bluuebunny/crossref_metadata_2025 huggingface dataset:
The dust emission SED of X-ray emitting regions in Stephan's Quintet
Authors: Natale G. , Tuffs R. J. , Xu C. K. , Popescu C. C. , Fischera J. , Lisenfeld U. , Lu N. , Appleton P. , Dopita M. , Duc P.-A. , Gao Y. , Reach W. , Sulentic J. , Yun M.
Published: August 2012

We analysed the Spitzer maps of Stephan's Quintet in order to investigate the nature of the dust emission associated with the X-ray emitting regions of the large scale intergalactic shock and of the group halo. This emission can in principle be powered by dust-gas particle collisions, thus providing efficient cooling of the hot gas. However the results of our analysis suggest that the dust emission from those regions is mostly powered by photons. Nonetheless dust collisional heating could be important in determining the cooling of the IGM gas and the large scale star formation morphology observed in SQ.
Cosmic-Ray induced diffuse emissions from the Milky Way and Local Group galaxies
Authors: Porter Troy A.
Published: August 2012

Cosmic rays fill up the entire volume of galaxies, providing an important source of heating and ionisation of the interstellar medium, and may play a significant role in the regulation of star formation and galactic evolution. Diffuse emissions from radio to high-energy γ-rays (>100 MeV) arising from various interactions between cosmic rays and the interstellar medium, interstellar radiation field, and magnetic field, are currently the best way to trace the intensities and spectra of cosmic rays in the Milky Way and other galaxies. In this contribution, I describe our recent work to model the full spectral energy distribution of galaxies like the Milky Way from radio to γ-ray energies. The application to other galaxies, in particular the Magellanic Clouds and M31 that are now resolved in high-energy γ-rays by the Fermi-LAT, is also discussed.
The H.E.S.S. view of the Milky Way in TeV light
Authors: Deil Christoph
Published: August 2012

Since 2003 the H.E.S.S. collaboration has been operating an array of four imaging Cherenkov telescopes in the Khomas Highlands of Namibia. H.E.S.S. can detect gamma rays in the energy range 100 GeV to 100 TeV, has a large field of view (5 degree), good angular resolution (0.1 degree), energy resolution (15%) and sensitivity (a 1% Crab flux point source is detected at 5 sigma significance in 25 h). About half of the available observing time has been spent on the Milky Way, either in scan mode or on individual sources, resulting in the detection of more than 60 Galactic TeV sources. In this talk the two most numerous source classes will be discussed, pulsar wind nebulae and supernova remnants. For the identification and understanding of the TeV emission seen by H.E.S.S. additional measurements of non-thermal emission, mainly in the radio, X-ray and lower-energy gamma-ray bands, are critical. Since August 2008 the Fermi Large Area Telescope has been scanning the whole sky in the energy range from 20 MeV to more than 300 GeV and has detected about 200 Galactic sources as well as diffuse emission from the Milky Way. This talk will give an overview of Galactic H.E.S.S. observations in the multi-wavelength context, with a focus on Fermi.
The star formation rate in the Milky Way: Results from stars and planetary nebulae
Authors: Macie Walter J. , Rocha-Pinto Helio J. , Costa Roberto D. D.
Published: August 2012

The star formation rate (SFR) is still a poorly known characteristic of the Milky Way, especially concerning the possibility of an irregular SFR, compared to a constant rate. Some recent results based on the distribution of dwarf stars with chromospheric ages suggest at least two major bursts in the past 10 Gyr, while other investigations are consistent with an approximately constant SFR. The SFR also shows important spatial variations, particularly concerning the radial variations along the galactic disc. In this work, we investigate two different problems relative to the galactic SFR: (i) We estimate the star formation rate in the galactic disc based on the age distribution of the planetary nebula central stars (CSPN), and compare these results with previous investigations based on dwarf stars. The CSPN ages were derived on the basis of five different methods, involving the observed nebular metallicities and kinematical properties; (ii) We derive radial abundance gradients from several elements in planetary nebulae, and compare these results with recent determinations based on younger objects, such as HII regions and cepheid variables. Since the gradients are linked to the formation process of the galactic disc, we can estimate the spatial variation of the SFR. Preliminary results indicate that at least one major star formation burst is obtained, as well as a relatively smooth variation of the SFR along the galactocentric radius.
High-energy emission from galaxies: the star-formation/gamma-ray connection
Authors: Ohm Stefan , Hinton Jim
Published: August 2012

The impact of non-thermal processes on the spectral energy distributions of galaxies can be dramatic, but such processes are often neglected in considerations of their structure and evolution. Particle acceleration associated with high mass star formation and AGN activity not only leads to very broad band (radio-γ-ray) emission, but may also produce very significant feedback effects on galaxies and their environment. The recent detections of starburst galaxies at GeV and TeV energies suggest that γ-ray instruments have now reached the critical level of sensitivity to probe the connection between particle acceleration and star-formation in galaxies. In this paper we will try to summarise this recent progress, put it into a multi-wavelength context and also discuss the prospects for more precise and sensitive γ-ray measurements with the upcoming CTA observatory.
The resolved radio–FIR correlation in nearby galaxies with Herschel and Spitzer
Authors: Tabatabaei Fatemeh S. , Schinnerer Eva , Murphy Eric , Beck Rainer , Hughes Annie , Groves Brent ,   The KINGFISH Team
Published: August 2012

We investigate the correlation between the far-infrared (FIR) and radio continuum emission from NGC6946 on spatial scales between 0.9 and 17 kpc. We use the Herschel PACS (70, 100, 160μm) and SPIRE (250μm) data from the KINGFISH project. Separating the free-free and synchrotron components of the radio continuum emission, we find that FIR is better correlated with the free-free than the synchrotron emission. Compared to a similar study in M33 and M31, we find that the scale dependence of the synchrotron–FIR correlation in NGC6946 is more similar to M31 than M33. The scale dependence of the synchrotron–FIR correlation can be explained by the turbulent-to-ordered magnetic field ratio or, equivalently, the diffusion length of the cosmic ray electrons in these galaxies.
No evidence for evolution in the Far-Infrared-Radio correlation out to z ~ 2 in the ECDFS
Authors: Mao Minnie Y. , Huynh Minh T. , Norris Ray P. , Dickinson Mark , Frayer Dave , Helou George , Monkiewicz Jacqueline A.
Published: August 2012

The Far-Infrared Radio Correlation (FRC) is the tightest and most universal correlation known among global parameters of galaxies. Here we present the results of our investigation of the 70 μm FRC of starforming galaxies in the Extended Chandra Deep Field South (ECDFS) out to z > 2. In order to quantify the evolution of the FRC we used both survival analysis and stacking techniques, which gave similar results. We also calculated the FRC using total infrared luminosity and rest-frame radio luminosity, qTIR, and find that qTIR is constant (within 0.22) over the redshift range 0 - 2. We see no evidence for evolution in the FRC at 70 μm, which is surprising given the many factors that are expected to change this ratio at high redshifts.
The non-thermal broadband spectral energy distribution of radio galaxies
Authors: Romero Gustavo E.
Published: August 2012

I present a model for the non-thermal production of electromagnetic radiation in the jets of radio galaxies. The model goes far beyond the simple one-zone models usually applied to these sources. The transport equation is solved in the co-moving frame of the jet, taken into account the inhomogeneous structure of the outflow. Energy distributions for all types of particles are then obtained in a self-consistent way, including protons, electrons, and secondaries. The spectral energy distribution resulting from all relevant radiative processes is computed, including synchrotron radiation, relativistic Bremsstrahlung, proton-proton collisions and subsequent decays, photo-meson production, radiation from pairs formed by photon absorption and injection from decays, as well as direct pair production. Absorbing fields in the host galaxy are considered when computing the final SED. The model is applied to Centaurus A and compared with the available multi-wavelength data.
Very high energy γ-radiation from the radio quasar 4C 21.35
Authors: González Josefa Becerra , Maraschi Laura , Mazin Daniel , Prandini Elisa , Saito Koji , Sitarek Julian , Stamerra Antonio , Tavecchio Fabrizio , Terzić Tomislav , Treves Aldo ,   MAGIC Collaboration
Published: August 2012

A very high energy (VHE) γ-radiation was detected from a flat spectrum radio quasar (FSRQ) 4C 21.35 (PKS1222+21) by MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes on June 17th 2010. 4C 21.35 is only the 3rd FSRQ detected in VHE γ-rays. With its hard spectrum (Γ = 2.72±0.34) with no apparent cut-off at energies below 130 GeV and an extremely fast variation of flux (doubling in 8.6+1.1−0.9 minutes), this detection poses a challenge to existing models of VHE γ-radiation from FSRQs. The most important results of observations performed by MAGIC telescopes are presented here, as well as some possible explanations of those results.
Synchrotron radiation from giant e± pair halos
Authors: Eungwanichayapant A. , Maithong W. , Ruffolo D.
Published: August 2012

A giant e± pair halo is formed by electromagnetic cascades developing around an AGN under the intergalactic magnetic field (1nG - 1μG). Many studies have been focussed on the pair halos in the gamma band because it has been predicted that the e±s in the pair halos up-scatter the Cosmic Microwave Background (CMB) to be gamma-rays. However, the pair halos do not emit only gamma photons but also X-ray photons via synchrotron radiation. In this paper, the Spectral Energy Distributions (SEDs) and the angular distributions of the synchrotron radiation of the pair halos from the Monte Carlo simulations will be discussed.
Spectrophotometric measurement of the Extragalacic Background Light
Authors: Mattila Kalevi , Lehtinen Kimmo , Väisänen Petri , von Appen-Schnur Gerhard , Leinert Christoph
Published: August 2012

The Extragalactic Background Light (EBL) at UV, optical and NIR wavelengths consists of the integrated light of all unresolved galaxies along the line of sight plus any contributions by intergalactic matter including hypothetical decaying relic particles. The measurement of the EBL has turned out to be a tedious problem. This is because of the foreground components of the night sky brightness, much larger than the EBL itself: the Zodiacal Light (ZL), Integrated Starlight (ISL), Diffuse Galactic Light (DGL) and, for ground-based observations, the Airglow (AGL) and the tropospheric scattered light. We have been developing a method for the EBL measurement which utilises the screening effect of a dark nebula on the EBL. A differential measurement in the direction of a high-latitude dark nebula and its surrounding area provides a signal that is due to two components only, i.e. the EBL and the diffusely scattered ISL from the cloud. We present a progress report of this method where we are now utilising intermediate resolution spectroscopy with ESO's VLT telescope. We detect and remove the scattered ISL component by using its characteristic Fraunhofer line spectral signature. In contrast to the ISL, in the EBL spectrum all spectral lines are washed out. We present a high quality spectrum representing the difference between an opaque position within our target cloud and several clear OFF positions around the cloud. We derive a preliminary EBL value at 400 nm and an upper limit to the EBL at 520 nm. These values are in the same range as the EBL lower limits derived from galaxy counts.

Unit: We will use in this paper the abbreviation 1 cgs = 10−9erg s−1cm−2sr−1Å−1
An empirical approach to the extragalactic background light from AEGIS galaxy SED-type fractions
Authors: Domínguez Alberto
Published: August 2012

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ-ray astronomy. However, the overall spectrum of the EBL between 0.1 and 1000 μm has never been determined directly, neither from observed luminosity functions (LFs), over a wide redshift range, nor from any multiwavelength observation of galaxy spectral energy distributions (SEDs). The evolving overall spectrum of the EBL is derived here utilizing a novel method based on observations only. It is emphasized that the local EBL seems already well constrained from the UV up to the mid-IR. Different independent methodologies such as direct measurement, galaxy counts, γ-ray attenuation and realistic EBL modelings point towards the same EBL intensity level. Therefore, a relevant contribution from Pop III stars to the local EBL seems unlikely.
Determining the average SFR of K+A galaxies
Authors: Nielsen Danielle M. , de Propris Roberto , Ridgway Susan E. , Goto Tomotsugu
Published: August 2012

We stack FIRST survey cutout images of 811 K+A galaxies to derive a mean 1.4 GHz radio image of our sample from which we measure a mean K+A flux density of 56 μJy. We carry out Monte Carlo simulations by randomly selecting radio-quiet white dwarfs to create 10,000 stacks equivalent to our K+A stack. From the measured fluxes of these stacks, we establish a 5σ detection limit of 43 μJy for stacked images. For the average redshift of our sample, we find an mean star formation rate of ~1.7 M⊙ yr−1. We split the sample by age and find a mean radio flux of 60 μJy, which corresponds to a star formation rate of 1.6 M⊙ yr−1, for galaxies with starburst ages less than 250 Myr.
Cosmic Infrared Background ExpeRiment (CIBER): A probe of Extragalactic Background Light from reionization
Authors: Cooray Asantha , Bock Jamie , Kawada Mitsunobu , Keating Brian , Lange Andrew , Lee Dae-Hee , Levenson Louis , Matsumoto Toshio , Matsuura Shuji , Renbarger Tom , Sullivan Ian , Tsumura Kohji , Wada Takehiko , Zemcov Michael
Published: August 2012

The Cosmic Infrared Background ExpeRiment (CIBER) is a rocket-borne absolute photometry imaging and spectroscopy experiment optimized to detect signatures of first-light galaxies present during reionization in the unresolved IR background. CIBER-I consists of a wide-field two-color camera for fluctuation measurements, a low-resolution absolute spectrometer for absolute EBL measurements, and a narrow-band imaging spectrometer to measure and correct scattered emission from the foreground zodiacal cloud. CIBER-I was successfully flown in February 2009 and July 2010 and four more flights are planned by 2014, including an upgrade (CIBER-II). We propose, after several additional flights of CIBER-I, an improved CIBER-II camera consisting of a wide-field 30 cm imager operating in 4 bands between 0.5 and 2.1 microns. It is designed for a high significance detection of unresolved IR background fluctuations at the minimum level necessary for reionization. With a FOV 50 to 2000 times larger than existing IR instruments on satellites, CIBER-II will carry out the definitive study to establish the surface density of sources responsible for reionization.
Extragalactic science with ALMA
Authors: Bendo George J. ,   the UK ALMA Regional Centre Node
Published: August 2012

The Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope comprising 66 antennas that is located in the Atacama Desert in Chile, one of the driest locations on Earth. When the telescope is fully operational, it will perform observations over ten receiver bands at wavelengths from 9.5-0.32 mm (31-950 GHz) with unprecedented sensitivities to continuum emission from cold (<20 K) dust, Bremsstrahlung, and synchrotron emission as well as submillimetre and millimetre molecular lines. With baselines out to 16km and dynamic reconfiguration, ALMA will achieve spatial resolutions ranging from 3″ to 0.010″, allowing for detailed imaging of continuum or molecular line emission from 0.1-1 kpc scale gas and dust discs in high-redshift sources or 10-100 pc scale molecular clouds and substructures within nearby galaxies. Science observations started on 30 September 2011 with 16 antennas and four receiver bands on baselines up to 400 m. The telescope's capabilities will steadily improve until full operations begin in 2013.
Looking at the distant universe with the MeerKAT Array (LADUMA)
Authors: Holwerda B. W. , Blyth S.-L. , Baker A. J. ,   the LADUMA team
Published: August 2012

The MeerKAT (64 x 13.5m dish radio interferometer) is South Africa's precursor instrument for the Square Kilometre Array (SKA), exploring dish design, instrumentation, and the characteristics of a Karoo desert site and is projected to be on sky in 2016. One of two top-priority, Key Projects is a single deep field, integrating for 5000 hours total with the aim to detect neutral atomic hydrogen through its 21 cm line emission out to redshift unity and beyond. This first truly deep HI survey will help constrain fueling models for galaxy assembly and evolution. It will measure the evolution of the cosmic neutral gas density and its distribution over galaxies over cosmic time, explore evolution of the gas in galaxies, measure the Tully-Fisher relation, measure OH maser counts, and address many more topics. Here we present the observing strategy and envisaged science case for this unique deep field, which encompasses the Chandra Deep Field-South (and the footprints of GOODS, GEMS and several other surveys) to produce a singular legacy multi-wavelength data-set.
Retrieving the stellar content in distant starbursts
Authors: Rodrigues Myriam A. , Hammer François , Puech Mathieu
Published: August 2012

In starburst galaxies, the light emitted by the young and massive stars dominates the photon budget along most of the SED and hides the old and intermediate stellar populations. The fraction of old stars and the stellar mass are systematically underestimated by current methods (Wuyts et al. (2009)). We have implemented a new method to retrieve stellar masses and stellar populations in distant galaxies from photometry and spectral features. The method uses a complex SFH description and a new constraint has been introduced: the star-formation rate (SFR).
Star formation properties in barred galaxies
Authors: Zhou Zhi-Min , Cao Chen , Wu Hong
Published: August 2012

Stellar bars are important structures for the internal secular evolution of galaxies. They can drive gas into the central region of galaxies, and result in an enhancement of star formation activity there. Previous studies are limited in the comparisons between barred and unbarred galaxies. Here we try to investigate the connection between star formation activities and different bars, based on multi-wavelength data in a sample of barred spirals. We find that there is no clearly trend of the surface star formation rates in different structures along the bar strength. In addition, there is larger scatter for the properties of star formation activity in the galaxies with middle-strength bars, which may indicate that a variety of star formation stages are more likely associated with these bars.
High resolution 3D P wave velocity structure beneath Tenerife Island (Canary Islands, Spain) based on tomographic inversion of active‐source data
Authors: García‐Yeguas Araceli , Koulakov Ivan , Ibáñez Jesús M. , Rietbrock A.
Published: August 2012

We present a high resolution 3 dimensional (3D) P wave velocity model for Tenerife Island, Canaries, covering the top of Teide volcano (3,718 m a.s.l.) down to around 8 km below sea level (b.s.l). The tomographic inversion is based on a large data set of travel times obtained from a 3D active seismic experiment using offshore shots (air guns) recorded at more than 100 onshore seismic stations. The obtained seismic velocity structure is strongly heterogeneous with significant (up to 40%) lateral variations. The main volcanic structure of the Las Cañadas‐Teide‐Pico Viejo Complex (CTPVC) is characterized by a high P wave velocity body, similar to many other stratovolcanoes. The presence of different high P wave velocity regions inside the CTPVC may be related to the geological and volcanological evolution of the system. The presence of high P wave velocities at the center of the island is interpreted as evidence for a single central volcanic source for the formation of Tenerife. Furthermore, reduced P wave velocities are found in a small confined region in CTPVC and are more likely related to hydrothermal alteration, as indicated by the existence of fumaroles, than to the presence of a magma chamber beneath the system. In the external regions, surrounding CTPVC a few lower P wave velocity regions can be interpreted as fractured zones, hydrothermal alterations, porous materials and thick volcaniclastic deposits.
Permafrost degradation as a control on hydrogeological regime shifts in a warming climate
Authors: Bense V. F. , Kooi H. , Ferguson G. , Read T.
Published: August 2012

Using numerical models, we evaluate hydrogeological regime changes in high‐latitude river basins under conditions of ground surface warming. These models describe transient heat‐ and fluid flow coupled to the hydrogeological impacts of phase‐changes from ice to liquid water. We consider an idealized unconsolidated sedimentary aquifer system in which groundwater flow is driven by topography, representing a series of small drainage basins in riverine terrain of relatively subdued topography. Various temporal and spatial surface temperature conditions are considered to control the initial permafrost distributions for the simulations. The simulated rates of increase in groundwater contribution to streamflow during and after permafrost thaw, are in the order of magnitude comparable to hydrogeological regime changes over the past decades as reported for several (sub‐)Arctic rivers. The simulations further show that two distinct features of the subsurface response control the temporal evolution of base flow increase: (1) shifts in aquifer permeability architecture during permafrost degradation and (2) uptake of water into aquifer storage when sub‐permafrost hydraulic heads rise. Model analysis shows that the latter process delays base flow increase by several decades to centuries. In order to evaluate the relative importance of both processes in natural systems, the current hydraulic regime of sub‐permafrost aquifer systems as well as patterns of permafrost heterogeneity, taliks and their hydraulic connectivity are insufficiently known.
Continuous rice cropping has been sequestering carbon in soils in Java and South Korea for the past 30 years
Authors: Minasny Budiman , McBratney Alex B. , Hong Suk Young , Sulaeman Yiyi , Kim Myung Sook , Zhang Yong Seon , Kim Yi Hyun , Han Kyung Hwa
Published: August 2012

The soil system represents the dominant terrestrial reservoir of carbon in the biosphere. Deforestation, poor land management, and excessive cropping lead to a decrease in soil carbon stocks, but intensive cropping can reverse this trend. We discuss long‐term soil organic carbon data from two major rice‐growing areas: Java (Indonesia) and South Korea. Soil organic carbon content in the top 15 cm for both countries has increased in recent decades. In South Korea, the top 15 cm of soils store about 31 Tg (1012 g) of carbon (C) with a sequestration rate of 0.3 Tg C per year. In Java, the agricultural topsoils accumulated more than 1.7 Tg C per year over the period 1990–2010. We attribute the increase in measured SOC mainly to increases in above‐ and below‐ ground biomass due to fertilization. Good agronomic practices can maintain and increase soil carbon, which ensures soil security to produce food and fiber.
InSAR analysis of the 2008 Reno‐Mogul earthquake swarm: Evidence for westward migration of Walker Lane style dextral faulting
Authors: Bell John W. , Amelung Falk , Henry Christopher D.
Published: August 2012

Analysis and modeling of InSAR data covering the 2008 Reno‐Mogul M 4.7 earthquake swarm indicate that the main event was produced by slip on a previously unrecognized strike‐slip fault in the Reno basin. Deformation of 0.5–2.5 cm in radar line‐of‐sight was produced by the main event and post‐seismic slip over an area of more than ∼150 km2. This earthquake is one of the smallest magnitude events modeled with InSAR to date in the seismically active western Basin and Range, and it provides new insights into regional neotectonic relations. Inverse modeling of the InSAR data suggests that the earthquake swarm was generated by 25–75 cm of dextral displacement on a N44W‐striking fault with a ∼3 km rupture length and a rupture depth of ∼2 km. The InSAR‐detected strike‐slip ground deformation is unique for the Reno basin which is in the purely extensional domain of the Sierra Nevada‐Basin and Range Transition Zone, an area dominated by north‐striking normal faults. The InSAR modeling of the 2008 earthquake swarm supports the concept of westward migration of Walker Lane transcurrent faulting and overprinting of extensional Basin and Range structures, in this case the westward migration of dextral shear associated with the northern Walker Lane into the extension‐dominated Reno basin.
Scale dependence of the variance anisotropy near the proton gyroradius scale: Additional evidence for kinetic Alfvén waves in the solar wind at 1 AU
Authors: Podesta John J. , TenBarge Jason M.
Published: August 2012

The kinetic Alfvén wave (KAW) has the property that for βp ∼ 1 the ratio (δB∥)2/(δB⊥)2 approaches zero in the small wave number limit k⊥ρp ≪ 1 and increases monotonically to values of order unity when k⊥ρp ∼ 1, where ρp is the thermal proton gyroradius. In this study, the wave number dependence of the ratio (δB∥)2/(δB⊥)2 is used to investigate the existence of KAWs in the solar wind near the proton gyroradius scale k⊥ρp = 1. To facilitate comparisons between theory and observations, solar wind measurements of (δB∥)2/(δB⊥)2 are restricted to times when the local mean magnetic field B0 is nearly perpendicular to the local flow velocity of the solar wind V. The quantity (δB∥)2 is the average magnetic power in the B0 direction and (δB⊥)2 is the average magnetic power in the V × B0 direction. The analysis of 20 high speed streams in the ecliptic plane near 1 AU from 2007 through 2011 consistently yield quantitatively similar results which all show a steady increase in the ratio (δB∥)2/(δB⊥)2 in the neighborhood of k⊥ρp= 1 that is in reasonable agreement with the theory of KAWs derived from the Vlasov‐Maxwell dispersion relation. These results are interpreted as evidence for the existence of an axisymmetric spectrum of KAWs in the fast solar wind at wave numbers neark⊥ρp = 1 where the energy spectrum of solar wind fluctuations steepens and kinetic physics becomes important.
Tsunami‐induced phase and amplitude perturbations of subionospheric VLF signals
Authors: Rozhnoi A. , Shalimov S. , Solovieva M. , Levin B. , Hayakawa M. , Walker S.
Published: August 2012

A network of VLF receivers, sited in the Far East, has been used to observe the response of the lower ionosphere to tsunamis resulting from the November 15, 2006 (Kuril region) and the March 11, 2011 (Tohoku region) earthquakes. Specific perturbations in the phase and amplitude of VLF signals have been found for both cases. A qualitative interpretation of the observed effects is suggested in terms of the interaction of internal gravity waves with lower ionosphere.
A new analytical framework for assessing the effect of sea‐level rise and dredging on tidal damping in estuaries
Authors: Cai Huayang , Savenije Hubert H. G. , Toffolon Marco
Published: August 2012

This paper explores different analytical solutions of the tidal hydraulic equations in convergent estuaries. Linear and quasi‐nonlinear models are compared for given geometry, friction, and tidal amplitude at the seaward boundary, proposing a common theoretical framework and showing that the main difference between the examined models lies in the treatment of the friction term. A general solution procedure is proposed for the set of governing analytical equations expressed in dimensionless form, and a new analytical expression for the tidal damping is derived as a weighted average of two solutions, characterized by the usual linearized formulation and the quasi‐nonlinear Lagrangean treatment of the friction term. The different analytical solutions are tested against fully nonlinear numerical results for a wide range of parameters, and compared with observations in the Scheldt estuary. Overall, the new method compares best with the numerical solution and field data. The new accurate relationship for the tidal damping is then exploited for a classification of estuaries based on the distance of the tidally averaged depth from the ideal depth (relative to vanishing amplification) and the critical depth (condition for maximum amplification). Finally, the new model is used to investigate the effect of depth variations on the tidal dynamics in 23 real estuaries, highlighting the usefulness of the analytical method to assess the influence of human interventions (e.g. by dredging) and global sea‐level rise on the estuarine environment.
Spectral aerosol direct radiative forcing from airborne radiative measurements during CalNex and ARCTAS
Authors: LeBlanc Samuel E. , Schmidt K. S. , Pilewskie P. , Redemann J. , Hostetler C. , Ferrare R. , Hair J. , Langridge J. M. , Lack D. A.
Published: August 2012

This study presents the aerosol radiative forcing derived from airborne measurements of shortwave spectral irradiance during the 2010 Research at the Nexus of Air Quality and Climate Change (CalNex). Relative forcing efficiency, the radiative forcing normalized by aerosol optical thickness and incident irradiance, is a means of comparing the aerosol radiative forcing for different conditions. In this study, it is used to put the aerosol radiative effects of an air mass in the Los Angeles basin in context with case studies from three field missions that targeted other regions and aerosol types, including a case study from the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS). For CalNex, we relied on irradiance measurements onboard the NOAA P‐3 aircraft during a flight on 19 May 2010 over a ground station. CalNex presented a difficulty for determining forcing efficiency since one of the input parameters, optical thickness, was not available from the same aircraft. However, extinction profiles were available from a nearby aircraft. An existing retrieval algorithm was modified to use those measurements as initial estimate for the missing optical thickness. In addition, single scattering albedo and asymmetry parameter (secondary products of the method), were compared with CalNex in situ measurements. The CalNex relative forcing efficiency spectra agreed with earlier studies that found this parameter to be constrained at each wavelength within 20% per unit of aerosol optical thickness at 500 nm regardless of aerosol type and experiment, except for highly absorbing aerosols sampled near Mexico City. The diurnally averaged below‐layer forcing efficiency integrated over the wavelength range of 350–700 nm for CalNex is estimated to be −58.6 ± 13.8 W/m2, whereas for the ARCTAS case it is −48.7 ± 11.5 W/m2.
An alternative scaling for unsteady penetrative free convection
Authors: Catalano Franco , Moroni Monica , Dore Valentina , Cenedese Antonio
Published: August 2012

The daytime evolution of the atmospheric boundary layer under high pressure, anticyclonic synoptic systems over a homogeneous terrain can be successfully described by a penetrative free convection model, evolving from an initially stably stratified environment. In this article dimensional analysis has been employed to derive a new set of scaling parameters, which are functions of external, time‐dependent, fluid properties and boundary conditions. This novel theoretical framework has been adopted to compare laboratory scale experiments, performed using a thermally controlled water tank and a Large Eddy Simulation (LES) numerical model. Both these have been developed for the characterization of the instabilities associated with the development of the Convective Boundary Layer (CBL). The characteristic length and time scales of the thermal plumes, their spatial distribution and interaction with the overlying stable layer are analyzed. The proposed scaling parameters appear to be representative of the bulk and turbulent properties of the CBL, as confirmed by both numerical and laboratory results.
Global maps of anhydrous minerals at the surface of Mars from OMEGA/MEx
Authors: Ody A. , Poulet F. , Langevin Y. , Bibring J.‐P. , Bellucci G. , Altieri F. , Gondet B. , Vincendon M. , Carter J. , Manaud N.
Published: August 2012

We here reassess the global distribution of several key mineral species using the entire OMEGA/Mars Express VIS‐NIR imaging spectrometer data set, acquired from orbit insertion in January 2004 to August 2010. Thirty‐two pixels per degree global maps of ferric oxides, pyroxenes and olivines have been derived. A significant filtering process was applied in order to exclude data acquired with unfavorable observation geometries or partial surface coverage with water and CO2 frosts. Because of strong atmospheric variations over the 3.6 Martian years of observations primarily due to the interannual variability of the aerosol opacity, a new filter based on the atmospheric dust opacity calibrated by the Mars Exploration Rovers measurements has also been implemented. The Fe3+absorption features are present everywhere on the surface, with a variety of intensities indicating distinct formation processes. The pyroxene‐bearing regions are localized in low albedo regions, while the bright regions are spectrally comparable to anhydrous nanophase ferric oxides. The expanded data set increases by a factor of about 2, the number of olivine detections reported in previous OMEGA‐based studies. Olivine is mainly detected in three types of areas over the Martian surface: discontinuous patches on the terraces of the three main basins; smooth inter‐crater plains and smooth crater floors throughout the southern highlands; and crater sand dunes, crater ejectas and extended bedrock exposures in the northern plains. Olivine is also detected in the low albedo pyroxene‐bearing dunes surrounding the northern polar cap.
Academic labour shortages
Authors: Hunter Philip
Published: August 2012

A shortage of skilled science labour in Europe could hold back research progress. The EU will increase science funding to address the problem, but real long‐term measures need to start in schools, not universities.
Meiotic pairing by non‐coding RNA?
Authors: Yamashita Akira , Kariyazono Ryo , Watanabe Yoshinori
Published: August 2012

How are homologous chromosomes identified during meiosis? A report in Science suggests the answer may be non‐coding RNAs, but much work remains to be done.
Design and synthesis of a novel series of cyclohexyloxy-pyridyl derivatives as inhibitors of diacylglycerol acyl transferase 1
Authors: Plowright Alleyn T. , Barton Peter , Bennett Stuart , Birch Alan M. , Birtles Susan , Buckett Linda K. , Butlin Roger J. , Davies Robert D. M. , Ertan Anne , Gutierrez Pablo Morentin , Kemmitt Paul D. , Leach Andrew G. , Svensson Per H. , Turnbull Andrew V. , Waring Michael J.
Published: August 2012

Design and synthesis of a novel series of cyclohexyloxy-pyridyl inhibitors of diacylglycerol acyl transferase 1.
Thomson scattering diagnostic for the measurement of ion species fraction
Authors: Ross J. S. , Park H.-S. , Amendt P. , Divol L. , Kugland N. L. , Rozmus W. , Glenzer S. H.
Published: August 2012

Simultaneous Thomson scattering measurements of collective electron-plasma and ion-acoustic fluctuations have been utilized to determine ion species fraction from laser produced CH plasmas. The CH2 foil is heated with 10 laser beams, 500 J per beam, at the Omega Laser facility. Thomson scattering measurements are made 4 mm from the foil surface using a 30 J 2ω probe laser with a 1 ns pulse length. Using a series of target shots the plasma evolution is measured from 2.5 ns to 9 ns after the rise of the heater beams. Measuring the electron density and temperature from the electron-plasma fluctuations constrains the fit of the two-ion species theoretical form factor for the ion feature such that the ion temperature, plasma flow velocity and ion species fraction are determined. The ion species fraction is determined to an accuracy of ±0.06 in species fraction.
A high etendue spectrometer suitable for core charge eXchange recombination spectroscopy on ITER
Authors: Jaspers R. J. E. , Scheffer M. , Kappatou A. , van der Valk N. C. J. , Durkut M. , Snijders B. , Marchuk O. , Biel W. , Pokol G. I. , Erdei G. , Zoletnik S. , Dunai D.
Published: August 2012

A feasibility study for the use of core charge exchange recombination spectroscopy on ITER has shown that accurate measurements on the helium ash require a spectrometer with a high etendue of 1mm2sr to comply with the measurement requirements [S. Tugarinov et al., Rev. Sci. Instrum. 74, 2075 (2003)]10.1063/1.1537443. To this purpose such an instrument has been developed consisting of three separate wavelength channels (to measure simultaneously He/Be, C/Ne, and H/D/T together with the Doppler shifted direct emission of the diagnostic neutral beam, the beam emission (BES) signal), combining high dispersion (0.02 nm/pixel), sufficient resolution (0.2 nm), high efficiency (55%), and extended wavelength range (14 nm) at high etendue. The combined measurement of the BES along the same sightline within a third wavelength range provides the possibility for in situ calibration of the charge eXchange recombination spectroscopy signals. In addition, the option is included to use the same instrument for measurements of the fast fluctuations of the beam emission intensity up to 2 MHz, with the aim to study MHD activity.
Enhanced photoswitching of bridged azobenzene studied by nonadiabatic ab initio simulation
Authors: Böckmann Marcus , Doltsinis Nikos L. , Marx Dominik
Published: August 2012

Photoisomerization of a bridged azobenzene derivative (AB-C2) is studied by nonadiabatic ab initio molecular dynamics simulation. The effect of the alkyl bridge linking the two phenyl rings on the Z → E and E → Z photoisomerization pathways and efficiencies is analyzed by detailed comparison to the unbridged parent compound. It is found that the bridge makes E → Z photoisomerization considerably faster and increases its quantum yield, whereas Z → E photoswitching is slightly hindered and has a significantly lower quantum yield although still being ultrafast. The simulations reveal that unsuccessful Z → E photoisomerization attempts can interconvert two pro-enantiomeric forms of Z-AB-C2 via pseudorotation in the excited electronic state.
Applications of non-periodic multilayer optics for high-resolution x-ray microscopes below 30 keV
Authors: Troussel Ph. , Dennetiere D. , Rousseau A. , Darbon S. , Høghøj P. , Hedacq S. , Krumrey M.
Published: August 2012

Multilayer mirrors with enhanced bandwidth were developed with special performances for dense plasma diagnostics and mainly for high spatial resolution x-ray imaging. The multilayer coatings are designed to provide broadband x-ray reflectance at low grazing incidence angles. They are deposited onto toroidal mirror substrates. Our research is directed at the development of non-periodic (depth graded) W/Si multilayer specifically designed for use in the 1 to 30 keV photon energy band. First, we present a study for a 5 to 22 keV x-ray spectral window at 0.45° grazing angle. The goal is to obtain a high and constant reflectivity. Second, we have modeled a broadband mirror coating for harder x-rays in the range from 10 to 30 keV, with a non-periodic structure containing 300 W/SiC layers with periods in the range from 0.8 to 4 nm, designed for 0.35° grazing incidence angle.
Enhanced NIF neutron activation diagnostics
Authors: Yeamans C. B. , Bleuel D. L. , Bernstein L. A.
Published: August 2012

The NIF neutron activation diagnostic suite relies on removable activation samples, leading to operational inefficiencies and a fundamental lower limit on the half-life of the activated product that can be observed. A neutron diagnostic system measuring activation of permanently installed samples could remove these limitations and significantly enhance overall neutron diagnostic capabilities. The physics and engineering aspects of two proposed systems are considered: one measuring the 89Zr/89mZr isomer ratio in the existing Zr activation medium and the other using potassium zirconate as the activation medium. Both proposed systems could improve the signal-to-noise ratio of the current system by at least a factor of 5 and would allow independent measurement of fusion core velocity and fuel areal density.
A new compact, high sensitivity neutron imaging system
Authors: Caillaud T. , Landoas O. , Briat M. , Rossé B. , Thfoin I. , Philippe F. , Casner A. , Bourgade J. L. , Disdier L. , Glebov V. Yu. , Marshall F. J. , Sangster T. C. , Park H. S. , Robey H. F. , Amendt P.
Published: August 2012

We have developed a new small neutron imaging system (SNIS) diagnostic for the OMEGA laser facility. The SNIS uses a penumbral coded aperture and has been designed to record images from low yield (109–1010 neutrons) implosions such as those using deuterium as the fuel. This camera was tested at OMEGA in 2009 on a rugby hohlraum energetics experiment where it recorded an image at a yield of 1.4 × 1010. The resolution of this image was 54 μm and the camera was located only 4 meters from target chamber centre. We recently improved the instrument by adding a cooled CCD camera. The sensitivity of the new camera has been fully characterized using a linear accelerator and a 60Co γ-ray source. The calibration showed that the signal-to-noise ratio could be improved by using raw binning detection.
Alternating current induced-charge electrophoresis of leaky dielectric Janus particles
Authors: Boymelgreen Alicia M. , Miloh Touvia
Published: August 2012

We hereby provide a semi-analytic and numerical solution for the nonlinear, induced-charge electrophoretic motion of an electrically inhomogeneous Janus sphere—comprising two hemispheres with differing dielectric permittivities—under the application of a uniform, time-dependent (ac) electric field. No assumptions are made regarding the size of the electric double layer (EDL) and thus the analysis remains valid even in the case of nanoparticles where the particle radius can be of the same order as the EDL thickness. We consider a number of practical and realistic configurations of metallic and dielectric hemispheres and predict the variations in particle mobility as a function of the conductivity of the two hemispheres and the electrolyte, the frequency of the applied electric field and the EDL length. It is determined that there exist critical values for the conductivity of each hemisphere and the frequency of the applied field, which when exceeded, can cause the mobility to decay rapidly to zero.
Development of a diagnostic technique based on Cherenkov effect for measurements of fast electrons in fusion devices
Authors: Plyusnin V. V. , Jakubowski L. , Zebrowski J. , Duarte P. , Malinowski K. , Fernandes H. , Silva C. , Rabinski M. , Sadowski M. J.
Published: August 2012

A diagnostic technique based on the Cherenkov effect is proposed for detection and characterization of fast (super-thermal and runaway) electrons in fusion devices. The detectors of Cherenkov radiation have been specially designed for measurements in the ISTTOK tokamak. Properties of several materials have been studied to determine the most appropriate one to be used as a radiator of Cherenkov emission in the detector. This technique has enabled the detection of energetic electrons (70 keV and higher) and the determination of their spatial and temporal variations in the ISTTOK discharges. Measurement of hard x-ray emission has also been carried out in experiments for validation of the measuring capabilities of the Cherenkov-type detector and a high correlation was found between the data of both diagnostics. A reasonable agreement was found between experimental data and the results of numerical modeling of the runaway electron generation in ISTTOK.
Effect of dimensionality on the continuum percolation of overlapping hyperspheres and hypercubes. II. Simulation results and analyses
Authors: Torquato S. , Jiao Y.
Published: August 2012

In the first paper of this series [S. Torquato, J. Chem. Phys. 136, 054106 (2012)10.1063/1.3679861], analytical results concerning the continuum percolation of overlapping hyperparticles in d-dimensional Euclidean space $\mathbb {R}^d$Rd were obtained, including lower bounds on the percolation threshold. In the present investigation, we provide additional analytical results for certain cluster statistics, such as the concentration of k-mers and related quantities, and obtain an upper bound on the percolation threshold ηc. We utilize the tightest lower bound obtained in the first paper to formulate an efficient simulation method, called the rescaled-particle algorithm, to estimate continuum percolation properties across many space dimensions with heretofore unattained accuracy. This simulation procedure is applied to compute the threshold ηc and associated mean number of overlaps per particle ${\cal N}_c$Nc for both overlapping hyperspheres and oriented hypercubes for 3 ⩽ d ⩽ 11. These simulations results are compared to corresponding upper and lower bounds on these percolation properties. We find that the bounds converge to one another as the space dimension increases, but the lower bound provides an excellent estimate of ηc and ${\cal N}_c$Nc, even for relatively low dimensions. We confirm a prediction of the first paper in this series that low-dimensional percolation properties encode high-dimensional information. We also show that the concentration of monomers dominate over concentration values for higher order clusters (dimers, trimers, etc.) as the space dimension becomes large. Finally, we provide accurate analytical estimates of the pair connectedness function and blocking function at their contact values for any d as a function of density.
Slip or not slip? A methodical examination of the interface formation model using two-dimensional droplet spreading on a horizontal planar substrate as a prototype system
Authors: Sibley David N. , Savva Nikos , Kalliadasis Serafim
Published: August 2012

We consider the spreading of a thin two-dimensional droplet on a planar substrate as a prototype system to compare the contemporary model for contact line motion based on interface formation of Shikhmurzaev [Int. J. Multiphase Flow 19, 589–610 (1993)]10.1016/0301-9322(93)90090-H, to the more commonly used continuum fluid dynamical equations augmented with the Navier-slip condition. Considering quasistatic droplet evolution and using the method of matched asymptotics, we find that the evolution of the droplet radius using the interface formation model reduces to an equivalent expression for a slip model, where the prescribed microscopic dynamic contact angle has a velocity dependent correction to its static value. This result is found for both the original interface formation model formulation and for a more recent version, where mass transfer from bulk to surface layers is accounted for through the boundary conditions. Various features of the model, such as the pressure behaviour and rolling motion at the contact line, and their relevance, are also considered in the prototype system we adopt.