bluuebunny/crossref_metadata_2025 huggingface dataset:
Compatibilized poly(ether imide)/amorphous polyamide blends by means of poly(ethylene terephthalate) addition
Authors: Ramiro J. , Eguiazábal J. I. , Nazábal J.
Published: July 2006

Compatibilized poly(ether imide)/amorphous polyamide (PEI/a‐PA) blends were obtained in the melt state by substitution of 20% PEI by poly(ethylene terephthalate), PET. The two amorphous phases of the blends comprised both a miscibilized 80/20 PEI/PET blend and an a‐PA‐rich phase in which small amounts of PET and probably PEI were present. The presence of PET in the two phases of most of the blends was the main reason for the clear decrease in the particle size that indicated compatibilization. The smaller interfacial tension of the blends after PET addition also proved that compatibilization had occurred. The deviation of the modulus with respect to the direct rule of mixtures was positive in PEI‐rich blends and negative in the blends very rich in a‐PA. The modulus values were tentatively attributed to a different orientation of the components of the blends in the blends and in the neat state. The clear increases in ductility and the impact strength after PET addition further demonstrated the compatibilization effect of PET. POLYM. ENG. SCI., 46: 1292–1298, 2006. © 2006 Society of Plastics Engineers
Preparation of diblock copolymers consisting of methoxy poly(ethylene glycol) and poly(ε‐caprolactone)/poly(L‐lactide) and their degradation property
Authors: Hyun Hoon , Kim Moon Suk , Jeong Sung Chan , Kim Yu Han , Lee Soo Young , Lee Hai Bang , Khang Gilson
Published: July 2006

Methoxy poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (MPEG‐PCL) or MPEG‐b‐poly(L‐lactide) (MPEG‐PLLA) diblock copolymers were prepared by the polymerization of CL or LA, using MPEG as an initiator in the presence of stannous octoate. MPEG‐b‐poly(ε‐caprolactone‐ran‐L‐lactide) (MPEG‐PCLA) diblock copolymers with different chemical composition of PCL and PLLA were also prepared by adjusting the amount of CL and LA from MPEG in the presence of stannous octoate. In degradation study, the degradation of the MPEG‐PCLA diblock copolymers mainly depends on the PCL and PLLA segments present in their structure. MPEG‐PCLA, with intermediate ratio of PCL and PLLA segment, completely degraded after 14 weeks. Meanwhile, partially degraded MPEG‐PCLA segments and parent MPEG segments were observed at higher PCL or PLLA segment contents. Introduction of PLLA into the PCL segments caused a lowering of the crystallinity of the diblock copolymers, thus, inducing a faster incoming of water into the copolymers. We confirmed that the diblock copolymers, with lower degree of crystallinity, have degraded more rapidly. POLYM. ENG. SCI., 46: 1242–1249, 2006. © 2006 Society of Plastics Engineers
Single‐polymer composites based on slowly crystallizing polymers
Authors: Yao Donggang , Li Ruihua , Nagarajan Pratapkumar
Published: July 2006

An approach of using slowly crystallizing polymers to form single‐polymer composites (SPCs) was investigated. The method was demonstrated using poly(ethylene terephthalate) (PET) as a model system, with which two distinct physical forms, namely, amorphous PET films and highly crystalline PET fibers can be readily obtained. Because of the large difference between the rubbery softening temperature of the amorphous phase and the melting temperature of the crystalline phase, the new process is characterized by its wide process window and enhanced manufacturability. The heating temperature and holding time were found to play a profound role in influencing the properties of the SPC. Excellent fiber–matrix interfacial adhesion was obtained at heating temperature 180°C and holding time 10 s. The results also indicated that the heating rate plays a significant role in affecting the fusion and adhesion of the composite. With reduced heating rates, the fusion and adhesion properties are rapidly deteriorated. POLYM. ENG. SCI., 46: 1223–1230, 2006. © 2006 Society of Plastics Engineers
Thermal and shear flow effects on microstructure of a thermotropic liquid crystalline polymer
Authors: Guo Tianren , Naskar Amit K. , Harrison Graham M. , Ogale Amod A.
Published: July 2006

The effects of annealing time and temperature on the texture and transient shear rheological behavior of a thermotropic liquid crystalline polymer were investigated. The texture evolution during annealing included two processes: the reduction of the defect density and the increase of the domain size but decrease of the domain number. We confirmed that the threaded texture caused the first shear stress peak and the shear stress minimum during shear flow startup. More importantly, using the wide‐angle X‐ray diffraction technique, we determined that the second shear stress peak during flow startup can be attributed to the evolution of the molecular orientation. POLYM. ENG. SCI., 46:1215–1222, 2006. © 2006 Society of Plastics Engineers
Crystallization, morphology, and mechanical behavior of polylactide/poly(ε‐caprolactone) blends
Authors: López‐Rodríguez N. , López‐Arraiza A. , Meaurio E. , Sarasua J.R.
Published: July 2006

Optically pure polylactides, poly(L‐lactide) (PLLA) and poly(D‐lactide) (PDLA), were blended across the range of compositions with poly(ε‐caprolactone) (PCL) to study their crystallization, morphology, and mechanical behavior. Differential scanning calorimetry and dynamic mechanical analysis (DMA) of the PLA/PCL blends showed two Tgs at positions close to the pure components revealing phase separation. However, a shift in the tan δ peak position by DMA from 64 to 57°C suggests a partial solubility of PCL in the PLA‐rich phase. Scanning electron microscopy reveals phase separation and a transition in the phase morphology from spherical to interconnected domains as the equimolar blend approaches from the outermost compositions. The spherulitic growth of both PLA and PCL in the blends was followed by polarized optical microscopy at 140 and 37°C. From tensile tests at speed of 50 mm/min Young's modulus values between 5.2 and 0.4 GPa, strength values between 56 and 12 MPa, and strain at break values between 1 and 400% were obtained varying the blend composition. The viscoelastic properties (E′ and tan δ) obtained at frequency of 1 Hz by DMA are discussed and are found consistent with composition, phase separation, and crystallization behavior of the blends. POLYM. ENG. SCI., 46:1299–1308, 2006. © 2006 Society of Plastics Engineers
Isothermal and nonisothermal crystallization kinetics of poly(ε‐caprolactone)/multi‐walled carbon nanotube composites
Authors: Wu Tzong‐Ming , Chen Erh‐Chiang
Published: July 2006

Differential scanning calorimeter (DSC) and polarized optical microscopy (POM) have been used to investigate the isothermal and nonisothermal crystallization behavior of poly(ε‐caprolactone) (PCL)/multi‐walled carbon nanotube (MWNT) composites. PCL/MWNT composites have been prepared by mixing the PCL polymer with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) in tetrahydrofuran solution. Raman spectrum of c‐MWNT indicated the possible presence of carboxylic acid groups at both ends and on the sidewalls of the MWNTs. The TEM micrograph showed that the c‐MWNT is well separated and uniformly dispersed in the PCL matrix. DSC isothermal results showed that the introduction of c‐MWNT into the PCL initiates strongly heterogeneous nucleation, which induced a change of the crystal growth process. The activation energy of PCL significantly decreases by adding 0.25 wt% c‐MWNT into PCL/c‐MWNT composites and then increases as c‐MWNT content increases. The result demonstrates that the addition of c‐MWNT into PCL induces the heterogeneous nucleation at lower c‐MWNT content and then inhibits the polymer chain transportation ability during crystallization at higher c‐MWNT content. In this study, we have also studied the nonisothermal crystallization kinetics and melting behavior of PCL/c‐MWNT composites at various cooling rates. The correlation among isothermal and nonisothermal crystallization kinetics and melting behavior of PCL/c‐MWNT composites can be also discussed. POLYM. ENG. SCI., 46:1309–1317, 2006. © 2006 Society of Plastics Engineers
Facile syntheses of surface‐functionalized micelles and shell cross‐linked nanoparticles
Authors: O'Reilly Rachel K. , Joralemon Maisie J. , Hawker Craig J. , Wooley Karen L.
Published: July 2006

Block copolymer micelles and shell cross‐linked nanoparticles (SCKs) presenting Click‐reactive functional groups on their surfaces were prepared using two separate synthetic strategies, each employing functionalized initiators for the controlled radical polymerization of acrylate and styrenic monomers to afford amphiphilic block copolymers bearing an alkynyl or azido group at the α‐terminus. The first route for the synthesis of the azide‐functionalized nanostructures was achieved via sequential nitroxide‐mediated radical polymerization (NMP) of tert‐butyl acrylate and styrene, originating from a benzylic chloride‐functionalized initiator, followed by deprotection of the acrylic acids, supramolecular assembly of the block copolymer in water and conversion of the benzylic chloride to a benzylic azide. In contrast, the second strategy utilized an alkynyl‐functionalized reversible addition fragmentation transfer (RAFT) agent directly for the RAFT‐based sequential polymerization of tetrahydropyran acrylate and styrene, followed by selective cleavage of the tetrahydropyran esters to give the α‐alkynyl‐functionalized block copolymers. These Click‐functionalized polymers, with the functionality located at the hydrophilic polymer termini, were then self‐assembled using a mixed‐micelle methodology to afford surface‐functionalized “Clickable” micelles in aqueous solutions. The optimum degree of incorporation of the Click‐functionalized polymers was investigated and determined to be ca. 25%, which allowed for the synthesis of well‐defined surface‐functionalized nanoparticles after cross‐linking selectively throughout the shell layer using established amidation chemistry. Functionalization of the chain ends was shown to be an efficient process under standard Click conditions and the resulting functional groups revealed a more “solution‐like” environment when compared to the functional group randomly inserted into the hydrophilic shell layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5203–5217, 2006
Erosion of multilayered films fabricated from degradable polyamines: Characterization and evidence in support of a mechanism that involves polymer hydrolysis
Authors: Zhang Jingtao , Fredin Nathaniel J. , Lynn David M.
Published: July 2006

Multilayered polyelectrolyte assemblies fabricated using hydrolytically degradable polyamines (1–3) erode gradually when incubated in physiologically relevant media. This investigation sought to characterize physically and chemically the erosion of films fabricated from these polymers and sodium poly(styrene sulfonate) (SPS) and to investigate specifically the potential role of polymer hydrolysis in governing film erosion. The characterization of erosion using reflective infrared spectroscopy revealed changes in the carbonyl region of the spectrum that were consistent with the generation of polymer hydrolysis products. To evaluate the role of the esters in these materials more directly, we also synthesized a structural analogue of polymer 2 containing amide functionality rather than ester functionality. Assemblies fabricated from this amide‐containing polymer did not erode significantly or release SPS into solution when incubated in phosphate‐buffered saline (PBS). Finally, we characterized the erosion of assemblies fabricated from polymer 1 in PBS buffer prepared with D2O rather than H2O. These assemblies eroded significantly more slowly in deuterated media than in buffer prepared with H2O. These results, when combined, provide support for the view that polymer hydrolysis plays an important role in governing the erosion of assemblies fabricated from these degradable polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5161–5173, 2006
Irreversibility line and critical current studies in κ‐(BEDT‐TTF)2Cu[N(CN)2]Br organic superconductor: effect of the structural transformation near 80 K
Authors: Tirbiyine A. , Senoussi S. , Taoufik A. , Ramzi A. , Haouam A. , Labrag A.
Published: July 2006

We report systematic magnetic measurements on organic superconductor κ‐(BEDT‐TTF)2Cu[N(CN)2]‐Br. The irreversibility line Hirr(T) and the critical current density Jc were studied. Our results show the strong dependence of Hirr(T) and Jc on the cooling rate. The Hirr(T) data follow power dependence H ∝ (1 – T /T c)m where m depends on the sample cooling. The structural transformation which occurs at the vicinity of 80 K influences very strongly the physics of vortex lattice and the associated magnetic behavior. This has a pronounced effect on the critical current density and the superconducting transition temperature Tc. Rapid cooling through 80 K will freeze the high temperature magnetic phase to low temperatures and the presence of local magnetic moments suppresses the superconducting Tc. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and magnetic characterization of GdSr2RuCu2O8 films deposited by d.c. sputtering
Authors: Guarino A. , Fittipaldi R. , Nigro A. , Gombos M. , Vecchione A. , Ciancio R. , Pace S. , Cimberle M. R. , Tropeano M. , Zola D. , Polichetti M.
Published: July 2006

GdSr2RuCu2O8 oriented films have been deposited on SrTiO3 (100) substrate by d.c. sputtering. Films deposited in pure oxygen atmosphere have shown c‐axis oriented GdSr2RuCu2O8 phase after an appropriate ex‐situ thermal treatment in oxygen atmosphere. X‐ray diffraction, scanning electron microscopy and energy dispersive spectrometry have been used to check the crystal structure, the morphology and the composition of the samples. The investigations have been performed before and after the oxygen annealing pointing out an increased structural order.The samples have been characterized magnetically in the range from 1.9 to 400 K. A selected sample has exhibited a possible ferromagnetic transition with a Curie temperature of about 150 K. All the samples measured by transport measurements show a semiconducting behaviour down to 4.2 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallographic and magnetic properties of a new rare‐earth iron nitride Nd2–xSmxFe17Ny (y ∼ 3)
Authors: Ben Kraiem M. S. , Cheikhrouhou A.
Published: July 2006

The effect of nitrogen insertion on the structural and magnetic properties of Nd2–xSmxFe17 metallic alloys has been investigated. X‐ray powder diffraction characterizations show that all the nitrides are single phase and crystallize in the Th2Zn17‐type structure. The lattice parameters of the Nd2–xSmxFe17Ny compounds decrease with samarium content. Magnetization studies show that all the samples are ferromagnetic at room temperature. Nitrogen insertion leads to an increase of the Curie temperature Tc. Tc is found to increase from 370 K for NdSmFe17 to 760 K for NdSmFe17N2.8. It leads also to an increase of the saturation magnetization Ms. $ { {{\rm M}_{\rm s}({\rm y}) - {\rm M}_{\rm s}(0)} \over {{\rm M}_{\rm s}(0)} } $ decreases with increasing samarium content from 58% for x = 0 to 45% for x = 2. X‐ray diffraction characterizations on magnetically aligned powder samples of Nd2–xSmxFe17Ny reveal a change in the easy magnetization direction from planar for x = 0 to c axis for x = 2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Praseodymium deficiency effects on the physical properties of Pr1.2–x□xSr1.8Mn2O7 bilayer manganese oxides
Authors: Triki M. , Zouari S. , Cheikhrouhou A. , Strobel P.
Published: July 2006

The praseodymium deficiency effects on the structural, magnetic and electrical properties of the lacunar bilayers manganese oxides Pr1.2–x□xSr1.8Mn2O7 (0 ≤ x ≤ 0.15) were studied. Rietveld refinements of the X‐ray diffraction patterns show that all our samples are single phase and crystallize in the tetragonal structure with I4/mmm space group. All our samples exhibit a paramagnetic‐ferromagnetic transition on cooling. The praseodymium deficiency leads to a decrease of the Curie temperature. Resistivity measurements as a function of temperature show that only the parent sample Pr1.2Sr1.8Mn2O7 exhibits a semiconducting‐metallic transition with decreasing temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Charge distribution consequences of the magnetic order in TbB6
Authors: Galéra R. M. , Amara M. , Aviani I. , Givord F. , Zontone F. , Kunii S.
Published: July 2006

The antiferromagnetic state of TbB6 has been investigated by way of magnetostriction and X‐ray scattering measurements on a single crystal. The magnetostriction data reveal a well defined tetragonal symmetry lowering and a weak volume increase below TN . The X‐ray scattering investigation shows charge satellites, related to the 〈${1 \over 2}$00〉 and 〈${1 \over 2}$${1 \over 2}$0〉 wave vectors stars. The 〈${1 \over 2}$00〉 satellites are characteristic of exchange displacement waves, similar to those observed in GdB6, whereas the 〈${1 \over 2}$${1 \over 2}$0〉 ones could result as well from 4f multipolar scattering. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the magnetic properties and hyperfine fields in Fe‐containing alloys: A theoretical study
Authors: Samara Q. , Al‐Sharif A. I. , Mahmood S. H.
Published: July 2006

In this work, WIEN2k package has been used to calculate the structural and magnetic characteristics, and the hyperfine fields in a series of 1:1 ordered iron binary alloys and intermetallics FeT (T = Ti, V, Cr, Mn, Co, Ni). This is done by solving Kohn‐Sham equations using the Full‐Potential Linearized Augmented Plane Wave (FP‐LAPW) method. In the calculations, the Local Spin Density Approximation (LSDA) and the Generalized Gradient Approximation (GGA) were used for comparison. The results were compared with other theoretical and experimental measurements. Based on our results, GGA is found to be better than the LSDA in evaluating the hyperfine fields. Also the hyperfine fields in the ordered phases were found to be smaller than the hyperfine fields in the disordered phases of the studied systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dipolar interaction, surface anisotropy and alloying effect on magnetic properties of the superlattice Ni1–xFex/Cu
Authors: Fahmi A. , Elharfaoui M. , Qachaou A.
Published: July 2006

The magnetic properties of superlattices Ni1–xFex/Cu are studied within the spin wave theory framework for 0 ≤ x ≤ 0.2 and x = 1. The excitation spectra and the magnetization are calculated using a Green's function method. The results show that for each wave vector value, there are N coupled planar modes for a superlattice with N planes. A competition between the effects of long‐range dipolar interaction and surface anisotropy is shown. The exchange and magnetic stability are reinforced when x increases. A comparison between the calculated and the measured magnetization under magnetic applied field gives a satisfactory estimation of the exchange integral values. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
U‐PVC gelation level assessment, part 1: Comparison of different techniques
Authors: Fillot Louise‐Anne , Hajji Philippe , Gauthier Catherine , Masenelli‐Varlot Karine
Published: July 2006

Several different gelation assessment methods such as differential scanning calorimetry, capillary rheometry, solvent absorption, wide angle x‐ray scattering, transmission electron microscopy, and atomic force microscopy were applied to a typical PVC window profile formulation subjected to various thermomechanical histories. Shear applied during the process could be decomposed into two components: (i) a thermal component corresponding to the self‐heating that was generated and (ii) a “mechanical” component associated with a “pure” shearing action deprived of any thermal aspect. Shear sensitivity of the above‐mentioned gelation assessment techniques was evaluated by considering both aspects. Gelation levels established by differential scanning calorimetry and capillary rheometry were especially compared, thus allowing a comparison of the two physical aspects evidenced by each technique, i.e., crystallite melting and macromolecular network development. It appeared that as soon as the PVC particulate structure had been fragmented into micronic entities (primary particles) the gelation process was governed mainly by the thermal aspect, i.e., crystallite melting. J. VINYL. ADDIT. TECHNOL. 12:98–107, 2006. © 2006 Society of Plastics Engineers.
Degradation mechanism and mechanical properties of PVC in PVC‐PE melt blends: Effects of molecular architecture, content, and MFI of PE
Authors: Thongpin C. , Santavitee O. , Sombatsompop N.
Published: July 2006

Thermal degradation mechanism and mechanical properties of poly(vinyl chloride) (PVC) in PVC–polyethylene (PE) mixtures with varying types, contents, and melt flow indexes of the PE were studied. The degradation behavior was investigated in terms of decomposition temperature and glass transition temperature, polyene index, and morphology of the PVC in the mix. The results suggested that adding small amounts of PE (5 phr) in PVC‐PE mixtures could thermally stabilize the PVC, as noted by an increase in its decomposition temperature. At higher PE loading, the PVC encountered more degradation as a result of a consumption of the heat stabilizer by PE radicals and the dehydrochlorination reaction. A radical transfer reaction was proposed to explain the degradation mechanism of the PVC in the PVC‐PE melt, specifically a progressive increase of the glass transition temperature of the PVC in the mix as a result of increasing PE content. The PVC‐PE blend using HDPE with high MFI exhibited more pronounced thermal and structural changes of PVC. The mechanical properties of the PVC‐PE blend were very much dependent on the PE content, but slightly affected by the type and MFI value of the PE. The dispersion level of the PE in the PVC phase was found to play an important role in affecting the mechanical properties of the PVC‐PE mixtures. J. VINYL. ADDIT. TECHNOL. 12:115–123, 2006. © 2006 Society of Plastics Engineers
HYPOTENSION DURING SPINAL ANAESTHESIA FOR CAESAREAN SECTION: IMPLICATIONS, DETECTION PREVENTION AND TREATMENT
Authors: KHAW KIM S , KEE WARWICK D NGAN , LEE SHARA WY
Published: July 2006

Regional anaesthesia is preferred by most anaesthetists for the majority of caesarean sections. The major advantage of regional anaesthesia is the avoidance of maternal morbidity and mortality associated with general anaesthesia. The importance of this can be seen in the most recent Report of Confidential Enquires into Maternal Deaths in which it was reported that of the direct maternal deaths attributed to anaesthesia, all six were associated with difficulties during general anaesthesia. Although a number of regional anaesthesia techniques are available, spinal anaesthesia is particularly popular because it is fast, easy to perform and provides excellent intraoperative analgesia.
A comparison and uncertainty assessment of system analysis techniques for short‐term quantitative precipitation nowcasting based on radar images
Authors: Montanari Laura , Montanari Alberto , Toth Elena
Published: July 2006

An evaluation of system analysis techniques for obtaining short‐term quantitative precipitation forecasting, based on radar images, is presented. The analysis considers eight rainfall events monitored through radar scans collected at San Pietro Capofiume (northern Italy). These images have temporal and spatial resolutions equal to 15 min and 1 × 1 km2, respectively, and are composed by 256 × 256 pixels. The nowcasting is performed by considering four different approaches, ranging from purely heuristic techniques to system analysis methods for modeling storm advection and dynamic storm evolution in a Lagrangian reference frame, traveling along with the storm. Stochastic models of the autoregressive type, as well as neural networks, are applied for modeling the Lagrangian storm dynamics. The sensitivity of the forecasting performances with respect to prediction lead time and spatial resolution of the radar images is investigated. Finally, the study presents a meta‐Gaussian approach for the quantitative evaluation of the uncertainty of the forecast. This method aims to obtain an estimate of the probability distribution of the nowcasting error, conditioned on the predicted future rainfall depth.
A study of the lightning channel corona sheath
Authors: Maslowski Grzegorz , Rakov Vladimir A.
Published: July 2006

Dynamics of lightning channel corona sheath surrounding thin channel core is examined on the basis of three transmission‐line‐type models of the return stroke that specify different attenuation of longitudinal current with height. The corona sheath conductivity is estimated using measured radial electric field in the immediate vicinity of the lightning channel and measured channel base current. The corona sheath radius, velocity of corona sheath radial expansion, and corona current are examined using a multiexponential approximation of the lightning channel base current waveform. Additionally, energy dissipated in the corona sheath is estimated and compared to that dissipated in the channel core.
A Bayesian geostatistical transfer function approach to tracer test analysis
Authors: Fienen Michael N. , Luo Jian , Kitanidis Peter K.
Published: July 2006

Reactive transport modeling is often used in support of bioremediation and chemical treatment planning and design. There remains a pressing need for practical and efficient models that do not require (or assume attainable) the high level of characterization needed by complex numerical models. We focus on a linear systems or transfer function approach to the problem of reactive tracer transport in a heterogeneous saprolite aquifer. Transfer functions are obtained through the Bayesian geostatistical inverse method applied to tracer injection histories and breakthrough curves. We employ nonparametric transfer functions, which require minimal assumptions about shape and structure. The resulting flexibility empowers the data to determine the nature of the transfer function with minimal prior assumptions. Nonnegativity is enforced through a reflected Brownian motion stochastic model. The inverse method enables us to quantify uncertainty and to generate conditional realizations of the transfer function. Complex information about a hydrogeologic system is distilled into a relatively simple but rigorously obtained function that describes the transport behavior of the system between two wells. The resulting transfer functions are valuable in reactive transport models based on traveltime and streamline methods. The information contained in the data, particularly in the case of strong heterogeneity, is not overextended but is fully used. This is the first application of Bayesian geostatistical inversion to transfer functions in hydrogeology but the methodology can be extended to any linear system.
Wind‐driven and steric fluctuations of sea surface height in the southwest Pacific
Authors: Bowen Melissa M. , Sutton Philip J. H. , Roemmich Dean
Published: July 2006

Large fluctuations in sea surface height (SSH) occurred in the southwest Pacific between New Zealand and Fiji in the late 1990s. A model of SSH including steric heating and wind‐driven Rossby waves explains more than 40% of the observed SSH variance in the region over the 12 years of satellite measurements. The modelled SSH also agrees with dynamic height calculated from subsurface temperatures measured along an expendable bathythermograph (XBT) line between New Zealand and Fiji. The model simulations show a large high in SSH was created by anomalous downward Ekman pumping during 1998 when the seasonal change to upwelling failed to occur. The 50‐year wind record shows other downwelling events have occurred in the region predominantly during El Niño conditions.
The diffusive ocean conveyor
Authors: Holzer Mark , Primeau François W.
Published: July 2006

We use a novel path‐density transport diagnostic to trace out the deep branch of the ocean conveyor in a global circulation model. Our results suggest that the majority of the world's deep water is not transported back to the surface along the current systems of the standard great ocean conveyor (GOC). Standard GOC routes are evident only for waters with interior residence times, τ, less than about a thousand years, accounting for less than a quarter of the ventilation‐to‐re‐exposure flux. Waters with longer τ are spread across the deep oceans by the “diffusive conveyor” and, by τ ∼ 3000 years, organized into a characteristic deep‐North‐Pacific pattern that is dominated by eddy diffusion. The observed depletion of oxygen and 14C in the deep N Pacific is consistent with a diffusive conveyor and should not be interpreted as evidence of an advective terminus of the GOC deep branch.
Rapid estimation of first‐order rupture characteristics for large earthquakes using surface waves: 2004 Sumatra‐Andaman earthquake
Authors: Ammon Charles J. , Velasco Aaron A. , Lay Thorne
Published: July 2006

Broadband surface waves from large earthquakes can be rapidly processed to estimate seismic moment, faulting duration, and general slip distribution, supplying important information for hazard response efforts, including tsunami warnings. Deconvolution of surface‐wave Green's functions removes propagation effects, yielding azimuthally varying effective source time functions. Even a single fault‐perpendicular time function can provide robust first‐order estimates of the temporal history of seismic radiation and associated slip distribution. Simplified two‐dimensional finite‐fault modeling using a few surface‐wave time functions can reliably characterize the smooth component of the overall rupture process. These procedures are demonstrated using 13 Rayleigh wave observations for the 26 December 2004 Sumatra‐Andaman earthquake, yielding satisfactory agreement with models based on more complete seismic data sets. Depending on source and station locations, stable slip estimates can be obtained within 15–60 minutes of the onset of a large earthquake.
Nonequilibrium quantum dynamics in the condensed phase via the generalized quantum master equation
Authors: Zhang Ming-Liang , Ka Being J. , Geva Eitan
Published: July 2006

The Nakajima-Zwanzig generalized quantum master equation provides a general, and formally exact, prescription for simulating the reduced dynamics of a quantum system coupled to a quantum bath. In this equation, the memory kernel accounts for the influence of the bath on the system’s dynamics, and the inhomogeneous term accounts for initial system-bath correlations. In this paper, we propose a new approach for calculating the memory kernel and inhomogeneous term for arbitrary initial state and system-bath coupling. The memory kernel and inhomogeneous term are obtained by numerically solving a single inhomogeneous Volterra equation of the second kind for each. The new approach can accommodate a very wide range of projection operators, and requires projection-free two-time correlation functions as input. An application to the case of a two-state system with diagonal coupling to an arbitrary bath is described in detail. Finally, the utility and self-consistency of the formalism are demonstrated by an explicit calculation on a spin-boson model.
On the ground state energy for a magnetic Schrödinger operator and the effect of the DeGennes boundary condition
Authors: Kachmar Ayman
Published: July 2006

Motivated by the Ginzburg-Landau theory of superconductivity, we estimate in the semiclassical limit the ground state energy of a magnetic Schrödinger operator with De Gennes boundary condition and we study the localization of the ground states. We exhibit cases when the De Gennes boundary condition has strong effects on this localization.
Colloidal dispersions of octadecyl grafted silica spheres in toluene: A global analysis of small angle neutron scattering contrast variation and concentration dependence measurements
Authors: Kohlbrecher Joachim , Buitenhuis Johan , Meier Gerhard , Lettinga M. Paul
Published: July 2006

In this paper we report measurements of the form factor and the structure factor of a sterically stabilized colloidal dispersion consisting of silica spheres coated with octadecane in toluene by small angle neutron scattering (SANS). The phase diagram of this system shows the liquid-liquid coexistence line and also a jamming transition at higher concentrations, where the jamming line intersects the coexistence line roughly at the critical point. We have performed SANS experiments at a temperature well above the transition temperature and at various volume fractions ϕ, spanning from the very dilute regime (ϕ=0.2%) to the critical concentration (ϕ=16%) and the highly viscous regime (ϕ=39.2%). Except for the very dilute regime, we observe a structure factor S(q) in all other cases. We fitted our data over the whole concentration regime using a global fitting routine with a core-shell model for the form factor P(q), taking into account the structure factor, which we describe with the Robertus model for an adhesive polydisperse core-shell particle. At a volume fraction of ϕ=5% a SANS contrast variation experiment has been performed. From that the product of the volume of the shell and the amount of solvent within the corona of our core-shell particle could be determined. At the most probable shell thickness of 2.3nm a solvent content of about 50% within the corona was found. Moreover we could conclude that the core is not interpenetrated by solvent molecules. From the contrast variation experiment followed that the structure factor at zero average contrast exhibits a strong q dependence, which is an effect of an inhomogeneous particle in combination with a size distribution.
Configurable-bandwidth imaging spectrometer based on an acousto-optic tunable filter
Authors: Vila-Francés Joan , Calpe-Maravilla Javier , Muñoz-Mari Jordi , Gómez-Chova Luis , Amorós-López Julia , Ribes-Gómez Emilio , Durán-Bosch Vicente
Published: July 2006

This article presents a new imaging spectrometer called autonomous tunable filtering system. The instrument acquires sequential images at different spectral wavelengths in the visible and near infrared range of the electromagnetic spectrum. The spectral selection is performed by an acousto-optic tunable filter (AOTF), which is driven by a custom radio-frequency (rf) generator based on a direct digital synthesizer (DDS). The DDS allows a high flexibility in terms of acquisition speed and bandwidth selection. The rf power is dynamically controlled to drive the AOTF with the optimum value for each wavelength. The images are formed through a carefully designed optical layout and acquired with a high performance digital camera. The application software controls the instrument and acquires the raw spectral images from the camera. This software optionally corrects the image for the AOTF nonidealities, such as diffraction efficiency variations, spatial nonuniformity, and chromatic aberration, and generates a single multiband image file. Moreover, the software can calculate the reflectance or transmittance of the acquired images. The instrument has been calibrated to give precise and repetitive measurements and has been validated against a high performance point spectrometer. As a case example, the instrument has been successfully used for the mapping of chlorophyll content of plant leaves from their multispectral reflectance images.
Modeling of nanofabricated paddle bridges for resonant mass sensing
Authors: Lobontiu N. , Ilic B. , Garcia E. , Reissman T. , Craighead H. G.
Published: July 2006

The modeling of nanopaddle bridges is studied in this article by proposing a lumped-parameter mathematical model which enables structural characterization in the resonant domain. The distributed compliance and inertia of all three segments composing a paddle bridge are taken into consideration in order to determine the equivalent lumped-parameter stiffness and inertia fractions, and further on the bending and torsion resonant frequencies. The approximate model produces results which are confirmed by finite element analysis and experimental measurements. The model is subsequently utilized to quantify the amount of mass which attaches to the bridge by predicting the modified resonant frequencies in either bending or torsion.
Can microbunch instability on solar flare accelerated electron beams account for bright broadband coherent synchrotron microwaves?
Authors: Kaufmann Pierre , Raulin Jean-Pierre
Published: July 2006

The physical processes producing bright broadband coherent synchrotron radiation (CSR) bursts in laboratory accelerators are proposed to happen also in solar flares, bringing a plausible explanation to serious interpretation constraints raised by the discovery of a solar flare sub-mm-wave spectral emission component peaking in the terahertz (THz) range simultaneous to the well-known microwaves component. The THz component is due to incoherent synchrotron radiation (ISR) produced by a beam of ultrarelativistic electrons. Beam density perturbations, on a scale of the order of or smaller than the emitting wavelength, sets a microbunch instability producing the intense CSR at lower frequencies. Hard x-ray/γ-ray emissions may include a significant synchrotron emission component from the same ISR spectrum, bringing a new possibility to explain the so called “solar flare electron number paradox.”
Quantitative NMR analysis of the protein G B1 domain in
Xenopus laevis
egg extracts and intact oocytes
Authors: Selenko Philipp , Serber Zach , Gadea Bedrick , Ruderman Joan , Wagner Gerhard
Published: July 2006

We introduce a eukaryotic cellular system, the
Xenopus laevis
oocyte, for in-cell NMR analyses of biomolecules at high resolution and delineate the experimental reference conditions for successful implementations of
in vivo
NMR measurements in this cell type. This approach enables quantitative NMR experiments at defined intracellular concentrations of exogenous proteins, which is exemplified by the description of in-cell NMR properties of the protein G B1 domain (GB1). Additional experiments in
Xenopus
egg extracts and artificially crowded
in vitro
solutions suggest that for this biologically inert protein domain, intracellular viscosity and macromolecular crowding dictate its
in vivo
behavior. These contributions appear particularly pronounced for protein regions with high degrees of internal mobility in the pure state. We also evaluate the experimental limitations of this method and discuss potential applications toward the
in situ
structural characterization of eukaryotic cellular activities.
Transcriptional inactivation of a regulatory site for replication of
Vibrio cholerae
chromosome II
Authors: Venkova-Canova Tatiana , Srivastava Preeti , Chattoraj Dhruba K.
Published: July 2006

The bacterium
Vibrio cholerae
has two chromosomes. The origin of replication of chromosome I is similar to that of
Escherichia coli
. The origin-containing region of chromosome II (
oriCII
) resembles replicons of plasmids such as P1, except for the presence of an additional gene,
rctA
[Egan, E. S. & Waldor, M. K. (2003)
Cell
114, 521–530]. The
oriCII
region that includes the initiator gene,
rctB
, can function as a plasmid in
E. coli
. Here we show that RctB suffices for the
oriCII
-based plasmid replication, and
rctA
in cis or trans reduces the plasmid copy number, thereby serving as a negative regulator. The inhibitory activity could be overcome by increasing the concentration of RctB, suggesting that
rctA
titrates the initiator. Purified RctB bound to a DNA fragment carrying
rctA
, confirming that the two can interact. Although
rctA
apparently works as a titrating site, it is nonetheless transcribed. We find that the transcription attenuates the inhibitory activity of the gene, presumably by interfering with RctB binding. RctB, in turn, repressed the
rctA
promoter and, thereby, could control its own titration by modulating the transcription of
rctA
. This control circuit appears to be a putative novel mechanism for homeostasis of initiator availability.
Involvement of Rad18 in somatic hypermutation
Authors: Bachl Jürgen , Ertongur Isin , Jungnickel Berit
Published: July 2006

Somatic hypermutation of Ig genes is initiated by transcription-coupled cytidine deamination in Ig loci. Error-prone processing of the resultant DNA lesions is thought to cause extensive mutagenesis, but it is presently an enigma how and why error-prone rather than error-free repair pathways are recruited. During DNA replication, recruitment of error-prone translesion polymerases may be mediated by Rad6/Rad18-mediated ubiquitination of proliferating cell nuclear antigen, a major switchboard controlling the fidelity of DNA lesion bypass in eukaryotes. By inactivation of Rad18 in the DT40 B cell line, we show that the Rad6 pathway is involved in somatic hypermutation in these cells. Our findings imply that targeted recruitment of mutagenic polymerases by the Rad6 pathway contributes to the complex process of somatic hypermutation and provide a framework for more detailed mechanistic studies of the mutagenesis phase of secondary Ig diversification.
The Congenital Intrahepatic Arterioportal Fistula Syndrome
Authors: Norton Seamus P. , Jacobson Kevan , Moroz Stanley P. , Culham Gordon , Ng Vicky , Turner Justine , John Philip
Published: July 2006

Congenital intrahepatic arterioportal fistula is a rare but treatable cause of portal hypertension for which early recognition may lead to successful radiological management. We report an infant presenting with severe failure to thrive, melena and splenomegaly due to a congenital intrahepatic arterioportal fistula, successfully ablated after multiple trials of superselective transarterial embolization. Comprehensive review of congenital cases provides an understanding of the key clinical features defining this syndrome. A classification system is proposed, upon which treatment decisions may be based.
Functional Fecal Soiling Without Constipation, Organic Cause or Neuropsychiatric Disorders?
Authors: Pakarinen Mikko P. , Koivusalo Antti , Rintala Risto J.
Published: July 2006

Background:

The aetiology of fecal incontinence in children has traditionally been attributed to idiopathic constipation, structural defects or neuropsychiatric disorders. We describe a new subgroup of otherwise healthy children who have fecal soiling without any underlying cause for the incontinence.

Methods:

The hospital records of children with fecal incontinence were screened to detect patients without any history, signs or symptoms of constipation or an organic, neurological or psychiatric cause for the incontinence. Anorectal manometry findings were compared with those of age‐matched children with idiopathic constipation and soiling.

Results:

Eight boys and 5 girls were identified. The median age at diagnosis was 7.9 years. Soiling had lasted median of 4.1 years, occurred at least every other day in 9, at least once a week in 2 and occasionally in 2 and required change of underwear or use of protective pads. Abdominal x‐ray and barium enema showed normal findings. Sacral x‐ray and/or MRI of the spinal cord showed normal bony spine and spinal cord. Five children had coexisting night and/or daytime wetting. Impaired rectal sensation was the only identifiable abnormality that was detected. The median volume required for the first sensation was 45 mL (range, 15‐100 mL; normal, <15 mL). Anorectal manometry alone was unable to differentiate patients with functional fecal soiling from those with idiopathic constipation associated soiling. The median follow‐up time after the diagnosis was 9.1 months. Treatment of fecal soiling consisted of education, dietary modification or stimulatory laxatives to establish regular toileting routines. Treatment improved fecal continence in 6 out of 8 cases with follow‐up longer than 6 months.

Conclusions:

There is a small subgroup of children with fecal soiling who are otherwise healthy without constipation or any other underlying cause for the incontinence. These children seem to have isolated impairment of rectal sensation. In most, the prognosis is good with conservative treatment.
The Role of Pro‐Inflammatory Cytokines in Inflammatory Bowel Disease Growth Retardation
Authors: Wong S.C. , MacRae V.E. , McGrogan P. , Ahmed S.F.
Published: July 2006

Childhood inflammatory bowel disease (IBD) especially those with Crohn disease is commonly complicated by faltering growth and pubertal delay. Pro‐inflammatory cytokines are often elevated in IBD and may affect linear growth and puberty either systemically or at the level of the growth plate. Further study of the underlying mechanisms of the deleterious effects of cytokines on the growth plate may improve management of faltering growth in childhood IBD. Well‐controlled clinical studies of the respective effect of nutritional support, immunomodulatory therapy, biological agents and growth and puberty promoting agents on managing faltering growth also require further attention.
Rhamnose and Rhamnitol in Dual Sugar Permeability Tests
Authors: Malagon Ignacio , Onkenhout Willem , Klok Margreet , van der Poel Petrus F.H. , Bovill James G. , Hazekamp Mark G.
Published: July 2006

Rhamnose is one of the sugars regularly used to conduct the dual sugar permeability test. For more than 30 years, it has been assumed that rhamnose is an inert sugar not metabolized by the human body and only fermented by some colonic bacteria into rhamnulose. While conducting an investigation on gut permeability in children undergoing cardiac surgery, increased concentrations of rhamnitol were found in the urine samples. The present report suggests that rhamnose is not an inert sugar and it is partially metabolized into rhamnitol by the human body.
Serum Leptin and Cytokines in Whole Blood in Relation to Clinical and Nutritional Status in Cystic Fibrosis
Authors: Schmitt‐Grohé Sabina , Hippe Valerie , Igel Michael , von Bergmann Klaus , Posselt Hans G. , Krahl Andreas , Smaczny Christina , Wagner Thomas O.F. , Nikolaizik Wilfried , Lentze Michael J. , Zielen Stefan
Published: July 2006

Objectives:

Leptin plays an important role in the energy balance and may be affected by hormonal and metabolic derangement associated with chronic disease. The aim of this study was to assess the correlation between leptin, proinflammatory cytokines and nutritional status with regard to clinical status in homozygous delta F 508 cystic fibrosis patients.

Methods:

Patients with mild (Shwachman score 71‐100 points, group A) disease were compared with those with moderate disease (Shwachman score 41‐55 points, group B) and age‐matched controls (group C, n = 22). Leptin was assessed by enzyme‐linked immunosorbent assay and cytokines (interleukin‐8, tumor necrosis factor α) before and after stimulation with 5 ng lipopolysaccharide by a chemiluminescent immunometric assay.

Results:

Twenty‐two patients were recruited for each group (median A/B/C forced expiratory volume in 1 second 80%/59%/‐; median age 12/13.5/12.5 years). Leptin (median 3.25/2.65/3.3 pg/mL; P = 0.083) and body mass index were lower (group A/B/C 18.55/16.75/20.5 kg/m2; P = 0.023), but dietary intake was significantly higher (group A/B/C 50.5/68/43 kcal/kg body weight; P = 0.026) in moderate disease. Cytokines before stimulation with lipopolysaccharide were highest in moderate disease, but there was no significant difference after stimulation (interleukin‐8 median A/B/C before‐15/25.1/8.0 pg/mL, P < 0.005; after‐570.5/573.5/415.5 pg/mL, not significant; tumor necrosis factor α median A/B/C 43/56/30 pg/mL, P < 0.0001; 580/427/720.5 pg/mL, not significant.).

Conclusions:

There is a physiological regulation of leptin even in more advanced states of disease with significantly lower body mass index than controls. However, our data do not support the idea of elevated cytokine levels inducing anorexia in homozygous delta F 508 cystic fibrosis patients.