bluuebunny/crossref_metadata_2025 huggingface dataset:
Emergency medicine residents’ ability to identify ocular pathology in a live porcine model
Authors: Ball Vincent L. , Younggren Bradley N. , Bothwell Jason D.
Published: February 2011

Objective

To evaluate emergency medicine residents’ ability to detect ocular pathology using portable ultrasound (US) in a live porcine model.

Methods

This was a pilot study to evaluate emergency medicine residents’ ability to accurately diagnose ocular pathology in a porcine model using handheld US. Subjects were emergency medicine residents who had all undergone a 2-day US course as part of their emergency medicine orientation month and had reviewed an 1 h self-instruction computer tutorial on ocular US prior to the study. Vitreous hemorrhages, retro-orbital hematomas and intraocular foreign bodies were simulated by placement of porcine blood and metallic objects under ultrasound guidance out of view of the subject population. Residents then performed self-directed US of two eyes each and were asked to comment on any pathology observed. Some residents were also asked to identify central retinal artery flow. Time required for each scan was noted.

Results

A total of 36 residents scanned 6 porcine eyes over 2 lab iterations. EM residents were able to detect a significant abnormality greater than 93% of the time. Vitreous hemorrhages were the most detectable injuries with 95% accuracy. A significant abnormality was detected in the models with intraocular foreign bodies 97% of the time with a clear diagnosis of foreign body noted in 73% of the cases. Retro-orbital hematoma was the most difficult to detect with 62% accuracy. The average time taken for scanning two eyes was 7 min 38 s. Central retinal artery flow was detected in 100% of the 26 cases in which this was documented. Accuracy of diagnoses was similar across levels of EM training.

Conclusion

EM residents can accurately diagnose significant ocular pathology using handheld US in a live porcine model.
Congenital tumors: imaging when life just begins
Authors: Alamo Leonor , Beck-Popovic Maja , Gudinchet François , Meuli Reto
Published: February 2011

Background

The technical developments of imaging methods over the last 2 decades are changing our knowledge of perinatal oncology. Fetal ultrasound is usually the first imaging method used and thus constitutes the reference prenatal study, but MRI seems to be an excellent complementary method for evaluating the fetus. The widespread use of both techniques has increased the diagnosis rates of congenital tumors. During pregnancy and after birth, an accurate knowledge of the possibilities and limits of the different imaging techniques available would improve the information obtainable, thus helping the medical team to make the most appropriate decisions about therapy and to inform the family about the prognosis.

Conclusion

In this review article, we describe the main congenital neoplasms, their prognosis and their imaging characteristics with the different pre- and postnatal imaging methods available.
Transcranial magnetic stimulation of the ventromedial prefrontal cortex impairs theory of mind learning
Authors: Lev-Ran S. , Shamay-Tsoory S.G. , Zangen A. , Levkovitz Y.
Published: February 2011

Imaging and lesion studies indicate that the prefrontal cortex plays a prominent role in mediating theory of mind (ToM) functioning. Particularly, the ventromedial prefrontal cortex (VMPFC) appears to be involved in mediating ToM functioning. This study utilized slow repetitive transcranial magnetic stimulation (rTMS) over the VMPFC in 13 healthy subjects in order to test whether normal functioning of the VMPFC is necessary for ToM functioning. We found that rTMS to the VMPFC, but not sham-rTMS, significantly disrupted ToM learning. Performance on a control task, not involving affective ToM functioning, was not significantly altered after applying rTMS to the VMPFC or sham-rTMS. In an additional experiment, rTMS to the vertex did not significantly affect ToM learning, confirming specificity of the VMPFC region. These findings indicate that the VMPFC is critical for intact ToM learning and shed further light on the concept and localization of ToM in particular and empathic functioning in general.
Multiscale tip asymptotics in hydraulic fracture with leak-off
Authors: GARAGASH DMITRY I. , DETOURNAY EMMANUEL , ADACHI JOSE I.
Published: February 2011

This paper is concerned with an analysis of the near-tip region of a fluid-driven fracture propagating in a permeable saturated rock. The analysis is carried out by considering the stationary problem of a semi-infinite fracture moving at constant speedV. Two basic dissipative processes are taken into account: fracturing of the rock and viscous flow in the fracture, and two fluid balance mechanisms are considered – leak-off and storage of the fracturing fluid in the fracture. It is shown that the solution is characterized by a multiscale singular behaviour at the tip, and that the nature of the dominant singularity depends both on the relative importance of the dissipative processes and on the scale of reference. This solution provides a framework to understand the interaction of representative physical processes near the fracture tip, as well as to track the changing nature of the dominant tip process(es) with the tip velocity and its impact on the global fracture response. Furthermore, it gives a universal scaling of the near-tip processes on the scale of the entire fracture and sets the foundation for developing efficient numerical algorithms relying on accurate modelling of the tip region.
Coating of a textured solid
Authors: SEIWERT JACOPO , CLANET CHRISTOPHE , QUÉRÉ DAVID
Published: February 2011

We discuss how a solid textured with well-defined micropillars entrains a film when extracted out of a bath of wetting liquid. At low withdrawal velocity V, it is shown experimentally that the film exactly fills the gap between the pillars; its thickness hd is independent of V and corresponds to the pillar height hp. At larger velocity, hd slowly increases with V and tends towards the Landau–Levich–Derjaguin (LLD) thickness hLLD observed on a flat solid. We model the entrainment by adapting the LLD theory to a double layer consisting of liquid trapped inside the texture and covered by a free film. This model allows us to understand quantitatively our different observations and to predict the transition between hp and hLLD.
Childhood nutrition and poverty
Authors: Nelson Michael
Published: February 2011

One in three children in Britain lives in poverty (households whose income was less than 50 % average earnings). Low income is associated with poor nutrition at all stages of life, from lower rates of breast-feeding to higher intakes of saturated fatty acids and lower intakes of antioxidant nutrients. Moreover, there is increasing evidence that poor nutrition in childhood is associated with both short-term and long-term adverse consequences such as poorer immune status, higher caries rates and poorer cognitive function and learning ability. These problems arise primarily because parents do not have enough money to spend on food, not because money is being spent unwisely. Policy options to improve the dietary health of poor children include: giving more money to the parents by increasing Income Support (social security) payments, providing food stamps or vouchers, and using food budget standards to inform the levels of income needed to purchase an adequate diet; feeding children directly at school (not only at lunchtime but also at breakfast or homework clubs), by providing free fruit at school, and by increasing entitlement to free food amongst children living in households with low incomes; improving access to a healthy and affordable diet by first identifying ‘food deserts’ and then considering with retailers and local planners how best to provide food in an economical and sustainable way. The value of using food budget standards is illustrated with data relating expenditure on food to growth in children from ‘at-risk’ families (on low income, overcrowded, headed by a lone parent or with four or more children under 16 years of age) living in a poor area in London. Lower levels of expenditure are strongly associated with poorer growth and health, independent of factors such as birth weight, mother’s height, or risk score. The present paper provides evidence that supports the need to review Government legislation in light of nutrition-related inequalities in the health of children.
‘I Let the Language Lead the Dance’: Politics, Musicality, and Voyeurism
Authors: Greig David
Published: February 2011

David Greig is one of Britain's most versatile and exciting playwrights, whose awardwinning work – commissioned by, among others, Suspect Culture, the Royal Shakespeare Company, the National Theatre of Scotland, the Edinburgh International Festival, and the Traverse Theatre – has been performed all over the world. His personal voice is characterized by the sensitive musicality of his text, an individual sense of humour, and an acute awareness of the world around us. Whether his protagonists are Cambridge ornithologists, Scottish lords, or American pilots, Greig creates works of extreme visual beauty and emotional directness in lyrical soundscapes. In the interview which follows, completed in June 2010, he discusses the themes of politics and national identities; language, music, and experimental forms; directors, directing, and adaptations; and watching bodies on stage. Greig believes that theatre is a form of voyeurism, ‘a consensual exchange’ to ‘look at people and watch how they behave’. In his work, the act of watching thus acquires a new role surpassing the simple function of pleasure, and enabling the viewer to engage further with the theatre's mediation to comment, justify, explain, and promote a better understanding of the complexities of human nature – voyeurism in theatre being re-read as a new freedom of the gaze, and its fetishistic attributes re-evaluated as an emancipation of restrained energy, testing the boundaries of taboo. George Rodosthenous is Lecturer in Music Theatre at the School of Performance and Cultural Industries of the University of Leeds. He is Artistic Director of the Altitude North theatre company, and also works as a freelance composer for the theatre. He is currently working on the book Theatre as Voyeurism: the Pleasure(s) of Watching.
Clocking on at the Play Factory: Some Thoughts on Running a Regional Theatre
Authors: Hughes Gwenda
Published: February 2011

At a time when funding cuts may mean that many theatres need to struggle for their very existence, it becomes more important than ever that the teams working together in a particular company, or on a particular production, should feel comfortable with each other, and with the director – on whose shoulders may fall many problems and decisions beyond the straightforwardly artistic. Gwenda Hughes has been Artistic Director of Watford Palace Theatre in Education Company, an Associate Director at Birmingham Rep (where she directed some twenty-five productions), and from 1998 until 2006 was Artistic Director of the New Vic Theatre in Staffordshire. She has also worked as a freelance director for M6, Women's Theatre Group, the Young Vic, Oldham Coliseum, Salisbury Playhouse, Theatre Centre, and Lip Service. Drawing on this extensive and varied experience, she here offers some practical guidance on the pitfalls which face the director and/or the artistic director, and how they can be avoided – or if not avoided, overcome – whether in the rehearsal room, on the ‘top floor’ of management, or in dealing with the public, from fussy members of the audience and local councillors making funding decisions, to visiting royals in need of tactful guidance to the lavatory.
‘Look Again’: Indeterminacy and Contemporary British Drama
Authors: Morin Emilie
Published: February 2011

The integration into conceptual art of techniques inspired by Fluxus (the international aggregate of artists who saw indeterminacy as imaginatively and linguistically enabling) has, in turn, given rise to a specific line in British playwriting since the mid-1990s, as evidenced in plays by Martin Crimp, Sarah Kane, and Tim Crouch which gesture towards conceptual art, performance art, and the event score. In this article Emilie Morin brings to light the affinities between this artistic moment in contemporary British theatre and the international avant-garde. She discusses the shared interest of Crimp, Kane, and Crouch in indeterminacy and the fusion between artistic media, paying particular attention to Crouch's redefinition of the status of the modern artwork in his play for galleries England (2007). Critical recognition of the experimental mode in which these playwrights operate has remained subsumed under a non-specific appreciation of their relationship to conceptual art, leaving important questions of form and legacy unaddressed. Here, the proximity between this marginal trend in British playwriting and developments in experimental music and performance art exploring ideas of indeterminacy is highlighted, and the contemporary problematization of performance as event and concept is reconfigured in relation to the legacies of Marcel Duchamp, John Cage, and Fluxus. Emilie Morin is Lecturer in the Department of English and Related Literature at the University of York and the author of Samuel Beckett and the Problem of Irishness (Palgrave Macmillan, 2009). Her research interests lie in European modernism and the avant-garde.
Imaging biofilm architecture within porous media using synchrotron‐based X‐ray computed microtomography
Authors: Iltis Gabriel C. , Armstrong Ryan T. , Jansik Danielle P. , Wood Brian D. , Wildenschild Dorthe
Published: February 2011

A new method to resolve biofilms in three dimensions in porous media using high‐resolution synchrotron‐based X‐ray computed microtomography (CMT) has been developed. Imaging biofilms in porous media without disturbing the natural spatial arrangement of the porous medium and associated biofilm has been a challenging task, primarily because porous media generally preclude conventional imaging via optical microscopy; X‐ray tomography offers a potential alternative. Using silver‐coated microspheres for contrast, we were able to differentiate between the biomass and fluid‐filled pore spaces. The method was validated using a two‐dimensional micromodel flow cell where both light microscopy and CMT imaging were used to image the biofilm.
Evaluation of single‐well injection‐withdrawal tests in Swedish crystalline rock using the Lagrangian travel time approach
Authors: Cvetkovic V. , Cheng H.
Published: February 2011

A series of 10 single‐well injection‐withdrawal (SWIW) tests are evaluated with two tracers each: uranine and cesium (Cs). An evaluation tool for SWIW tests in crystalline rock is presented on the basis of the Lagrangian travel time approach, whereby probabilities of tracer particle residence times are computed for key stages of the test cycle. Calibration results for three transport parameters and each breakthrough curve are presented. We show that estimates of the controlling retention parameter group are robust for Cs but highly uncertain for uranine. The estimated retention for Cs is larger for the Laxemar‐Simpevarp site compared to the Forsmark site. Deviations from the −3/2 asymptotic breakthrough curve slope observed in a few of the tests at Forsmark are possibly due to a thin fracture coating that has been identified in mineralogical studies at some locations of the site.
Thermo-responsive cellulose-based architectures: tailoring LCST using poly(ethylene glycol) methacrylates
Authors: Porsch Christian , Hansson Susanne , Nordgren Niklas , Malmström Eva
Published: February 2011

Preparation of biomedically interesting HPC-g-PEGMA comb architectures with tunable thermo-responsive behavior, and self-assembling properties.
Fizeau interferometer system for fast high resolution studies of spectral line shapes
Authors: Novák O. , Falconer I. S. , Sanginés R. , Lattemann M. , Tarrant R. N. , McKenzie D. R. , Bilek M. M. M.
Published: February 2011

A monochromator/Fizeau interferometer/intensified CCD camera system is described that was developed for the measurement of the shape of spectral lines that are rapidly time varying. The most important operating parameter that determines the performance of the instrument is the size of the entrance aperture as this determines both the light throughput and the effective interferometer wavelength resolution. This paper discusses, both theoretically and experimentally, the effect of the finite source area on the instrumental resolution to assist in optimizing the choice of this parameter. A second effect that often produces a practical limit to the quality of the spectra is drift of the interferometer plates. Measurements of the shapes of spectral lines of ions and atoms ejected from the cathode spot of continuous and pulsed cathodic arcs are presented to demonstrate the utility of this instrument.
Nuclei-selected NMR shielding calculations: A sublinear-scaling quantum-chemical method
Authors: Beer Matthias , Kussmann Jörg , Ochsenfeld Christian
Published: February 2011

An ab initio method for the direct calculation of NMR shieldings for selected nuclei at the Hartree–Fock and density-functional theory level is presented. Our method shows a computational effort scaling only sublinearly with molecular size, as it is motivated by the physical consideration that the chemical shielding is dominated by its local environment. The key feature of our method is to avoid the conventionally performed calculation of all NMR shieldings but instead to solve directly for specific nuclear shieldings. This has important implications not only for the study of large molecules, but also for the simulation of solvent effects and molecular dynamics, since often just a few shieldings are of interest. Our theory relies on two major aspects both necessary to provide a sublinear scaling behavior: First, an alternative expression for the shielding tensor is derived, which involves the response density matrix with respect to the nuclear magnetic moment instead of the response to the external magnetic field. Second, as unphysical long-range contributions occur within the description of distributed gauge origin methods that do not influence the final expectation value, we present a screening procedure to truncate the B-field dependent basis set, which is crucial in order to ensure an early onset of the sublinear scaling. The screening is in line with the r−2 distance decay of Biot–Savarts law for induced magnetic fields. Our present truncation relies on the introduced concept of “individual gauge shielding contributions” applied to a reformulated shielding tensor, the latter consisting of gauge-invariant terms. The presented method is generally applicable and shows typical speed-ups of about one order of magnitude; moreover, due to the reduced scaling behavior of \documentclass[12pt]{minimal}\begin{document}$\rm {\cal O}(1)$\end{document}O(1) as compared to \documentclass[12pt]{minimal}\begin{document}$\rm {\cal O}(N)$\end{document}O(N), the wins become larger with increasing system size. We illustrate the validity of our method for several test systems, including ring-current dominated systems and biomolecules with more than 1000 atoms.
Rotating full- and reduced-dimensional quantum chemical models of molecules
Authors: Fábri Csaba , Mátyus Edit , Császár Attila G.
Published: February 2011

A flexible protocol, applicable to semirigid as well as floppy polyatomic systems, is developed for the variational solution of the rotational–vibrational Schrödinger equation. The kinetic energy operator is expressed in terms of curvilinear coordinates, describing the internal motion, and rotational coordinates, characterizing the orientation of the frame fixed to the nonrigid body. Although the analytic form of the kinetic energy operator might be very complex, it does not need to be known a priori within this scheme as it is constructed automatically and numerically whenever needed. The internal coordinates can be chosen to best represent the system of interest and the body-fixed frame is not restricted to an embedding defined with respect to a single reference geometry. The features of the technique mentioned make it especially well suited to treat large-amplitude nuclear motions. Reduced-dimensional rovibrational models can be defined straightforwardly by introducing constraints on the generalized coordinates. In order to demonstrate the flexibility of the protocol and the associated computer code, the inversion-tunneling of the ammonia (14NH3) molecule is studied using one, two, three, four, and six active vibrational degrees of freedom, within both vibrational and rovibrational variational computations. For example, the one-dimensional inversion-tunneling model of ammonia is considered also for nonzero rotational angular momenta. It turns out to be difficult to significantly improve upon this simple model. Rotational–vibrational energy levels are presented for rotational angular momentum quantum numbers J = 0, 1, 2, 3, and 4.
Multistage ab initio quantum wavepacket dynamics for electronic structure and dynamics in open systems: Momentum representation, coupled electron-nuclear dynamics, and external fields
Authors: Pacheco Alexander B. , Iyengar Srinivasan S.
Published: February 2011

We recently proposed a multistage ab initio wavepacket dynamics (MS-AIWD) treatment for the study of delocalized electronic systems as well as electron transport through donor–bridge–acceptor systems such as those found in molecular-wire/electrode networks. In this method, the full donor–bridge–acceptor open system is treated through a rigorous partitioning scheme that utilizes judiciously placed offsetting absorbing and emitting boundary conditions. In this manner, the electronic coupling between the bridge molecule and surrounding electrodes is accounted. Here, we extend MS-AIWD to include the dynamics of open-electronic systems in conjunction with (a) simultaneous treatment of nuclear dynamics and (b) external electromagnetic fields. This generalization is benchmarked through an analysis of wavepackets propagated on a potential modeled on an Al27 − C7 − Al27 nanowire. The wavepacket results are inspected in the momentum representation and the dependence of momentum of the wavepacket as well as its transmission probabilities on the magnitude of external bias are analyzed.
Analysis of the equilibrium and kinetics of the ankyrin repeat protein myotrophin
Authors: Faccin Mauro , Bruscolini Pierpaolo , Pelizzola Alessandro
Published: February 2011

We apply the Wako-Saito-Muñoz-Eaton model to the study of myotrophin, a small ankyrin repeat protein, whose folding equilibrium and kinetics have been recently characterized experimentally. The model, which is a native-centric with binary variables, provides a finer microscopic detail than the Ising model that has been recently applied to some different repeat proteins, while being still amenable for an exact solution. In partial agreement with the experiments, our results reveal a weakly three-state equilibrium and a two-state-like kinetics of the wild-type protein despite the presence of a nontrivial free-energy profile. These features appear to be related to a careful “design” of the free-energy landscape, so that mutations can alter this picture, stabilizing some intermediates and changing the position of the rate-limiting step. Also, the experimental findings of two alternative pathways, an N-terminal and a C-terminal one, are qualitatively confirmed, even if the variations in the rates upon the experimental mutations cannot be quantitatively reproduced. Interestingly, the folding and unfolding pathways appear to be different, even if closely related: a property that is not generally considered in the phenomenological interpretation of the experimental data.
Construction and evaluation of a disposable pH sensor based on a large core plastic optical fiber
Authors: Rovati Luigi , Fabbri Paola , Ferrari Luca , Pilati Francesco
Published: February 2011

The fabrication and characterization of a disposable optical fiber sensor for the detection of pH in the range 5–8 are described. The sensing element is a drop of sol–gel hybrid material containing phenol red and deposited onto the tip of a large core plastic optical fiber. This fiber is also exploited for the optical interrogation. This probe can be used as a disposable part of a measuring system. The dynamic range and temporal response of the sensor are here investigated.
A self-heating 2ω method for Seebeck coefficient measurement of thermoelectric materials
Authors: Miao Tingting , Ma Weigang , Zhang Xing , Li Zhen
Published: February 2011

A novel and reliable self-heating 2ω method has been developed to measure the Seebeck coefficient of the microscale/nanoscale thermoelectric materials. Based on the analytical solution of the transient heat-conduction equation of the specimen heated by a harmonic current, two measurement modes have been developed: (1) the Seebeck coefficient can be directly extracted from the ratio of experimentally measured 2ω Seebeck voltage to theoretically predicted 2ω temperature drop oscillation; and (2) the Seebeck coefficient can be steadily extracted from the measured 2ω and 3ω voltages. This approach has been applied to a 25.4 μm thick K-type thermocouple and the measured Seebeck coefficient corresponds well with the nominal value.
[001]-oriented nonepitaxial growth in L1-ordered FePt thin film by SiO2 addition and rapid thermal annealing
Authors: Narisawa T. , Hasegawa T. , Ishio S. , Yamane H.
Published: February 2011

A highly L10-ordered FePt film with a crystalline [001] orientation was prepared by SiO2 addition and rapid thermal postannealing on an oxidized Si substrate. In order to clarify the mechanism of L10 ordering and the crystalline orientation of a nonepitaxial FePt film, we investigated the effect of the preparation conditions on the film structure. The crystalline quality was strongly dependent on the additive amount of SiO2; a high chemical order without the distribution of the chemical order and a nearly perfect [001] orientation were obtained at a SiO2 composition of 10 vol %. The nucleation of L10 grains with a high chemical order and a [001] orientation was observed from an initial phase transformation stage at a low annealing temperature. The as-deposited FePt–SiO2 film consisted of a nanocrystalline structure in which SiO2 segregated at the grain boundaries; SiO2 diffused with the grain growth during thermal annealing. Because the in-plane tensile stress among the grains was a dominant origin for the [001] texture formation, two-dimensional grain growth with the annihilation of grain boundaries played a crucial role in the [001] ordering in nonepitaxial FePt films. It was also crucial to maintain a high stress during annealing, and the [001] ordering was enhanced by rapid heating.
Peculiar surface behavior of some ionic liquids based on active pharmaceutical ingredients
Authors: Restolho José , Mata José Luis , Saramago Benilde
Published: February 2011

The ionic liquids based on biologically active cations and anions, commonly designated by ionic liquids based on active pharmaceutical ingredients (ILs-APIs), are interesting compounds for use in pharmaceutical applications. Lidocaine docusate, ranitidine docusate, and didecyldimethylammonium ibuprofen are examples of promising ILs-APIs that were recently synthesized. They were submitted to biological testing and calorimetric measurements, but nothing is known about their surface properties. In this work, we measured the surface tension and the contact angles on both hydrophilic and hydrophobic surfaces in a temperature range as wide as possible. Based on the wettability data, the polarity fractions were estimated using the Fowkes theory. The peculiar surface behavior observed was tentatively attributed to the presence of mesophases.
Raman and emission characteristics of a-plane InGaN/GaN blue-green light emitting diodes on r-sapphire substrates
Authors: Dong Yanqun , Song Jae-Ho , Kim Ho-Jong , Kim Tae-Soo , Ahn Byung-Jun , Song Jung-Hoon , Cho In-Sung , Im Won-Taek , Moon Youngboo , Hwang Sung-Min , Hong Soon-Ku , Lee Seog-Woo
Published: February 2011

Raman and emission properties of a nonpolar a-plane InGaN/GaN blue-green light emitting diode (LED) on an r-sapphire substrate are investigated and compared with a conventional c-plane blue-green LED. The output power of the a-plane LED was 1.4 mW at 20 mA. The c-plane LED has higher EQE, but it reaches the maximum at a lower forward current and the droop is faster than the a-plane counterpart. As the reverse bias increased, a blueshift in the PL spectra was not observed in the a-plane structure, which is indicative of an absence of quantum confined Stark effects. However, a strong blueshift in the electroluminescence spectra was still present, which means the In localization effects are relevant in nonpolar InGaN/GaN quantum wells. In the Raman spectra, a strong anisotropy of E2(high) phonon modes was observed. By comparing the frequency of the E2(high) modes, we demonstrate that the residual compressive strain in an a-plane LED is significantly smaller than in the polar counterpart.
Cyclotron maser radiation from inhomogeneous plasmas
Authors: Cairns R. A. , Vorgul I. , Bingham R. , Ronald K. , Speirs D. C. , McConville S. L. , Gillespie K. M. , Bryson R. , Phelps A. D. R. , Kellett B. J. , Cross A. W. , Roberston C. W. , Whyte C. G. , He W.
Published: February 2011

Cyclotron maser instabilities are important in space, astrophysical, and laboratory plasmas. While extensive work has been done on these instabilities, most of it deals with homogeneous plasmas with uniform magnetic fields while in practice, of course, the systems are generally inhomogeneous. Here we expand on our previous work [R. A. Cairns, I. Vorgul, and R. Bingham, Phys. Rev. Lett. 101, 215003 (2008)] in which we showed that localized regions of instability can exist in an inhomogeneous plasma and that the way in which waves propagate away from this region is not necessarily obvious from the homogeneous plasma dispersion relation. While we consider only a simple ring distribution in velocity space, because of its tractability, the ideas may point toward understanding the behavior in the presence of more realistic distributions. The main object of the present work is to move away from consideration of the local dispersion relation and show how global growing eigenmodes can be constructed.
Resolving electron scale turbulence in spherical tokamaks with flow shear
Authors: Guttenfelder W. , Candy J.
Published: February 2011

This paper presents nonlinear gyrokinetic simulations of electron temperature gradient (ETG) turbulence based on spherical tokamak (ST) parameters. Most significantly the simulations include the strong toroidal flow and flow shear present in STs that suppress ion-scale turbulence while using kinetic ions at full mass ratio (mi/me=3600). The flow shear provides a physical long-wavelength cutoff mechanism that aids saturation of the simulations, which has previously been demonstrated to be problematic depending on magnetic shear. As magnetic shear varies widely in STs we systematically demonstrate saturation and convergence of the ETG simulations with respect to grid resolution, physical domain size, and boundary conditions. While using reduced ion mass or adiabatic ions can lessen computational expense they do not always provide reliable results. The resulting spectra from converged simulations are anisotropic everywhere in contrast to previous ETG simulations without flow shear. These results have implications for interpreting turbulence measurements, and represent an important step in determining when and where ETG turbulence is expected to be relevant in ST plasmas. They are also important in the context of validating simulations with both experimental transport analysis and turbulence measurements.
Optical absorption of small copper clusters in neon: Cun, (n = 1–9)
Authors: Lecoultre S. , Rydlo A. , Félix C. , Buttet J. , Gilb S. , Harbich W.
Published: February 2011

We present optical absorption spectra in the UV-visible range (1.6 eV < ℏω < 5.5 eV) of mass selected neutral copper clusters Cun(n = 1–9) embedded in a solid neon matrix at 7 K. The atom and the dimer have already been measured in neon matrices, while the absorption spectra for sizes between Cu3 and Cu9 are entirely (n = 6–9) or in great part new. They show a higher complexity and a larger number of transitions distributed over the whole energy range compared to similar sizes of silver clusters. The experimental spectra are compared to the time dependent density functional theory (TD-DFT) implemented in the TURBOMOLE package. The analysis indicates that for energies larger than 3 eV the transitions are mainly issued from d-type states; however, the TD-DFT scheme does not reproduce well the detailed structure of the absorption spectra. Below 3 eV the agreement for transitions issued from s-type states is better.
Interatomic Coulombic decay in mixed NeKr clusters
Authors: Arion Tiberiu , Mucke Melanie , Förstel Marko , Bradshaw Alex M. , Hergenhahn Uwe
Published: February 2011

We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A well-defined feature ranging from 9 to 12 eV in kinetic energy is observed in coincidence with the Ne 2s photoelectrons. It derives from an ICD process, in which an initial Ne 2s vacancy is filled by a Ne 2p electron and an electron is emitted from a 4p level on a neighboring Kr atom. We have studied the dependence of the effect on photon energy, cluster composition, and cluster size. Interestingly, the ICD electron energy increases slightly and grows a shoulder on going from 2% to 5% Kr in the coexpansion process, which we interpret in terms of surface versus bulk effects.
Gyrokinetic equations and full f solution method based on Dirac’s constrained Hamiltonian and inverse Kruskal iteration
Authors: Heikkinen J. A. , Nora M.
Published: February 2011

Gyrokinetic equations of motion, Poisson equation, and energy and momentum conservation laws are derived based on the reduced-phase-space Lagrangian and inverse Kruskal iteration introduced by Pfirsch and Correa-Restrepo [J. Plasma Phys. 70, 719 (2004)]. This formalism, together with the choice of the adiabatic invariant J=⟨p⃗⋅∂x⃗/∂ϕ⟩ as one of the averaging coordinates in phase space, provides an alternative to the standard gyrokinetics. Within second order in gyrokinetic parameter, the new equations do not show explicit ponderomotivelike or polarizationlike terms. Pullback of particle information with an iterated gyrophase and field dependent gyroradius function from the gyrocenter position defined by gyroaveraged coordinates allows direct numerical integration of the gyrokinetic equations in particle simulation of the field and particles with full distribution function. As an example, gyrokinetic systems with polarization drift either present or absent in the equations of motion are considered.
A pure single-walled carbon nanotube thin film based three-terminal microelectromechanical switch
Authors: Jang Min-Woo , Chen Chia-Ling , Partlo Walter E. , Patil Shruti R. , Lee Dongjin , Ye Zhijang , Lilja David , Taton T. Andrew , Cui Tianhong , Campbell Stephen A.
Published: February 2011

The electrical and physical properties of pure single-walled carbon nanotube thin films deposited through a layer-by-layer-self-assembly process are discussed. The film thickness was proportional to the number of dipping cycles. The film resistivity was estimated as 2.19×10−3 Ω cm after thermal treatment processes were performed. The estimated specific contact resistance to gold electrodes was 6.33×10−9 Ω m2 from contact chain measurements. The fabricated three-terminal microelectromechanical switch using these films functioned as a beam for multiple switching cycles with a 4.5 V pull-in voltage. This switch is believed to be a promising device for low power digital logic applications.
Numerical investigation of momentum exchange between particles and coherent structures in low Re turbulent channel flow
Authors: Dritselis Chris D. , Vlachos Nicholas S.
Published: February 2011

The interaction between particles and coherent structures is studied by using discrete particle simulation combined with direct numerical simulation of gaseous flow in a vertical channel. A conditional sampling scheme is used to examine the modifications of the near-wall quasistreamwise vortices by the momentum exchange between the phases. The particle effect on the fluid flow is modeled by a point-force approximation. The particle diameters are smaller than both the smallest flow length scales and the computational grid spacing. Results are obtained for particle ensembles with four response times ranging from 10 to 200 wall units in numerical simulations with and without gravitational settling in the streamwise direction and interparticle collisions. It is found that the size of the quasistreamwise vortices is increased up to 25% in the presence of particles. The increase is larger for the smallest inertia particles studied, which is partly due to their locally nonuniform spatial distribution. The underlying organized fluid motions induced by the structures are substantially attenuated due to the momentum coupling of the phases. A reduction of 5%–55% is observed in the coherent fluid velocities and vorticities. The size of the coherent structures is additionally augmented by streamwise gravitational settling and interparticle collisions, accompanied by more obvious modifications in the surrounding fluid flow. The latter findings are explained by the stronger direct particle effect in these cases, which is also reflected on the energy redistribution between the fluid velocity components, affecting further the fluid turbulence.
High pressure cell for neutron reflectivity measurements up to 2500 bar
Authors: Jeworrek Christoph , Steitz Roland , Czeslik Claus , Winter Roland
Published: February 2011

The design of a high pressure (HP) cell for neutron reflectivity experiments is described. The cell can be used to study solid–liquid interfaces under pressures up to 2500 bar (250 MPa). The sample interface is based on a thick silicon block with an area of about 14 cm2. This area is in contact with the sample solution which has a volume of only 6 cm3. The sample solution is separated from the pressure transmitting medium, water, by a thin flexible polymer membrane. In addition, the HP cell can be temperature-controlled by a water bath in the range 5–75°C. By using an aluminum alloy as window material, the assembled HP cell provides a neutron transmission as high as 41%. The maximum angle of incidence that can be used in reflectivity experiments is 7.5°. The large accessible pressure range and the low required volume of the sample solution make this HP cell highly suitable for studying pressure-induced structural changes of interfacial proteins, supported lipid membranes, and, in general, biomolecular systems that are available in small quantities, only. To illustrate the performance of the HP cell, we present neutron reflectivity data of a protein adsorbate under high pressure and a lipid film which undergoes several phase transitions upon pressurization.
High detectivity squaraine-based near infrared photodetector with nA/cm2 dark current
Authors: Binda M. , Iacchetti A. , Natali D. , Beverina L. , Sassi M. , Sampietro M.
Published: February 2011

We demonstrate an organic photodetector showing high detectivity (3.4×1012 Hz0.5 cm/W) at a wavelength of 700 nm, based on squaraine/phenyl-C61-butyric-acid-methyl-ester bulk-heterojunction active material. This result is achieved by suppressing the device dark currents while simultaneously preserving its external quantum efficiency, as high as 15% at 700 nm. To this aim, a thin cross-linked film based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] is exploited to suppress electron injection from the device anode into the organic blend, thus reducing the dark currents by a factor of 30, to the extremely low value of 2 nA/cm2. Also, the detector bandwidth (∼1 MHz) is unaffected by the introduction of a blocking layer.
Effect of edge threading dislocations on the electronic structure of InN
Authors: Kalesaki E. , Kioseoglou J. , Lymperakis L. , Komninou Ph. , Karakostas Th.
Published: February 2011

The open issue of the n-type conductivity and its correlation to threading dislocations (TDs) in InN is addressed through first principles calculations on the electronic properties of a-edge TDs. All possible dislocation core models are considered (4-, 5/7-, and 8-atom cores) and are found to modify the band structure of InN in a distinct manner. In particular, nitrogen and indium low coordinated atoms in the eight-atom core induce states near the valence band maximum and above the conduction band minimum, respectively. The formation of a nitrogen–nitrogen “wrong” bond is observed at the 5/7-atom core resulting in a state inside the band gap. The 4- and 5/7-atom cores induce occupied states resonant in the conduction band due to In–In strain induced interactions and wrong bonds, respectively. These occupied states designate TDs as a source of higher electron concentrations in InN and provide direct evidence that TDs contribute to its inherent n-type conductivity.
Variational nature, integration, and properties of Newton reaction path
Authors: Bofill Josep Maria , Quapp Wolfgang
Published: February 2011

The distinguished coordinate path and the reduced gradient following path or its equivalent formulation, the Newton trajectory, are analyzed and unified using the theory of calculus of variations. It is shown that their minimum character is related to the fact that the curve is located in a valley region. In this case, we say that the Newton trajectory is a reaction path with the category of minimum energy path. In addition to these findings a Runge–Kutta–Fehlberg algorithm to integrate these curves is also proposed.
On-chip measurement of the Brownian relaxation frequency of magnetic beads using magnetic tunneling junctions
Authors: Donolato M. , Sogne E. , Dalslet B. T. , Cantoni M. , Petti D. , Cao J. , Cardoso F. , Cardoso S. , Freitas P. P. , Hansen M. F. , Bertacco R.
Published: February 2011

We demonstrate the detection of the Brownian relaxation frequency of 250 nm diameter magnetic beads using a lab-on-chip platform based on current lines for exciting the beads with alternating magnetic fields and highly sensitive magnetic tunnel junction (MTJ) sensors with a superparamagnetic free layer. The first harmonic out-of-phase component of the MTJ response gives the imaginary part of the magnetic bead susceptibility, which peaks at the Brownian relaxation frequency. This work paves the way to on-chip implementation of Brownian magnetorelaxometry in innovative “lab-on-a-bead” assays for biomolecular recognition.
Inhibition of In desorption in diluted nitride InAsN quantum dots
Authors: Reyes D. F. , González D. , Sales D. L. , Gargallo-Caballero R. , Guzmán A. , Ulloa J. M. , Hierro A.
Published: February 2011

The effect of low N-alloying on the structure of capped InAs/GaAs quantum dots is analyzed by transmission electron microscopy related techniques. A statistical study of interplanar distances in InAsN quantum dots shows an increase in the lattice parameter compared to the InAs case. We suggest that the addition of nitrogen blocks the Ga/In exchange processes during the quantum dot capping process, leading to an In enrichment. The observed strong photoluminescence redshift of InAsN structures must therefore be attributed not only to the effect of nitrogen in the band gap, but also to a minor depletion of indium during the capping process.
Manipulating the spin polarization of excitons in a single quantum dot by optical means
Authors: Larsson L. A. , Moskalenko E. S. , Holtz P. O.
Published: February 2011

Circular polarization studies of photoluminescence from the neutral (X0) and the positively charged (X+) excitons are reported for individual InAs/GaAs quantum dots (QDs). High polarization degrees, 60% for X0 and 73% for X+, were recorded without any external magnetic field applied. These studies show that the QD polarization and population dynamics are controllable either by varying the photoexcitation intensity or by using a second IR laser excitation.
Suppression criteria of parasitic mode oscillations in a gyrotron beam tunnel
Authors: Kumar Nitin , Singh Udaybir , Singh T. P. , Sinha A. K.
Published: February 2011

This paper presents the design criteria of the parasitic mode oscillations suppression for a periodic, ceramic, and copper loaded gyrotron beam tunnel. In such a type of beam tunnel, the suppression of parasitic mode oscillations is an important design problem. A method of beam-wave coupling coefficient and its mathematical formulation are presented. The developed design criteria are used in the beam tunnel design of a 42 GHz gyrotron to be developed for the Indian TOKAMAK system. The role of the thickness and the radius of the beam tunnel copper rings to obtain the developed design criteria are also discussed. The commercially available electromagnetic code CST and the electron trajectory code EGUN are used for the simulations.
Magnetohydrodynamic structure of a plasmoid in fast reconnection in low-beta plasmas
Authors: Zenitani Seiji , Miyoshi Takahiro
Published: February 2011

Plasmoid structures in fast reconnection in low-beta plasmas are investigated by two-dimensional magnetohydrodynamic simulations. A high-resolution shock-capturing code enables us to explore a variety of shock structures: vertical slow shocks behind the plasmoid, another slow shock in the outer-region, and the shock-reflection in the front side. The Kelvin–Helmholtz-like turbulence is also found inside the plasmoid. It is concluded that these shocks are rigorous features in reconnection in low-beta plasmas, where the reconnection jet speed or the upstream Alfvén speed exceeds the sound speed.
The magnetic Rayleigh–Taylor instability and flute waves at the ion Larmor radius scales
Authors: Onishchenko O. G. , Pokhotelov O. A. , Stenflo L. , Shukla P. K.
Published: February 2011

The theory of flute waves (with arbitrary spatial scales compared to the ion Larmor radius) driven by the Rayleigh–Taylor instability (RTI) is developed. Both the kinetic and hydrodynamic models are considered. In this way we have extended the previous analysis of RTI carried out in the long wavelength limit. It is found that complete finite ion Larmor radius stabilization is absent when the ion diamagnetic velocity attains the ion gravitation drift velocity. The hydrodynamic approach allowed us to deduce a new set of nonlinear equations for flute waves with arbitrary spatial scales. It is shown that the previously deduced equations are inadequate when the wavelength becomes of the order of the ion Larmor radius. In the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Padé approximation corresponds to the results of the fully kinetic treatment. The development of such a theory gives us enough grounds for an adequate description of the RTI stabilization by the finite ion Larmor radius effect.