bluuebunny/crossref_metadata_2025 huggingface dataset:
Invading white‐tailed deer change wolf–caribou dynamics in northeastern Alberta
Authors: Latham A. David M. , Latham M. Cecilia , Mccutchen Nicole A. , Boutin Stan
Published: March 2011

Human‐caused habitat change has been implicated in current woodland caribou (Rangifer tarandus caribou) population declines across North America. Increased early seral habitat associated with industrial footprint can result in an increase in ungulate densities and subsequently those of their predator, wolves (Canis lupus). Higher wolf densities can result in increased encounters between wolves and caribou and consequently higher caribou mortality. We contrasted changes in moose (Alces alces) and deer (Odocoileusspp.) densities and assessed their effects on wolf–caribou dynamics in northeastern Alberta, Canada, pre (1994–1997) versus post (2005–2009) major industrial expansion in the region. Observable white‐tailed deer (O. virginianus) increased 17.5‐fold but moose remained unchanged. Wolf numbers also increased from approximately 6–11.5/1,000 km2. Coincident with these changes, spatial overlap between wolf pack territories and caribou range was high relative to the mid‐1990s. The high number of wolf locations in caribou range suggests that forays were not merely exploratory, but rather represented hunting forays and denning locations. Scat analysis indicated that wolf consumption of moose declined substantively during this time period, whereas use of deer increased markedly and deer replaced moose as the primary prey of wolves. Caribou increased 10‐fold in the diet of wolves and caribou population trends in the region changed from stable to declining. Wolf use of beaver (Castor canadensis) increased since the mid‐1990s. We suggest that recent declines in woodland caribou populations in the southerly extent of their range have occurred because high deer densities resulted in a numeric response by wolves and consequently higher incidental predation on caribou. Our results indicate that management actions to conserve caribou must now include deer in primary prey and wolf reduction programs. © 2010 The Wildlife Society
Non‐native species impacts on pond occupancy by an anuran
Authors: Adams Michael J. , Pearl Christopher A. , Galvan Stephanie , Mccreary Brome
Published: March 2011

Non‐native fish and bullfrogs (Lithobates catesbeianus) are frequently cited as contributing to the decline of ranid frogs in the western United States, so we hypothesized that non‐native species, habitat, or a combination of these relate to the probability of local extinction for northern red‐legged frogs (Rana aurora) in Oregon, USA. We also hypothesized that the probability of colonization relates to land use, wetland size, or riparian forest. In a 5‐yr study, we found no support for an effect of non‐native species on northern red‐legged frogs. Instead, probability of local extinction decreased with the extent of emergent vegetation and riparian forest. This finding suggests that managers consider the role of habitat when confronting non‐native species problems. © 2010 The Wildlife Society.
Response of timber rattlesnakes to commercial logging operations
Authors: Reinert Howard K. , Munroe William F. , Brennan Curt E. , Rach Matthew N. , Pelesky Samuel , Bushar Lauretta M.
Published: March 2011

Forest management practices in the eastern United States directly impact large parcels of land that serve as habitat for timber rattlesnakes (Crotalus horridus). We assessed the behavioral response of timber rattlesnakes to commercial logging activities and the impact of such activities on a timber rattlesnake population in northcentral Pennsylvania. We radiotelemetrically monitored 67 individual snakes over periods of up to 4 years, marked and recaptured 306 snakes, and conducted search and survey efforts before, during, and after commercial logging operations on 3 timber sale parcels (totaling 154.2 ha). Location and timing of timber sales created the maximum opportunity for interaction of snakes with logging operations and with altered habitat. Observed logging‐related mortality of snakes was low (<2% of the population/yr), but potential mortality could have reached 7%. Logging activity and resulting habitat changes did not alter behavior or movement patterns of telemetrically monitored snakes. Snakes with established activity ranges in timber sale areas continued to use these areas both during and after logging operations. Similarly, snakes with activity patterns that did not include timber sale areas did not alter their movement patterns to include such sites in the short‐term. Timbering increased structural diversity of the habitat and, concurrently, diversity of habitat used by timber rattlesnakes increased. Our results suggest that the opportunity exists to develop forest management practices that provide timber products while limiting impacts on behavior and habitat use of timber rattlesnakes. To further reduce impacts to timber rattlesnake populations we recommend that management agencies require commercial logging contractors, sub‐contractors, and field employees to adhere strictly to a policy that prohibits the intentional killing of rattlesnakes encountered during logging activities. © 2010 The Wildlife Society.
Managing up the generational ladder
Authors: Johnson Larry , Johnson Meagan
Published: March 2011

As Boomers postpone retirement, many Gen X and Gen Y leaders find themselves in the awkward position of managing people who are older and have much more experience. The Johnsons—a father‐and‐daughter team—offer four keys to younger leaders on working well with their older counterparts.
General treatment of a kinetic scheme with chain length dependent termination
Authors: Oskar Friedrich Olaj , Zifferer Gerhard
Published: March 2011

Without making reference to any special type of the dependence of the rate constant of bimolecular termination kt (m,n) on the chain lengths (m and n) of the two radicals involved universal relations are derived between the basic quantities characteristic of the polymerization kinetics of such a system. In case kt (m,n) can be factorized simple expressions may be obtained also if termination is by recombination. These universal relationships have been successfully tested for a power, law dependence of kt on various means m̄,n̄, kt = kt °(m̄,n̄)−b. Their use provides comfortable access to resolving the kinetic scheme. Thus, for the geometric mean, m̄,n̄ = √mn, in its long chain approximation a complete resolution of a kinetic scheme including chain transfer could be worked out, which is free from any further assumptions. In addition, the numeric results obtained for various means m̄,n̄ are discussed and analyzed with respect to the possibility of obtaining experimental information on which type of mean m̄,n̄ is operative in the bimolecular termination process of free radical polymerization. In a further effort it is shown for some selected examples that any individual functional dependence of kt on m and n will coincide with that for the apparent (i.e. experimentally detectable) termination constant on (average) degree of polymerization of dead polymer, k̄t (P̄), as long as kt is a continuous and monotonous function of m and n.
Initiators of cationic polymerization of olefins arising from interaction between two lewis acids
Authors: Marek M. , Pecka J. , Halaška V.
Published: March 2011

By an interaction between two relatively weak Lewis acids, highly effective initiators of the cationic polymerization of olefins are obtained. Under conditions where the polymerization of isobutylene with BCl3, TiCl4 or VOCl3 does not proceed in methylene chloride or heptane solution, it can be initiated with a small or even trace quantity of FeCl3. The formation of complex compounds was investigated by UV spectroscopy and by the conductometric titration in methylene chloride. Hydrogen chloride, which has no co‐initiation effect on polymerization in heptane solution initiated with metal halides alone, is an effective co‐initiator in a mixture of Lewis acids containing a small quantity of FeCl3. The results support a hypothesis regarding the initiation of polymerization of olefins by cations of metal halides arising by the ionization of a weaker acid with a stronger one.
Some reactions of polymers
Authors: Bevington John C. , Thorpe F. Gordon
Published: March 2011

Three topics are discussed. First, structural irregularities are considered in connection with polyformaldehyde,. poly(vinyl chloride) and poly(vinyl acetate) and with the stabilities of polymers in general. The second topic concerns the distribution of sites of reaction when polymers are modified chemically. The final section deals briefly with polymeric reagents, including some designed for photochemical systems.
A modified method for the acid hydrolysis of grafted cellulose
Authors: Fernández M. J. , Casinos I. , Guzmán G. M.
Published: March 2011

The hydrolytic method using 72% sulphuric acid was modified in order to characterize the graft copolymer cellulose‐g‐poly(vinyl acetate‐co‐methyl acrylate). This method involves appropriate cellulose hydrolysis conditions, and the extraction of a fraction of cellulose only when the samples have a low ratio of synthetic polymer to cellulose. In this way, an undesired chemical transformation of the grafted chains is avoided and the polysaccharide is completely removed from the synthetic polymer. This method might be extended to other cellulosic graft copolymers whose carbohydrate part cannot be completely separated and their grafted chains are labile in the reaction conditions reported in the literature.
The kinetics of the cyclodehydration reaction of polyhydrazides
Authors: Gebben B. , Mulder M. H. V. , Smolders C. A.
Published: March 2011

The kinetics of the thermal cyclodehydration reaction of poly‐(1, 3‐phenyl‐1, 4‐phenyl)‐hydrazidea) to poly‐(1, 3‐phenyl‐1, 4‐phenyl)‐oxadiazoleb) have been studied by thermo‐gravimetrical analyses. Both an isothermal method and the non‐isothermal Ozawa method have been used to evaluate the kinetic parameters. The kinetics seem to depend upon the physical state of the polymer i.e. the rubbery or glassy state. During isothermal conversions at elevated temperatures the polymer is expected to be initially in its rubbery state followed by a rubber‐glass transition showing a considerable transition in the observed kinetics. The results obtained from the non‐isothermal Ozawa method and the isothermal method agreed well for the polymer in its glassy state. With the non‐isothermal method the process can be followed as a function of the degree of conversion. In this way a parallel reaction could be observed which starts at the end of the conversion process. The morphological state or the history of the polymer seems to have a considerable influence on the kinetics. The film form of the polymer shows a much higher conversion rate than the powder form.
Etude par diffusion Raman de la transition ferro‐paraelectrique dans les copolymeres de fluorure de vinylidene et de trifluorethylene p(VF2‐TrFE)
Authors: Abénoza Michel , Armengaud Alain , Chouh Saíd
Published: March 2011

The ferro‐paraelectric transition in the 80/20 and 70/30 mol/mol copolymer of vinylidene fluoride and trifluoroethylene is studied by Raman spectroscopy. The Curie transition temperature is depending on the composition and the orientation of the material. At the transition drastic modifications occur in the observed Raman spectra: vanishing of the 842, 1300 and 1350 cm−1 Raman band intensities; strong variation of the band polarizations, this change being not completely reversible when lowering the temperature.

This study shows that the Raman spectra evolution is consistent with a conformational change between the extended “all trans” form and a rich gauche‐sequence configuration. Moreover, polarization changes along the studied temperature cycle show that the paraelectric phase is highly disordered and that after the cycle is carried out a part of this chain disorientation remains in the ferroelectric phase.
Molecular order in poly(3‐tert‐butyloxetane)
Authors: Bello A. , Pérez E. , Fatou J. G.
Published: March 2011

The properties of poly(3‐tert‐butyloxetane), an asymmetric polymer obtained by ring‐opening polymerization of the corresponding oxetane, have been studied. Although the solution NMR spectrum shows that the polymer is atactic, well‐defined melting endotherms and sharp X‐ray diffraction peaks were obtained. From these studies, the equilibrium melting temperature and the enthalpy of fusion are estimated.
Experimental and theoretical data on excluded volume effect of ultrahigh‐molecular‐weight polymethacrylates
Authors: Simionescu Cristofor I. , Ioan Silvia , Simionescu Bogdan C.
Published: March 2011

A comparison of theoretical predictions on excluded volume effect with experimental data for ultrahigh‐molecular‐weight polymethacrylates in dilute solutions is presented. The excluded volume parameter Z, determined on the basis of different theoretical expressions, has high values. The analysis of the validity criteria of the theories on the excluded volume effect and of the experimental data for the expansion factor shows that for magnified image, the experimental data for Z and for the interpenetration function φ (Z) are in good agreement with those predicted by the Kurata‐Yamakawa‐Tanake theory and in an even closer agreement with those of the Douglas‐and‐Freed theory.
Transitions and relaxations in amorphous polymers
Authors: Cebeillac P. , Chatain D. , Megret C. , Lacabanne C. , Bernes A. , Dupuis P.
Published: March 2011

In amorphous homopolymers, the relaxation modes observed by Thermally Stimulated Current (TSC) around and above the glass transition (Tg) have common features:

– The TSC peak isolated around Tg is constituted of elementary processes characterized by relaxation times obeying an Arrhenius equation. Moreover, the activation enthalpies and entropies follow a compensation law. This mode is the dielectric manifestation of the glass transition.

Since the polarization can be taken as order parameter, the width of the distribution of the relaxation time characterizes the distribution of the local order.

Data obtained on polystyrenes with various orientation show the relationship between order parameter and orientation.

The TSC peak observed some 50 °C above Tg is characterized by relaxation times well described by the Fulcher‐Vogel equation. This mode has been associated with the dielectric manifestation of the liquid‐liquid transition (Tll) observed by other non‐flow techniques such as adiabatic or differential scanning calorimetry. This transition is missing in chemical or physical networks.

In amorphous copolymers, polymerization conditions play a key role on the relaxation spectra. A comparative study of butyl acrylate/styrene has been done.

– The semicontinuous introduction of monomers gives relatively homogeneous statistical copolymers, with a DSC trace analogous with the one of a monophasic polymer. The TSC study confirms this result. Indeed, the TSC peak observed around Tg, is constituted of elementary processes following a single compensation law.

The introduction by steps of monomers leads to a block copolymer, with a broad transition region on a DSC thermogram. Two TSC peaks are observed in the same temperature region. Their fine structure shows the existence of two compensation phenomena and so, confirms the presence of two well‐resolved mechanisms. These results are coherent with the existence of a core shell structure.
Relaxations and molecular motions in the glass‐transition region of glassy polymers
Authors: Colmenero J. , Alegría A. , Del Val J. J. , Alberdi J. M.
Published: March 2011

Different kinds of relaxation techniques as both mechanical and dielectric spectroscopies (DMTA and DETA), as well as Thermally Stimulated Depolarization Current (TSDC) have been used in this work in order to study the temperature behaviour of the main time scales for relaxation around the glass‐transition of several glass‐forming polymeric systems. The results obtained show that both mechanical and dielectric relaxation times behave in a similar way with the temperature. Moreover, there is a crossover from a Vogel‐Fulcher behaviour (above the glass‐transition) to an Arrhenius‐like behaviour (glassy zone) for all the polymers investigated. This universal behaviour has been interpreted in the frame of a kinetic free volume model previously proposed by some of the authors. A possible extension of the model which would allow to introduce the effects of a distribution of the relaxation times is also outlined here. Finally, the new α'‐relaxation which has been recently detected at temperatures just below the glass‐transition in both, several glassy polymers and metallic glasses, can be understood in the frame of such an extended model, at least qualitatively.
Parameter estimation in emulsion copolymerization
Authors: De La Cal José C. , Adams Mary E. , Asua José M.
Published: March 2011

An approach for the estimation of kinetic parameters in emulsion copolymerization systems is presented. This approach is based on an algorithm for parameter estimation in differential equations and uses the time evolution of the conversions of the monomers in chemically initiated seeded emulsion copolymerizations. The approach is used to estimate the kinetic parameters of a mathematical model useful for predictive work. This mathematical model includes material balances for the monomers, population balances for particles containing i radicals and the free radical balance in the aqueous phase. Analysis of the variability of the parameters of the model during polymerization showed changes as large as 18% in the values of the parameters. These values were mainly due to changes in the particle size rather than to a shift in the composition of the reaction mixture. Combination of the present approach with methods for both parameter estimation in emulsion homopolymerization and estimation of reactivity ratios in emulsion copolymerization systems allows a reasonable good estimation of these varying kinetic parameters as constant parameters. Additionally, it was found that when the dependence of the parameters on the particle size was included in the estimation process, the parameters of the model were accurately estimated.
Miniemulsion copolymerization of styrene‐methyl methacrylate: Effect of transport phenomena
Authors: Asua J. M. , Rodriguez V. S. , Silebi C. A. , El‐Aasser M. S.
Published: March 2011

The mechanisms of mass transfer between miniemulsion droplets and polymer particles in the miniemulsion copolymerization of styrene‐methyl methacrylate were studied. A mathematical model was developed for the process. This model includes the mass transfer of highly water‐insoluble compounds from miniemulsion droplets to polymer particles by both molecular diffusion and collision between droplets and particles. According to previous results, the concentration of the monomers in the different phases were assumed to be under thermodynamic equilibrium. Both homogeneous nucleation and heterogeneous nucleation were accounted for. The mathematical model also includes the calculation of the average number of radicals per particle when a mixture of oil‐soluble initiator and water‐soluble initiator was used. This model was used to analyze a previously reported experimental result of seeded copolymerizations carried out in the presence of miniemulsion droplets containing a water‐insoluble inhibitor at different stirring speeds. The simulation results indicated that at 30 rpm, about 66% of the mass transfer of the highly water‐insoluble inhibitor occurred by diffusion and the rest by collision. On the other hand, at 120 rpm only about 20% of the inhibitor's mass transfer was by molecular diffusion, whereas 80% occurred by collision.
Film formation: Aspects on the coaleschence of latex particles
Authors: Leonardo Rios‐Guerrero
Published: March 2011

The mechanism of the formation of a latex film is discussed. Two opposite sets of forces may simultaneously act during water evaporation:

To produce coalescence: Interfacial tension (Fs), Capillary forces (Fc), Van der Waals attraction forces (Fv), Force of gravity (Fg), Thermodynamic forces (Ft), Potential energy to surpass the maximum of repulsion energy (Fw).

To prevent coalescence:

Electrostatic or steric repulsion forces between the polymer paricles (Fe), Particle resistance to deformation (Fve).

A general expression to predict latex film formation is deduced when forces to produce coalescence are higher than the forces to prevent it:
Cationic ring‐opening polymerization of lactones in the presence of alcohol
Authors: Okamoto Yoshihisa
Published: March 2011

Cationic ring‐opening polymerization of e‐caprolactone using triethyloxonium hexafluorophosphate initiator in the presence of alcohol to produce low molecular weight polyester glycol was examined. The polymerization proceeded by an activated monomer mechanism; thus the polymer molecular weight increased directly with the monomer conversion. Polymerization of lactones other than ϵ‐caprolactone were also examined, and the overall rate of polymerization was in the order δ‐valerolactone> ϵ‐caprolactone>> β‐butyrolactone> diketene> γ‐butyrolactone.
Ring‐opening polymerization and copolymerization of cyclic carbonates
Authors: Höcker H. , Keul H. , Kuhllng S. , Hovestadt W.
Published: March 2011

The anionic ring‐opening polymerization may result in a broad variety of homo‐ and copolycarbonates. Upon suitable selection of monomers, polymers with functional groups may be obtained which are eligible to cross‐linking reactions or exert a high degree of hydrophilicity. Copolymers with lactones are readily obtained, provided both polymerization reactions follow the same mechanism; the ring‐opening polymerization of cyclic carbonates is exclusively initiated by alcoholate ions and not by carboxylate anions. Since butyllithium is a suitable Initiator for the ring‐opening anionic polymerization of cyclic carbonates, living vinyl polymers may be used as initiators as well to obtain the respective blockcopolymers. Instead of living vinyl polymers obtained in the conventional manner, using carbanionic Initiators, also living polymers obtained by group transfer polymerization may be used as initiators for the ring‐opening polymerization of cyclic carbonates; the mechanism for the latter polymerization, however, then is rather a non‐metallic anionic one than a group transfer mechanism.
Anionic ring‐opening polymerization of cyclotetrasilanes
Authors: Matyjaszewski Krzysztof
Published: March 2011

Various cyclopolysilanes are discussed as potential monomers for the ring‐opening polymerization in terms of reactivity and thermodynamic feasibility. Strained and polymerizable 1,2,3,4‐tetramethyl‐1,2,3,4‐tetraphenylcyclotetrasilanes (1) are prepared from octaphenylcyclotetrasilane by substitution of four phenyl groups with triflate groups using triflic acid, and followed by displacement of triflate groups by methyl substituents using methylmagnesium bromide. Anionic ring‐opening polymerization of a mixture of stereoisomers of (1) provides poly(methylphenylsilylene) with molecular weights up to M=100 000. Anionic polymerization of 1 was initiated by butyllithium and silylpotassium initiators with and without cryptands. Strong solvent effects on polymerization and subsequent cyclization were observed.
The reactivity‐selectivity principle in polymerization. The case of polymerization of ϵ‐caprolactone
Authors: Penczek Stanislaw , Duda Andrzej , Slomkowski Stanislaw
Published: March 2011

Anionic and pseudoanionic polymerizations of ϵ‐caprolactone (CL) have been compared in terms of the principle relating reactivity with selectivity (reactivity‐selectivity principle, RSP). RSP can be formulated as follows: there are two reagents X and Y; reagent X reacts faster with substrates A and B than reagent Y does (i.e. kxa>kya and kxb>kyb, where kxa, kya, kxb and kyb are the respective rate constants); moreover, reactions with A are faster than reactions with B (i.e. kxa>kxb and kya>kyb); finally, if RSP is operative the inequality kya/kyb>kxa/kxb holds. Comparison of the anionic and pseudoanionic polymerizations of CL reveals that this system conforms to the RSP. Propagation on the …‐O−Na+ ion pairs proceeds much faster than on the …−OAIR2 covalent species (kp∓ = 1,7 l/mol · s vs kpc = 3,0 · 10−2 l/mol · s, THF solvent, 20°C). Propagation is accompanied by transesterification and cyclization. Formation of the cyclic dimer (with the rate constant kb (2)) was taken as a measure of an extent of these “side” reactions. Following selectivity coefficients ß = kp/kb(2) have been measured (in l/mol): 1, 55 · 103 (…−O−Na+), 4, 6 · 104 (…‐OAl(C2H5)2), and 7,7 · 104 (…−OAl(i‐C4H9)2). Thus, kpc/kbc(2)>kp∓/kb∓(2). Therefore formation of the linear, high molar mass polymer is more pronounced in the system with the less reactive active centers.
Studies on the mechanism of amine‐catalyzed cyclic oligomeric carbonate formation
Authors: Brunelle Daniel J. , Boden Eugene P.
Published: March 2011

A mechanism for the selective formation of cyclic oligomeric carbonates via triethylamine‐catalyzed, pseudo‐high dilution hydrolysis/‐condensation of bisphenol A‐bischloroformate is proposed. The mechanism is based on results of model and cyclization reactions using amines of various structure. Intermediacy of an acyl ammonium salt is invoked for both hydrolysis and condensation reactions. An oligomeric carbonate with a phenoxide on one end and an acyl ammonium salt on the other end is proposed as the immediate precursor to a cyclic oligomer.
Application of fluorescence quenching techniques to the study of emulsion polymerization and latex characterization
Authors: Winnik Mitchell A. , Xu Huilin , Satguru R.
Published: March 2011

We investigate two aspects of emulsion polymerization through fluorescence studies of models of those processes. The first is the uptake of monomer by seed latex using poly(butyl methacrylate) (PBMA) seeds labeled with phenanthrene (Phe) groups. Nitroalkanes serve as models for the monomer. Data analysis gives the partition coefficients and the diffusion coefficients (D) of monomer inside the latex (D = 6 × 10−8cm2s−1). The second aspect involves the generation of core‐shell structures in poly(methyl methacrylate) (PMMA) latex where the Phe‐labeled seed is treated, during the second stage polymerization, with additional MMA plus a polymerizable anthracene (An) derivative. The extent of Phe to An energy transfer in the final latex measures the amount of mixing of added monomer during the second stage polymerization.
Influence of components and interface conditions on mechanical properties of composites and blends
Authors: Pegoraro M. , Di Landro L.
Published: March 2011

Filler‐matrix adhesion, particularly in case of thermoplastic matrices, is influenced by the presence of residual stresses due to the cooling of the material from the processing temperature to the final temperature (usually room temperature). A model for the evaluation of thermal stresses in fibre composites at the fibre level is presented which, starting from relationships valid in case of purely elastic components, extends the analysis to account for the matrix viscoelasticity. A Master Curve is needed for this purpose.

Thermal stresses around a single fibre are thus evaluated as a function of the final temperature and of the cooling rate of the composite. Fibre matrix adhesion at different temperatures was measured by the single fibre composite method applied to polyetherimide matrix/carbon fibre composites and the results are related to the calculated residual stresses.

The relationship between filler‐matrix adhesion efficiency and mechanical (tensile and impact) strength of spherical particle filled composites is also discussed.
Chemical approaches to oriented protein immobilization
Authors: Voivodov Kamen , Chan Wai‐Han , Scouten William
Published: March 2011

A procedure has been developed for converting 1,1′‐carbonyldiimidazole‐modified agarose to activated agarose capable of coupling protein in an oriented fashion. This procedure is based on replacing the imidazole groups with orthonitrophenyl derivatives containing ionic and/or hydrophobic groups. The degree of orientation of immobilized chymotrypsin and trypsin was estimated by comparing the activity of both proteases toward low‐ and high‐molecular‐weight substrates. The differences in these activities were greater in the case of enzymes immobilized on agarose gel containing hydrophobic activating agents such as 4‐hydroxy‐3‐nitrobenzophenone and 2‐nitro‐4‐benzylphenol than in those immobilized on gels containing ionic activating agents.
Structure elucidation and NMR assignments of two new triterpenoids from the stems of Paragonia pyramidata (Bignoniaceae)
Authors: Wang Xiao‐Ling , Hay Anne‐Emmanuelle , Matheeussen An , Gupta Mahabir P. , Hostettmann Kurt
Published: March 2011

Phytochemical investigation of dichloromethane (DCM) extract from the stems of Paragonia pyramidata var. pyramidata L. Rich. (Bur.) resulted in the isolation and characterization of two new triterpenoids 3β,19β‐dihydroxylup‐12, 20(29)‐diene‐28‐oic acid (1) and 3β,19β‐dihydroxylup‐12‐en‐28‐oic acid (2), three known triterpenoids lupeol (3), spinosic acid A (4) and oleanolic acid (5), together with four known steroids (20R)‐22E‐24‐ethylcholesta‐4,22‐dien‐3‐one (6), (20R)‐24‐ethylcholest‐4‐en‐3‐one (7), stigmasterol (8) and β‐sitosterol (9). HREIMS, GC–MS and NMR experiments including HSQC, HMBC, COSY and NOESY were used for the determination of the structures and NMR spectral assignments. This is the first report about the chemical constituents for this plant. Copyright © 2011 John Wiley & Sons, Ltd.
Studies of some monocyclic and bicyclic arylacetonitriles
Authors: Manimekalai A. , Balamurugan A.
Published: March 2011

The high‐resolution 1H, 13C, 1H1H COSY and 1H13C COSY NMR spectra have been recorded in CDCl3 for arylacetonitriles 1–12 and analyzed. The arylacetonitriles 3–7 exist in two isomeric forms E (methyl group is anti to cyano group) and Z (the methyl group is syn to cyano group) in solution. Normal chair conformation with equatorial orientations of phenyl rings at C‐2 and C‐6 for monocyclic nitriles 1 and 2, epimeric chair structure EC (axial configuration of methyl group at C‐3) for both the E and Z isomers of arylacetonitrile derivatives (3–7) and a distorted boat form, B3, for the N‐acylacetonitrile derivatives (8–10) have been proposed based on NMR data. The bicyclic nitriles 11 and 12 exist in twin chair conformations in solution. DFT calculations and chemical shifts also support these conformations. Geometry optimizations for 1–12 were carried out according to density functional theory using B3LYP/6‐31G(d,p) basis set and for 1 and 8 the theoretical geometrical parameters have been compared with those of single crystal measurements. Copyright © 2011 John Wiley & Sons, Ltd.
1H, 13C and 15N NMR spectral assignments of adenosine derivatives with different amino substituents at C6‐position
Authors: Casati Silvana , Manzocchi Ada , Ottria Roberta , Ciuffreda Pierangela
Published: March 2011

The complete 1H, 13C and 15N NMR signals assignment of adenosine derivatives differently substituted at C6‐position was achieved using one‐ and two‐dimensional experiments (gs‐COSY, gs‐NOESY, gs‐HSQC and gs‐HMBC). Copyright © 2011 John Wiley & Sons, Ltd.
TROMBONE: T1‐relaxation‐oblivious mapping of transmit radio‐frequency field (B1) for MRI at high magnetic fields
Authors: Fleysher Roman , Fleysher Lazar , Inglese Matilde , Sodickson Daniel
Published: March 2011

Fast, 3D radio‐frequency transmit field (B1) mapping is important for parallel transmission, spatially selective pulse design and quantitative MRI applications. It has been shown that actual flip angle imaging—two interleaved spoiled gradient recalled echo images acquired in steady state with two very short time delays (TR1, TR2)—is an attractive method of B1 mapping. Herein, we describe the TROMBONE method that efficiently integrates actual flip angle imaging with EPI imaging, alleviates very short TR requirement of actual flip angle imaging and through their synergy yields up to 16 times higher precision in B1 estimation in the same experimental time. High precision of TROMBONE can be traded for faster scans. The map of B1 reconstructed from the ratio of intensities of two images is insensitive to longitudinal relaxation time (T1) in the physiologically relevant range. A table of the optimal acquisition protocol parameters for various target experimental conditions is provided. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Quantitative mapping of T2 using partial spoiling
Authors: Bieri Oliver , Scheffler Klaus , Welsch Goetz H. , Trattnig S. , Mamisch Tallal C. , Ganter Carl
Published: March 2011

Fast quantitative MRI has become an important tool for biochemical characterization of tissue beyond conventional T1, T2, and T2*‐weighted imaging. As a result, steady‐state free precession (SSFP) techniques have attracted increased interest, and several methods have been developed for rapid quantification of relaxation times using steady‐state free precession. In this work, a new and fast approach for T2 mapping is introduced based on partial RF spoiling of nonbalanced steady‐state free precession. The new T2 mapping technique is evaluated and optimized from simulations, and in vivo results are presented for human brain at 1.5 T and for human articular cartilage at 3.0 T. The range of T2 for gray and white matter was from 60 msec (for the corpus callosum) to 100 msec (for cortical gray matter). For cartilage, spatial variation in T2 was observed between deep (34 msec) and superficial (48 msec) layers, as well as between tibial (33 msec), femoral, (54 msec) and patellar (43 msec) cartilage. Excellent correspondence between T2 values derived from partially spoiled SSFP scans and the ones found with a reference multicontrast spin‐echo technique is observed, corroborating the accuracy of the new method for proper T2 mapping. Finally, the feasibility of a fast high‐resolution quantitative partially spoiled SSFP T2 scan is demonstrated at 7.0 T for human patellar cartilage. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Measurement of glycine in the human brain in vivo by 1H‐MRS at 3 T: application in brain tumors
Authors: Choi Changho , Ganji Sandeep K. , DeBerardinis Ralph J. , Dimitrov Ivan E. , Pascual Juan M. , Bachoo Robert , Mickey Bruce E. , Malloy Craig R. , Maher Elizabeth A.
Published: March 2011

Glycine is a key metabolic intermediate required for the synthesis of proteins, nucleic acids, and other molecules, and its detection in cancer could, therefore, provide biologically relevant information about the growth of the tumor. Here, we report measurement of glycine in human brain and gliomas by an optimized point‐resolved spectroscopy sequence at 3 T. Echo time dependence of the major obstacle, myo‐inositol (mI) multiplet, was investigated with numerical simulations, incorporating the 3D volume localization. The simulations indicated that a subecho pair (TE1, TE2) = (60, 100) ms permits detection of both glycine and mI with optimum selectivity. In vivo validation of the optimized point‐resolved spectroscopy was conducted on the right parietal cortex of five healthy volunteers. Metabolite signals estimated from LCModel were normalized with respect to the brain water signal, and the concentrations were evaluated assuming the total creatine concentration at 8 mM. The glycine concentration was estimated as 0.6 ± 0.1 mM (mean ± SD, n = 5), with a mean Cramér‐Rao lower bound of 9 ± 1%. The point‐resolved spectroscopy sequence was applied to measure the glycine levels in patients with glioblastoma multiforme. Metabolite concentrations were obtained using the water signal from the tumor mass. The study revealed that a subset of human gliomas contains glycine levels elevated 1.5–8 fold relative to normal. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Diffusion characteristics associated with neuronal injury and glial activation following hypoxia‐ischemia in the immature brain
Authors: Lodygensky Gregory A. , West Tim , Moravec Matthew D. , Back Stephen A. , Dikranian Krikor , Holtzman David M. , Neil Jeffrey J.
Published: March 2011

To identify quantitative MRI indices of injury in the brain following neonatal hypoxic‐ischemic brain injury, we subjected mouse pups to hypoxia‐ischemia on postnatal day 7 and obtained conventional and diffusion‐weighted in vivo images of the brain 24 h later followed by histological assessment. T2‐weighted images showed increased signal intensity in the CA1 and CA2 regions of the hippocampus ipsilateral to the injury and adjacent white matter. In contrast, diffusion imaging showed reduced apparent diffusion coefficient (ADC) values in CA1 and CA2, but increased values in the adjacent white matter. Histological analysis showed widespread gliosis with degenerating oligodendrocytes in the ipsilateral hippocampus. In addition, white matter areas that were abnormal by MRI showed an increase in the number of activated microglia (CD45 positive cells). Activated caspase‐3 immunostaining showed a marked increase in neurons in the hippocampal regions corresponding to those with reduced ADC, and a quantitative measure of staining showed a statistically significant correlation with the ADC. In contrast, ADC was higher in adjacent white matter, where histology showed activation of microglia and reactive oligodendrocytes but not caspase‐3 activation. These results suggest that the ADC response differs between areas of neuronal injury as compared with those showing glial changes without marked cell death. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
A measurement setup for direct 17O MRI at 7 T
Authors: Hoffmann Stefan H. , Begovatz Paul , Nagel Armin M. , Umathum Reiner , Schommer Kai , Bachert Peter , Bock Michael
Published: March 2011

An efficient breathing system was designed for direct 17O MRI to perform oxygen metabolism studies of the human brain. The breathing system consists of a demand oxygen delivery device for 17O2 supply and a custom‐built re‐breathing circuit with pneumatic switching valve. To efficiently deliver the 17O gas to the alveoli of the lungs, the system applies short gas pulses upon an inspiration trigger via a nasal cannula. During and after 17O2 administration, the exhaled gas volumes are stored and filtered in the re‐breathing section to make the most efficient use of the rare 17O gas. In an inhalation experiment, 2.2 ± 0.1 L of 70%‐enriched 17O2 were administered to a healthy volunteer and direct 17O MRI was performed for a total imaging time of 38 min with a temporal resolution of 50 s per 3D data set. Mapping of the maximum signal increase was carried out showing regional variations of oxygen concentration of up to 30% over the natural abundance of 17O water. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
k‐t group sparse: A method for accelerating dynamic MRI
Authors: Usman M. , Prieto C. , Schaeffter T. , Batchelor P. G.
Published: March 2011

Compressed sensing (CS) is a data‐reduction technique that has been applied to speed up the acquisition in MRI. However, the use of this technique in dynamic MR applications has been limited in terms of the maximum achievable reduction factor. In general, noise‐like artefacts and bad temporal fidelity are visible in standard CS MRI reconstructions when high reduction factors are used. To increase the maximum achievable reduction factor, additional or prior information can be incorporated in the CS reconstruction. Here, a novel CS reconstruction method is proposed that exploits the structure within the sparse representation of a signal by enforcing the support components to be in the form of groups. These groups act like a constraint in the reconstruction. The information about the support region can be easily obtained from training data in dynamic MRI acquisitions. The proposed approach was tested in two‐dimensional cardiac cine MRI with both downsampled and undersampled data. Results show that higher acceleration factors (up to 9‐fold), with improved spatial and temporal quality, can be obtained with the proposed approach in comparison to the standard CS reconstructions. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Imaging pH and metastasis
Authors: Hashim Arig Ibrahim , Zhang Xiaomeng , Wojtkowiak Jonathan W. , Martinez Gary V. , Gillies Robert J.
Published: March 2011

Metastasis is a multistep process that culminates in the spread of cells from a primary tumor to a distant site or organs. For tumor cells to be able to metastasize, they have to locally invade through basement membrane into the lymphatic and the blood vasculatures. Eventually they extravasate from the blood and colonize in the secondary organ. This process involves multiple interactions between the tumor cells and their microenvironments. The microenvironment surrounding tumors has a significant impact on tumor development and progression. A key factor in the microenvironment is an acidic pH. The extracellular pH of solid tumors is more acidic in comparison to normal tissue as a consequence of high glycolysis and poor perfusion. It plays an important role in almost all steps of metastasis. The past decades have seen development of technologies to non‐invasively measure intra‐ and/or extracellular pH. Most successful measurements are MR‐based, and sensitivity and accuracy have dramatically improved. Quantitatively imaging the distribution of acidity helps us understand the role of the tumor microenvironment in cancer progression. The present review discusses different MR methods in measuring tumor pH along with emphasizing the importance of extracelluar tumor low pH on different steps of metastasis; more specifically focusing on epithelial‐to‐mesenchymal transition (EMT), and anti cancer immunity. Copyright © 2011 John Wiley & Sons, Ltd.
Determining the in vivo regulation of cardiac pyruvate dehydrogenase based on label flux from hyperpolarised [1‐13C]pyruvate
Authors: Schroeder Marie A. , Atherton Helen J. , Heather Lisa C. , Griffin Julian L. , Clarke Kieran , Radda George K. , Tyler Damian J.
Published: March 2011

Pyruvate dehydrogenase (PDH) is a key regulator of cardiac substrate selection and is regulated by both pyruvate dehydrogenase kinase (PDK)‐mediated phosphorylation and feedback inhibition. The extent to which chronic upregulation of PDK protein levels, acutely increased PDK activity and acute feedback inhibition limit PDH flux remains unclear because existing in vitro assessment methods inherently disrupt the regulation of the enzyme complex. We have demonstrated previously that hyperpolarised 13C‐labelled metabolic tracers coupled with MRS can monitor flux through PDH in vivo. The aim of this study was to determine the relative contributions of acute and chronic changes in PDK and PDH activities to in vivo myocardial PDH flux. We examined both fed and fasted rats with either hyperpolarised [1‐13C]pyruvate alone or hyperpolarised [1‐13C]pyruvate co‐infused with malate [to modulate mitochondrial nicotinamide adenine dinucleotide (NADH/NAD+) and acetyl‐coenzyme A (acetyl‐CoA)/CoA ratios, which alter both PDH activity and flux]. To confirm the metabolic fate of infused malate, we performed in vitro 1H NMR spectroscopy on cardiac tissue extracts. We observed that, in fed rats, where PDH activity was high, the presence of malate increased PDH flux by 27%, whereas, in the fasted state, malate infusion had no effect on PDH flux. These observations suggest that pyruvate oxidation is limited by feedback inhibition from acetyl‐CoA only when PDH activity is high. Therefore, in the case of PDH, and potentially other enzymes, hyperpolarised 13C MRI can be used to assess noninvasively enzymatic regulation. Copyright © 2011 John Wiley & Sons, Ltd.
Assessment of glycosaminoglycan distribution in human lumbar intervertebral discs using chemical exchange saturation transfer at 3 T: feasibility and initial experience
Authors: Kim Mina , Chan Queenie , Anthony Marina‐Portia , Cheung Kenneth M.C. , Samartzis Dino , Khong Pek‐Lan
Published: March 2011

Recent studies have proposed that glycosaminoglycan chemical exchange saturation transfer (gagCEST) is associated with a loss of glycosaminoglycans (GAGs), which may be an initiating factor in intervertebral disc (IVD) degeneration. Despite its promising potential, this application has not been reported in human in vivo IVD studies because of the challenges of B0 magnetic field inhomogeneity in gagCEST. This study aimed to evaluate the feasibility of quantifying CEST values in IVDs of healthy volunteers using a clinical 3 T scanner. A single‐slice turbo spin echo sequence was used to quantify the CEST effect in various GAG phantoms and in IVDs of 12 volunteers. The phantom results indicated high correlation between gagCEST and GAG concentrations (R2 = 0.95). With optimal B0 inhomogeneity correction, in vivo CEST maps of IVDs showed robust contrast between the nucleus pulposus (NP) and the annulus fibrosus (AF) (p < 0.01), as well as higher signal in the central relative to the peripheral NP. In addition, a trend of decreasing CEST values from upper to lower disc levels was evident in NP. Our results demonstrate that in vivo gagCEST quantification in human lumbar IVDs is feasible at 3 T in combination with successful B0 inhomogeneity correction, but without significant hardware modifications. Our initial findings suggest that it would be worthwhile to perform direct correlation studies between CEST and GAGs using cadaver samples, and to extend this novel technique to studies on patients with degenerative discs to better understand its distinct imaging features relative to conventional techniques. Copyright © 2011 John Wiley & Sons, Ltd.
Regional determination of oxygen uptake in rodent lungs using hyperpolarized gas and an analytical treatment of intrapulmonary gas redistribution
Authors: Kadlecek Stephen , Mongkolwisetwara Puttisarn , Xin Yi , Ishii Masaru , Profka Harilla , Emami Kiarash , Rizi Rahim
Published: March 2011

A method is presented which allows for the accurate extraction of regional functional metrics in rodent lungs using hyperpolarized gas. The technique is based on the combination of measured T1 decay, an independent measure of specific ventilation and mass balance considerations to extract the regional oxygen levels and uptake. In phantom and animal experiments, it is demonstrated that the redistribution of gas during the measurement is a significant confounding factor, and this effect is addressed analytically. The resulting parameterization of gas flow increases the accuracy of oxygen‐sensitive MRI, and may also be used independently to assess air trapping and airway constriction. Limitations of the technique with respect to spatial resolution and robustness are also discussed. Copyright © 2011 John Wiley & Sons, Ltd.