bluuebunny/crossref_metadata_2025 huggingface dataset:
A laboratory and theoretical study of silicon hydroxide SiOH
Authors: McCarthy M. C. , Tamassia F. , Woon D. E. , Thaddeus P.
Published: November 2008

The rotational spectrum of the triatomic free radical SiOH in its X A2′ ground electronic state has been observed in a supersonic molecular beam by Fourier transform microwave spectroscopy. The fundamental (10,1→00,0) transition has been detected for normal SiOH and for three rare isotopic species: S30iOH, SiO18H, and SiOD. The same transition has also been observed in two of three excited vibrational states, v2 and v3, for the most abundant species. Precise spectroscopic constants, including those that describe the effective spin doubling and hydrogen hyperfine structure, have been derived for each isotopic species or vibrational state. To complement the laboratory work, theoretical calculations of the structure, dipole moment, and energies of the X A2′ and low-lying 1 A2″ states have also been undertaken at the coupled cluster level of theory. In agreement with theoretical predictions, we conclude from the hyperfine constants that SiOH is a best described as a π-type radical, with the unpaired electron localized on a p orbital on the silicon atom. Assuming a bond angle of 118.5°, the Si–O bond length is 1.647(2) Å and the O–H bond length is 0.969(4) Å.
Templated control of Au nanospheres in silica nanowires
Authors: Tringe Joseph W. , Vanamu Ganesh , Zaidi Saleem H.
Published: November 2008

The formation of regularly spaced metal nanostructures in selectively placed insulating nanowires is an important step toward realization of a wide range of nanoscale electronic and optoelectronic devices. Here we report templated synthesis of Au nanospheres embedded in silica nanowires, with nanospheres consistently spaced with a period equal to three times their diameter. Under appropriate conditions, nanowires form exclusively on Si nanostructures because of enhanced local oxidation and reduced melting temperatures relative to templates with larger dimensions. We explain the spacing of the nanospheres with a general model based on a vapor-liquid-solid mechanism, in which an Au/Si alloy dendrite remains liquid in the nanotube until a critical Si concentration is achieved locally by silicon oxide-generated nanowire growth. Additional Si oxidation then locally reduces the surface energy of the Au-rich alloy by creating a new surface with smaller area inside of the nanotube. The isolated liquid domain subsequently evolves to become an Au nanosphere, and the process is repeated.
Pulse accumulation, radial heat conduction, and anisotropic thermal conductivity in pump-probe transient thermoreflectance
Authors: Schmidt Aaron J. , Chen Xiaoyuan , Chen Gang
Published: November 2008

The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for measuring both cross-plane and in-plane thermal conductivities of thermally anisotropic thin films is described. As verification, the technique is used to extract the cross-plane and in-plane thermal conductivities of highly ordered pyrolytic graphite. Results are found to be in good agreement with literature values.
Reliability of range-separated hybrid functionals for describing magnetic coupling in molecular systems
Authors: Rivero Pablo , Moreira Ibério de P. R. , Illas Francesc , Scuseria Gustavo E.
Published: November 2008

The performance of the Heyd–Scuseria–Ernzerhorf (HSE) and single parameter long-range corrected Perdew–Burke–Ernzerhorf (LC-ωPBE) range-separated hybrids for predicting magnetic coupling constants has been investigated for a broad set of magnetic molecular systems for which accurate experimental data exist. The set includes the H–He–H model system, two organic diradicals with different magnetic behaviors, and a series of Cu dinuclear complexes with a broad range of magnetic coupling values. Both HSE and LC-ωPBE provide a significant improvement to standard hybrids such as the well-known hybrid Becke-3-parameters exchange with Lee–Yang–Parr correlation (B3LYP) functional. Nevertheless, the performance of these two range-separated hybrid functionals is different: HSE overestimates antiferromagnetic and ferromagnetic interactions in Cu dinuclear complexes (although significantly less than B3LYP), whereas LC-ωPBE treats ferro- and antiferromagnetic couplings on a much more balanced way. The increased accuracy of LC-ωPBE suggests that the inclusion of 100% Hartree–Fock exchange considered in the definition of this long-range corrected hybrid functional has important consequences for an accurate description of exchange and correlation effects on the electronic structure of open shell systems. On the other hand, HSE, which was developed with periodic systems in mind, also performs quite well (and better than B3LYP) thus opening the possibility of magnetic coupling studies in metal oxides and other challenging solids.
Coarse molecular-dynamics analysis of an order-to-disorder transformation of a krypton monolayer on graphite
Authors: Amat Miguel A. , Arienti Marco , Fonoberov Vladimir A. , Kevrekidis Ioannis G. , Maroudas Dimitrios
Published: November 2008

The thermally induced order-to-disorder transition of a monolayer of krypton (Kr) atoms adsorbed on a graphite surface is studied based on a coarse molecular-dynamics (CMD) approach for the bracketing and location of the transition onset. A planar order parameter is identified as a coarse variable, ψ, that can describe the macroscopic state of the system. Implementation of the CMD method enables the construction of the underlying effective free-energy landscapes from which the transition temperature, Tt, is predicted. The CMD prediction of Tt is validated by comparison with predictions based on conventional molecular-dynamics (MD) techniques. The conventional MD computations include the temperature dependence of the planar order parameter, the specific heat, the Kr–Kr pair correlation function, the mean square displacement and corresponding diffusion coefficient, as well as the equilibrium probability distribution function of Kr-atom coordinates. Our findings suggest that the thermally induced order-to-disorder transition at the conditions examined in this study appears to be continuous. The CMD implementation provides substantial computational gains over conventional MD.
Magnetic instability in irradiated MgB2 dense samples
Authors: Durán A. , Verdín E. , Galván D. H. , Romero-Salazar C. , Morales F. , Adem E. , Rickards J. , Maple M. B. , Escudero R.
Published: November 2008

High density magnesium diboride samples were irradiated with low dosages of γ-rays, protons, and electrons. They were investigated by magnetization and thermal studies in order to determine if the irradiation increases the flux pinning and consequently the critical current density Jc. Zero field cooled magnetic susceptibility and specific heat measurements confirm the bulk transition temperature (Tc) with diamagnetic signal at ∼38.5 K. Magnetic instabilities were observed in the superconducting hysteresis loop at temperatures between 2 and 23 K in all studied polycrystalline MgB2 dense samples. The occurrence of flux jumps depended of the type of irradiation and the number of jumps decreases as temperature increases. The critical current density Jc, estimated from the magnetization hysteresis using the Bean’s model, is improved for gamma irradiated sample at H=0 and T=2 K. At low temperature, the Jc decreases and several steep drops in Jc are observed as a function of applied magnetic field. Furthermore, it is observed that the influence of crystalline defects plus local disorder, induced by hot isostatic pressure and irradiation with energetic atoms, increase the Jc but at the same time the magnetothermal instabilities increase in a broad range of temperature.
Variational derivation of the dispersion relation of kinetic coherent modes in the acoustic frequency range in tokamaks
Authors: Nguyen C. , Garbet X. , Smolyakov A. I.
Published: November 2008

In the present paper, we compare two modes with frequencies belonging to the acoustic frequency range: the geodesic acoustic mode (GAM) and the Beta Alfvén eigenmode (BAE). For this, a variational gyrokinetic energy principle coupled to a Fourier sidebands expansion is developed. High order finite Larmor radius and finite orbit width effects are kept. Their impact on the mode structures and on the Alfvén spectrum is calculated and discussed. We show that in a local analysis, the degeneracy of the electrostatic GAM and the BAE dispersion relations is verified to a high order and based in particular on a local poloidal symmetry of the two modes. When a more global point of view is taken, and the full radial structures of the modes are computed, differences appear. The BAE structure is shown to have an enforced localization, and to possibly connect to a large magnetohydrodynamic structure. On the contrary, the GAM is seen to have a wavelike, nonlocalized structure, as long as standard slowly varying monotonic profiles are considered.
Nonequilibrium thermodynamics of interfaces using classical density functional theory
Authors: Johannessen Eivind , Gross Joachim , Bedeaux Dick
Published: November 2008

A vapor-liquid interface introduces resistivities for mass and heat transfer. These resistivities have recently been determined from molecular simulations, as well as theoretically using the van der Waals square gradient model. This model, however, does not allow for direct quantitative comparison to experiment or results from molecular simulations. The classical density functional theory is used here in order to determine the equilibrium profiles of vapor-liquid interfaces. Equilibrium profiles are sufficient in the framework of nonequilibrium thermodynamics for determining the interfacial resistivities. The interfacial resistivities for heat transfer, for mass transfer, and for the coupling of heat and mass transfer can all be related to only one local thermal resistivity. This is done with integral relations for the interfacial resistivities. All interfacial resistivities can be consistently described in their temperature behavior with good accuracy.
Highly efficient excimer-based white phosphorescent devices with improved power efficiency and color rendering index
Authors: Yang Xiaohui , Wang Zixing , Madakuni Sijesh , Li Jian , Jabbour Ghassan E.
Published: November 2008

Power efficiency, Commission Internationale d’Énclairage (CIE) coordinates, and color rendering index (CRI) of white phosphorescent excimer devices were improved by utilizing two platinum complexes as emissive dopants and exploring different device structures. Compared with devices containing two emissive layers each having a different dopant, devices having two dopants incorporated in a single host layer showed better color stability with the change in operating voltage. White phosphorescent excimer devices having the double-doped emissive layer showed an external quantum efficiency and a power efficiency of 14.5% and 17 lm/W, respectively, at 500 cd/m2. The CIE coordinates and CRI of the devices were (0.382, 0.401) and 81, which were almost independent of the drive voltage.
Multiphase improved Steinberg–Guinan model for vanadium
Authors: Rudd Robert E. , Klepeis John E.
Published: November 2008

Vanadium has been observed recently to transform from the body-centered cubic (bcc) crystal structure to a rhombohedral structure at high pressure (∼0.69 Mbar) [Y. Ding et al., Phys. Rev. Lett. 98, 085502 (2007)]. Recent theoretical work predicts a transformation to a second rhombohedral phase at 1.2 Mbar before transforming back to the bcc structure at 2.8 Mbar at absolute zero temperature [B. Lee et al., Phys. Rev. B 75, 180101(R) (2007)]. Here we develop an analytic model for the shear modulus in these phases based on ab initio calculations of the single-crystal elastic moduli and a finite element based homogenization technique. The form of the shear modulus is suited to application in strength models such as in the Steinberg–Guinan form and other analogous continuum-level models.
Berreman effect in infrared absorption spectroscopy of ionic oxide coatings formed by atomic layer deposition on three-dimensional structures
Authors: Scarel Giovanna , Hyde G. Kevin , Hojo Daisuke , Parsons Gregory N.
Published: November 2008

We show through modeling and experimentation that the Berreman effect, physically manifested and investigated on planar surfaces for more than four decades, can be readily realized and studied in three-dimensional nonplanar structures. The Berreman effect is also used as a nonlocal probe to evaluate topography and homogeneity of insulating ionic oxide layers in nonplanar geometries. During infrared transmission studies the macroscopic angular dependence of the longitudinal optical mode absorbance deviates from that observed in the planar case, and the angular dependence is shown to be physically linked to geometry and homogeneity of the ionic oxide layer. Spectroscopic modeling confirms the observations on the angular dependence of longitudinal optical mode absorbance on various nonplanar systems. A linear combination of [sin(θ)]4 with appropriate coefficients is found to describe the trend of longitudinal optical mode absorbance in nonplanar structures.
Annealing effects on the characteristics of high Tc lead-free barium titanate-based positive temperature coefficient of resistivity ceramics
Authors: Xiang Ping-Hua , Harinaka Hisashi , Takeda Hiroaki , Nishida Takashi , Uchiyama Kiyoshi , Shiosaki Tadashi
Published: November 2008

Annealing effects on the positive temperature coefficient of resistivity (PTCR) behavior of (Bi1/2Na1/2)TiO3 and (Bi1/2K1/2)TiO3 modified BaTiO3 semiconducting ceramics are investigated. The annealing treatments result in the occurrence of the PTCR effect and the increased resistivity jump. The impedance spectra reveal that the resistivity of grain interior of annealed sample is little influenced by the annealing process, indicating that the increase in the overall resistivity is entirely a grain-boundary effect. A higher annealing temperature leads to an increase in acceptor state density, potential barrier height and barrier layer width, which contributes to the improved PTCR effect in the annealed samples.
Theory and simulation of lower-hybrid drift instability for current sheet with guide field
Authors: Yoon P. H. , Lin Y. , Wang X. Y. , Lui A. T. Y.
Published: November 2008

The stability of a thin current sheet with a finite guide field is investigated in the weak guide-field limit by means of linear theory and simulation. The emphasis is placed on the lower-hybrid drift instability (LHDI) propagating along the current flow direction. Linear theory is compared against the two-dimensional linear simulation based on the gyrokinetic electron/fully kinetic ion code. LHDI is a flute mode characterized by k⋅Btotal=0; hence, it is stabilized by a finite guide field if one is confined to k vector strictly parallel to the cross-field current. Comparison of the theory and simulation shows qualitatively good agreement.
Stability of three-dimensional electron holes
Authors: Berthomier M. , Dubois G. , Muschietti L.
Published: November 2008

A self-consistent kinetic model of three-dimensional (3D) electron holes in a strongly magnetized collisionless plasma is presented. A stability study of these localized electrostatic structures has been carried out. The analysis of the motion of trapped particles in the 3D potential structure suggests using the Hamiltonian approach to describe how electron holes interact with an external electrostatic perturbation. Using 3D action-angle variables and perturbation theory, it is shown that, in addition to standard Landau resonance of passing (i.e., untrapped) particles, trapped particles resonate with the perturbation in such a way that they amplify it. A growth rate for this process is derived and application to magnetospheric plasma conditions shows that the stability of 3D electron holes is strongly dependent on the anisotropy of the underlying potential structure. Possible production of electrostatic whistler waves by a train of electron holes in the auroral region of the Earth’s magnetosphere is emphasized.
Electro-optical modeling of bulk heterojunction solar cells
Authors: Kirchartz Thomas , Pieters Bart E. , Taretto Kurt , Rau Uwe
Published: November 2008

We introduce a model for charge separation in bulk heterojunction solar cells that combines exciton transport to the interface between donor and acceptor phases with the dissociation of the bound electron/hole pair. We implement this model into a standard semiconductor device simulator, thereby creating a convenient method to simulate the optical and electrical characteristics of a bulk heterojunction solar cell with a commercially available program. By taking into account different collection probabilities for the excitons in the polymer and the fullerene, we are able to reproduce absorptance, internal and external quantum efficiency, as well as current/voltage curves of bulk heterojunction solar cells. We further investigate the influence of mobilities of the free excitons as well as the mobilities of the free charge carriers on the performance of bulk heterojunction solar cells. We find that, in general, the highest efficiencies are achieved with the highest mobilities. However, an optimum finite mobility of free charge carriers can result from a large recombination velocity at the contacts. In contrast, Langevin-type of recombination cannot lead to finite optimum mobilities even though this mechanism has a strong dependence on the free carrier mobilities.
Effect of dislocations on electrical and optical properties of n-type Al0.34Ga0.66N
Authors: Chen K. X. , Dai Q. , Lee W. , Kim J. K. , Schubert E. F. , Grandusky J. , Mendrick M. , Li X. , Smart J. A.
Published: November 2008

The effect of edge and screw dislocations on the electrical and optical properties of n-type Al0.34Ga0.66N is investigated. It is found that edge dislocations strongly affect the electrical properties of n-type Al0.34Ga0.66N. Both free carrier concentration and mobility decrease with increasing edge dislocation density. Edge dislocations also enhance nonradiative recombination, which is indicated by decreasing near-band-edge UV as well as parasitic blue photoluminescence. The UV/blue ratio is found to be independent of the edge dislocation density but strongly depends on the Si doping concentration.
The magnetoelectric domains and cross-field switching in multiferroic BiFeO3
Authors: Li L. J. , Li J. Y. , Shu Y. C. , Yen J. H.
Published: November 2008

Bi Fe O 3 is an exciting multiferroic material because of its room temperature multiferrocity, excellent ferroelectric properties, and recently demonstrated electric control of antiferromagnetic domains. In this letter we report a theoretical study on the structure and evolution of magnetoelectric domains in BiFeO3. We not only observed the coupled ferroelectric and antiferromagnetic domains and demonstrated the electric control of antiferromagnetic ordering, both in consistency with experiments, but also revealed the switching of antiferromagnetic domains by mechanical stress that is yet to be explored in experiments.
Room temperature ferromagnetism at self-assembled monolayer modified Ag nanocluster–ZnO nanowire interface
Authors: Deng S. , Loh K. P. , Yi J. B. , Ding J. , Tan H. R. , Lin M. , Foo Y. L. , Zheng M. , Sow C. H.
Published: November 2008

Magnetic characterization of ZnO nanowires (NW) decorated with thiol-capped Ag nanoclusters (NCs) reveals spontaneous field-dependent magnetization and hysteresis at room temperature. The saturation magnetization is temperature independent for the 13nm thiol-capped Ag NCs but unexpectedly increases with temperature for the 4nm thiol-capped Ag NCs. The high magnetic moment results from the efficient dispersal of Ag NCs on the ZnO NW scaffold and charge transfer interaction between Ag and ZnO. The anomalous magnetic behavior in 4nm NCs may be due to the spin reorientation of Ag–S dipoles mediated by Zn–S dipoles.
Origin of dielectric loss induced by oxygen plasma on organo-silicate glass low-k dielectrics
Authors: Shi H. , Bao J. , Smith R. S. , Huang H. , Liu J. , Ho P. S. , McSwiney M. L. , Moinpour M. , Kloster G. M.
Published: November 2008

This study investigated the origin of dielectric loss induced by O2 plasma on organo-silicate glass low-k dielectrics. The contributions from the polarization components to dielectric constant were delineated by analyzing the results from capacitance-voltage measurement, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy together with the Kramers–Kronig dispersion relation. The dielectric loss was found to be dominated by the dipole contribution, compared with the electronic and ionic polarizations. The origin of the dipole contribution was further investigated by performing quantum chemistry calculations. The physisorbed water molecules were found to be primarily responsible for the dipole moment increase and the dielectric loss.
The effect of injector barrier thickness and doping level on current transport and optical transition width in a λ∼8.0 μm quantum cascade structure
Authors: Howard Scott S. , Howard Daniel P. , Franz Kale , Hoffman Anthony , Sivco Deborah L. , Gmachl Claire F.
Published: November 2008

We experimentally study the optical transition width and current transport properties of a set of λ∼8.0 μm quantum cascade (QC) structures with varying injector barrier thickness and doping level. For this high-performance QC laser structure, a 50% reduction in doping level and a 33% reduction in injection barrier thickness yield five times stronger luminescence, 20% smaller optical transition linewidth, and improved current-voltage characteristics. These results demonstrate how high-performance QC laser structures can be engineered to produce narrow gain spectra at and above room temperature.
Resistance and non-resistance to boundary crossing in translation research
Authors: Brownlie Siobhan
Published: November 2008

Ideas, concepts, theories and methods spread within and across disciplines, communities, countries and traditions. RichardDawkins (1976: 214)has suggested that memes (units of cultural transmission) are in competition for survival, and that in some situations of stability it is difficult for a new meme to invade. My interest is in concepts, theories and methods in academia, and the fact that these memes have more or less difficulty in spreading. They encounter more or less resistance in jumping boundaries, whether those boundaries are disciplinary or boundaries constituted by national research traditions. The aim of my paper is to discuss the spread of ideas, and situations of resistance and non-resistance to the spread of ideas, taking as examples three cases of boundary-crossing research projects in Translation Research. I shall suggest through those examples how resistance may be overcome.
The Role of Private Military Companies in US-Africa Policy
Authors: Aning Kwesi , Jaye Thomas , Atuobi Samuel
Published: November 2008

This article discusses the increasing use of private military companies (PMCs) in United States’ security policy in Africa, and examines this phenomenon in relation to the US’ various military training programmes on the continent. We argue that the increasing use of PMCs in US security policy has evolved due to two critical and mutually dependent developments; African state weakness and resource stringency on the one hand, and the US's overwhelming security commitments around the world, combined with military downsizing, on the other. The article further argues that the involvement of PMCs is to a large extent informed by US concerns about access to African resources, especially oil, in the face of stiff competition from China. We conclude that the increasing US engagement in Africa is highly militaristic and state-centric, and that it is primarily conditioned by US strategic interests and does not necessarily reflect African security concerns: human security for development.
Totipotent stem cells bearing del(20q) maintain multipotential differentiation in Shwachman Diamond syndrome
Authors: Crescenzi Barbara , La Starza Roberta , Sambani Constantina , Parcharidou Agapi , Pierini Valentina , Nofrini Valeria , Brandimarte Lucia , Matteucci Caterina , Aversa Franco , Martelli Massimo Fabrizio , Mecucci Cristina
Published: November 2008

SBDS/7q11 gene mutations underlie the congenital Shwachman Diamond syndrome (SDS), characterized by bone marrow failure and high risk of haematological malignancies. In two cases of SDS with bone marrow failure and isolated del(20q) interphase fluorescence in situ hybridization (I‐FISH) found no abnormalities in FHIT/3p14.2, IKZF1/7p13, D7S486/7q31, PTEN/10q23.3, WT1/11p13, ATM/11q23, D13S25/13q14, TP53/17p13, NF1/17q11, SMAD2/18q21, RUNX1/21q22. Fluorescence immunophenotype combined with I‐FISH found del(20q) in a totipotent haematopoietic stem cell (CD34+, CD133+) and downstream myelocyte (CD33+, CD14+, CD13+), erythrocyte (Glycophorin A+) and lymphocyte lineages (CD19+, CD20+, CD3+, CD7+). These findings and clinical follow‐ups confirm the benign course of SDS with isolated del(20q).
The role of specialist and general nurses working with people with multiple sclerosis
Authors: While Alison , Forbes Angus , Ullman Roz , Mathes Lucia
Published: November 2008

Aim.  To describe the perceived role of nurses and other carers of people with multiple sclerosis from the perspective of different stakeholders (people with multiple sclerosis, non‐specialist nurses, specialist nurses and other health care professionals).

Background.  Multiple sclerosis is one of the commonest causes of disability in young adults. People with multiple sclerosis require supportive care during the disease trajectory. The role of different health and social care providers has not been reported previously.

Design.  Survey.

Method.  Questionnaire data collected in 2002 during the first phase of scale development (health professionals n = 459; people with multiple sclerosis n = 65; total response rate 59·4%). The data were reanalysed to compare responses across sample groups.

Results.  There was consensus that neurologists and specialist nurses were the most appropriate professionals in the provision of specialist care with specialist nurses also being identified as key providers of emotional support. However, there were also significant differences in nominations reflecting the different perspectives of the stakeholder groups and a self‐report bias. Each stakeholder group frequently emphasised their own perceived contribution to care. The different perspective of people with multiple sclerosis was also noteworthy with their greater emphasis on social care and lay support.

Conclusions.  The findings indicate a dissonance in the views of different stakeholders within the care system. The division of labour associated with nursing care requires further exploration. The contrasting paradigms of health care professionals and people with multiple sclerosis regarding models of disability were highlighted.

Relevance to clinical practice.  Multiple sclerosis, like other chronic illnesses, requires substantial nursing care. There is a growing number of specialist nurses in the workforce, however, little is known how their role interfaces with other nurses.
Children, health and gender: recognition in nursing research?
Authors: Taylor Julie , Green Lorraine
Published: November 2008

Aim.  This paper examines the hitherto mostly unrecognised relationship between gender, health and children; its significance for nursing practice and how it has been considered in nursing research.

Background.  Holistic nursing practice with children requires adequate assessment and consideration of all potential influences on children’s lives. Socioeconomic disparities have received widespread attention and gender inequalities in adult health have been studied in some depth. The links between gender, health and children, however, have received little consideration. The paper first considers this context in depth; it then applies the context to research in practice.

Design.  Systematic review.

Methods.  A systematic literature search was undertaken on four mainstream nursing research journals over 38 months up to February 2007. A total of 567 articles met the key word searches. Duplicates, opinion pieces and articles not focusing on children were removed. The remaining 23 nursing studies relevant to child health were examined for their gender sensitivity.

Results.  Full consideration of gender issues was found largely to be absent in nursing research on children. Eight studies gave specific consideration to gender relevance, where boys and girls may have responded differently to care. Only six studies specifically addressed gender sensitivity. Allowing children a voice, however, was a strength in these studies, with 18 reflecting children’s views directly.

Conclusions.  Major gaps still exist in research and theorisation relating to children, health and gender. These need to be acknowledged and investigated, particularly in relation to how they might impact on nursing care.

Relevance to clinical practice.  Nursing practice and research needs to account for all potential health issues, of which gender may often be important.
An exploration of mothers’ and fathers’ views of their identities in chronic‐kidney‐disease management: parents as students?
Authors: Swallow Veronica
Published: November 2008

Aim.  To explore parents’ views of their identities as they learn to manage their child’s chronic kidney disease.

Background.  Parents are expected to participate in management and usually learn necessary skills from the multidisciplinary team. Research highlights the importance of professionals defining parents’ management roles in chronic disease; but little is known about parents’ views on their own identities as the complex and dynamic process of teaching and learning unfolds around their child’s condition. According to positioning theory, identity development is a dynamic and fluid process that occurs during interaction, with each person positioning themselves while simultaneously positioning the other person, yet this concept has not been considered in relation to parents’ contributions to disease management.

Design.  A longitudinal, grounded theory study conducted in a UK Children’s Kidney Unit.

Method.  This paper focuses on one aspect of a larger study exploring family learning in disease management. Six mothers and two fathers of six children with a recently diagnosed chronic kidney disease participated in a total of 21 semi‐structured interviews during the 18 months after referral to the unit. Interviews included discussion about the parts they played in relation to professionals during the management process. Findings were interpreted within a framework of positioning theory.

Results.  Parents participated in teaching/learning/assessment that was both planned (involving allocated clinical lessons and tasks) and spontaneous (in response to current situations), to facilitate their participation. They positioned multidisciplinary team members as teachers as well as professionals, simultaneously positioning themselves as students as well as parents.

Conclusion.  Parents’ clinical duties and obligations are not an automatic part of parenting but become part of the broader process of sharing disease management, this can lead to them assuming the additional identity of a ‘student’.

Relevance to clinical practice.  Involving parents in ongoing discussions about their positions in management may help promote their active and informed participation.
Patterns of genetic variation in US federal bison herds
Authors: HALBERT NATALIE D. , DERR JAMES N.
Published: November 2008

Like many wide‐ranging mammals, American bison (Bison bison) have experienced significant range contraction over the past two centuries and are maintained in artificially isolated populations. A basic understanding of the distribution of genetic variation among populations is necessary to facilitate long‐term germplasm preservation and species conservation. The 11 herds maintained within the US federal system are a critically important source of germplasm for bison conservation, as they include many of the oldest herds in the USA and have served as a primary resource for the establishment of private and public herds worldwide. In this study, we used a panel of 51 nuclear markers to investigate patterns of neutral genetic variation among these herds. Most of these herds have maintained remarkably high levels of variation despite the severe bottleneck suffered in the late 1800s. However, differences were noted in the patterns of variation and levels of differentiation among herds, which were compared with historical records of establishment, supplementation, herd size, and culling practices. Although some lineages have been replicated across multiple herds within the US federal system, other lineages with high levels of genetic variation exist in isolated herds and should be considered targets for the establishment of satellite herds. From this and other studies, it is clear that the genetic variation represented in the US federal system is unevenly distributed among National Park Service and Fish and Wildlife Service herds, and that these resources must be carefully managed to ensure long‐term species conservation.
Prevention of work‐related airway allergies; summary of the advice from the Health Council of the Netherlands
Authors: Rijnkels J. M. , Smid T. , Van den Aker E. C. , Burdorf A. , Van Wijk R. G. , Heederik D. J. J. , Houben G. F. , Van Loveren H. , Pal T. M. , Van Rooy F. G. B. G. J. , Van der Zee J. S.
Published: November 2008

The Health Council of the Netherlands published a report in which the best procedure and method for recommending health‐based occupational exposure limits (OELs) for inhaled allergens were identified by evaluating the scientific state of the art. Many respiratory disorders in the workplace arise from inhalation of substances which can cause allergy. To protect workers against respiratory allergy, various preventive measures are taken, one of them being reduction of exposure by setting legally binding standards. These are based on health‐based OELs that specify a level of exposure to an airborne substance, a threshold level, below which it may reasonably be expected that there is no risk of adverse health effects. The Council is of the opinion that an OEL should prevent against allergic sensitization, as sensitization plays a crucial biological role and is a prerequisite for the development of allergy. Furthermore, the Council considers it most likely that the exposure level below which no allergic sensitization develops for most allergens is so low, that OELs are difficult to set with the current knowledge and technical feasibilities. An alternative approach is to accept exposure, which carries a small predefined risk in developing allergic sensitization. In addition, it is worth considering periodic screening of exposed workers on allergic sensitization, because timely intervention can prevent worse. The feasibility of periodic screening and what else is needed to comply with the most important criteria, should however be judged case‐by‐case.
Variability of anti‐αGal antibodies in human serum and their relation to serum cytotoxicity against pig cells
Authors: Kujundzic Milan , Koren Eugen , Neethling Francisca A. , Mitotic Franko , Koscec Mirna , Kujundzic Tatjana , Martin Mic , Cooper David K.C.
Published: November 2008

Abstract: One of the major obstacles in pig‐to‐human xenografting is hyperacute rejection (HAR) of pig cells caused by preformed anti‐pig antibodies and complement. In 1991 we suggested that anti‐αGal antibodies play a major role in the HAR of pig cells. Anti‐αGal antibodies recognize terminal α‐galactose‐containing epitopes on glycoproteins and glycolipids. They are present in humans, apes, and Old World monkeys, but not in lower mammals such as pigs. However, pigs, unlike humans, express terminal α‐galactose epitopes on vascular endothelium which represent targets for human anti‐αGal antibodies. Despite increasing recognition that anti‐αGal antibodies are an important factor, many questions related to their precise role in HAR remain to be answered.

In this study, we analyzed 75 human AB sera in terms of (i) cytotoxic activity against cultured pig (PK‐15) cells, (ii) anti‐αGal titers, (iii) immunoglobulin‐binding to pig cells, and (iv) immunoglobulin concentrations. The results demonstrated considerable variability in cytotoxicity, anti‐αGal titers, and immunoglobulin binding to pig cells, whereas the serum immunoglobulin concentrations were less variable. Positive correlations were found between cytotoxicity and binding of IgG and IgM to the surface of pig cells. The surface‐bound IgG and IgM also correlated with the serum anti‐αGal IgG and IgM titers. Anti‐αGal IgA, however, did not show any relation with cytotoxicity or cell binding. Concentrations of serum total immunoglobulins correlated with neither I cytotoxic activity nor cell binding.
Prophylactic trypsin inhibition during the isolation procedure guarantees reproducible, high porcine islet yields
Authors: Heiser Axel , Ulrichs Karin , Müller‐Ruchholtz Wolfgang
Published: November 2008

Abstract: For isolating islets from the porcine pancreas, we established a semiautomated digestion method. Although the isolation technique was standardized and collagenase of controlled quality was used, until now the reproducibility of high islet yields was unsatisfactory. Our hypothesis was that pancreatic trypsin was responsible for this failure. The aim of this study was to investigate the effect of endogenous trypsin on islet yield. Our results demonstrate that a high trypsin level correlates with poor islet yield, whereas low trypsin activity always correlates with high islet yield. Specific inhibition of trypsin results in low trypsin activity and reproducible, high islet yields.
Engraftment of rat bone marrow and its role in negative selection of murine T cells in mice conditioned with a modified nonmyeloablative regimen
Authors: Tomita Yukihiro , Lee Lorri A. , Sykes Megan
Published: November 2008

Abstract: We have recently demonstrated that xenogeneic (rat) bone marrow engraftment and donor‐specific tolerance can be induced in mice conditioned with a nonmyeloablative regimen consisting of administration of anti‐CD4, ‐CD8, ‐Thy‐1.2, and ‐NK1.1 mAbs on days ‐6 and ‐1, 3 Gy whole body irradiation (WBI) on day 0, and 7 Gy thymic irradiation on day 0, followed by injection of T cell‐depleted (TCD) F344 BMC. We have now investigated the mechanism of tolerance in these mixed xenogeneic chimeras by evaluating the capacity of rat bone marrow‐derived cells to induce clonal deletion of mouse T cell subsets. Both Vβ5+ and Vβ11+ murine T cell subsets were markedly depleted in peripheral blood of chimeras but not of normal B1O mice. These results demonstrate that rat molecules contribute to the ligand for negative selection of these Vβ families of mouse T cells, and that rat bone marrow‐derived cells participate in negative selection of the murine T cell repertoire, suggesting that clonal deletion is probably a major mechanism of tolerance induction in this model. In addition, based on results in a similar allogeneic BMT model, we hypothesized that, if sufficient quantities of mAbs were administered, thymic irradiation could be eliminated from this regimen without compromising the ability to induce mixed xenogeneic chimerism and tolerance. We now demonstrate induction of comparable multilineage mixed xenogeneic chimerism in animals receiving this conditioning regimen with or without 7 Gy thymic irradiation. Thus, if a similar approach were applied clinically, the potential toxicity of this regimen might be reduced further by the elimination of thymic irradiation.
Islet autotransplantation studies in pigs to assess viability and implantation site as a prelude to xenotransplantation
Authors: Wahoff David C. , Papalois Basil E. , Nelson Lindsey A. , Gores Paul F. , Sutherland David E.R.
Published: November 2008

Abstract: Before pig‐to‐human xenotransplantation trials can begin, it must be demonstrated that porcine islets can engraft and function in pig recipients. Collagenase dispersion of the pancreas followed by density gradient centrifugation is effective in preparing viable discrete islets from species such as rodents and dogs, but these methods frequently results in marked fragmentation of porcine islets. Thus, we hypothesized that by limiting the digestion period and eliminating the purification step to minimize islet fragmentation, a viable preparation suitable for transplantation would be obtained. Purification is known to be unnecessary in dogs and humans as long as a site able to accommodate impure tissue is used. In this study, we autotransplanted impure islets prepared by two different methods (collagenase/semi‐automated or mechanical chopping) without further purification into either the peritoneal cavity (N=46), spleen (N=5), or liver (N=5) of 56 pancreatectomized pigs. The semi‐automated method (N=45) yielded a mean of 426,000 ± 41,696 islets, and the mechanical chopping method (N=11) yielded 165,438 ± 19,611 islets (P<0.05). Intraportal transplantation of impure islets was uniformly lethal due to portal hypertension. Intraperitoneal transplants were well tolerated with no pigs dying periooperatively. None of the mechanically prepared islet grafts transplanted in the peritoneal cavity functioned (N=11). Of the grafts prepared by the collagenase/semi‐automated method, none transplanted into the spleen functioned; however, 13 of the 35 (37%) transplanted into the peritoneal cavity did function (30 day insulin‐independent survival). Of these, four recipients were normoglycemic (blood glucose <200 mg/dl), and glucose disposal during an intravenous glucose tolerance test was similar to normal pigs. Although islets prepared by the semi‐automated/collagenase digestion function in less than half of recipients, the intraperitoneal site generally is less receptive than other sites of engraftment. Unlike pigs, humans can tolerate the transplantation of impure islets intraportally. Thus, the proportion that functioned in this study likely under estimates the potential function rate using the intraportal site in humans. This study demonstrates by in vivo testing the viability of an impure porcine islet preparation and supports its use in preclinical xenograft models and human xenograft trials.
Problems associated with the use of dispersed pancreatic tissue for xenotransplantation: A possible solution
Authors: Wahoff David C. , Nelson Lindsey A. , Sutherland David E.R. , Gores Paul F.
Published: November 2008

Abstract: In light of the disappointing clinical results with purified islets, we propose that a simple preparation of impure islets may provide a better graft for both future allogeneic and xenogeneic transplantation trials. We hypothesize that the simplest, least traumatic procedure to disperse the pancreas, which minimizes the disruption of normal cellular associations, will yield an islet graft of maximum viability. The peritoneal cavity is an attractive site for the transplantation of such preparations since it can accommodate nearly unlimited graft volumes, and is easily accessible. In the present study, we tested the ability of impure islet autografts transplanted in the peritoneal cavity to reverse diabetes in a preclinical model. Dogs (N=29) underwent total pancreatectomy and were divided into three groups: group I (N=7) received intraportal pure islets; group II (N=13) received intraperitoneal pure islets; group III (N=9) received intraperitoneal impure islets. There were no significant differences in islet mass transplanted in the groups: group I 11,686 ± 2,514 IE/kg, group II 10,274 ± 1,125 IE/kg, and group III 11,735 ± 1,497. At 15 months, all purified grafts in group I failed, and all but one purified graft in group II failed, while five impure grafts in group III continued to function (P < 0.05, versus group I and II, X2). Glucose disposal in dogs with functioning grafts did not differ between groups. In conclusion, free impure islets are able to engraft within the peritoneal cavity and reverse diabetes in a large animal. Impure islets grafts were superior to purified grafts in initial engraftment and long‐term functional survival. Thus, the peritoneal cavity represents a site that can support the engraftment and long‐term function of both impure islet allografts and possibly xenografts if sufficient immune suppression or tolerance is achieved.
Design of a simple, in vitro method for evaluating the efficiency of crude Clostridium histolyticum collagenase and its components for porcine islet isolation
Authors: Johnson P.R.V. , van Suylichem P.T.R. , Roberts D.L , Vos‐Scheperkeuter G.H. , White SA , van Schilfgaarde R. , London N.J.M.
Published: November 2008

Abstract: The wide variability of different batches of crude collagenase is one of the major factors influencing the isolation of porcine islets of Langerhans. In order to enable the production of reproducible collagenase batches, however, it is first necessary to determine which of the many components of crude collagenase are required for porcine islet isolation. For this to be done, experiments must control for the inter‐pancreatic variation seen with porcine pancreata, and this requires methodology that enables many different crude collagenases or collagenase components to be tested on any one pancreas. The aim of this study was to assess four different in vitro methods for evaluating different batches of crude collagenase. Each of the methods involved placing blocks of either distended or undistended pancreas in centrifuge tubes, adding crude collagenase in various concentrations dissolved in Hanks' and incubating the tubes in a waterbath at 35°C. The remainder of the pancreas was simultaneously processed using the semi‐automated method. Every 10 min, samples were taken from both the semi‐automated circuit and the relevant centrifuge tubes and assessed for number of cleaved islets, cleavage index, degree of fragmentation and quality of exocrine digestion. A correlation was made between each in vitro method and the “gold standard” semi‐automated method. We conclude that it is possible to use an in vitro method to evaluate crude collagenase that correlates well with the digestion occurring in the Ricordi chamber and that enables the testing of many batches or components of crude collagenase on any one porcine pancreas.