bluuebunny/crossref_metadata_2025 huggingface dataset:
Disjunctive datalog with existential quantifiers: Semantics, decidability, and complexity issues
Authors: ALVIANO MARIO , FABER WOLFGANG , LEONE NICOLA , MANNA MARCO
Published: September 2012

Datalogis one of the best-known rule-based languages, and extensions of it are used in a wide context of applications. An importantDatalogextension is DisjunctiveDatalog, which significantly increases the expressivity of the basic language. DisjunctiveDatalogis useful in a wide range of applications, ranging from Databases (e.g., Data Integration) to Artificial Intelligence (e.g., diagnosis and planning under incomplete knowledge). However, in recent years an important shortcoming ofDatalog-based languages became evident, e.g. in the context of data-integration (consistent query-answering, ontology-based data access) and Semantic Web applications: The language does not permit any generation of and reasoning with unnamed individuals in an obvious way. In general, it is weak in supporting many cases of existential quantification. To overcome this problem,Datalog∃has recently been proposed, which extends traditionalDatalogby existential quantification in rule heads. In this work, we propose a natural extension of DisjunctiveDatalogandDatalog∃, calledDatalog∃,˅, which allows both disjunctions and existential quantification in rule heads and is therefore an attractive language for knowledge representation and reasoning, especially in domains where ontology-based reasoning is needed. We formally define syntax and semantics of the languageDatalog∃,˅, and provide a notion of instantiation, which we prove to be adequate forDatalog∃,˅. A main issue ofDatalog∃and hence also ofDatalog∃,˅is that decidability is no longer guaranteed for typical reasoning tasks. In order to address this issue, we identify many decidable fragments of the language, which extend, in a natural way, analog classes defined in the non-disjunctive case. Moreover, we carry out an in-depth complexity analysis, deriving interesting results which range from Logarithmic Space to Exponential Time.
Quantification of Human Neural Stem Cell Fate Using Volocity® 3D Image Analysis Software
Authors: Piltti Katja , Daffertshofer Martin , Cummings Brian
Published: September 2012

The promise of stem cell therapy offers hope for the treatment of many human diseases and injuries. Spinal cord and traumatic brain injuries can cause the loss of neurons and glial cells. These lost cells may be partially replaced by transplanting multipotent human neural stem cells (hNSCs), which can differentiate into specialized neural cell types. The potential for these remarkable cells to promote recovery of neural function has made them a strong focus of researchers in this field.
To Buy or to Outsource: Either Way, Your Equipment Manufacturer Can Help
Authors: Vicéns Marie C.
Published: September 2012

Many industrial companies do not have the expertise, experience, or in-house analytical instrumentation to conduct routine laboratory testing. As such, selecting a contract analytical services provider is a common task. Outsourcing is a cost-effective alternative that can allow companies to increase analytical information available for timely decisions regarding product development and production (see Figure 1).
Image and Diffraction Pattern Rotations in the TEM
Authors: Carpenter Graham J.C.
Published: September 2012

When electrons pass through the electromagnetic lenses in a transmission electron microscope (TEM), they follow a spiral path that results in image rotation. In many TEMs, the image or diffraction pattern that appears at the final imaging plane has therefore suffered a significant rotation compared to the actual specimen. The extent of the rotation is equal to the sum of the contributions from each lens. In some recent instruments an extra lens is built into the column to compensate for these rotations. In the case of a scanning TEM (STEM), where the image is created by scanning a focused beam on the specimen, the orientation of the image to the specimen is fixed but can be controlled electronically by the computer processor.
GRB Prompt X-ray Emission
Authors: Sakamoto Takanori
Published: September 2012

I present the observational properties of the prompt emission of supernova associated GRBs (SN-GRBs) focusing on temporal and spectral characteristics. I compare the properties of SN-GRBs with typical long GRBs to see whether there is a distinct difference or not. Furthermore, I present our attempt to search for hard X-ray emission prior to the discovery date from optically identified type Ibc supernovae using Swift BAT survey data.
Ultraviolet-Bright Type IIP Supernovae from Massive Red Supergiants
Authors: Moriya Takashi J. , Tominaga Nozomu , Blinnikov Sergei I. , Baklanov Petr V. , Sorokina Elena I.
Published: September 2012

Red supergiants (RSGs) are progenitors of Type IIP supernovae (SNe). It is suggested that RSGs can experience a mass loss with a very high mass-loss rate (even as high as 0.01 M⊙ yr−1) due to, e.g., dynamical instabilities of their envelopes (e.g., Yoon & Cantiello (2010)). Because of the extensive mass loss, RSGs can have very dense circumstellar medium (CSM) around them. If a SN explosion occurs soon after the extensive mass loss of a RSG, the SN ejecta will collide with the dense CSM. Due to the collision, the kinetic energy of the ejecta is converted to radiation energy and such SNe with collision can be brighter than usual Type IIP SNe. By performing one-dimensional multi-group radiation hydrodynamical calculations, we investigate the effects of the collision on Type IIP SN LCs. We show that if RSGs explode within a dense CSM, the SN will be very bright, especially in ultraviolet, at early epochs. We also compare our models with the ultraviolet-bright Type IIP SN 2009kf and show that the progenitor of SN 2009kf can be a massive RSG which experienced extensive mass loss just before its explosion. We conclude that this is evidence that massive RSGs experience extensive mass loss and the existence of such mass loss can actually be the cause of the contradiction between theoretical and observational mass ranges of Type IIP SN progenitors.
GRB Progenitors and Observational Criteria
Authors: Zhang Bing
Published: September 2012

Phenomenologically, two classes of GRBs (long/soft vs. short/hard) are identified based on their γ-ray properties. The boundary between the two classes is vague. Multi-wavelength observations lead to identification of two types of GRB progenitors: one related to massive stars (Type II), and another related to compact stars (Type I). Evidence suggests that the majority of long GRBs belong to Type II, while at least the majority of nearby short GRBs belong to Type I. Nonetheless, counter examples do exist. Both long-duration Type I and short-duration Type II GRBs have been observed. In this talk, I review the complications in GRB classification and efforts in diagnosing GRB progenitors based on multiple observational criteria. In particular, I raise the caution to readily accept that all short/hard GRBs detected by BATSE are due to compact star mergers. Finally, I propose to introduce “amplitude” as the third dimension (besides “duration” and “hardness”) to quantify burst properties, and point out that the “tip-of-the-iceberg” effect may introduce confusion in defining the physical category of GRBs, especially for low-amplitude, high-redshift GRBs.
3D Core-Collapse Supernova Simulations: Neutron Star Kicks and Nickel Distribution
Authors: Wongwathanarat Annop , Janka Hans-Thomas , Müller Ewald
Published: September 2012

We perform a set of neutrino-driven core-collapse supernova (CCSN) simulations studying the hydrodynamical neutron star kick mechanism in three-dimensions. Our simulations produce neutron star (NS) kick velocities in a range between ~100-600 km/s resulting mainly from the anisotropic gravitational tug by the asymmetric mass distribution behind the supernova shock. This stochastic kick mechanism suggests that a NS kick velocity of more than 1000 km/s may as well be possible. An enhanced production of heavy elements in the direction roughly opposite to the NS recoil direction is also observed as a result of the asymmetric explosion. This large scale asymmetry might be detectable and can be used to constrain the NS kick mechanism.
The soft X-ray landscape of gamma-ray bursts: thermal components
Authors: Starling Rhaana , Page Kim , Sparre Martin
Published: September 2012

The repository of GRB (gamma-ray burst) observations made by the Swift X-ray Telescope, now consisting of over 650 bursts, is a valuable and unique resource for the study of GRB X-ray emission. The observed soft X-ray spectrum typically arises from an underlying power law continuum, absorbed by gas along the line-of-sight. However, particularly at early times in a burst's evolution the continuum emission is not always understood and may comprise multiple components including thermal emission unexpected in the standard model. A thermal X-ray component has been discovered in two very unusual GRBs, perhaps suggesting an association only with this subset of events. However, evidence exists for thermal emission from more typical examples and here we present a new discovery of one such case and describe a systematic search for thermal components among all early GRB X-ray spectra.
The Optically Unbiased GRB Host (TOUGH) Survey
Authors: Jakobsson Páll , Hjorth Jens , Malesani Daniele , Fynbo Johan P. U. , Krühler Thomas , Milvang-Jensen Bo , Tanvir Nial R.
Published: September 2012

We present the results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sample of Swift gamma-ray bursts (GRBs). The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. We have carefully selected a sample, obeying strict and well-defined criteria: 69 targets in total. Among the results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample), and 15 new GRB redshifts with the mean redshift of the host sample assessed to be 〈z〉 ≳ 2.2.
Star Formation and the Metallicity Aversion of Long-Duration Gamma-Ray Bursts
Authors: Graham John F. , Fruchter Andrew S.
Published: September 2012

It has been suggested that the apparent bias of long-duration GRBs (LGRBs) to low metallicity environments might be a result of the fact that star-formation is anti-correlated with metallicity. However, if this were the cause, one would expect other indicators of star formation, such as Type II and Type Ic SNe to demonstrate a similar bias. Here we show that local Type Ic and Type II SNe track the star-formation weighted metallicity distribution of the SDSS galaxies. In contrast LGRBs are typically found at far-lower metallicities than would be expected based on the distribution of star-formation. This is true even when one takes into account so-called “dark bursts”. Indeed, while we will present data that show that some LGRBs form at very high metallicities, these objects enter the sample because of the large effective search volume produced by their bright hosts. The bias of LGRBs to low metallicity is real and must be related to a mechanism which is crucial in their formation.
Detecting the First Supernovae in the Universe with JWST
Authors: Whalen Daniel J.
Published: September 2012

Massive Population III stars die as pair-instability supernovae (PI SNe), the most energetic thermonuclear explosions in the universe with energies up to 100 times those of Type Ia or Type II SNe. Their extreme luminosities may allow them to be observed from the earliest epochs, revealing the nature of Pop III stars and the primitive galaxies in which they reside. We present numerical simulations of Pop III PI SNe done with the radiation hydrodynamics code RAGE and calculations of their light curves and spectra performed with the SPECTRUM code. We find that 150 - 250 M⊙ PI SNe will be visible to the James Webb Space Telescope (JWST) out to z ~ 30 and to z ~ 15 - 20 in all-sky NIR surveys by the Wide Field Infrared Survey Telescope (WFIRST).
Relativistic and Newtonian Shock Breakouts
Authors: Nakar Ehud
Published: September 2012

Observations of the first light from a stellar explosion can open a window to a wealth of information on the progenitor system and the explosion itself. Here I briefly discuss the theoretical expectation of that emission, comparing Newtonian and relativistic breakouts. The former takes place in regular core-collapse supernovae (SNe) while the latter is expected in SNe that are associated with gamma-ray bursts (GRBs), extremely energetic SNe (e.g., SN2007bi) and white dwarf explosions (e.g., type Ia and .Ia SNe, accretion induced collapse). I present the characteristic observable signatures of both types of breakouts, when spherical. Finally, I discuss Newtonian shock breakouts through wind, which produce a very luminous signal, with an X-ray component that is weak around the breakout, and becomes brighter afterwards.
Population III Gamma-Ray Burst
Authors: Ioka Kunihito , Suwa Yudai , Nagakura Hiroki , de Souza Rafael S. , Yoshida Naoki
Published: September 2012

Gamma-ray bursts (GRBs) are unique probes of the first generation (Pop III) stars. We show that a relativistic gamma-ray burst (GRB) jet can potentially pierce the envelope of a very massive Pop III star even if the Pop III star has a supergiant hydrogen envelope without mass loss, thanks to the long-lived powerful accretion of the envelope itself. While the Pop III GRB is estimated to be energetic (Eγ,iso ~ 1055 erg), the supergiant envelope hides the initial bright phase in the cocoon component, leading to a GRB with a long duration ~1000 (1 + z) s and an ordinary isotropic luminosity ~ 1052 erg s−1 (~ 10−9 erg cm−2 s−1 at redshift z ~ 20), although these quantities are found to be sensitive to the core and envelope mass. We also show that Pop III.2 GRBs (which are primordial but affected by radiation from other stars) occur >100 times more frequently than Pop III.1 GRBs, and thus should be suitable targets for future X-ray and radio missions. The radio transient surveys are already constraining the Pop III GRB rate and promising in the future.
On the Origin of the 6.4 keV line from the GRXE
Authors: Eze Romanus , Saitou Kei , Ebisawa Ken
Published: September 2012

The Galactic Ridge X-ray Emission (GRXE) spectrum has strong iron emission lines at 6.4, 6.7, and 7.0 keV, each corresponding to the neutral (or low-ionized), He-like, and H-like iron ions. The 6.4 keV fluorescence line is due to irradiation of neutral (or low ionized) material (iron) by hard X-ray sources, indicating uniform presence of the cold matter in the Galactic plane. In order to resolve origin of the cold fluorescent matter, we examined the contribution of the 6.4 keV line emission from white dwarf surfaces in the hard X-ray emitting symbiotic stars (hSSs) and magnetic cataclysmic variables (mCVs) to the GRXE. In our spectral analysis of 4 hSSs and 19 mCVs observed with Suzaku, we were able to resolve the three iron emission lines. We found that the equivalent-widths (EWs) of the 6.4 keV lines of hSSs are systematically higher than those of mCVs, such that the average EWs of hSSs and mCVs are 180−10+50 eV and 93−3+20 eV, respectively. The EW of hSSs compares favorably with the typical EWs of the 6.4 keV line in the GRXE of 90–300 eV depending on Galactic positions. Average 6.4 keV line luminosities of the hSSs and mCVs are 9.2 × 1039 and 1.6 × 1039 photons s−1, respectively, indicating that hSSs are intrinsically more efficient 6.4 keV line emitters than mCVs. We estimated required space densities of hSSs and mCVs to account for all the GRXE 6.4 keV line emission flux to be 2 × 10−7 pc−3 and 1 × 10−6 pc−3, respectively. We also estimated the actual 6.4 keV line contribution from the hSSs, which is as much as 30% of the observed GRXE flux, and that from the mCV is about 50%. We therefore conclude that the GRXE 6.4 keV line flux is primarily explained by hSSs and mCVs.
Turbulent Magnetic Field Amplification behind Strong Shock Waves in GRB and SNR
Authors: Inoue Tsuyoshi
Published: September 2012

Using three-dimensional (special relativistic) magnetohydrodynamics simulations, the amplification of magnetic field behind strong shock wave is studied. In supernova remnants and gamma-ray bursts, strong shock waves propagate through an inhomogeneous density field. When the shock wave hit a density bump or density dent, the Richtmyer-Meshkov instability is induced that cause a deformation of the shock front. The deformed shock leaves vorticity behind the shock wave that amplifies the magnetic field due to the stretching of field lines.
Neutrino-driven supernova explosions powered by nuclear reactions
Authors: Nakamura K. , Takiwaki T. , Kotake K. , Nishimura N.
Published: September 2012

We have investigated the revival of a shock wave by nuclear burning reactions at the central region of core-collapse supernovae. For this purpose, we performed hydrodynamic simulations of core collapse and bounce for 15 M⊙ progenitor model, using ZEUS-MP code in axi-symmetric coordinates. Our numerical code is equipped with a simple nuclear reaction network including 13 α nuclei form 4He to 56Ni, and accounting for energy feedback from nuclear reactions as well as neutrino heating and cooling. We found that the energy released by nuclear reactions is significantly helpful in accelerating shock waves and is able to produce energetic explosion even if the input neutrino luminosity is low.
Study of very early phase GRB afterglows with MITSuME
Authors: Saito Yoshihiko , Yatsu Yoichi , Nakajima Hideya , Kawai Nobuyuki , Asano Katsuaki , Aoki Yu , Hayashi Mayumi , Song Seongdeng , Kawakami Kosuke , Tokoyoda Kazuki , Enomoto Takahiro , Usui Ryuichi , Kuroda Daisuke , Yanagisawa Kenshi , Shimizu Hiroyasu , Toda Hiroyuki , Nagayama Shogo , Hanayama Hidekazu , Yoshida Michitoshi , Ohta Koji
Published: September 2012

We review the results of very early phase optical follow-up observations of recent gamma-ray bursts (GRBs) with the multi-color optical telescopes “MITSuME”. The MITSuME telescopes were designed to perform “real time” and “automatic” follow-up observations prompted by the GCN alerts via the Internet. The rapidly slewing equatorial mounts allow MITSuME to start photometric observations within 100 seconds after the trigger for several GRBs. In particular, we detected a brightening just after the trigger for two GRBs. These phenomena could be interpreted as the “on-set” of afterglow. In this paper we summarize these optical observations with a brief interpretation.
Evolution of stars just below the critical mass for iron core formation
Authors: Takahashi Koh , Umeda Hideyuki , Yoshida Takashi
Published: September 2012

We calculate the evolution of stars with their initial mass of 9-11M⊙ under very fine initial mass grid of 0.01M⊙. We determine the lower critical mass for Ne ignition in an ONe core that has not undergone the thermal pulse episode. The values are 9.83M⊙ for the initial mass and 1.365M⊙ for the CO core mass. A star with an initial mass slightly larger than the critical, undergoes an off-center Ne+O ignition. Since the energy production rate of Ne+O burning and lasting electron capture reactions is sufficiently large to ignite Si, an Fe core forms as a result of shell Si burning. For a star just below the critical mass, an ONe core continues to contract. In such a high density core, electron capture by nuclei produced through C burning affects the core evolution. After 20Ne starts to capture electrons, the core may ignite O and undergo O detonation. The fate may be an Electron Capture Supernova.
3D hydrodynamic core-collapse SN simulations for an 11.2 M⊙ star with spectral neutrino transport
Authors: Takiwaki Tomoya , Kotake Kei , Suwa Yudai
Published: September 2012

We have performed three-dimensional (3D) hydrodynamical simulations of core-collapse supernovae (SNe) with multigroup neutrino transport to study non-axisymmetric effects in the context of neutrino heating explosion mechanism. By comparing one- (1D) and two dimensional (2D) results with those of 3D, we study how the increasing spatial multi-dimensionality affects the postbounce SN dynamics. The calculations were performed with an energy-dependent treatment of the neutrino transport that is solved by the isotropic diffusion source approximation scheme. In agreement with previous studies, our 1D model does not produce explosions for the 11.2 M⊙ star, while the neutrino-driven revival of the stalled bounce shock is obtained both in the 2D and 3D models. Our results show that convective matter motions below the gain radius become much more violent in 3D than 2D, making the neutrino luminosity larger for 3D. Enhanced by the large neutrino luminosity, the shock of the 3D model expands faster than that of the 2D. Our results show that the evolution of the shock is sensitive to the employed numerical resolutions. To draw a robust conclusion, 3D simulations with much higher numerical resolution and more advanced treatment of neutrino transport and gravity is needed.
GRB 100816A and the nature of intermediate duration gamma-ray bursts
Authors: Tunnicliffe Rachel L. , Levan Andrew
Published: September 2012

Gamma-ray bursts are normally split into two classes, primarily determined by their observed duration, so called long (> 2s) and short (< 2s) GRBs. There have been many claims of a third duration class, with emission lasting for intermediate periods between 2 - 5s, although the reality of this class remains controversial. Here, we investigate this further utilising the 2.9s duration, spectrally hard GRB 100816A. This burst lies well offset from its host galaxy, has no evidence for an associated supernova (albeit to only moderately constraining limits), and has properties which appear to be genuinely intermediate between long- and short- population bursts. We extend this analysis by comparing the physical locations of a population of intermediate duration GRBs with those of short-GRBs and long-GRBs, concluding that the intermediate sample is indistinguishable from the long-GRB population, whose locations are very different from other transients.
Classification of long Gamma Ray Bursts using cosmologically corrected temporal estimators
Authors: Vasquez Nicolas A. , Vasconez Christian
Published: September 2012

The canonical classification of GRBs establishes two types of bursts, long and short. Although an intermediate class of GRBs was suggested, its existence is not yet conclusive. In the present work, we explore the temporal classification of GRBs in the burst frame, because in recent years the statistics of bursts with known redshifts has increased. We studied a sample of Swift GRBs with known redshifts to determine three different time estimators: autocorrelation functions, emission times and duration times. In order to look for a subclass in long GRBs, we studied the distribution of the cosmologically corrected time estimators. The distribution of time estimators of the sample suggests an internal division of long GRBs. The proposed bimodality is also supported in the isotropic luminosity - time estimator planes and we discuss some possible implications of the classification of GRBs in the burst frame.
Structure Formation and Characterization in Supernova Explosions
Authors: Young Patrick A. , Ellinger Carola , Fryer Chris , Rockefeller Gabe
Published: September 2012

Observations of supernova remnants show that large- and small scale structures form at various points in the explosion. We present a case study of structure formation in 3D in a 15 M⊙ supernova for different parameters. We investigate the structure formation and morphology of the Rayleigh-Taylor unstable region. We also propose a method of characterizing the sizes of overdense clumps that can be compared directly with observations. The RT instabilities result in clumps that are overdense by 1-2 orders of magnitude with respect to the ambient gas, have size scales on the level of a few% of the remnant diameter, and are not diffused after the first ~30 yrs of the remnant evolution, in the absence of a surrounding medium.
THE UBIQUITY OF CONSERVATIVE TRANSLATIONS
Authors: JEŘÁBEK EMIL
Published: September 2012

We study the notion of conservative translation between logics introduced by (Feitosa & D’Ottaviano2001). We show that classical propositional logic (CPC) is universal in the sense that every finitary consequence relation over a countable set of formulas can be conservatively translated into CPC. The translation is computable if the consequence relation is decidable. More generally, we show that one can take instead of CPC a broad class of logics (extensions of a certain fragment of full Lambek calculus FL) including most nonclassical logics studied in the literature, hence in a sense, (almost) any two reasonable deductive systems can be conservatively translated into each other. We also provide some counterexamples, in particular the paraconsistent logic LP is not universal.
Heritability and Whole Genome Linkage of Pulse Pressure in Chinese Twin Pairs
Authors: Jiang Wengjie , Zhang Dongfeng , Pang Zengchang , Li Shuxia , Duan Haiping , Wang Shaojie , Tan Qihua
Published: September 2012

Elevated pulse pressure is associated with cardiovascular disorders and mortality in various populations. The genetic influence on pulse pressure has been confirmed by heritability estimates using related individuals. Recently, efforts have been made in mapping genes that are linked to the phenotype. We report results on our heritability and linkage study conducted on the Chinese population in mainland China where cardiovascular and cerebrovascular diseases are becoming the leading cause of death. A total of 630 pairs of middle-aged Chinese twins were collected for heritability analysis, from which 63 dizygotic twin pairs were randomly selected for genome-wide linkage analysis using Affymetrix 6.0 SNP array. Regression analysis reconfirmed the significant effects of age, sex, and BMI on pulse pressure. Comparison of twin models suggested the parsimonious AE model as the best model with a heritability estimate of 0.45. Genome-wide non-parametric linkage analysis identified three significant linkage peaks on chromosome 11 (lod score 4.06 at 30.5 cM), chromosome 12 (lod score 3.97 at 100.7 cM), and chromosome 18 (lod score 4.01 at 70.7 cM) with the last two peaks closely overlapping with linkage peaks reported by two American studies. In addition, multiple regions with suggestive linkage were identified with many of them overlapping with published linkage regions. Our results provide both epidemiological and molecular genetic evidence for the genetic dissection of pulse pressure in the Chinese population, which could help in fine mapping and in characterizing genes that are involved in the regulation of pulse pressure.
Whether weather affects music
Authors: Aplin Karen L. , Williams Paul D.
Published: September 2012

The creative output of composers, writers, and artists is often influenced by their surroundings. To give a literary example, it has been claimed recently that some of the characters in Oliver Twist and A Christmas Carol were based on real‐life people who lived near Charles Dickens in London [Richardson, 2012]. Of course, an important part of what we see and hear is not only the people with whom we interact but also our geophysical surroundings. Of all the geophysical phenomena to influence us, the weather is arguably the most significant because we are exposed to it directly and daily. The weather was a great source of inspiration for artists Claude Monet, John Constable, and William Turner, who are known for their scientifically accurate paintings of the skies [e.g., Baker and Thornes, 2006].
Dams impact carbon dynamics in U.S. rivers
Authors: Bhattacharya Atreyee
Published: September 2012

Dissolved organic carbon (DOC)—which leaches into freshwater systems from plants, soils, and sediments, and from other detritus present in the water itself—is the major food supplement for microorganisms and plays an important role in several environmental processes and in the global carbon cycle. In some aquatic systems such as estuaries, the optically measurable colored component of dissolved organic matter (CDOM) is often proportional to the concentration of DOC. CDOM forms when light‐absorbing compounds are released into the water by decaying organic material and through photochemical degradation of certain organic compounds. Hence, CDOM reflects not just the environment and ecosystem, which is the source of the detritus, but also the processes that deliver the organic matter into aquatic systems. Human activities, such as logging, agriculture, and waste water treatment, also affect CDOM levels in aquatic systems. It is relatively easy and inexpensive to measure the CDOM content in small volumes of water.
Abrupt change in atmospheric CO2 during the last ice age
Authors: Ahn Jinho , Brook Edward J. , Schmittner Andreas , Kreutz Karl
Published: September 2012

During the last glacial period atmospheric carbon dioxide and temperature in Antarctica varied in a similar fashion on millennial time scales, but previous work indicates that these changes were gradual. In a detailed analysis of one event we now find that approximately half of the CO2increase that occurred during the 1500‐year cold period between Dansgaard‐Oeschger (DO) events 8 and 9 happened rapidly, over less than two centuries. This rise in CO2 was synchronous with, or slightly later than, a rapid increase of Antarctic temperature inferred from stable isotopes.
Uncovering the nonadiabatic response of geosynchronous electrons to geomagnetic disturbance
Authors: Gannon J. L. , Elkington S. R. , Onsager T. G.
Published: September 2012

We describe an energy spectrum method for scaling electron integral flux, which is measured at a constant energy, to phase space density at a constant value of the first adiabatic invariant which removes much of the variation due to reversible adiabatic effects. Applying this method to nearly a solar cycle (1995–2006) of geosynchronous electron integral flux (E > 2.0 MeV) from the GOES satellites, we see that much of the diurnal variation in electron phase space density at constant energy can be removed by the transformation to phase space density at constant μ (4000 MeV/G). This allows us a clearer picture of underlying nonadiabatic electron population changes due to geomagnetic activity. Using scaled phase space density, we calculate the percentage of geomagnetic storms resulting in an increase, decrease, or no change in geosynchronous electrons as 38%, 7%, and 55%, respectively. We also show examples of changes in the electron population that may be different from the unscaled fluxes alone suggest. These examples include sudden electron enhancements during storms which appear during the peak of negative Dst for μ‐scaled phase space density, contrary to the slow increase seen during the recovery phase for unscaled phase space density for the same event.
Photometric and ionization masses of meteors with simultaneous EISCAT UHF radar and intensified video observations
Authors: Campbell‐Brown M. D. , Kero J. , Szasz C. , Pellinen‐Wannberg A. , Weryk R. J.
Published: September 2012

There are significant uncertainties in the calculation of photometric and ionization masses of meteors, particularly those derived from meteor head echoes observed by high power, large aperture radars. Simultaneous observations of meteors with the EISCAT UHF tristatic system and narrow field two‐station intensified video were conducted in October 2007; 11 hours of data produced four useful meteors observed on all three radar receivers and both cameras. The positions and speeds calculated on the two systems generally agree to within the observational uncertainty. The photometric and ionization masses for each meteor were calculated using several values of luminous efficiency and ionization probability from literature, and all of these masses were found to agree to within the estimated error in the methods. More observations are required to select among the various values of ionization coefficient and luminous efficiency.
Distribution of methane in the tropical upper troposphere measured by CARIBIC and CONTRAIL aircraft
Authors: Schuck T. J. , Ishijima K. , Patra P. K. , Baker A. K. , Machida T. , Matsueda H. , Sawa Y. , Umezawa T. , Brenninkmeijer C. A. M. , Lelieveld J.
Published: September 2012

We investigate the upper tropospheric distribution of methane (CH4) at low latitudes based on the analysis of air samples collected from aboard passenger aircraft. The distribution of CH4 exhibits spatial and seasonal differences, such as the pronounced seasonal cycles over tropical Asia and elevated mixing ratios over central Africa. Over Africa, the correlations of methane, ethane, and acetylene with carbon monoxide indicate that these high mixing ratios originate from biomass burning as well as from biogenic sources. Upper tropospheric mixing ratios of CH4were modeled using a chemistry transport model. The simulation captures the large‐scale features of the distributions along different flight routes, but discrepancies occur in some regions. Over Africa, where emissions are not well constrained, the model predicts a too steep interhemispheric gradient. During summer, efficient convective vertical transport and enhanced emissions give rise to a large‐scale CH4 maximum in the upper troposphere over subtropical Asia. This seasonal (monsoonal) cycle is analyzed with a tagged tracer simulation. The model confirms that in this region convection links upper tropospheric mixing ratios to regional sources on the Indian subcontinent, subtropical East Asia, and Southeast Asia. This type of aircraft data can therefore provide information about surface fluxes.
Hydrogeomorphology of the hyporheic zone: Stream solute and fine particle interactions with a dynamic streambed
Authors: Harvey J. W. , Drummond J. D. , Martin R. L. , McPhillips L. E. , Packman A. I. , Jerolmack D. J. , Stonedahl S. H. , Aubeneau A. F. , Sawyer A. H. , Larsen L. G. , Tobias C. R.
Published: September 2012

Hyporheic flow in streams has typically been studied separately from geomorphic processes. We investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand‐bed stream before, during, and after a flood. A conservatively transported solute tracer (bromide) and a fine particles tracer (5 μm latex particles), a surrogate for fine particulate organic matter, were co‐injected during base flow. The tracers were differentially stored, with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute. Tracer injections lasted 3.5 h after which we released a small flood from an upstream dam one hour later. Due to shallower storage in the bed, fine particles were rapidly entrained during the rising limb of the flood hydrograph. Rather than being flushed by the flood, we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms. Three important timescales determined the fate of solutes and fine particles: (1) flood duration, (2) relaxation time of flood‐enlarged bedforms back to base flow dimensions, and (3) resulting adjustments and lag times of hyporheic flow. Recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed, i.e., below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths. Thus, physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained, which affects decomposition rate and metabolism of this southeastern Coastal Plain stream. In summary we found that dynamic interactions between hyporheic flow, bed mobility, and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates. These hydrogeomorphic relationships have implications for microbial respiration of organic matter, carbon and nutrient cycling, and fate of contaminants in streams.
High resolution NMR study of T1 magnetic relaxation dispersion. III. Influence of spin 1/2 hetero-nuclei on spin relaxation and polarization transfer among strongly coupled protons
Authors: Korchak Sergey E. , Ivanov Konstantin L. , Pravdivtsev Andrey N. , Yurkovskaya Alexandra V. , Kaptein Robert , Vieth Hans-Martin
Published: September 2012

Effects of spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 129, 234513 (2008)10.1063/1.3040272; S. E. Korchak, K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 133, 194502 (2010)10.1063/1.3495988], spin-spin interactions have a pronounced effect on the relaxivity tending to equalize the longitudinal relaxation times once the spins become strongly coupled at a sufficiently low magnetic field. In addition, we have found influence of 19F nuclei on the proton NMRD, although in the whole field range, studied protons and fluorine spins were only weakly coupled. In particular, pronounced features in the proton NMRD were found; but each feature was predominantly observed only for particular spin states of the hetero-nuclei. The features are explained theoretically; it is shown that hetero-nuclei can affect the proton NMRD even in the limit of weak coupling when (i) protons are coupled strongly and (ii) have spin-spin interactions of different strengths with the hetero-nuclei. We also show that by choosing the proper magnetic field strength, one can selectively transfer proton spin magnetization between spectral components of choice.
One directional polarized neutron reflectometry with optimized reference layer method
Authors: Masoudi S. Farhad , Jahromi Saeed S.
Published: September 2012

In the past decade, several neutron reflectometry methods for determining the modulus and phase of the complex reflection coefficient of an unknown multilayer thin film have been worked out among which the method of variation of surroundings and reference layers are of highest interest. These methods were later modified for measurement of the polarization of the reflected beam instead of the measurement of the intensities. In their new architecture, these methods not only suffered from the necessity of change of experimental setup but also another difficulty was added to their experimental implementations. This deficiency was related to the limitations of the technology of the neutron reflectometers that could only measure the polarization of the reflected neutrons in the same direction as the polarization of the incident beam. As the instruments are limited, the theory has to be optimized so that the experiment could be performed. In a recent work, we developed the method of variation of surroundings for one directional polarization analysis. In this new work, the method of reference layer with polarization analysis has been optimized to determine the phase and modulus of the unknown film with measurement of the polarization of the reflected neutrons in the same direction as the polarization of the incident beam.
Phonon-limited electron mobility in graphene calculated using tight-binding Bloch waves
Authors: Sule N. , Knezevic I.
Published: September 2012

We present a calculation of the electron-phonon scattering rates in ideal monolayer graphene using the third-nearest-neighbor (3NN) tight-binding (TB) electronic Bloch wave functions formed by the analytical carbon 2pz orbitals with an effective nuclear charge of Zeff=4.14. With these wave functions, the band structure is also represented very accurately over the entire Brillouin zone. By fitting the rates calculated using the TB Bloch wave functions to those calculated by density functional theory (DFT), we extract the “bare” acoustic and optical deformation potential constants, which do not include the effect of the wave function overlap or substrate, to be Dac=12 eV and Dop=5×109 eV/cm, respectively. The phonon-limited electron mobility based on these rates is calculated within the relaxation-time approximation and presented for various doping densities and temperatures, with representative values being of order 107 cm2/Vs (50 K) and 106 cm2/Vs (300 K) at the carrier density of 1012 cm−2. The electron mobility values are in good agreement with those reported by DFT and exceed the experimentally obtained values, where the substrate plays an important role. We discuss the utility of the 3NN TB approximation for transport calculations in graphene-based nanostructures.
Turbulent concentration diffusion in multiphase flow
Authors: Ramshaw John D.
Published: September 2012

In multifluid multiphase flow models, the velocity of each phase is determined by its own momentum equation, which is coupled to the other phases by pairwise interphase drag forces proportional to velocity differences. When the drag coefficients are large, the phase velocities become nearly equal and the relative motion of the phases becomes diffusional rather than inertial. The multifluid momentum equations then reduce to a single momentum equation for the mixture and a system of linear relations that determine the small residual velocity differences between the phases. We derive such diffusional relations in a very general form that applies to nearly all multiphase flow models of this type. The simplest such models then reduce to “drift flux” models that exhibit pressure diffusion but not ordinary (Fick's law) diffusion driven by concentration gradients. The question then arises of how to consistently account for turbulent concentration diffusion in models of this type. This question is resolved by specializing the general diffusional relations to a rather typical single-pressure multiphase flow model which includes turbulent momentum transport due to Reynolds stresses. This special case serves as a paradigm which illustrates that (a) turbulent concentration diffusion in multiphase flow is a direct consequence of the isotropic (turbulent pressure) part of the Reynolds stresses, provided the latter are expressed in their proper divergence form; and (b) the order of magnitude of the resulting turbulent diffusivities is just what one would anticipate on dimensional grounds. Properly formulated models of this type therefore automatically include turbulent concentration diffusion, and consequently require no further additions or modifications to introduce it.
Inelastic tunneling spectroscopy of gold-thiol and gold-thiolate interfaces in molecular junctions: The role of hydrogen
Authors: Demir Firuz , Kirczenow George
Published: September 2012

It is widely believed that when a molecule with thiol (S−H) end groups bridges a pair of gold electrodes, the S atoms bond to the gold and the thiol H atoms detach from the molecule. However, little is known regarding the details of this process, its time scale, and whether molecules with and without thiol hydrogen atoms can coexist in molecular junctions. Here, we explore theoretically how inelastic tunneling spectroscopy (IETS) can shed light on these issues. We present calculations of the geometries, low bias conductances, and IETS of propanedithiol and propanedithiolate molecular junctions with gold electrodes. We show that IETS can distinguish between junctions with molecules having no, one, or two thiol hydrogen atoms. We find that in most cases, the single-molecule junctions in the IETS experiment of Hihath et al. [Nano Lett. 8, 1673 (2008)10.1021/nl080580e] had no thiol H atoms, but that a molecule with a single thiol H atom may have bridged their junction occasionally. We also consider the evolution of the IETS spectrum as a gold STM tip approaches the intact S–H group at the end of a molecule bound at its other end to a second electrode. We predict the frequency of a vibrational mode of the thiol H atom to increase by a factor ∼2 as the gap between the tip and molecule narrows. Therefore, IETS should be able to track the approach of the tip towards the thiol group of the molecule and detect the detachment of the thiol H atom from the molecule when it occurs.
Acoustic radiation efficiency of a periodically corrugated rigid piston
Authors: Estrada Héctor , Uris Antonio , Meseguer Francisco
Published: September 2012

The radiation of sound by a periodically corrugated rigid piston is explored using theoretical and numerical approaches and compared with the radiation of flat rigid piston. The depth and the period of the corrugation are considered to be comparable with the wavelength in the surrounding fluid. Radiation enhancement is predicted due to cavity resonances and coherent diffraction. In addition, broad regions of low radiation efficiency are observed. Both effects could have an impact in acoustic transducers technology, either to increase the piston radiated power or to create a source of evanescent acoustic waves. The possibilities offered by this strategy in the nonlinear acoustic regime are also briefly discussed.
Self-accelerating parabolic beams in quadratic nonlinear media
Authors: Dolev Ido , Libster Ana , Arie Ady
Published: September 2012

We present experimental observation of self-accelerating parabolic beams in quadratic nonlinear media. We show that the intensity peaks of the first and second harmonics are asynchronous with respect to one another in the two transverse coordinates. In addition, the two coupled harmonics have the same acceleration within and after the nonlinear medium. We also study the evolution of second harmonic accelerating beams inside the quadratic media and their correlation with theoretical beams.
Electrotaxis of oral squamous cell carcinoma cells in a multiple-electric-field chip with uniform flow field
Authors: Tsai Hsieh-Fu , Peng Shih-Wei , Wu Chun-Ying , Chang Hui-Fang , Cheng Ji-Yen
Published: September 2012

We report a new design of microfluidic chip (Multiple electric Field with Uniform Flow chip, MFUF chip) to create multiple electric field strengths (EFSs) while providing a uniform flow field simultaneously. MFUF chip was fabricated from poly-methyl methacrylates (PMMA) substrates by using CO2 laser micromachining. A microfluidic network with interconnecting segments was utilized to de-couple the flow field and the electric field (EF). Using our special design, different EFSs were obtained in channel segments that had an identical cross-section and therefore a uniform flow field. Four electric fields with EFS ratio of 7.9:2.8:1:0 were obtained with flow velocity variation of only 7.8% CV (coefficient of variation). Possible biological effect of shear force can therefore be avoided. Cell behavior under three EFSs and the control condition, where there is no EF, was observed in a single experiment. We validated MFUF chip performance using lung adenocarcinoma cell lines and then used the chip to study the electrotaxis of HSC-3, an oral squamous cell carcinoma cell line. The MFUF chip has high throughput capability for studying the EF-induced cell behavior under various EFSs, including the control condition (EFS = 0).
Flexoelectricity in several thermoplastic and thermosetting polymers
Authors: Chu Baojin , Salem D. R.
Published: September 2012

The flexoelectricity of several thermoplastic and thermosetting polymers was investigated by testing the dielectric polarization response under bending deformation of polymer cantilevers. All the polymers studied showed a flexoelectric response with a flexoelectric coefficient of the order of the 10−9–10−8 C/m. Based on a comparison of the flexoelectric response of the different polymers studied, we discuss factors that may influence the generation of flexoelectricity in polymeric materials.