bluuebunny/crossref_metadata_2025 huggingface dataset:
Analogues of Cores and Stars in Simulated Molecular Clouds
Authors: Wadsley James , Reid Michael , Qamar Farid , Sills Alison , Petitclerc Nicholas
Published: April 2011

We use images derived from collapsing, turbulent molecular cloud simulations without sinks to explore the effects of finite image angular resolution and noise on the derived clump mass function. These effects randomly perturb the clump masses, producing a lognormal clump mass function with a Salpeter-like high mass end. We show that the characteristic break mass of the simulated clump mass functions changes with the angular resolution of the images in a way that is entirely consistent with the observations. We also present some cautionary tales regarding sink particles and highlight the need to ensure that sinks actually correspond to distinct collapsing objects. We test several popular numerical sink criteria in the literature and compare to converged, non-sink results.
The universality hypothesis: binary and stellar populations in star clusters and galaxies
Authors: Kroupa Pavel
Published: April 2011

It is possible to extract, from the observations, distribution functions of the birth dynamical properties of a stellar population, and to also infer that these are quite invariant to the physical conditions of star formation. The most famous example is the stellar IMF, and the initial binary population (IBP) seems to follow suit. A compact mathematical formulation of the IBP can be derived from the data. It has three broad parts: the IBP of the dominant stellar population (0.08–2M⊙), the IBP of the more-massive stars and the IBP of brown dwarfs. These three mass regimes correspond to different physical regimes of star formation but not to structure in the IMF. With this formulation of the IBP it becomes possible to synthesize the stellar-population of whole galaxies.
Magnetic fields and Turbulence in Star Formation using Smoothed Particle Hydrodynamics
Authors: Price Daniel J.
Published: April 2011

Firstly, we give a historical overview of attempts to incorporate magnetic fields into the Smoothed Particle Hydrodynamics method by solving the equations of Magnetohydrodynamics (MHD), leading an honest assessment of the current state-of-the-art in terms of the limitations to performing realistic calculations of the star formation process. Secondly, we discuss the results of a recent comparison we have performed on simulations of driven, supersonic turbulence with SPH and Eulerian techniques. Finally we present some new results on the relationship between the density variance and the Mach number in supersonic turbulent flows, finding σ2ln ρ = ln(1 + b22 with b = 0.33 up to Mach 20, consistent with other numerical results at lower Mach number (Lemaster & Stone 2008) but inconsistent with observational constraints on σρ and in Taurus and IC5146.
Interstellar Turbulence and Star Formation
Authors: Kritsuk Alexei G. , Ustyugov Sergey D. , Norman Michael L.
Published: April 2011

We provide a brief overview of recent advances and outstanding issues in simulations of interstellar turbulence, including isothermal models for interior structure of molecular clouds and larger-scale multiphase models designed to simulate the formation of molecular clouds. We show how self-organization in highly compressible magnetized turbulence in the multiphase ISM can be exploited in simple numerical models to generate realistic initial conditions for star formation.
SPH Radiative Hydrodynamics Methods
Authors: Susa Hajime
Published: April 2011

In this paper, we review the radiative hydrodynamics methods based upon Smoothed Particle Hydrodynamics(SPH). There are already various implementations so far, which can be categorized into three types: moment equation solvers, Monte Carlo methods, and ray-tracing schemes. These codes have been applied to various astrophysical problems including dynamics of dense proto-stellar cores, photoionization feedback of massive stars on molecular clouds, radiative feedback in the early universe, etc. Among these different methods, we focus on the ray-tracing schemes. We also describe one particular ray-tracing code RSPH in some details.
Ray Casting and Flux Limited Diffusion
Authors: Nordlund Åke
Published: April 2011

Solving radiative transfer problems with ray casting methods is compared with the commonly used ‘Flux Limited Diffusion’ approximation. Whereas ray casting produces solutions that converge to the exact one as the number of rays is increased, flux-limited-diffusion is fundamentally a ‘look-alike’ method, which produces solutions that are reminiscent of the correct solution but which cannot be made to converge to it.
The formation of brown dwarfs in discs: Physics, numerics, and observations
Authors: Stamatellos Dimitris , Whitworth Anthony
Published: April 2011

A large fraction of brown dwarfs and low-mass stars may form by gravitational fragmentation of relatively massive (a few 0.1 M⊙) and extended (a few hundred AU) discs around Sun-like stars. We present an ensemble of radiative hydrodynamic simulations that examine the conditions for disc fragmentation. We demonstrate that this model can explain the low-mass IMF, the brown dwarf desert, and the binary properties of low-mass stars and brown dwarfs. Observing discs that are undergoing fragmentation is possible but very improbable, as the process of disc fragmentation is short lived (discs fragment within a few thousand years).
Radiative, magnetic and numerical feedbacks on small-scale fragmentation
Authors: Commerçon Benoît , Hennebelle Patrick , Audit Edouard , Chabrier Gilles , Teyssier Romain
Published: April 2011

Radiative feedback and magnetic field are understood to have a strong impact on the protostellar collapse. We present high resolution numerical calculations of the collapse of a 1 M⊙ dense core in solid body rotation, including both radiative transfer and magnetic field. Using typical parameters for low-mass cores, we study thoroughly the effect of radiative transfer and magnetic field on the first core formation and fragmentation. We show that including the two aforementioned physical processes does not correspond to the simple picture of adding them separately. The interplay between the two is extremely strong, via the magnetic braking and the radiation from the accretion shock.
Observations of Winds, Jets, and Turbulence Generation in GMCs
Authors: Bally John
Published: April 2011

Protostellar outflows can inject sufficient mass, momentum, and kinetic energy into their parent star-forming clumps to dramatically alter their structure, generate turbulence, and even to disrupt them. Outflows represent the lowest rung on a ‘feedback ladder’ consisting of increasingly powerful mechanisms which kick-in if star formation escalates towards the production of more massive stars, higher efficiency, and larger clusters. Outflow feedback may dominate turbulence generation and cloud disruption on the scale of cluster-forming clumps having dimensions up to a few parsecs. Outflows inject energy and momentum on a wide-range of length-scales from less than 0.01 pc to over 30 pc. However, they fail by several orders of magnitude to inject sufficient momentum and kinetic energy to drive turbulent motions on the size and mass-scales of GMCs. Injection from higher rungs on the feedback ladder or momentum injected by Galactic-scale processes are needed to power the observed turbulence on the 10 to 100 pc scales of GMCs.
Origin of the prestellar core mass function and link to the IMF – Herschel first results
Authors: André Ph. , Men'shchikov A. , Könyves V. , Arzoumanian D.
Published: April 2011

We briefly review ground-based (sub)millimeter dust continuum observations of the prestellar core mass function (CMF) and its connection to the stellar initial mass function (IMF). We also summarize the first results obtained on this topic from the Herschel Gould Belt survey, one of the largest key projects with the Herschel Space Observatory. Our early findings with Herschel confirm the existence of a close relationship between the CMF and the IMF. Furthermore, they suggest a scenario according to which the formation of prestellar cores occurs in two main steps: 1) complex networks of long, thin filaments form first, probably as a result of interstellar MHD turbulence; 2) the densest filaments then fragment and develop prestellar cores via gravitational instability.
Outflows and Turbulence in Young Stellar Clusters — An Observer's View
Authors: Arce Héctor G.
Published: April 2011

Recent numerical studies have focused their interest on the impact outflows have on the cloud's turbulence. The contradictory results obtained by these studies indicate that it is essential for observers to provide the required data to constrain the models. Here we discuss the impact of outflows on the environment surrounding clusters of young stellar objects, from an observer's point of view. We have conducted several studies of outflows in different active star-forming regions. In all cases it is clear that outflows have the power to sustain the observed turbulence in the gas surrounding protostellar clusters. We investigate whether there is a correlation between outflow strength and star formation efficiency, as predicted by numerical simulations, for six different regions in the Perseus molecular cloud complex. We argue that results of other recent studies that use CO line maps to study the turbulence driving length should not be used to discard outflows as major drivers of turbulence in clusters.
Discs, outflows, and feedback in collapsing magnetized cores
Authors: Duffin Dennis F. , Pudritz Ralph E.
Published: April 2011

The pre-stellar cores in which low mass stars form are generally well magnetized. Our simulations show that early protostellar discs are massive and experience strong magnetic torques in the form of magnetic braking and protostellar outflows. Simulations of protostellar disk formation suggest that these torques are strong enough to suppress a rotationally supported structure from forming for near critical values of mass-to-flux. We demonstrate through the use of a 3D adaptive mesh refinement code – including cooling, sink particles and magnetic fields – that one produces transient 1000 AU discs while simultaneously generating large outflows which leave the core region, carrying away mass and angular momentum. Early inflow/outflow rates suggest that only a small fraction of the mass is lost in the initial magnetic tower/jet event.
Radiation-MHD Simulations of HII Region Expansion in Turbulent Molecular Clouds
Authors: Arthur S. J. , Henney W. J. , Mellema G. , de Colle F. , Vázquez-Semadeni E.
Published: April 2011

We use numerical simulations to investigate how the expansion of an HII region is affected by an ambient magnetic field. First we consider the test problem of expansion in a uniform medium with a unidirectional magnetic field. We then describe the expansion of an HII region in a turbulent medium, taking as our initial conditions the results of and MHD turbulence simulation. We find that although in the uniform medium case the magnetic field does produce interesting effects over long length and timescales, in the turbulent medium case the main effect of the magnetic field is to reduce the efficiency of fragmentation of the molecular gas.
Supernova Feedback on the Interstellar Medium and Star Formation
Authors: Hensler Gerhard
Published: April 2011

Supernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the development of the complexity of investigations aiming at understanding the interchange between supernovae and their released hot gas with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and apply multiple recipes of these parameters, only a representative selection of studies can be discussed here.
The interaction of an Hii region with a fractal molecular cloud
Authors: Walch Steffi , Whitworth Ant , Bisbas Thomas , Wünsch Richard , Hubber David
Published: April 2011

We describe an algorithm for constructing fractal molecular clouds that obeys prescribed mass and velocity scaling relations.The algorithm involves a random seed, so that many different realisations corresponding to the same fractal dimension and the same scaling relations can be generated. It first generates all the details of the density field, and then position the SPH particles, so that the same simulation can be repeated with different numbers of particles to explore convergence. It can also be used to initialise finite-difference simulations. We then present preliminary numerical simulations of Hii regions expanding into such clouds, and explore the resulting patterns of star formation. If the cloud has low fractal dimension, it already contains many small self-gravitating condensations, and the principal mechanism of star formation is radiatively driven implosion. This results in star formation occurring quite early, throughout the cloud. The stars resulting from the collapse and fragmentation of a single condensation are often distributed in a filament pointing radially away from the source of ionising radiation; as the remainder of the condensation is dispersed, these stars tend to get left behind in the Hii region. If the cloud has high fractal dimension, the cloud does not initially contain dense condensations, and star formation is therefore delayed until the expanding Hii region has swept up a sufficiently massive shell. The shell then becomes gravitationally unstable and breaks up into protostars. In this collect-and-collapse mode, the protostars are distributed in tangential arcs, they tend to be somewhat more massive, and as the expansion of the shell stalls they move ahead of the ionisation front.
Observational Comparison of Star Formation in Different Galaxy Types
Authors: Grebel Eva K.
Published: April 2011

Galaxies cover a wide range of masses and star formation histories. In this review, I summarize some of the evolutionary key features of common galaxy types. At the high-mass end, very rapid, efficient early star formation is observed, accompanied by strong enrichment and later quiescence, well-described by downsizing scenarios. In the intermediate-mass regime, early-type galaxies may still show activity in low-mass environments or when being rejuvenated by wet mergers. In late-type galaxies, we find continuous, though variable star formation over a Hubble time. In the dwarf regime, a wide range of properties from bursty activity to quiescence is observed. Generally, stochasticity dominates here, and star formation rates and efficiencies tend to be low. Morphological types and their star formation properties correlate with environment.
Star Formation in the Central Molecular Zone of the Milky Way
Authors: Kim Sungsoo S. , Saitoh Takayuki R. , Jeon Myoungwon , Merritt David , Figer Donald F. , Wada Keiichi
Published: April 2011

Gas materials in the inner Galactic disk continuously migrate toward the Galactic center (GC) due to interactions with the bar potential, magnetic fields, stars, and other gaseous materials. Those in forms of molecules appear to accumulate around 200 pc from the center (the central molecular zone, CMZ) to form stars there and further inside. The bar potential in the GC is thought to be responsible for such accumulation of molecules and subsequent star formation, which is believed to have been continuous throughout the lifetime of the Galaxy. We present 3-D hydrodynamic simulations of the CMZ that consider self-gravity, radiative cooling, and supernova feedback, and discuss the efficiency and role of the star formation in that region. We find that the gas accumulated in the CMZ by a bar potential of the inner bulge effectively turns into stars, supporting the idea that the stellar cusp inside the central 200 pc is a result of the sustained star formation in the CMZ. The obtained star formation rate in the CMZ, 0.03–0.1 M⊙, is consistent with the recent estimate based on the mid-infrared observations by Yusef-Zadeh et al. (2009).
Control of galactic scale star formation by gravitational instability or midplane pressure?
Authors: Mac Low Mordecai-Mark
Published: April 2011

Star formation in galaxies has been suggested to depend on large-scale gravitational instability or on the pressure required to form molecular hydrogen. I present numerical models and analysis of observations in support of the gravitational instability hypothesis. I also consider whether the correlation between the surface densities of molecular hydrogen and star formation implies causation, and if so in which direction.
Modeling Formation of Globular Clusters: Beacons of Galactic Star Formation
Authors: Gnedin Oleg Y.
Published: April 2011

Modern hydrodynamic simulations of galaxy formation are able to predict accurately the rates and locations of the assembly of giant molecular clouds in early galaxies. These clouds could host star clusters with the masses and sizes of real globular clusters. I describe current state-of-the-art simulations aimed at understanding the origin of the cluster mass function and metallicity distribution. Metallicity bimodality of globular cluster systems appears to be a natural outcome of hierarchical formation and gradually declining fraction of cold gas in galaxies. Globular cluster formation was most prominent at redshifts z > 3, when massive star clusters may have contributed as much as 20% of all galactic star formation.
The formation of super-star clusters in disk and dwarf galaxies
Authors: Weidner Carsten , Bonnell Ian A. , Zinnecker Hans
Published: April 2011

Super-star clusters are probably the largest star-forming entities in our local Universe, containing hundreds of thousands to millions of young stars usually within less than a few parsecs. While no such systems are known in the Milky Way (MW), they are found especially in pairs of interacting galaxies but also in some dwarf galaxies like R 136 in the Large Magelanic Cloud (LMC). With the use of SPH calculations we show that a natural explanation for this phenomenon is the presence of shear in normal spiral galaxies which facilitates the formation of low-density loose OB associations from giant molecular clouds (GMC) instead of dense super-star clusters. In contrast, in interacting galaxies and in dwarf galaxies, regions can collapse without having a large-scale sense of rotation. This lack of rotational support allows the giant molecular clouds to concentrate into a single, dense and gravitationally bound system.
Numerical Cosmology powered by GPUs
Authors: Aubert Dominique
Published: April 2011

Graphics Processing Units (GPUs) offer a new way to accelerate numerical calculations by means of on-board massive parallelisation. We discuss two examples of GPU implementation relevant for cosmological simulations, an N-Body Particle-mesh solver and a radiative transfer code. The latter has also been ported on multi-GPU clusters. The range of acceleration (x30-x80) achieved here offer bright perspective for large scale simulations driven by GPUs.
GAMER with out-of-core computation
Authors: Schive Hsi-Yu , Tsai Yu-Chih , Chiueh Tzihong
Published: April 2011

GAMER is a GPU-accelerated Adaptive-MEsh-Refinement code for astrophysical simulations. In this work, two further extensions of the code are reported. First, we have implemented the MUSCL-Hancock method with the Roe's Riemann solver for the hydrodynamic evolution, by which the accuracy, overall performance and the GPU versus CPU speed-up factor are improved. Second, we have implemented the out-of-core computation, which utilizes the large storage space of multiple hard disks as the additional run-time virtual memory and permits an extremely large problem to be solved in a relatively small-size GPU cluster. The communication overhead associated with the data transfer between the parallel hard disks and the main memory is carefully reduced by overlapping it with the CPU/GPU computations.
A Fast Explicit Scheme for Solving MHD Equations with Ambipolar Diffusion
Authors: Kim Jongsoo
Published: April 2011

We developed a fast numerical scheme for solving ambipolar diffusion MHD equations with the strong coupling approximation, which can be written as the ideal MHD equations with an additional ambipolar diffusion term in the induction equation. The mass, momentum, magnetic fluxes due to the ideal MHD equations can be easily calculated by any Godunov-type schemes. Additional magnetic fluxes due to the ambipolar diffusion term are added in the magnetic fluxes, because of two same spatial gradients operated on the advection fluxes and the ambipolar diffusion term. In this way, we easily kept divergence-free magnetic fields using the constraint transport scheme. In order to overcome a small time step imposed by ambipolar diffusion, we used the super time stepping method. The resultant scheme is fast and robust enough to do the long term evolution of star formation simulations. We also proposed that the decay of alfen by ambipolar diffusion be a good test problem for our codes.
Ambipolar Diffusion Effects on Weakly Ionized Turbulence Molecular Clouds
Authors: Li Pak Shing , McKee Christopher F. , Klein Richard I.
Published: April 2011

Ambipolar diffusion (AD) is a key process in molecular clouds (MCs). Non-ideal MHD turbulence simulations are technically very challenging because of the large Alfvén speed of ions in weakly ionized clouds. Using the Heavy-Ion Approximation method (Li, McKee & Klein 2006), we have carried out two-fluid simulations of AD in isothermal, turbulent boxes at a resolution of 5123, to investigate the effect of AD on the weakly ionized turbulence in MCs. Our simulation results show that the neutral gas component of the two-fluid system gradually transforms from an ideal MHD turbulence system to near a pure hydrodynamic turbulence system within the standard AD regime, in which the neutrals and ions are coupled over a flow time. The change of the turbulent state has a profound effect on the weakly ionized MCs.
Radiative Transfer Modeling of Simulation and Observational Data
Authors: Steinacker Jürgen , Henning Thomas , Bacmann Aurore
Published: April 2011

Radiative Transfer (RT) is considered to be one of the four Grand Challenges in Computational Astrophysics aside of Astrophysical Fluid Dynamics, N-Body Problems in Astrophysics, and Relativistic Astrophysics. The high dimensionality (7D instead of 4D for MHD) and the underlying integro-differential transport equation have forced coders to implement approximative RT methods in order to fit spectra and images or to treat RT in their HD and MHD codes.

The central role of RT in star formation (SF) is based on several facts: a) The dense dusty gas in SF regions alters the radiation substantially making SF one of the most complex applications of RT. b) Radiation transports energy within the object and is therefore an essential part of any dynamical SF model. c) RT calculations tell us which of the processes/structures are visible at what wavelength by which telescope/instrument. Hence, RT is the central tool to analyze simulation results or to explore the scientific capabilities of planned instruments. d) With inverse RT, we can obtain the 1D-3D density and temperature structure from observations, completely decoupled from any (M)HD modeling (and the approximations made within).

In this review, we summarize the main difficulties and the currently used computational techniques to calculate the RT in SF regions. Recent applications of 3D continuum RT in molecular clouds and disks around young massive stars are discussed to illustrate the capabilities and limits of current RT modeling.
Galactic star formation in parsec-scale resolution simulations
Authors: Powell Leila C. , Bournaud Frederic , Chapon Damien , Devriendt Julien , Slyz Adrianne , Teyssier Romain
Published: April 2011

The interstellar medium (ISM) in galaxies is multiphase and cloudy, with stars forming in the very dense, cold gas found in Giant Molecular Clouds (GMCs). Simulating the evolution of an entire galaxy, however, is a computational problem which covers many orders of magnitude, so many simulations cannot reach densities high enough or temperatures low enough to resolve this multiphase nature. Therefore, the formation of GMCs is not captured and the resulting gas distribution is smooth, contrary to observations. We investigate how star formation (SF) proceeds in simulated galaxies when we obtain parsec-scale resolution and more successfully capture the multiphase ISM. Both major mergers and the accretion of cold gas via filaments are dominant contributors to a galaxy's total stellar budget and we examine SF at high resolution in both of these contexts.
Cosmological simulations of low-mass galaxies: some potential issues
Authors: Colín Pedro , Avila-Reese Vladimir , Valenzuela Octavio
Published: April 2011

Cosmological Adaptive Mesh Refinement simulations are used to study the specific star formation rate (sSFR=SSF/Ms) history and the stellar mass fraction, fs=Ms/MT, of small galaxies, total masses MT between few × 1010 M⊙ to few ×1011 M⊙. Our results are compared with recent observational inferences that show the so-called “downsizing in sSFR” phenomenon: the less massive the galaxy, the higher on average is its sSFR, a trend seen at least since z ~ 1. The simulations are not able to reproduce this phenomenon, in particular the high inferred values of sSFR, as well as the low values of fs constrained from observations. The effects of resolution and sub-grid physics on the SFR and fs of galaxies are discussed.
Comparison between Simulations and Theory: where we stand
Authors: Monaghan Joe J.
Published: April 2011

In this paper I relate progress in the simulation of star formation to a remarkable early (1962) paper by Fowler and Hoyle who analyzed star formation in terms of the relevant energies starting from the formation of a large (100 pc) cloud and ending with the final mass distribution of the stars. The way in which modern simulations have clarified and corrected the Fowler-Hoyle picture, and areas where we could improve our simulations, are discussed.
Concluding Remarks: Playing by the Numbers
Authors: Trimble Virginia
Published: April 2011

Advances in available computing facilities, judiciously employed by our colleagues, have undoubtedly enhanced our understanding of the processes by which stars (and planets) form, from very diffuse gas to something you could almost live around. Nevertheless we remain very far from being able to describe (let alone explain) what is going on in many cases. And this is likely to remain true even as Moore's Law growth begins to hit its head against energy and power considerations. A large fraction of long-standing questions appear to have honest answers of the general form, “yes and no”, “all of the above”, or “some of them are and some of them aren't”. This includes many of my favorites, like triggering, formation of binary populations, and the role of magnetic fields. Rather few questions have actually been retired from the universe of discourse in recent years.
Two faces of patient safety and care quality: a Franco-American comparison
Authors: Degos Laurent , Rodwin Victor G.
Published: April 2011

Patient safety, and more broadly the quality of care, is typically discussed with reference to the reduction of preventable adverse events within hospitals and adherence to practice guidelines on care processes. We call it the ‘care-centered approach’ and recognize that the United States is a leader in the field. Another face of patient safety and care quality may be defined as the ‘system-centered approach’. It focuses on access to a timely and effective continuum of health-care services – clinical prevention, primary care and appropriate referral to and receipt of specialty care. Although France's efforts to pursue a care-centered approach to patient safety are limited, its system-centered approach yields some benefits. Based on the evidence we have reviewed for access to primary care (hospital discharges for avoidable hospital conditions), mortality amenable to medical intervention and consumer satisfaction, in the United States and France, there appear to be good grounds for bolstering the system-centered approach in the United States.
Regulating agriculture in the WTO
Authors: Smith Fiona
Published: April 2011

This article argues there is value in exploring the resonance between the regulation of international agricultural trade as a specific topic and the general notion of international trade regulation in the World Trade Organisation (WTO). It explores particular problems to illuminate more general concerns. In this ascendant way of looking at things, certain aspects of agricultural trade regulation have direct resonance for other areas covered by the WTO agreements. We might see these additional dimensions as addressing a different series of questions: the nature of agreement and the different ways in which agreement can manifest itself. The two dimensions are the nature of international agricultural trade as a polycentric problem and the way accepted concepts and categories influence how we see problems in international agricultural trade. Polycentrism goes to the nature of the stability of the Agreement on Agriculture, whereas the question of concepts and categories concerns the way in which we represent the problem as coherent to ourselves.
Law is not (best considered) an essentially contested concept
Authors: Ehrenberg Kenneth M.
Published: April 2011

Absrtact

I argue that law is not best considered an essentially contested concept. After first explaining the notion of essential contestability and disaggregating law into several related concepts, I show that the most basic and general concept of law does not fit within the criteria offered for essential contestation. I buttress this claim with the explanation that essential contestation is itself a framework for understanding complex concepts and therefore should only be applied when it would yield a greater understanding of uses of the concept to which it is applied. I then show that, even if law meets some basic criteria of essential contestation, applying the appellation does not helpfully illuminate the most general concept of law and therefore it should not be used, while allowing that it might be more useful for the related concept of the rule of law.
Thinking culturally about risk
Authors: Burgess Adam
Published: April 2011

Ferrari's book is a welcome addition to the still limited literature on the bovine spongiform encephalopathy (BSE) experience which, unlike any other specific response to a disease, played an important role in reshaping modern governance and consolidating key assumptions about the world around us. The ‘mad cow’ crisis began in 1986 when the unfathomable bovine brain disease was identified, but was then reignited with the shocking discovery a decade later that it could pass, and had passed, to humans despite the controls put in place. Scientific confirmation in 1996 that there was a human form of BSE led to political panic and further undermined the then exhausted Conservative Party rule. The retrospective lessons of the experience went far beyond agriculture. The problem was perceived to be one of openness and independence: perhaps government was too dependent upon lobbies and financial interests such as agriculture and, whilst utilising scientific advice, did not allow their independent voice to have influence. Less widely recognised, but even more importantly, the political lesson of the BSE experience was to henceforth tend to avoid being seen to downplay risk, based on the retrospective view that the danger could, and should, have been announced before it was scientifically confirmed. Better to overestimate even apparently limited risks than be caught again committing the now cardinal sin of downplaying them, or simply remaining silent. This is not so much a new-found principle of risk aversion as a variation on an age-old political truism of, above all, making sure that the next crisis is ‘not on my watch’.
Optical two-tone generation and SSB modulation using electro-optic modulator with suppressing redundant spectrum components
Authors: Enokihara Akira , Kawai Tadashi , Kawanishi Tetsuya
Published: April 2011

Doubled frequency optical two-tone generation and optical single sideband (SSB) modulation by the dual-electrode-type electro-optic (EO) modulator with a single Mach–Zehnder (MZ) interferometer were considered. We theoretically showed that redundant spectrum components in the modulated optical signals, which are caused by the imbalance of light splitting ratio between the two arms of the interferometer, are significantly suppressed by controlling the input power ratio of RF modulation signals applied to each electrode. This effect was confirmed by the experiment, where an optical two-tone with the redundant components 49.8 dB lower than the primary two-tone components in intensity level was obtained. This method is also valid for suppression of undesired frequency components of RF signals that are generated at a photo detector from the optical two-tone waves propagated through a dispersive optical fiber.
Thermal effects in precision systems: Design considerations, modelling, compensation and validation techniques
Authors: Ruijl T. A. M.
Published: April 2011

In common high-end precision systems, thermal effects, in general, play a very important role with respect to the final performance of the system. Mainly driven by miniaturization, performance and reliability enhancement, the requirements of these systems have enormously increased over the last few decades. To stimulate exchange of knowledge and cooperation in the precision engineering community a special interest group was initiated by the Euspen. During a meeting in 2006 it turned out that thermal effects occur in many different applications and in all forms. The complexity of the thermal effects and the high impact on the performance of systems motivated the group to organize a conference in 2007. All kinds of applications were mentioned, starting from traditional machine tools up to next-generation lithography tools and analysis tools. The huge diversity of the thermal issues in all kinds of market segments was also very clearly discussed.
Extended X-ray absorption fine structure studies of magnetic nanoparticles
Authors: Agarwal A. , Singh M. K. , Kaneko T. , Nagamatsu S.-I. , Konishi T. , Fujikawa T.
Published: April 2011

We have synthesized nickel by means of pulsed laser ablation. A nickel disc was used for ablation with the focused output of fundamental harmonic from Nd:YAG laser. X-ray diffraction result shows that the synthesized nanoparticles are of pure metallic nickel with a face-centred cubic structure and the average particle size is 35 nm. The extended X-ray absorption fine structure (EXAFS) studies of pure nickel foil and the synthesized nanoparticles show similar structures. The position of the main peak is same in these nanoparticles with reference to the nickel foil. The only difference was observed in the reduction of the amplitude. The nearest-neighbour distance is similar as for pure nickel foil. The Debye–Waller factor is also similar. There is no trace of oxide and hydroxide in the EXAFS data, suggesting that the synthesized nanoparticles contain only nickel metal.
X-ray absorption spectroscopy characterization of the interface in capped ZnO nanoparticles
Authors: Guglieri C. , Chaboy J.
Published: April 2011

We report here an extensive study of the ZnO nanoparticles (NPs) capped with different organic molecules by X-ray absorption spectroscopy (XAS) methods to proceed in the understanding of their unusual magnetism. We have performed a detailed ab initio calculation of the Zn K-edge XAS aimed at determining the influence of the different coordination induced by the capping. The results suggest that the observed differences of the XAS spectra are due to the formation of a well-defined interface between the oxide NPs and the capping molecules. The appearance of magnetism should be related to the modifications induced in the NPs by the surface bonds between Zn and the capping molecule.
Konsensus-Empfehlungen zum Einsatz polyhexanidhaltiger Produkte in der Behandlung von Wunden
Authors: Roth  , Hotz  , Mayer  , Läuchli  , Traber
Published: April 2011

Polyhexanidhaltige Wundbehandlungs-Produkte werden häufig für die Behandlung von akuten und chronischen Wunden eingesetzt. Obwohl ausreichende Informationen zur Verwendung von Polyhexanid in der Literatur zu finden sind, ist die angemessene Anwendung dieser Produkte in der klinischen Praxis nicht immer klar. Das Ziel dieser Konsensus-Empfehlung ist es, Ärztinnen/Ärzten und Pflegefachleuten, die Patienten mit akuten und chronischen Wunden behandeln, klinisch relevante Empfehlungen zur Verfügung zu stellen. Dieser Bericht beschreibt die klinisch relevanten Eigenschaften von Polyhexanid und gibt Empfehlungen für die Prophylaxe und Behandlung von Wundinfektionen.
Une hypoxie réfractaire
Authors: Guillemin
Published: April 2011

On rapporte un cas d'hypoxie réfractaire chez un patient ancien tabagique de 85 ans, présentant des co-morbidités cardiaques et pulmonaires. L'ensemble du tableau clinique à l'admission à l'Hôpital laissait suspecter une décompensation cardiaque et une pneumonie à l'origine de l'insuffisance respiratoire. Malgré une prise en charge optimale de ces pathologies qui ont pu être stabilisées, le patient reste sévèrement hypoxique, mais relativement pauci-symptomatique. L'absence de réponse à l'oxygénothérapie et la péjoration des saturations en oxygène lors du passage de la position couchée à la position assise (ou debout) évoquent finalement la présence d'un syndrome de platypnée-orthodéoxie sur shunt cardiaque droite-gauche, diagnostic confirmé par une échocardiographie avec injection de microbulles qui révèle un important shunt inter-auriculaire droite-gauche. Le patient n'a pas souhaité envisager de traitement curatif (fermeture du shunt).
Geospace Environment Modeling 2008–2009 Challenge: Geosynchronous magnetic field
Authors: Rastätter L. , Kuznetsova M. M. , Vapirev A. , Ridley A. , Wiltberger M. , Pulkkinen A. , Hesse M. , Singer H. J.
Published: April 2011

In this paper the metrics‐based results of the inner magnetospheric magnetic field part of the 2008–2009 GEM Metrics Challenge are reported. The Metrics Challenge asked modelers to submit results for four geomagnetic storm events and five different types of observations that can be modeled by statistical or climatological or physics‐based (e.g., MHD) models of the magnetosphere‐ionosphere system. We present the results of 12 model settings that were run at the Community Coordinated Modeling Center and at the institutions of various modelers for these events. To measure the performance of each of the models against the observations, we use direct comparisons between the strength of the measured magnetic field (B), the sine of the elevation angle Θxz (τ), and the spectral power of fluctuations for both quantities. We find that model rankings vary widely by type of variable and skill score used. None of the models consistently performs best for all events. We find that empirical models perform well for weak storm events, and physics‐based (magnetohydrodynamic) models are better for strong storm events. Within a series of runs of the same model we find that higher resolution may not always improve results unless more physics of the inner magnetosphere, such as the kinetic description of the ring current, is included.
Calculating Occupancy when One does not have Baseline: A Comparison of Different Options
Authors: Kim Euitae , Howes Oliver D , Yu Kyung-Sang , Jeong Jae Min , Lee Jae Sung , Jang In-Jin , Shin Sang-Goo , Kapur Shitij , Kwon Jun Soo
Published: April 2011

Dopamine D2 receptor occupancy of antipsychotic drugs is calculated relative to the subject's D2 receptor binding potential (BP) in the drug-free state (baseline BP). Because baseline BP is seldom known in patients with schizophrenia, population means from unrelated control samples are often used to estimate it. However, this is likely to introduce bias and error into the occupancy measure. There is thus a need for a method to reliably estimate baseline BP for patient populations in whom it may be impractical or unethical to get baseline measurements. It has been previously found that the relationship between plasma concentration and dopamine receptor occupancy by antipsychotic drugs follows a sigmoid Emax model. Based on this, we developed a method for calculating dopamine D2 receptor occupancy by antipsychotic drugs using an inhibitory Emax model ( Imax method) that estimates individual baseline BPs. To validate this, we compared the result from the Imax method with actual occupancy and estimated occupancy calculated from the average baseline BP (substitution method). The data for validation were obtained from two different receptor occupancy studies with the antipsychotic medications YKP1358 and aripiprazole. We estimated the reliability between the true measured occupancy and the predicted occupancy using the intraclass correlation coefficient (ICC), and the variability of occupancy was also compared between the Imax and substitution methods. In YKP1358 study, all the ICCs of the Imax method were above 0.8, but those of the substitution method showed values lower than 0.8. In aripiprazole study, the ICCs of the Imax method were higher than those of the substitution method, but all the ICCs showed higher values than 0.8. The variability of Imax method was significantly smaller than that of substitution method in both studies. The Imax method shows better reliability and less variability than the substitution method. The Imax method can be applied for receptor occupancy study, and bring more reliability and accuracy to the occupancy study in patients with schizophrenia.
Quantitation of Translocator Protein Binding in Human Brain with the Novel Radioligand [18F]-FEPPA and Positron Emission Tomography
Authors: Rusjan Pablo M , Wilson Alan A , Bloomfield Peter M , Vitcu Irina , Meyer Jeffrey H , Houle Sylvain , Mizrahi Romina
Published: April 2011

This article describes the kinetic modeling of [18F]-FEPPA binding to translocator protein 18 kDa in the human brain using high-resolution research tomograph (HRRT) positron emission tomography. Positron emission tomography scans were performed in 12 healthy volunteers for 180 minutes. A two-tissue compartment model (2-CM) provided, with no exception, better fits to the data than a one-tissue model. Estimates of total distribution volume ( VT), specific distribution volume ( VS), and binding potential ( BPND) demonstrated very good identifiability (based on coefficient of variation ( COV)) for all the regions of interest (ROIs) in the gray matter ( COV VT < 7%, COV VS < 8%, COV BPND < 11%). Reduction of the length of the scan to 2 hours is feasible as VS and VT showed only a small bias (6% and 7.5%, respectively). Monte Carlo simulations showed that, even under conditions of a 500% increase in specific binding, the identifiability of VT and VS was still very good with COV<10%, across high-uptake ROIs. The excellent identifiability of VT values obtained from an unconstrained 2-CM with data from a 2-hour scan support the use of VT as an appropriate and feasible outcome measure for [18F]-FEPPA.
Metabolic and Perfusion Responses to Recurrent Peri-Infarct Depolarization during Focal Ischemia in the Spontaneously Hypertensive Rat: Dominant Contribution of Sporadic CBF Decrements to Infarct Expansion
Authors: Takeda Yoshimasa , Zhao Liang , Jacewicz Michael , Pulsinelli William A , Nowak Thaddeus S
Published: April 2011

Peri-infarct depolarizations (PIDs) contribute to the evolution of focal ischemic lesions. Proposed mechanisms include both increased metabolic demand under conditions of attenuated perfusion and overt vasoconstrictive responses to depolarization. The present studies investigated the relative contributions of metabolic and perfusion effects to PID-associated infarct expansion during middle cerebral artery (MCA) occlusion in the Spontaneously Hypertensive Rat. The initial distribution of ischemic depolarization (ID) was established within minutes after MCA occlusion at a cerebral blood flow threshold of ∼40 mL/100 g per minute, with expansion of the depolarized territory during 3hours detected in half of the animals. Peri-infarct depolarizations were associated with transient metabolic responses, comparable to those observed after spreading depression, with no evidence of cumulative energy failure after multiple transient depolarizations during 1 hour. Speckle contrast imaging of PID-associated flow transients documented prominent distal hyperemic flow responses that became progressively attenuated in regions of already impaired perfusion, with modest propagated flow decreases more proximal to the ischemic core. However, sporadic PIDs were associated with persistent decrements in perfusion, increasing tissue volume below the threshold for energy failure, ID and infarction. These latter, comparatively rare, events can account for the pattern of stepwise infarct expansion in this model.
Distribution of Vesicular Monoamine Transporter 2 Protein in Human Brain: Implications for Brain Imaging Studies
Authors: Tong Junchao , Boileau Isabelle , Furukawa Yoshiaki , Chang Li-Jan , Wilson Alan A , Houle Sylvain , Kish Stephen J
Published: April 2011

The choice of reference region in positron emission tomography (PET) human brain imaging of the vesicular monoamine transporter 2 (VMAT2), a marker of striatal dopamine innervation, has been arbitrary, with cerebellar, whole cerebral, frontal, or occipital cortices used. To establish whether levels of VMAT2 are in fact low in these cortical areas, we measured VMAT2 protein distribution by quantitative immunoblotting in autopsied normal human brain ( n = 6). Four or five species of VMAT2 immunoreactivity (75, 55, 52, 45, 35 kDa) were detected, which were all markedly reduced in intensity in nigrostriatal regions of patients with parkinsonian conditions versus matched controls ( n = 9 to 10 each). Using the intact VMAT2 immunoreactivity, cerebellar and cerebral neocortices had levels of the transporter > 100-fold lower than the VMAT2-rich striatum and with no significant differences among the cortical regions. We conclude that human cerebellar and cerebral cortices contain negligible VMAT2 protein versus the striatum and, in this respect, all satisfy a criterion for a useful reference region for VMAT2 imaging. The slightly lower PET signal for VMAT2 binding in occipital (the currently preferred reference region) versus cerebellar cortex might not therefore be explained by differences in VMAT2 protein itself but possibly by other imaging variables, for example, partial volume effects.
Role of subdominant stable modes in plasma microturbulence
Authors: Hatch D. R. , Terry P. W. , Jenko F. , Merz F. , Pueschel M. J. , Nevins W. M. , Wang E.
Published: April 2011

In gyrokinetic simulations, thousands of degrees of freedom are available to contribute to the fluctuation spectrum. For wavevectors with a single linear instability, the unstable eigenmode accounts for only one of these degrees of freedom. Little has been known about the role of the remaining fluctuations in the turbulent dynamics. In this paper, these fluctuations are characterized as modes in mode decompositions of gyrokinetic distribution functions from nonlinear simulations. This analysis reveals the excitation of a hierarchy of damped modes at the same perpendicular scales as the driving instabilities. Two effects of these subdominant modes are described: First, these damped modes define a potent energy sink, creating a situation where energy drive and energy dissipation peak at the same perpendicular scales. Second, damped modes with tearing parity (even parity about the outboard midplane for A|| fluctuations) are driven to significant amplitudes and facilitate the development of magnetic stochasticity in electromagnetic gyrokinetic simulations.