and Photophysical Properties of Some PEG Substitued Titanyl Phthalocyanine Derivatives
Authors: Kang Hyo‐Jin , Kang Eun‐Hee , Park Sang‐Wook , Lee Jae‐Wook , Lee Jin‐ Kook
Published: March 2006

Summary: Polyethylene glycol substituted titanyl phthalocyanine was prepared in two steps starting from phthalonitrile and characterized by FT‐IR, UV‐vis spectrophotometry, and fluorescence spectrophotometry. The titanyl phthocyanine derivatives (TiOPcs) showed high solubility in common organic solvents, such as, CH3Cl and DMF. These compounds decreased in absorbance intensity with increase of molecular weight of polyethylene glycol at maxima wavelength of visible range. The fluorescence spectra showed a fluorescence emission near 690 nm with a quantum yield of 0.05–0.32 (λex = 625 nm).
Ultrafiltration of Polymer‐Metal Complexes for Metal Ion Removal from Wastewaters
Authors: Molinari Raffaele , Argurio Pietro , Poerio Teresa
Published: March 2006

Summary: A case‐study using macromolecular metal complexes is described. The results of a process named Polymer Assisted Ultrafiltration (PAUF) for ion removal from various types of waters is reported. The water soluble polymers such as polyetilenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS) and poly(dimethylamine–co–epichlorohydrin–co–ethylenediamine) (PDEHED) as chelating agents, the Cu2+ as model ion and five ultrafiltration membranes have been used. The complexing agents were previously tested to establish the binding capacity and the best operating conditions for the process. Among the tested polymers the PEI appeared the most interesting one because its binding mechanism does not involve a counter ion release. It was tested in the simulation of wastewaters treatment containing the Cu2+ ion chelated with citric acid; this is a problem of interest in the recycling of water from soil washing operations. The polyethylenimine quantitatively bound the copper‐citrate chelate at pH 5.5 and the three component complex was separated by UF membranes producing a permeate with very low metal concentration. The polymer regeneration was carried out with good results by operating with the diafiltration method. The copper ion present in the diafiltration permeate in a form chelated with citric acid was recovered by oxidising the citrate in a membrane photoreactor. The positive results of the described case‐study show that Macromolecule‐Metal Complexes play a key role for running effectively and selectively the PAUF process for removing metal ions from various type of waters.
Effects of Nanocrystalline Porous TiO2 Films on Interface Adsorption of Phthalocyanines and Polymer Electrolytes in Dye‐Sensitized Solar Cells
Authors: Lee Hyun‐Jeong , Kim Woo‐Seok , Park Sung‐Hae , Shin Won Suk , Jin Sung‐Ho , Lee Jin‐Kook , Han Sang‐Min , Jung Ki‐Suck , Kim Mi‐Ra
Published: March 2006

Summary: We have synthesized three kinds of titanylphthalocyanines with different crystal structures (TiOPcs; PcT2000R, PcT3000R, and PcT1100S) and analyzed their crystal structure by X‐ray Diffraction (XRD), Fourier transfer IR (FT‐IR) spectroscopy, and Transmission Electron Microscope (TEM). From experimental results, we have confirmed that PcT2000R was estimated to be alpha‐form; PcT3000R was beta‐form, and PcT1100S was gamma‐form. Quasi‐solid state dye‐sensitized solar cell (DSSC) devices were prepared with a polymer electrolyte using TiOPcs as a co‐adsorbent. The DSSC device using TiOPc has higher power conversion efficiency than without TiOPc, due to decrease of electron transfer distance by the interface adsorption between TiO2 film and polymer electrolyte. Also, we have studied the effects of the crystal structures of TiOPcs on the property of polymer electrolyte and the performance of the DSSC device. The best result on power conversion efficiency was 7.13% in DSSC device using PcT3000R having its highest stability. The open‐circuit voltage (Voc) was 0.69 V, the short‐circuit current density (Jsc) was 20.02 mA/cm2, and the Fill Factor (FF) was 0.52. the addition of TiOPc as co‐adsorbent is useful for improve to the performances of DSSC devices such as Voc, Jsc, and power conversion efficiency.
Anion Influence in Metallocene‐based Olefin Polymerisation Catalysts
Authors: Wilson Polly A. , Hannant Mark H. , Wright Joseph A. , Cannon Roderick D. , Bochmann Manfred
Published: March 2006

The effects of perfluoroarylborate anions on the activities of metallocene‐based propylene polymerisation catalysts on the one hand, and on the cationic polymerisation of isobutylene to butyl rubber are summarised. In both systems the anions follow the same activity sequence, [CN{B(C6F5)3}2]−  > [H2N{B(C6F5)3{2]−] ≈ [B(C6F5)4]− > [MeB(C6F5)3]−. In an effort to maximise the delocalisation of negative charge over large volumes, new anions based on the very bulky borane B(C6F4‐2‐C6F5)3 (PBB) with longer linking groups have been prepared, e.g [N(CN‐PBB)2]−. The van der Waals volumes of representative anions and cations are reported. The influence of anions on the structure of catalytically active species is demonstrated using (SBI)Zr(CH2SiMe3)(µ‐Me)B(C6F5)3 and [(SBI)Zr(CH2SiMe3)+ · · · B(C6F5)] as examples. The alkyl ligand in the latter is stabilised by agostic bonding, which relegates the anion into the outer coordination sphere. The differences in ion pair structure profoundly influence the nature of chain termination in 1‐hexene polymerisations: whereas the MeB(C6F5) catalyst gives a mixture of vinylene and vinylidene terminations, with the latter predominanting at higher temperatures and conversions, the B(C6F5) system terminates exclusively after 2,1‐misinsertion to give vinylene‐terminated poly(1‐hexene).
Coordination Homopolymerization of ω–undecenyl Poly(styrene‐block‐isoprene) Macromonomers in the Presence of CGC‐Ti/MAO Complexes
Authors: Catarí Edgar , Peruch Frédéric , Isel François , Lutz Pierre Joseph
Published: March 2006

This paper deals with the coordination homopolymerization of ω–undecenyl poly(styrene‐block‐isoprene) macromonomers. The synthesis of the macromonomers made use of an anionic living poly(styrene‐block‐isoprene) copolymer which is deactivated at low temperature by 11‐bromo‐1‐undecene. The ability of these macromonomers to get involved in coordination homopolymerization in the presence of selected titanium catalysts was discussed. Special emphasis was given to the influence of polymerization temperature, macromonomer molar mass and concentration on the yield of homopolymerization and average degree of polymerization (DPn). In the presence of the CGC‐Ti/MAO catalyst, macromonomer conversion, determined by SEC, was between 35 to 52 wt.‐%, and DPn was between 5 to 14 depending upon the experimental conditions. However, as revealed by SEC/LS, the resulting comb‐shaped polymers (PE‐graft‐(PI‐block‐PS), are characterized by sharp molar distributions. Increasing macromonomer molar mass, led to only a slight decrease of DPn whereas conversion increased moderately. Other titanium catalysts such as CpTiCl3/MAO and Cp*TiCl3/MAO only caused macromonomer dimerization.
PP/PMMA Block Copolymers by Combination of ATRP and Metallocene Catalysis
Authors: Dix Albrecht , Ptacek Saija , Poser Sven , Arnold Manfred
Published: March 2006

PP‐b‐PMMA has been synthesized by a combination of metallocene catalysis and the controlled radical polymerization technique ATRP. Cp2ZrCl2/MAO and (Me4Cp)SiMe2(N‐tert‐Bu)TiCl2/MAO were used for the synthesis of atactic polypropylene. By a series of chemical modifications pp macroinitiators for the ATRP polymerization of MMA were synthesized. The PP‐b‐PMMA with polydispersities from 1.8–2.8 and an Mn ranging from 8 to 26 kg/mol was characterized by 1H‐NMR,SEC and DSC.
Polymerization of Polar Monomers Using Cyclopentadienyl Complexes of the Alkaline Earth Metals
Authors: Steffens Alexandra , Schumann Herbert
Published: March 2006

Tetramethylcyclopentadienyl complexes of magnesium, calcium and strontium are efficient catalysts at −78 °C for the solution polymerization of polar monomers such as alkyl methacrylates in the presence of only small amounts of triethylaluminium as cocatalyst. The molecular mass of the resulting polymers is predictable on the monomer/catalyst ratio. The polymerization reaction follows a first order kinetics with respect to the initial catalyst concentration. Block‐copolymers are easily available by sequential dosage of the monomer. A living polymerization mechanism is proposed involving activation of the catalyst by alkylation and subsequent insertion of coordinated monomers.
Activation of Metallacyclopropenes, five‐membered Metallacyclocumulenes and Metallacyclopentynes of Zirconium with iBu2AlH
Authors: Burlakov Vladimir V. , Bach Marc A. , Klahn Marcus , Arndt Perdita , Baumann Wolfgang , Spannenberg Anke , Rosenthal Uwe
Published: March 2006

The recently described reaction products of zirconacyclopropenes Cp′2Zr(η2‐Me3SiC2SiMe3) and five‐membered zirconacyclocumulenes (zirconacyclopenta‐2,3,4‐trienes) Cp*2Zr(η4‐1,2,3,4‐RC4R), Cp* = η5‐pentamethylcyclopentadienyl, R = Me, Me3Si and Ph, with i‐Bu2AlH are active catalysts in the polymerization of ethylene and in the ring opening polymerization of ε‐caprolactone. Here we describe the different activity of these complexes after thermal activation or if additional i‐Bu2AlH together with water are added. These results are compared to those which were obtained with the complexes Cp2Zr(η4‐1,2,3,4‐H2C4H2), rac‐(EBTHI)ZrF2, rac‐(EBTHI)ZrCl2, [rac‐(EBTHI)Zr(H)(µ‐H)]2 and rac (EBTHI)Zr(F)CH2‐CH2(2‐Py) after activation with i‐Bu2AlH together with water.
19F NMR Investigations of the Reaction of B(C6F5)3 with Different Tri(alkyl)aluminum Compounds
Authors: Janiak Christoph , Lassahn Paul‐Gerhard
Published: March 2006

Tris(pentafluorophenyl)borane, B(C6F5)3 reacts with triethylaluminum, AlEt3 to a mixture of Al(C6F5)3−nEtn and Al2(C6F5)6−nEtn compounds depending on the B/Al ratio. From excess borane to excess AlEt3 the species Al(C6F5)3 → Al(C6F5)2Et $\mathbin{\lower.3ex\hbox{$\buildrel\textstyle\leftarrow\over{\smash{\rightarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}}$ Al2(C6F5)4Et2 → Al2(C6F5)3Et3 → Al2(C6F5)2Et4 → Al2(C6F5)Et5 are formed and differentiated by their para‐F signal in 19F NMR. The reaction between B(C6F5)3 and the higher aluminum alkyls, tri(iso‐butyl)aluminum and tri(n‐hexyl)aluminum AlR3 (R = i‐Bu, n‐C6H13) is slower and requires AlR3 excess to shift the C6F5 $\leftrightarrow$ R exchange equilibria to almost complete formation of Al(C6F5)R2 and BR3. At equimolar ratio the equilibrium lies on the side of the unchanged borane together with its boranate [B(C6F5)3R]− anion. For tri(n‐octyl)aluminum even at large Al(n‐C8H17)3 excess no C6F5 $\leftrightarrow$ alkyl exchange can be observed, but boranate anions form.
Diffusion‐weighted imaging in Huntington's disease
Authors: Seppi Klaus , Schocke Michael F.H. , Mair Katherina J. , Esterhammer Regina , Weirich‐Schwaiger Helga , Utermann Barbara , Egger Karl , Brenneis Christian , Granata Roberta , Boesch Sylvia , Poewe Werner , Wenning Gregor K.
Published: March 2006

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder that results from an expanded trinucleotide (CAG) repeat on the huntingtin gene. Neurodegeneration in HD affects most prominently the basal ganglia. Therefore, diffusivity was obtained in the basal ganglia and thalamus of 29 patients with early HD and 27 healthy volunteers by means of the trace of the diffusion tensor (Trace(D)). Putaminal, caudate, pallidal, and thalamic Trace(D) values were increased in patients with HD compared with controls. Increased diffusivity in the putamen and caudate nucleus correlated with global functional impairment, CAG repeat length, as well as bicaudate ratio. Diffusion‐weighted imaging appears to be a promising surrogate marker for disease severity in HD. Sensitivity to change remains to be established longitudinally. © 2006 Movement Disorder Society
Analysis and equivalent circuit of aperture‐coupled cavity‐fed microstrip patch antenna
Authors: Kim Jeong Phill
Published: March 2006

A simple but accurate equivalent circuit of an aperture‐coupled cavity‐fed microstrip patch antenna is developed. It consists of ideal transformers, admittance elements, and transmission lines, and the related circuit‐element values are computed by applying the reciprocity theorem and complex power concept with the spectral‐domain immittance approach. The antenna input impedance calculated from network theory is compared with the measured data, and their good agreement validates the simplicity and accuracy of the proposed equivalent‐circuit model. Based on the proposed theory, the effect of structural parameters on the antenna characteristics is also examined. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 843–846, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21493
Left‐handed rectangular waveguide bandstop filters
Authors: Shelkovnikov Alexander , Budimir Djuradj
Published: March 2006

A novel type of rectangular waveguide bandstop filter is presented. Incorporating a dielectric slab patterned with single split‐ring resonators (SRRs), the electromagnetic properties of the structures are modified to allow propagation of backward waves in the rectangular waveguide. Filters are created through integration of SRRs, wireline, and additional metal strips as a loading for the propagation media. Using the printed circuit board (PCB) technique, SRRs, wireline, and metal strips are etched on a dielectric substrate and the slab is then inserted in the central plane of the metallic waveguide. A three‐unit cell SRR‐loaded waveguide is investigated against a three‐unit cell LHM waveguide configuration. A three‐unit LHM rectangular waveguide bandstop filter is designed and analyzed in order to performance wide stopband performance. The simulated results are presented for a WG‐18 waveguide. LHM rectangular waveguide bandstop filters are compact, low cost, and suitable for mass production. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 846–848, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21494
Calculation of circular birefringence based on analysis of stokes curve curvature
Authors: Perlicki K.
Published: March 2006

A novel method for circular‐birefringence calculation is proposed. The method is based on analysis of the curvature of a 3D curve (Stokes curve). The 3D curve segments are defined by a series of points that represent states of polarization. The obtained results indicate that the analysis of the curvature permits us to estimate the values of circular birefringence. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 854–856, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21497
Coaxial fed hexagonal dielectric resonator antenna for multifrequency operation
Authors: Hamsakutty V. , Praveen Kumar A. V. , Yohannan Jaimon , Bindu G. , Mathew K. T.
Published: March 2006

Hexagonal dielectric resonator antenna (HDRA) for multifrequency operation is proposed and investigated experimentally. The proposed antenna, excited by a single coaxial feed, resonates at four frequencies centered at 2.215, 2.784, 3.445, and 3.955 GHz with identical polarization. The return loss, VSWR, bandwidth, radiation patterns and half‐power beam width are measured and discussed. Multiple resonances with the same polarization and broad radiation patterns suggest the suitability of the antenna for multifrequency wireless applications. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 878–880, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21505
Extreme filtering applied to a microwave harmonic direction finding system
Authors: Zürcher J‐F.
Published: March 2006

A new harmonic direction finding (HDF) system, presented in [1], consists of a 2.45‐GHz transmitter with a +30‐dBm output power, a receiver at 4.9 GHz with a sensitivity better than −120 dBm, and a specially developed dual‐frequency helical antenna [2]. Besides high‐performance electronics, this system requires filters with extreme characteristics in order to avoid interferences between transmitter and receiver and filter out the harmonics of the transmitter. In this paper, various filter types are considered, simulated, realized, and measured. Only two types are found to be adequate for the application: a compact high‐pass filter made of a dielectric waveguide, and a stopband filter. The measured characteristics surpass the required ones. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 880–883, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21506
A planar dual‐meander‐line antenna for multiband mobile handsets
Authors: Hsiao Hai‐Ming , Lu Jui‐Han
Published: March 2006

A planar dual‐meander‐line antenna consisting of three branch strips for a low‐profile GSM/DCS/PCS/WLAN multiband mobile handset is proposed. The branch strips are designed to operate as quarter‐wavelength structures at 900 and 2000 MHz, respectively, and the obtained impedance bandwidths are 120 MHz (about 13.2%) and 924 MHz (about 44.4%) for covering the required bandwidths of the GSM (890–960 MHz) and DCS/PCS/UMTS/WLAN (1710–1880/1850–1990/1920–2170/2400–2484 MHz) bands. The proposed antenna can be mounted on top of a mobile phone with a low profile of 20 mm from ground plane. The measured antenna radiation patterns are approximately omnidirectional across the multiresonant bands. Peak antenna gains for operating frequencies across the GSM/DCS/PCS/UMTS/WLAN multiple bands are measured to be 1.8 and 2.9 dBi, respectively, with gain variations within 0.5 dBi. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 883–888, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21507
L‐band efficient and wavelength‐tunable Er3+/Yb3+ co‐doped cladding‐pumped fiber‐ring laser based on fiber‐loop mirror
Authors: Yu Fan , Fuyun Lu , Shumin Zhang , Shaojun Luo , Dai Wei , Xiaoyi Dong
Published: March 2006

We propose and demonstrate a novel, all‐fiber and wavelength tunable Er3+/Yb3+ co‐doped cladding‐pumped fiber‐ring laser, which utilized amplified spontaneous emission (ASE) as a secondary source so that it can operate in L‐band. The lasing threshold can be reduced to 30% by reflecting backward C‐band ASE into the same Er3+/Yb3+ co‐doped fiber (EYDF) using a fiber Bragg grating (FBG). By using a two‐section high‐birefringence fiber‐loop mirror (HiBi‐FLM) as the tunable wavelength filter, the tuning‐wavelength range can be up to 60 nm, from 1559.2 to 1619.4 nm, and the output power excursion of the laser at different wavelengths can be less than 0.2 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 892–895, 2006; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21509
Multimode‐fiber‐based edge filter for optical wavelength measurement application and its design
Authors: Wang Qian , Farrell Gerald
Published: March 2006

A novel all‐fiber edge filter for optical wavelength measurement application is proposed. The filter sandwiches a multimode fiber (MMF) section with an optimally designed length between two single‐mode fibers and utilizes the multimode interference in the MMF section. A measurable wavelength range of more than 50 nm is obtained with a desired spectral location through optimally choosing the length of the MMF section. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 900–902, 2006; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21512
Arrayed waveguide grating multiplexer with boxlike spectral response
Authors: Ma Chun‐Sheng , Qin Zheng‐Kun , Zhang Hai‐Ming , Li Han , Zhang Da‐Ming , Liu Shi‐Yong
Published: March 2006

An efficient technique is proposed to flatten the spectral response of an arrayed waveguide grating (AWG) multiplexer. By subtracting an increment from the length difference of odd arrayed waveguides and by adding the same increment to that of even arrayed waveguides, a boxlike spectral response can be obtained. The simulated result for a 17 × 17 polymer AWG shows that the boxlike spectral response has a 3‐dB bandwidth of 0.49 nm, and the crosstalk is about or less than −28 dB for every output channel. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 916–919, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21518
Study of properties of highly birefringent microstructured optical fibers
Authors: He Lina , Zhang Yejin , Yang Sigang , Chen Xiangfei , Xie Shizhong
Published: March 2006

A highly birefringent microstructured optical fiber (HB‐MOF) is investigated by using a UPML‐FDFD method. Based on the numerical results, the influence of the air‐hole size and pitch upon the mode birefringence, confinement loss, and single‐mode properties is analyzed. These properties and the influence among them are considered synthetically. Using the effective‐area method, the mode‐cutoff property of HB‐MOF is studied for the first time and the wavelength range for single‐mode operation can be obtained accurately. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 940–944, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21526
Miniature combined GSM‐GPS wire‐patch antenna
Authors: Zaid L. , Staraj R.
Published: March 2006

This paper describes a complete low‐cost radiating structure, combining a stacked wire‐patch GSM antenna, with an active GPS printed element located on the top of the GSM one. The GPS active amplifier and filter are located under the ground plane of GSM antenna and receive the DC bias voltage through the GPS coaxial probe feed. GSM antenna is a low‐profile, large‐bandwidth antenna with a dipolar radiation pattern. This structure, totally protected by a low‐cost dielectric radome, is very suitable for automobile applications needing a very small ground plane. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 970–972, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21536.
Thermally expanded core fiber with high numerical aperture for laser‐diode coupling
Authors: Lin Yu‐Cheng , Lin San‐Chien
Published: March 2006

A thermally expanded core fiber with high numerical aperture (HNA‐TEC) is demonstrated here to relax the tolerance of laser diode (LD) to fiber alignment. We experimentally clarify the dependence of mode field radius (MFR) on heating time for HNA‐TEC fiber. The MFR was expanded at the increasing rate of 0.067 μm/minute on the condition of 1100°C heat treatment. For a HNA‐TEC fiber with MFR 4.56 μm, the transverse and axial coupling tolerances were enlarged effectively by about 81% and 50%, respectively. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 979–981, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21539.
A single feed shorted patch antenna with low cross‐polarized fields
Authors: Kan H. K. , Waterhouse R. B. , Lee A. Y. J. , Pavlickovski D.
Published: March 2006

In this paper, we present a single‐feed shorted patch antenna with low cross‐polarized radiated fields. The printed antenna uses two shorted parasitic elements symmetrically located around the driven shorted patch. These elements electromagnetically balance the radiator. We have experimentally verified the new antenna and have found its cross‐polarized radiation patterns to be significantly lower than a conventional shorted patch by an order of more than 10 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 984–986, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21541
Influence of post‐treatment conditions on photoreactive effect of Zn:Fe:LiNbO3 crystals
Authors: Fang Shuang‐Quan , Ma De‐cai , Wang Biao , Ling Fu‐Ri , Wang G.
Published: March 2006

Three kinds of different Zn:Fe:LiNbO3 wafers are prepared by proper reduction or oxidation post‐treatment processes. The optical‐damage‐resistance abilities and photorefractive properties are studied using the optical compensator technique and two‐wave coupling measurement, respectively. The holographic storage properties, that is, diffraction efficiency, writing time, erasure time, photorefractive sensitivity, and dynamic range, are also measured or calculated. The analyses indicate that the sample disposed by reduction is the most proper media for holographic storage application. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 986–988, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21542