bluuebunny/crossref_metadata_2025 huggingface dataset:
Inertia–gravity-wave radiation by a sheared vortex
Authors: ÓLAFSDÓTTIR E. I. , DAALHUIS A. B. OLDE , VANNESTE J.
Published: January 2008

We consider the linear evolution of a localized vortex with Gaussian potential vorticity that is superposed on a horizontal Couette flow in a rapidly rotating strongly stratified fluid. The Rossby number, defined as the ratio of the shear of the Couette flow to the Coriolis frequency, is assumed small. Our focus is on the inertia–gravity waves that are generated spontaneously during the evolution of the vortex. These are exponentially small in the Rossby number and hence are neglected in balanced models such as the quasi-geostrophic model and its higher-order generalizations. We develop an exponential-asymptotic approach, based on an expansion in sheared modes, to give an analytic description of the three-dimensional structure of the inertia–gravity waves emitted by the vortex. This provides an explicit example of the spontaneous radiation of inertia–gravity waves by localized balanced motion in the small-Rossby-number regime.

The inertia–gravity waves are emitted as a burst of four wavepackets propagating downstream of the vortex. The approach employed reduces the computation of inertia–gravity-wave fields to a single quadrature, carried out numerically, for each spatial location and each time. This makes it possible to unambiguously define an initial state that is entirely free of inertia–gravity waves, and circumvents the difficulties generally associated with the separation between balanced motion and inertia–gravity waves.
Balance in non-hydrostatic rotating stratified turbulence
Authors: McKIVER WILLIAM J. , DRITSCHEL DAVID G.
Published: January 2008

It is now well established that two distinct types of motion occur in geophysical turbulence: slow motions associated with potential vorticity advection and fast oscillations due to inertia–gravity waves (or acoustic waves). Many studies have theorized the existence of a flow for which the entire motion is controlled by the potential vorticity (or one ‘master variable’) – this is known as balance. In real geophysical flows, deviations from balance in the form of inertia–gravity waves or ‘imbalance’ have often been found to be small. Here we examine the extent to which balance holds in rotating stratified turbulence which is nearly balanced initially.

Using the non-hydrostatic fluid dynamical equations under the Boussinesq approximation, we analyse properties of rotating stratified turbulence spanning a range of Rossby numbers (Ro≡|ζ|max/f) and the frequency ratios (c≡N/f) where ζ is the relative vertical vorticity, f is the Coriolis frequency and N is the buoyancy frequency. Using a recently introduced diagnostic procedure, called ‘optimal potential vorticity balance’, we extract the balanced part of the flow in the simulations and assess how the degree of imbalance varies with the above parameters.

We also introduce a new and more efficient procedure, building upon a quasi-geostrophic scaling analysis of the complete non-hydrostatic equations. This ‘nonlinear quasi-geostrophic balance’ procedure expands the equations of motion to second order in Rossby number but retains the exact (unexpanded) definition of potential vorticity. This proves crucial for obtaining an accurate estimate of balanced motions. In the analysis of rotating stratified turbulence at Ro≲1 and N/f≫1, this procedure captures a significantly greater fraction of the underlying balance than standard (linear) quasi-geostrophic balance (which is based on the linearized equations about a state of rest). Nonlinear quasi-geostrophic balance also compares well with optimal potential vorticity balance, which captures the greatest fraction of the underlying balance overall.

More fundamentally, the results of these analyses indicate that balance dominates in carefully initialized simulations of freely decaying rotating stratified turbulence up to O(1) Rossby numbers when N/f≫1. The fluid motion exhibits important quasi-geostrophic features with, in particular, typical height-to-width scale ratios remaining comparable to f/N.
Breaking size segregation waves and particle recirculation in granular avalanches
Authors: THORNTON A. R. , GRAY J. M. N. T.
Published: January 2008

Particle-size segregation is a common feature of dense gravity-driven granular free-surface flows, where sliding and frictional grain–grain interactions dominate. Provided that the diameter ratio of the particles is not too large, the grains segregate by a process called kinetic sieving, which, on average, causes the large particles to rise to the surface and the small grains to sink to the base of the avalanche. When the flowing layer is brought to rest this stratification is often preserved in the deposit and is known by geologists as inverse grading. Idealized experiments with bi-disperse mixtures of differently sized grains have shown that inverse grading can be extremely sharp on rough beds at low inclination angles, and may be modelled as a concentration jump or shock. Several authors have developed hyperbolic conservation laws for segregation that naturally lead to a perfectly inversely graded state, with a pure phase of coarse particles separated from a pure phase of fines below, by a sharp concentration jump. A generic feature of these models is that monotonically decreasing sections of this concentration shock steepen and eventually break when the layer is sheared. In this paper, we investigate the structure of the subsequent breaking, which is important for large-particle recirculation at the bouldery margins of debris flows and for fingering instabilities of dry granular flows. We develop an exact quasi-steady travelling wave solution for the structure of the breaking/recirculation zone, which consists of two shocks and two expansion fans that are arranged in a ‘lens’-like structure. A high-resolution shock-capturing numerical scheme is used to investigate the temporal evolution of a linearly decreasing shock towards a steady-state lens, as well as the interaction of two recirculation zones that travel at different speeds and eventually coalesce to form a single zone. Movies are available with the online version of the paper.
Convection in heated fluid layers subjected to time-periodic horizontal accelerations
Authors: PESCH W. , PALANIAPPAN D. , TAO J. , BUSSE F. H.
Published: January 2008

A theoretical study is presented of convection in a horizontal fluid layer heated from below or above which is periodically accelerated in its plane. The analysis is based on Galerkin methods as well as on direct numerical simulations of the underlying Boussinesq equations.

Shaking in a fixed direction breaks the original isotropy of the layer. At onset of convection and at small acceleration, we find longitudinal rolls, where the roll axis aligns parallel to the acceleration direction. With increasing acceleration amplitude, a shear instability takes over and transverse rolls with the axis perpendicular to the shaking direction nucleate at onset. In the nonlinear regime, the longitudinal rolls become unstable against transverse modulations very close to onset which leads to a kind of domain chaos between patches of symmetry degenerated oblique rolls.

In the case of circular shaking, the system is isotropic in the time average sense, however, with a broken chiral symmetry. The onset of convection corresponds to the transverse roll case studied before with the roll axis selected spontaneously. With increasing Rayleigh number, a heteroclinic cycle is observed with the roll changing its orientation periodically in time. At even higher Rayleigh number, this heteroclinic cycle becomes chaotic similarly to the case of the Küppers–Lortz instability.
Transition to turbulence in duct flow
Authors: BIAU DAMIEN , SOUEID HOUSSAM , BOTTARO ALESSANDRO
Published: January 2008

The transition of the flow in a duct of square cross-section is studied. Like in the similar case of the pipe flow, the motion is linearly stable for all Reynolds numbers; this flow is thus a good candidate to investigate the ‘bypass’ path to turbulence. Initially the so-called ‘linear optimal perturbation problem’ is formulated and solved, yielding optimal disturbances in the form of longitudinal vortices. Such optimals, however, fail to elicit a significant response from the system in the nonlinear regime. Thus, streamwise-inhomogeneous sub-optimal disturbances are focused upon; nonlinear quadratic interactions are immediately caused by such initial perturbations and an unstable streamwise-homogeneous large-amplitude mode rapidly emerges. The subsequent evolution of the flow, at a value of the Reynolds number at the boundary between fully developed turbulence and relaminarization, shows the alternance of patterns with two pairs of large-scale vortices near opposing parallel walls. Such edge states bear a resemblance to optimal disturbances.
Vortical structures and heat transfer in a round impinging jet
Authors: HADŽIABDIĆ M. , HANJALIĆ K.
Published: January 2008

In order to gain a better insight into flow, vortical and turbulence structure and their correlation with the local heat transfer in impinging flows, we performed large-eddy simulations (LES) of a round normally impinging jet issuing from a long pipe at Reynolds number Re = 20000 at the orifice-to-plate distance H = 2D, where D is the jet-nozzle diameter. This configuration was chosen to match previous experiments in which several phenomena have been detected, but the underlying physics remained obscure because of limitations in the measuring techniques applied. The instantaneous velocity and temperature fields, generated by the LES, revealed interesting time and spatial dynamics of the vorticity and eddy structures and their imprints on the target wall, characterized by tilting and breaking of the edge ring vortices before impingement, flapping, precessing, splitting and pairing of the stagnation point/line, local unsteady separation and flow reversal at the onset of radial jet spreading, streaks pairing and branching in the near-wall region of the radial jets, and others. The LES data provided also a basis for plausible explanations of some of the experimentally detected statistically-averaged flow features such as double peaks in the Nusselt number and the negative production of turbulence energy in the stagnation region. The simulations, performed with an in-house unstructured finite-volume code T-FlowS, using second-order-accuracy discretization schemes for space and time and the dynamic subgrid-scale stress/flux model for unresolved motion, showed large sensitivity of the results to the grid resolution especially in the wall vicinity, suggesting care must be taken in interpreting LES results in impinging flows.
Velocity fluctuations in a low-Reynolds-number fluidized bed
Authors: TEE SHANG-YOU , MUCHA P. J. , BRENNER M. P. , WEITZ D. A.
Published: January 2008

The velocity fluctuations of particles in a low-Reynolds-number fluidized bed have important similarities and differences with the velocity fluctuations in a low-Reynolds-number sedimenting suspension. We show that, like sedimentation, the velocity fluctuations in a fluidized bed are described well by the balance between density fluctuations due to Poisson statistics and Stokes drag. However, unlike sedimentation, the correlation length of the fluctuations in a fluidized bed increases with volume fraction. We argue that this difference arises because the relaxation time of density fluctuations is completely different in the two systems.
Descriptive epidemiology of intestinal helminth parasites from stray cat populations in Qatar
Authors: Abu-Madi M.A. , Pal P. , Al-Thani A. , Lewis J.W.
Published: January 2008

A total of 488 stray cats, 212 adult and 29 juvenile females plus 235 adult and 12 juvenile males, were examined post-mortem during the winter and summer months of 2006 from five sites in the vicinity of Doha and its outskirts. Five helminths, comprising three nematode and two cestode species were identified and the majority of cats harboured two of these species. The most prevalent was the cestodeTaenia taeniaeformis(75.8%), followed by the cestodeDiplopylidiumsp. (42.8%), and the nematodesAncylostoma tubaeforme(17.0%),Physalopterasp. (6.6%) andToxocara cati(0.8%). All five species were found to be typically overdispersed in their distribution. Using univariate and multivariate analyses, the prevalence and abundance of infections were primarily influenced by host gender and season, with females tending to harbour higher levels of infection during the summer. No significant differences were found relative to site except in the case ofPhysalopterasp. Using bivariate Pearson product moment correlations, significant positive co-occurrences were identified betweenDiplopylidiumsp. andT. taeniaeformisand also betweenA. tubaeformeandT. taeniaeformis. The results are discussed in relation to the effect of environmental conditions on the intestinal helminth infracommunities and their possible interactions in stray cat populations from such a harsh and arid region as Qatar.
The action of albendazole on hydatid cysts in sheep experimentally infected with eggs of Echinococcus granulosus
Authors: Santos H.T. , Santos A.F. , de la Rue M.L.
Published: January 2008

According to the Brazilian Agricultural Ministry, the prevalence of cystic echinococcosis in the state of Rio Grande do Sul, Brazil has decreased between 1990 and 1998, possibly due to the common use of albendazole to control parasites in sheep. Therefore, albendazole (ABZ) action was tested on hydatid cysts of sheep experimentally infected with eggs of Echinococcus granulosus in Uruguaiana County (RS) with the aim of evaluating the observed changes in the parasite's prevalence. The sheep were divided into three groups of 15 animals each and treated as follows. Group 01 was a control (without treatment), groups 02 and 03 received 7.5 mg/kg and 15 mg/kg, respectively, of ABZ orally for 12 months, at intervals between 36 and 45 days. At the end of the studied period the animals were necropsied and the viability of the hydatid cysts was evaluated. Lung and hepatic cysts of sheep treated with ABZ were reduced in size. Degeneration and evident calcification were seen in 87.3% (group 02) and 75.7% (group 03), which were significantly different (P < 0.01) from the 17.3% demonstrated in the control group. It could be concluded that ABZ used early and over long periods, even in small doses, is capable of promoting lesions that devitalize the cysts. This leads to a decrease in fertility of E. granulosus in sheep and could be the reason why the prevalence of cystic echinococcosis has decreased in recent years.
The stratification of knowledge in the thought of T. F. Torrance
Authors: Myers Benjamin
Published: January 2008

T. F. Torrance has made a significant contribution to theological method with his model of the stratified structure of theological knowledge. According to this model, which is grounded in Torrance's realist epistemology, the knowledge of God takes place at three distinctive levels of increasing conceptual refinement. First, at the level of tacit theology, we intuitively grasp God's trinitarian reality through personal experience, without yet understanding that reality conceptually. Second, at the level of formalised theology, we develop an understanding of the economic trinitarian structure which underlies our personal experience. Finally, at the meta-theological level, we penetrate more deeply into the structure of God's self-revelation in order to develop a refined conceptualisation of the perichoretic relations immanent in God's eternal being. The conceptuality achieved at this meta-theological level constitutes the ultimate grammar and the unitary basis of all theological knowledge; and a concentration of thought at this level offers the promise both of thoroughgoing theological simplification and of a shared ecumenical vision of the essential content of theological knowledge. Central to Torrance's entire model is the homoousial union of Jesus Christ with God: thehomoousionenables a movement from a personal encounter with Jesus Christ to a knowledge of the economic Trinity, just as it further enables a movement from the economic to the ontological Trinity. Although our theological thought thus moves towards increasingly refined concepts and relations, it remains always grounded in and coordinated with our personal knowledge of Jesus Christ.
On the Aubry–Mather theory for symbolic dynamics
Authors: GARIBALDI E. , LOPES A. O.
Published: January 2008

We propose a new model of ergodic optimization for expanding dynamical systems: the holonomic setting. In fact, we introduce an extension of the standard model used in this theory. The formulation we consider here is quite natural if one wants a meaning for possible variations of a real trajectory under the forward shift. In other contexts (for twist maps, for instance), this property appears in a crucial way. A version of the Aubry–Mather theory for symbolic dynamics is introduced. We are mainly interested here in problems related to the properties of maximizing probabilities for the two-sided shift. Under the transitive hypothesis, we show the existence of sub-actions for Hölder potentials also in the holonomic setting. We analyze then connections between calibrated sub-actions and the Mañé potential. A representation formula for calibrated sub-actions is presented, which drives us naturally to a classification theorem for these sub-actions. We also investigate properties of the support of maximizing probabilities.
A REPRESENTATION THEORY FOR A CLASS OF VECTOR AUTOREGRESSIVE MODELS FOR FRACTIONAL PROCESSES
Authors: Johansen SØren
Published: January 2008

Based on an idea of Granger (1986,Oxford Bulletin of Economics and Statistics48, 213–228), we analyze a new vector autoregressive model defined from the fractional lag operator 1 − (1 −L)d. We first derive conditions in terms of the coefficients for the model to generate processes that are fractional of order zero. We then show that if there is a unit root, the model generates a fractional processXtof orderd,d> 0, for which there are vectors β so that β‼Xtis fractional of orderd−b, 0 <b≤d. We find a representation of the solution that demonstrates the fractional properties. Finally we suggest a model that allows for a polynomial fractional vector, that is, the processXtis fractional of orderd, β‼Xtis fractional of orderd−b, and a linear combination of β‼Xtand ΔbXtis fractional of orderd− 2b. The representations and conditions are analogous to the well-known conditions forI(0),I(1), andI(2) variables.
Iterated realizability as a comma construction
Authors: HOFSTRA PIETER J. W.
Published: January 2008

We show that the 2-category of partial combinatory algebras, as well as various related categories, admit a certain type of lax comma objects. This not only reveals some of the properties of such categories, but it also gives an interpretation of iterated realizability, in the following sense. Let φ: A → B be a morphism of PCAs, giving a comma object A ⋉φB. In the realizability topos RT(B) over B, the object (A, φ) is an internal PCA, so we can construct the realizability topos over (A, φ). This topos is equivalent to the realizability topos over the comma-PCA A ⋉φB. This result is both an analysis and a generalization of a special case studied by Pitts in the context of the effective monad.
Uniform approximation by universal series on arbitrary sets
Authors: STEFANOPOULOS VANGELIS
Published: January 2008

By considering a tree-like decomposition of an arbitrary set we prove the existence of an associated series with the property that its partial sums approximate uniformly all elements in a relevant space of bounded functions. In a topological setting we show that these sums are dense in the space of continuous functions, hence in turn any Borel measurable function is the almost everywhere limit of an appropriate sequence of partial sums of the same series. The coefficients of the series may be chosen in c0, or in a weighted ℓp with 1 < p < ∞, but not in the corresponding weighted ℓ1.
On the action of the Hua subgroups in special Moufang sets
Authors: SEGEV YOAV , WEISS RICHARD M.
Published: January 2008

We show that in a special Moufang set, either the root groups are elementary abelian 2-groups, or the Hua subgroup H (= the Cartan subgroup) acts “irreducibly” on U, i.e. the only non-trivial H-invariant subgroup of a root group normalized by H is the whole root group.
Averages in vector spaces over finite fields
Authors: CARBERY ANTHONY , STONES BRENDAN , WRIGHT JAMES
Published: January 2008

We study the analogues of the problems of averages and maximal averages over a surface in $\mathbb{R}^{n}$ when the euclidean structure is replaced by that of a vector space over a finite field, and obtain optimal results in a number of model cases.
On the lines passing through two conjugates of a Salem number
Authors: DUBICKAS ARTŪRAS , SMYTH CHRIS
Published: January 2008

We show that the number of distinct non-parallel lines passing through two conjugates of an algebraic number α of degree d ≥ 3 is at most [d2/2]-d+2, its conjugates being in general position if this number is attained. If, for instance, d ≥ 4 is even, then the conjugates of α ∈ $\overline{\Q}$ of degree d are in general position if and only if α has 2 real conjugates, d-2 complex conjugates, no three distinct conjugates of α lie on a line and any two lines that pass through two distinct conjugates of α are non-parallel, except for d/2-1 lines parallel to the imaginary axis. Our main result asserts that the conjugates of any Salem number are in general position. We also ask two natural questions about conjugates of Pisot numbers which lead to the equation α1+α2=α3+α4 in distinct conjugates of a Pisot number. The Pisot number $\al_1\,{=}\,(1+\sqrt{3+2\sqrt{5}})/2$ shows that this equation has such a solution.
A Standard Computerized Version of the Reading Span Test in Different Languages
Authors: van den Noort Maurits , Bosch Peggy , Haverkort Marco , Hugdahl Kenneth
Published: January 2008

The Reading Span Test (RST) is a verbal working-memory test. The original RST ( Daneman & Carpenter, 1980 ), and derivatives of it, are being used increasingly as assessments of central executive functioning and for research on aging-associated cognitive decline ( Whitney, Arnett, Driver, & Budd, 2001 ). Several versions have been made in order to further improve the test or to develop a version in a different language. However, all versions changed different things, making direct comparisons of the results with the RST between different research groups and across different languages impossible. This paper presents the results of testing a new standard computerized version of the RST in four languages (Dutch, English, German, and Norwegian). The new RST meets strict methodological criteria that are the same for all four language versions. A plausibility test, an abstract-concrete rating scale, and a pilot-study were conducted on native speakers to test the new RST. In addition, the internal and external reliability and the ecological validity of the new RST were tested. The results showed that the new RST is a suitable test to investigate verbal working memory. Finally, an important advantage of the new RST is that the different language versions make cross-linguistic comparisons of RST results possible.
An IRT Analysis of the Personal Optimism Scale
Authors: Rauch Wolfgang A. , Schweizer Karl , Moosbrugger Helfried
Published: January 2008

Abstract. In this study the psychometric properties of the Personal Optimism scale of the POSO-E questionnaire ( Schweizer & Koch, 2001 ) for the assessment of dispositional optimism are evaluated by applying Samejima's (1969) graded response model, a parametric item response theory (IRT) model for polytomous data. Model fit is extensively evaluated via fit checks on the lower-order margins of the contingency table of observed and expected responses and visual checks of fit plots comparing observed and expected category response functions. The model proves appropriate for the data; a small amount of misfit is interpreted in terms of previous research using other measures for optimism. Item parameters and information functions show that optimism can be measured accurately, especially at moderately low to middle levels of the latent trait scale, and particularly by the negatively worded items.
A Do Re Mi Encore
Authors: Zweigenhaft Richard L.
Published: January 2008

Abstract. Through the development of the Short Test of Musical Preferences (STOMP) and a larger theory of music preferences, Rentfrow and Gosling (2003 , 2006 ) have helped guide the way toward understanding the role of music in people's lives, and the relationship between music preferences and personality. The four music dimensions they established in their 2003 study provide a broad-brush look at some of the relationships between music preferences and personality. This study of 83 undergraduates at Guilford College in Greensboro, NC, used the NEO-PI, rather than the Big Five Inventory, which allowed us to examine the six facets that make up each of the Big Five traits as well as those traits themselves, and it looked separately at the music genres that make up the four music dimensions identified by Rentfrow and Gosling (2003) . The findings provide general support for Rentfrow and Gosling's work, but they also demonstrate that the personality patterns for the specific music genres differ considerably from one another, even those that fall within the same broad music dimensions. The Openness trait was by far the most robust of the Big Five traits assessed by the NEO-PI, and preferences for some music genres (e.g., folk, international music, and rap/hip-hop) were far more revealing of personality than others (e.g., classical, rock, and electronic).
Near‐seafloor overpressure in the deepwater Mississippi Canyon, northern Gulf of Mexico
Authors: Dugan Brandon , Germaine John T.
Published: January 2008

Laboratory experiments constrain overpressure (25–50% of hydrostatic effective stress) above 30 mbsf at two sites in the Mississippi Canyon region, northern Gulf of Mexico. Overpressure at site 2562 is less than that at site 2567; however site 2562 has accumulated faster. One‐dimensional sedimentation‐consolidation models cannot recreate the overpressure without external fluid sources. A fluid source (specific discharge, q = 2–7 mm/yr) is required for site 2567, whereas a fluid sink (q = 10–12 mm/yr) is required for site 2562 to simulate the constrained overpressure. Although basal conditions differ, specific discharge of 2.1–4.2 mm/yr occurs at the sea floor. Shallow upward flow at each site, deep upward flow at site 2567 and deep downward flow at site 2562 is consistent with a two‐dimensional flow field where sites 2562 and 2567 are hydrologically connected at depth by a regional aquifer.
Friction loss correction in flowing well discharge tests
Authors: Wendland Edson
Published: January 2008

Artesian confined aquifers do not need pumping energy, and water from the aquifer flows naturally at the wellhead. This study proposes correcting the method for analyzing flowing well tests presented by Jacob and Lohman (1952) by considering the head losses due to friction in the well casing. The application of the proposed correction allowed the determination of a transmissivity (T = 411 m2/d) and storage coefficient (S = 3 × 10−4) which appear to be representative for the confined Guarani Aquifer in the study area. Ignoring the correction due to head losses in the well casing, the error in transmissivity evaluation is about 18%. For the storage coefficient the error is of 5 orders of magnitude, resulting in physically unacceptable value. The effect of the proposed correction on the calculated radius of the cone of depression and corresponding well interference is also discussed.
Arctic Sea Ice Extent Plummets in 2007
Authors: Stroeve Julienne , Serreze Mark , Drobot Sheldon , Gearheard Shari , Holland Marika , Maslanik James , Meier Walt , Scambos Ted
Published: January 2008

Arctic sea ice declined rapidly to unprecedented low extents in the summer of 2007, raising concern that the Arctic may be on the verge of a fundamental transition toward a seasonal ice cover.

Arctic sea ice extent typically attains a seasonal maximum in March and minimum in September. Over the course of the modern satellite record (1979 to present), sea ice extent has declined significantly in all months, with the decline being most pronounced in September. By mid‐July 2007, it was clear that a new record low would be set during the summer of 2007.
Developing a Three‐Dimensional Look at a Coral Reef
Authors: Showstack Randy
Published: January 2008

Researchers on board the U.S. Environmental Protection Agency's 224‐foot research flagship ocean survey vessel, the Bold, took samples and observed coral reef conditions at nearly 60 strategic areas around St. Croix in the U.S. Virgin Islands in early December with the aim of recording core measurements to develop first‐ever coral reef biological criteria for water quality. Dive teams identified, counted, measured, and made 360° observations to capture the complexity of the three‐dimensional structure of coral reefs. The survey initiates a long‐term monitoring program to observe conditions of corals around St. Croix.
Exploring Arctic Transpolar Drift During Dramatic Sea Ice Retreat
Authors: Gascard Jean‐Claude , Festy Jean , le Goff Hervé , Weber Matthieu , Bruemmer Burghard , Offermann Michael , Doble Martin , Wadhams Peter , Forsberg René , Hanson Susan , Skourup Henriette , Gerland Sebastian , Nicolaus Marcel , Metaxian Jean‐Philippe , Grangeon Jacques , Haapala Jari , Rinne Eero , Haas Christian , Wegener Alfred , Heygster Georg , Jakobson Erko , Palo Timo , Wilkinson Jeremy , Kaleschke Lars , Claffey Kerry , Elder Bruce , Bottenheim Jan
Published: January 2008

The Arctic is undergoing significant environmental changes due to climate warming. The most evident signal of this warming is the shrinking and thinning of the ice cover of the Arctic Ocean. If the warming continues, as global climate models predict, the Arctic Ocean will change from a perennially ice‐covered to a seasonally ice‐free ocean. Estimates as to when this will occur vary from the 2030s to the end of this century. One reason for this huge uncertainty is the lack of systematic observations describing the state, variability, and changes in the Arctic Ocean.
Seasonal Occurrence of Unique Sediment Plume in the Bay of Bengal
Authors: Sridhar Pattam N. , Ali Meer M. , Vethamony Ponnumony , Babu Madavana T. , Ramana Indrakandi V. , Jayakumar Seelam
Published: January 2008

The movement of sediment plumes, detectable from ocean color sensors [Klemas et al., 1975; Khorram, 1981; Nezlin and DiGiacomo, 2005], depends primarily on coastal circulation [Fong and Geyer, 2002]. Hence, sediment plumes become tracers for studying circulation patterns. The Indian remote sensing satellite Oceansat 1 carries an ocean color monitor (OCM) sensor along with a microwave sensor. Using the OCM data, we studied the suspended sediment concentrations (SSC) during 1999–2006 and observed a plume coming off the Krishna‐Godavari River Basin (KGB) that is the only plume within the Bay of Bengal whose movement is controlled by prevailing currents. The KGB is located in the central part of the east coast of India between 16°43′, 17°00′N and 82°15′, 82°22′E (Figure 1a). Though high sediment concentration is present all along India's east coast, the offshoot of the plume is present only at the coast of Kakinada. The presence, extent, orientation, and intensity of this plume have both seasonal and interannual variations.
Biological Evolution and the History of the Earth Are Foundations of Science
Authors: Anonymous
Published: January 2008

AGU affirms the central importance of including scientific theories of Earth history and biological evolution in science education. Within the scientific community, the theory of biological evolution is not controversial, nor have “alternative explanations” been found. This is why no competing theories are required by the U.S. National Science Education Standards. Explanations of natural phenomena that appeal to the supernatural or are based on religious doctrine—and therefore cannot be tested through scientific inquiry—are not scientific, and have no place in the science classroom.
Capability to Monitor the Comprehensive Nuclear‐Test‐Ban Treaty
Authors: Anonymous
Published: January 2008

In September 1996, the United States was the first country to sign the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT), an international agreement to ban all nuclear test explosions, now signed by 177 nations. The treaty is intended to impede the development of nuclear weapons as part of the international nonproliferation regime. The treaty is not yet in effect because it has not been ratified by enough countries—including the United States. As a result, many of its verification provisions have not yet been fully implemented. When implemented, the American Geophysical Union (AGU) and the Seismological Society of America (SSA) are confident that the combined worldwide monitoring resources will meet the verification goals of the CTBT.
Alley Receives 2007 Roger Revelle Medal
Authors: Broecker Wallace S. , Alley Richard B.
Published: January 2008

I can't think of anyone on the planet more deserving of the Roger Revelle Medal than Richard Alley. He's not only a brilliant climate scientist but also a highly gifted communicator.

Let me first say a few worlds about Richard's science. It centers on glaciers and branches out from there to many aspects of climate and paleoclimate. To me, Richard is the “answer man.” When I'm puzzled about something I read or hear, I call or e‐mail Richard. Nine times out of 10 he gives me a well‐reasoned, easily understood explanation, and if it's not on the tip of his tongue, he'll get back to me. Traditionally, his papers deal with the movement of glaciers over their substrates and how ice shelves influence this motion, but with the advent of the central Greenland ice core program, he has immersed himself in the reading of these records and what they have to tell us about the relationship between climate and ocean circulation.
Molecular and biogeochemical evidence for ammonia oxidation by marine Crenarchaeota in the Gulf of California
Authors: Beman J Michael , Popp Brian N , Francis Christopher A
Published: January 2008

Nitrification plays an important role in marine biogeochemistry, yet efforts to link this process to the microorganisms that mediate it are surprisingly limited. In particular, ammonia oxidation is the first and rate-limiting step of nitrification, yet ammonia oxidation rates and the abundance of ammonia-oxidizing bacteria (AOB) have rarely been measured in tandem. Ammonia oxidation rates have not been directly quantified in conjunction with ammonia-oxidizing archaea (AOA), although mounting evidence indicates that marine Crenarchaeota are capable of ammonia oxidation, and they are among the most abundant microbial groups in the ocean. Here, we have directly quantified ammonia oxidation rates by 15N labeling, and AOA and AOB abundances by quantitative PCR analysis of ammonia monooxygenase subunit A (amoA) genes, in the Gulf of California. Based on markedly different archaeal amoA sequence types in the upper water column (60 m) and oxygen minimum zone (OMZ; 450 m), novel amoA PCR primers were designed to specifically target and quantify ‘shallow’ (group A) and ‘deep’ (group B) clades. These primers recovered extensive variability with depth. Within the OMZ, AOA were most abundant where nitrification may be coupled to denitrification. In the upper water column, group A tracked variations in nitrogen biogeochemistry with depth and between basins, whereas AOB were present in relatively low numbers or undetectable. Overall, 15NH4+ oxidation rates were remarkably well correlated with AOA group A amoA gene copies (r2=0.90, P<0.001), and with 16S rRNA gene copies from marine Crenarchaeota (r2=0.85, P<0.005). These findings represent compelling evidence for an archaeal role in oceanic nitrification.
Labs Demonstrate Logic Gates for Quantum Computation
Authors: Schwarzschild Bertram
Published: January 2008

Since the early 1980s, theoreticians of various stripes have been carrying on a lively discussion about how and why one might build a quantum mechanical computer. (See the article by Charles H. Bennett, PHYSICS today, October 1995, page 24.) Now the appearance of two back-to-back papers in the 18 December issue of Physical Review Letters, reporting the demonstration of experimental “quantum logic gates,” has focused the discussion onto the physics laboratory.
Quantum Interference Used to Eliminate Optical Problem
Authors: Levi Barbara Goss
Published: January 2008

The series of images shown above depicts the onset of a problem in optical imaging (first two panels) and a solution to it (third panel). The panel on the left displays the undistorted image of a low-intensity laser beam that has passed through a circular aperture followed by a refracting medium.
Dimensional crossover and flux pinning of decoupled Cu50Ni50∕Nb multilayers
Authors: Huang S. Y. , Liang J.-J. , Tsai T. C. , Lin L. K. , Lin M. S. , Hsu S. Y. , Lee S. F.
Published: January 2008

The behaviors of superconducting transition temperature Tc and upper critical field Hc2 as a function of different superconductor thicknesses have been investigated in Cu50Ni50∕Nb trilayers and multilayers. We deduced superconductor critical thickness, below which superconductivity vanishes, by analyzing the data in terms of proximity theory. The temperature dependence of Hc2 measurement reveals the spatial dimensional crossover and the flux pinning mechanism in the superconductor. A strong pair-breaking effect was observed in the weak ferromagnetic Cu50Ni50 layers from both measurements. We attribute our observation to the high interface transparency between Cu50Ni50 and Nb.
The surface potential of GaN:Si
Authors: Köhler K. , Wiegert J. , Menner H. P. , Maier M. , Kirste L.
Published: January 2008

The surface potential of GaN:Si, of fundamental interest for knowledge of the electrostatic potential and electric field strength, is determined for Si doping in the device relevant range from 6×1017 cm−3 to 2.3×1019 cm−3, in layers grown by low-pressure metal-organic vapor-phase epitaxy. Comparing the Si doping concentration, measured by secondary ion mass spectrometry, to the free electron concentration, measured by Hall effect, shows that all Si doping atoms are activated. We used the sheet resistance of the samples with different thicknesses measured by eddy current, a nondestructive, contactless method, to determine the depleted region. From the width of the depletion layer, which is dependent on the doping concentration, we obtained the GaN:Si surface potential on the basis of the depletion approximation. The surface potential decreases with increasing carrier concentration from about 1.5 eV to 0.2 eV. A qualitative explanation based on the theoretical description of two surface states, an occupied surface state at 1.7 eV and an empty state 0.6 eV below the conduction band edge, is given.
Write and erase mechanisms for bulk metallic glass
Authors: Kumar Golden , Schroers Jan
Published: January 2008

Microfeatures are imprinted on Pt57.5Cu14.7Ni5.3P22.5 bulk metallic glass (BMG) using thermoplastic forming. Subsequent erasing is carried out by annealing in the supercooled liquid region. The driving force for the erasing process is the capillary force controlled by the curvature and surface tension of the liquid-vacuum surface. Sluggish crystallization kinetics in this alloy permit experimental observation at temperatures where the viscosity is sufficiently low to completely erase small surface features on a time scale smaller than the crystallization time. The kinetics of the writing and erasing processes suggest that BMGs may offer a viable alternative rewritable high-density data storage technology.
Correlated Electrons in a Million Gauss
Authors: Boebinger Greg
Published: January 2008

Because high-magnetic-field experiments have proved to be valuable tools for illuminating the physics of phenomena ranging from the quantum Hall effect to high-temperature superconductivity, magnet laboratories around the world are constantly striving to produce more intense magnetic fields, using both continuous- and pulsed-field magnets. To date, magnetic fields above 100 tesla have been achieved only by self-destructing (exploding or imploding) magnet technologies. These intense magnetic fields persist for only a few microseconds, and most of the destructive-magnet technologies also destroy the sample. However, the recent development of structurally stronger composite conductors has made feasible the design of pulsed magnets capable of nondestructively delivering 10-ms 100-T (that is, megagauss) pulses. (See the box on page 41). During the past five years, researchers in both Europe and the US have proposed building such magnets, along with experiments to exploit this new experimental regime.
New Measurements of Ancient Deuterium Boost the Baryon Density of the Universe
Authors: Schwarzschild Bertram
Published: January 2008

A side from ordinary hydrogen, only four other nuclear species (H2, He3, He4 and Li7 are left over from the Big Bang. Of these, deuterium (2H) is the one whose obsei^ved abundance provides the most accurate determination of the crucial cosmological parameter ρb, the present-day average mass density of ordinary baryonic matter (made up of protons and neutrons) in the universe. In principle, if one knows the primordial abundance of any one of these light nuclei, relative to H1, the theory of Big Bang nucleosynthesis specifies ρb. (See the figure below.)
The Discovery of Superconductivity
Authors: De Nobel Jacobus , Lindenfeld Peter
Published: January 2008

In their book La guerre du froid, Jean Matricon and Georges Way sand describe the first liquefaction of helium in 1908, including the moment of recognition after a bystander suggested that the cryostat be illuminated from below. They go on to state that no similar firsthand account exists for the discovery of superconductivity three years later, which also took place in Heike Kamerlingh Onnes's laboratory at Leiden University, In their words, “Although we have an account full of life and spirit of the liquefaction of helium, the birth of superconductivity has come down to us only as a cold scientific report of the measurement.”
Michigan State Upgrade to Produce Intense Radioactive Ion Beams by Fragmentation Technique
Authors: Lubkin Gloria B.
Published: January 2008

The study of very unstable nuclei is exciting interest in many labs throughout the world. When the Nuclear Science Advisory Committee (NSAC) published its long-range plan a year ago, it noted that, until recently, nuclear physicists had primarily studied nuclei near stability and those rich in protons, although these nuclei represent less than a tenth of the nuclear systems expected to exist. Tightly bound nuclei are at the bottom of the so-called valley of stability (See the figure on this page). “By adding either protons or neutrons one moves outward towards the ridges of the valley of stability, finally reaching the drip lines where the binding of nucleons [in the nucleus] ends,” NSAC wrote. With beams of short-lived radioactive nuclei becoming available, NSAC declared, “The scientific opportunities made available by world-class radioactive beams are extremely compelling and merit very high priority.”
Vortex Physics in High-Temperature Superconductors
Authors: Crabtree George W. , Nelson David R.
Published: January 2008

The discovery of high-temperature superconductors has stimulated dramatic growth in our understanding of the physics of quantized vortex lines. These superconductors exclude magnetic fields weaker than a lower critical field Hc1≤10−2 tesla. Stronger fields penetrate as an array of vortices, each consisting of exactly one quantum of flux (φ0 = hc/2e) surrounded in the plane perpendicular to the field by circulating supercurrents that extend radially a few hundred nanometers. The behavior of vortices dominates many physical properties of high-temperature superconductors up to the upper critical field Hc2∼102 tesla, where superconductivity gives way to normal metallic behavior and magnetic fields penetrate uniformly.
Finally a Gamma Ray Burster Shows Optical and X-Ray Afterglows
Authors: Schwarzschild Bertram
Published: January 2008

After decades of looking in vain, astronomers have finally found the optical and x-ray “afterglow” of a gamma-ray burster (GRB), together with a fuzzy object that may well be its parent galaxy. Of the several thousand GRBs that have been recorded by orbiting gamma detectors since the early 1970s, the one detected by the Italian-Dutch BeppoSAX satellite on 28 February is the first, and so far the only one, for which a transient or persistent counterpart has been identified at any other wavelength.
Unresolved Problems of Radioactive Waste: Motivation for a New Paradigm
Authors: Warner North D.
Published: January 2008

The management of radio-active waste has become an increasingly intractable problem. US programs for the disposal of spent nuclear fuel and high-level waste, for disposal of transuranic waste, for clean-up of former nuclear weapons production facilities and even for disposal of low-level waste are far behind schedule and mired in public controversy. The US public has acquired a deepseated fear of nuclear technology and its wastes, and mistrusts the institutions for managing these wastes. People's fear, mistrust and opposition are intensified when the proposed location for the wastes is nearby or is perceived to be a health or environmental hazard (see photo on page 49).
New Results Suggest X-Ray Emission is a Common Property of Comets
Authors: Day Charles
Published: January 2008

Comets—dubbed “dirty snowballs” by comet guru Fred Whipple—are among the last celestial bodies you'd expect to emit x rays, which typically come from matter at least as hot as 106 K. But last year, to the surprise of astronomers, Carey Lisse (University of Maryland) and Mike Mumma (NASA's Goddard Space Flight Center) discovered faint x-ray emission from comet Hyakutake. They observed the photogenic comet with the ROSAT satellite as the comet flew by Earth in March 1996. That same month, Mumma and Vladimir Krasnopolsky (Catholic University of America) detected the comet with the Extreme Ultraviolet Explorer (EUVE) satellite.
Revisiting the Rain of Cometary Snowballs
Authors: Schwarzschild Bertram
Published: January 2008

It's an intriguing idea: A steady rain of kiloton minicomets of loosely packed ice, pelting the top of the atmosphere at a rate of about a dozen per minute could, over geological time, account for most of the water in the oceans, and who knows what else. That's the picture suggested last year by Louis Frank and John Sigwarth at the University of Iowa, based on their observations with the Visual Imaging System (VIS), the Earth camera built by Frank and carried aboard NASA's Polar orbiter. (See PHYSICS TODAY, July 1997, page 18.)