bluuebunny/crossref_metadata_2025 huggingface dataset:
Protecting Louisiana's coasts
Authors: Showstack Randy
Published: January 2008

With numerous wetlands restoration and protection projects slated for Louisiana, a well‐developed implementation strategy that can address a number of uncertainties is important for the success of these projects, according to a 14 December report by the U.S. Government Accountability Office (GAO). GAO specifically urged maintaining the collaborative process that is used by Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) program agencies, with scientists, engineers, and others working together to plan and design restoration projects. The report also noted the need to address such other issues as having an integrated monitoring system to determine whether goals and objectives are met as well as to understand that projects can encounter significant setbacks due to storms and hurricanes, landscape and structural causes, and spiraling project costs. Louisiana state officials anticipate the state could receive about $8.5 billion over the next 10 years for coastal restoration and protection.
Sediment fluxes and budgets in high‐latitude and high‐altitude cold environments: Sediment budgets in cold environments (SEDIBUD) second workshop, Abisko, Sweden, 15–19 September 2007
Authors: Lamoureux Scott , Beylich Achim , Decaulne Armelle
Published: January 2008

Amplified climate change and ecological sensitivity of polar and cold regions have been highlighted as key global environmental issues. Projected climate change in cold regions is expected to alter melt season duration and intensity, along with total precipitation and the balance between snowfall and rainfall. Similarly, changes to the reduced extent of permafrost and increased active layer depth are also expected. These effects will undoubtedly change surface water environments in cold regions and alter the flux of sediment, nutrients, and solutes, but the absence of data and analysis to understand the sensitivity of the surface water environment is acute in cold regions.
Can Venice be raised by pumping water underground? A pilot project to help decide
Authors: Castelletto N. , Ferronato M. , Gambolati G. , Putti M. , Teatini P.
Published: January 2008

Recent field evidence suggests that injecting fluids below the ground surface can induce an anthropogenic land uplift of a few tens of centimeters over a time interval that may range from a few months to a few years. At the same time, new modeling studies using a lot of realistic hydrogeological and geomechanical information from the northern Adriatic basin indicate that pumping seawater into a 600–800 m deep brackish aquifer below the Venice Lagoon might help raise the city uniformly by 25–30 cm over 10 years (a). This could provide Venice with an important innovative defence from and a substantial mitigation to the so‐called “acqua alta,” i.e., the increasingly frequent floods that plague the city. To test the feasibility of an actual program of anthropogenic Venice uplift, a pilot project is designed with the aim of investigating the occurrence over a limited area selected on purpose within or in the margin of the lagoon where three boreholes down to 800 m are drilled and seawater properly treated for geochemical compatibility is pumped into the selected aquifer during 3 a. Using an improved reconstruction of the geology and lithostratigraphy from a new seismic survey to be carried out in the lagoon subsurface, the pilot project plans the instrumentation of the injection wells and other boreholes for the continuous monitoring and accurate measurement of (1) pore water overpressure; (2) expansion of the injected unit by the radioactive marker technique; (3) compaction, if any, of the upper fresh water aquifer system with the aid of an extensometer; and (4) vertical and horizontal motions of land surface via spirit leveling, GPS and interferometric synthetic aperture radar. Preliminary numerical simulations show that a constant saltwater injection rate of 12 × 103 m3 s−1 from each well might provide a maximum 7 cm uplift at the center of the selected site over a 3‐a time, namely, a limited amount that is nevertheless accurately measurable and should not raise concerns for the stability of the buildings and the preservation of the infrastructures in the area. A continuous control of the experiment is envisaged based on much refined hydrologic and geomechanical models properly updated and calibrated to the detailed lithostratigraphy resulting from the new seismic campaign, the ad hoc field analyses, and the current field observations of the event. The completion of the pilot project is expected to require 4 a including an initial year needed for the necessary authorizations and the operative implementation of the injection program. The planned cost is in the range of 5 MEuro/a. The present paper addresses the major issues concerned with the design of the pilot project and discusses the results from the experiment simulations with a glance at their prospective application to an actual project of anthropogenic uplift of Venice.
The Need for Full‐Scale Experiments in River Science
Authors: Wilcock Peter R. , Orr Cailin Huyck , Marr Jeffrey D. G.
Published: January 2008

Studying river processes in the laboratory offers important advantages, particularly the opportunity for precise experimental control and the ability to isolate specific processes. There is, however, a key trade‐off. To control essential variables and support tractable technical measurements, experiments are typically conducted at a reduced scale, which introduces a potential loss of realism. The methods and limitations of scale modeling are well developed in some aspects of river science (such as hydraulics and sediment transport) and are emerging in others (such as biogeochemical transport and flow/organism interactions).
Solomon Receives 2007 William Bowie Medal
Authors: Brasseur Guy , Solomon Susan
Published: January 2008

I am particularly pleased tonight to present Susan Solomon, who will receive one of the most prestigious AGU awards: the William Bowie Medal.
Multiple pathways for sorting mitochondrial precursor proteins
Authors: Bolender Natalia , Sickmann Albert , Wagner Richard , Meisinger Chris , Pfanner Nikolaus
Published: January 2008

Mitochondria import hundreds of different precursor proteins from the cytosol. More than 50% of mitochondrial proteins do not use the classical import pathway that is guided by amino‐terminal presequences, but instead contain different types of internal targeting signals. Recent studies have revealed an unexpected complexity of the mitochondrial protein import machinery and have led to the discovery of new transport pathways. Here, we review the versatility of mitochondrial protein import and its connection to mitochondrial morphology, redox regulation and energetics.
Novel molecules for intra-oral delivery of antimicrobials to prevent and treat oral infectious diseases
Authors: Raj Periathamby Antony , Rajkumar Latha , Dentino Andrew R.
Published: January 2008

New molecules were designed for efficient intra-oral delivery of antimicrobials to prevent and treat oral infection. The salivary statherin fragment, which has high affinity for the tooth enamel, was used as a carrier peptide. This was linked through the side chain of the N-terminal residue to the C-terminus of a defensin-like 12-residue peptide to generate two bifunctional hybrid molecules, one with an ester linkage and the other with an anhydride bond between the carrier and the antimicrobial components. They were examined for their affinity to a HAP (hydroxyapatite) surface. The extent of the antimicrobial release in human whole saliva was determined using 13C-NMR spectroscopy. The candidacidal activity of the molecules was determined as a function of the antimicrobial release from the carrier peptide in human saliva. The hybrid-adsorbed HAP surface was examined against Candida albicans and Aggregatibacter actinomycetemcomitans using the fluorescence technique. The bifunctional molecules were tested on human erythrocytes, GECs (gingival epithelial cells) and GFCs (gingival fibroblast cells) for cytotoxicity. They were found to possess high affinity for the HAP mineral. In human whole saliva, a sustained antimicrobial release over a period of more than 40–60 h, and candidacidal activity consistent with the extent of hybrid dissociation were observed. Moreover, the bifunctional peptide-bound HAP surface was found to exhibit antimicrobial activity when suspended in clarified human saliva. The hybrid peptides did not show any toxic influence on human erythrocytes, GECs and GFCs. These novel hybrids could be safely used to deliver therapeutic agents intra-orally for the treatment and prevention of oral infectious diseases.
Insights into the structural basis of the pH-dependent dimer–tetramer equilibrium through crystallographic analysis of recombinantDiocleinaelectins
Authors: Nagano Celso S. , Calvete Juan J. , Barettino Domingo , Pérez Alicia , Cavada Benildo S. , Sanz Libia
Published: January 2008

The structural ground underlying the pH-dependency of the dimer–tetramer transition of Diocleinae lectins was investigated by equilibrium sedimentation and X-ray crystal structure determination of wild-type and site-directed mutants of recombinant lectins. Synthetic genes coding for the full-length α-chains of the seed lectins of Dioclea guianensis (termed r-αDguia) and Dioclea grandiflora (termed r-αDGL) were designed and expressed in Escherichia coli. This pioneering approach, which will be described in detail in the present paper, yielded recombinant lectins displaying carbohydrate-binding activity, dimer–tetramer equilibria and crystal structures indistinguishable from their natural homologues. Conversion of the pH-stable tetrameric r-αDGL into a structure exhibiting pH-dependent dimer–tetramer transition was accomplished through mutations that abolished the interdimeric interactions at the central cavity of the tetrameric lectins. Both the central and the peripheral interacting regions bear structural information for formation of the canonical legume lectin tetramer. We hypothesize that the strength of the ionic contacts at these sites may be modulated by the pH, leading to dissociation of those lectin structures that are not locked into a pH-stable tetramer through interdimeric contacts networking the central cavity loops.
The histidine phosphatase superfamily: structure and function
Authors: Rigden Daniel J.
Published: January 2008

The histidine phosphatase superfamily is a large functionally diverse group of proteins. They share a conserved catalytic core centred on a histidine which becomes phosphorylated during the course of the reaction. Although the superfamily is overwhelmingly composed of phosphatases, the earliest known and arguably best-studied member is dPGM (cofactor-dependent phosphoglycerate mutase). The superfamily contains two branches sharing very limited sequence similarity: the first containing dPGM, fructose-2,6-bisphosphatase, PhoE, SixA, TIGAR [TP53 (tumour protein 53)-induced glycolysis and apoptosis regulator], Sts-1 and many other activities, and the second, smaller, branch composed mainly of acid phosphatases and phytases. Human representatives of both branches are of considerable medical interest, and various parasites contain superfamily members whose inhibition might have therapeutic value. Additionally, several phosphatases, notably the phytases, have current or potential applications in agriculture. The present review aims to draw together what is known about structure and function in the superfamily. With the benefit of an expanding set of histidine phosphatase superfamily structures, a clearer picture of the conserved elements is obtained, along with, conversely, a view of the sometimes surprising variation in substrate-binding and proton donor residues across the superfamily. This analysis should contribute to correcting a history of over- and mis-annotation in the superfamily, but also suggests that structural knowledge, from models or experimental structures, in conjunction with experimental assays, will prove vital for the future description of function in the superfamily.
The stability and aggregation of ovine prion protein associated with classical and atypical scrapie correlates with the ease of unwinding of helix-2
Authors: Fitzmaurice Tim J. , Burke David F. , Hopkins Lee , Yang Sujeong , Yu Shuiliang , Sy Man-Sun , Thackray Alana M. , Bujdoso Raymond
Published: January 2008

Susceptibility to scrapie disease in sheep, the archetypal prion disease, correlates with polymorphisms within the ovine PrP (prion-related protein) gene. The VRQ (Val136Arg154Gln171) and AL141RQ (Ala136Leu141Arg154Gln171) allelic variants are associated with classical scrapie, whereas the ARR (Ala136Arg154Arg171), AF141RQ (Ala136Phe141Arg154Gln171) and AHQ (Ala136His154Gln171) allelic variants are associated with atypical scrapie. Recent studies have suggested that there are differences in the stability of PrPSc (abnormal disease-specific conformation of PrP) associated with these different forms of scrapie. To address which structural features of ovine PrP may contribute to this difference, in the present study we have investigated the conformational stability and susceptibility to aggregation of allelic variants of ovine PrP associated with classical or atypical scrapie. We find that the melting temperature of ovine recombinant VRQ and AL141RQ PrP is higher than that of AF141RQ, AHQ and ARR. In addition, monoclonal-antibody studies show that the region around helix-1 of VRQ and AL141RQ is less accessible compared with other ovine PrP allelic variants. Furthermore, the extent of both the structural change to copper-ion-treatment and denaturant-induced aggregation was reduced in PrP associated with atypical scrapie compared with PrP associated with classical scrapie. Through the use of molecular dynamics simulations we have found that these biochemical and biophysical properties of ovine PrP correlate with the ease of unwinding of helix-2 and a concurrent conformational change of the helix-2–helix-3 loop. These results reveal significant differences in the overall stability and potential for aggregation of different allelic variants of ovine PrP and consequently have implications for the differences in stability of PrPSc associated with classical and atypical scrapie.
Validation of spermidine synthase as a drug target in African trypanosomes
Authors: Taylor Martin C. , Kaur Harparkash , Blessington Bernard , Kelly John M. , Wilkinson Shane R.
Published: January 2008

The trypanocidal activity of the ODC (ornithine decarboxylase) inhibitor DFMO (difluoromethylornithine) has validated polyamine biosynthesis as a target for chemotherapy. As DFMO is one of only two drugs used to treat patients with late-stage African trypanosomiasis, the requirement for additional drug targets is paramount. Here, we report the biochemical properties of TbSpSyn (Trypanosoma brucei spermidine synthase), the enzyme immediately downstream of ODC in this pathway. Recombinant TbSpSyn was purified and shown to catalyse the formation of spermidine from putrescine and dcSAM (decarboxylated S-adenosylmethionine). To determine the functional importance of TbSpSyn in BSF (bloodstream form) parasites, we used a tetracycline-inducible RNAi (RNA interference) system. Down-regulation of the corresponding mRNA correlated with a decrease in intracellular spermidine and cessation of growth. This phenotype could be complemented by expressing the SpSyn (spermidine synthase) gene from Leishmania major in cells undergoing RNAi, but could not be rescued by addition of spermidine to the medium due to the lack of a spermidine uptake capacity. These results therefore genetically validate TbSpSyn as a target for drug development and indicate that in the absence of a functional biosynthetic pathway, BSF T. brucei cannot scavenge sufficient spermidine from their environment to meet growth requirements.
Amino acids 39–456 of the large subunit and 210–262 of the small subunit constitute the minimal functionally interacting fragments of the unusual heterodimeric topoisomerase IB of Leishmania
Authors: Bosedasgupta Somdeb , Das Benu Brata , Sengupta Souvik , Ganguly Agneyo , Roy Amit , Tripathi Gayatri , Majumder Hemanta K.
Published: January 2008

The unusual, heterodimeric topoisomerase IB of Leishmania shows functional activity upon reconstitution of the DNA-binding large subunit (LdTOPIL; or L) and the catalytic small subunit (LdTOPIS; or S). In the present study, we generated N- and C-terminal-truncated deletion constructs of either subunit and identified proteins LdTOPIL39–456 (lacking amino acids 1–39 and 457–635) and LdTOPIS210–262 (lacking amino acids 1–210) as the minimal interacting fragments. The interacting region of LdTOPIL lies between residues 40–99 and 435–456, while for LdTOPIS it lies between residues 210–215 and 245–262. The heterodimerization between the two fragments is weak and therefore co-purified fragments showed reduced DNA binding, cleavage and relaxation properties compared with the wild-type enzyme. The minimal fragments could complement their respective wild-type subunits inside parasites when the respective subunits were down-regulated by transfection with conditional antisense constructs. Site-directed mutagenesis studies identify Lys455 of LdTOPIL and Asp261 of LdTOPIS as two residues involved in subunit interaction. Taken together, the present study provides crucial insights into the mechanistic details for understanding the unusual structure and inter-subunit co-operativity of this heterodimeric enzyme.
A growth walk model for estimating the canonical partition function of interacting self-avoiding walk
Authors: Narasimhan S. L. , Krishna P. S. R. , Ponmurugan M. , Murthy K. P. N.
Published: January 2008

We have explained in detail why the canonical partition function of interacting self-avoiding walk (ISAW) is exactly equivalent to the configurational average of the weights associated with growth walks, such as the interacting growth walk (IGW), if the average is taken over the entire genealogical tree of the walk. In this context, we have shown that it is not always possible to factor the density of states out of the canonical partition function if the local growth rule is temperature dependent. We have presented Monte Carlo results for IGWs on a diamond lattice in order to demonstrate that the actual set of IGW configurations available for study is temperature dependent even though the weighted averages lead to the expected thermodynamic behavior of ISAW.
Neutron Scattering in Europe
Authors: Pynn Roger , Fender Brian E. F.
Published: January 2008

Neutron scattering began in Europe, as in the United States, as a parasitic activity at nuclear reactors designed to operate as irradiation facilities or to test reactor technology. Through the 1950s and 1960s, research using neutron beams involved only a small number of scientists. Most of these scientists were from the reactor centers, although by the late 1960s the participation of university scientists was apparent, notably at the Munich and Harwell reactors. Nevertheless, the general picture remained one in which neutron-scattering experiments, which were principally in solid-state physics, were carried out by small groups of scientists somewhat isolated from the academic and industrial communities. Even when reactors designed to produce neutron beams became available, scientists working on neutron scattering remained relatively isolated.
Puzzling Positron Peaks Appear in Heavy-Ion Collisions at GSI
Authors: Schwarzschild Bertram
Published: January 2008

Searching for the “sparking of the vacuum,” one of the more exotic predictions of quantum electrodynamics, two groups of heavy-ion experimenters at the Gesellschaft für Schwerionenforschung in Darmstadt have found something quite unexpected, and very puzzling. If one had a nucleus of sufficiently high charge, Z, with a vacancy in the lowest-lying electron orbit, it would be energetically cheaper to create an electron-positron pair spontaneously out of the vacuum than to leave the orbit vacant. This is, in fact, the vacuum sparking—or “spontaneous positron emission”—predicted by QED. One might expect that this somewhat bizarre creation of an e+e− pair out of nothing but an ultrastrong electrostatic field in the vacuum would occur at Z = 137, the reciprocal of the fine-structure constant, where the bound-state solutions of the Dirac equation for a point-charge nucleus disappear. But for realistic, finite nuclear diameters, detailed QED calculations predict that spontaneous positron emission will first occur when Z is about 173.
Von Klitzing Wins Nobel Physics Prize for Quantum Hall Effect
Authors: Schwarzschild Bertram
Published: January 2008

The Royal Swedish Academy of Sciences has awarded the 1985 Nobel Prize in Physics to Klaus von Klitzing, a director of the Max Planck Institute for Solid-State Research in Stuttgart. The 1.8-million-kroner ($230 000) prize was awarded for his discovery of the quantized Hall effect in 1980. Von Klitzing, who was at the time a Heisenberg fellow at the University of Würzburg, discovered the effect at the high-field magnet laboratory in Grenoble, a joint facility of the Max Planck Institute and the CNRS.
Triple oscillating field technique for accurate distance measurements by solid-state NMR
Authors: Khaneja Navin , Nielsen Niels Chr.
Published: January 2008

We present a new concept for homonuclear dipolar recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating field technique. We demonstrate this technique as an efficient means to accomplish broadband dipolar recoupling of homonuclear spins, while decoupling heteronuclear dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it is possible to synthesize Ising interaction (2IzSz) Hamiltonians in homonuclear spin networks and thereby avoid dipolar truncation—a serious problem essentially all previous homonuclear dipolar recoupling experiments suffer from. Combination of this recoupling concept with rotor assisted dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly C13 labeled proteins through accurate measurement of C13–C13 internuclear distances. The concept is demonstrated experimentally by measurement of Cα–C′, Cβ–C′, and Cγ–C′ internuclear distances in powder samples of the amino acids L-alanine and L-threonine.
Crystal field splitting of rovibrational transitions of water monomers isolated in solid parahydrogen
Authors: Fajardo Mario E. , Lindsay C. Michael
Published: January 2008

We report polarized infrared absorption spectra of water isotopologues isolated in solid parahydrogen (pH2) which reveal the crystal field induced splittings of the 101←000 R(0) lines in the ν1 HDO, ν3 D2O, ν3 HDO, and ν3 H2O fundamental bands. For annealed pH2 solids, these spectra also reveal a strong alignment of the hexagonal-close-packed crystallites’ c axes with the deposition substrate surface normal. This alignment effect explains our failure to detect the parallel-polarized components of these R(0) lines in spectra of pH2 solids produced on a transparent deposition substrate [M. E. Fajardo et al., J. Mol. Struct. 695, 111 (2004)]. This lesson applies more generally to comparison of solid pH2 spectra obtained in different laboratories. The spectra are consistent with water monomers existing in solid pH2 as very slightly hindered rotors. The individual components of the R(0) absorption lines show a Lorentzian lineshape, with vibrational depopulation the most important source of line broadening.
Digital communication using Ge metal-insulator-semiconductor light-emitting diodes and photodetectors
Authors: Cheng T.-H. , Liao M. H. , Yeh Lingyen , Lee T.-L. , Liang M.-S. , Liu C. W.
Published: January 2008

Both Ge light-emitting diodes and photodetectors are demonstrated by using the same metal-insulator-semiconductor (MIS) tunneling structure. A Ge MIS tunneling diode biased at the accumulation region is used as a light-emitting device and a Ge MIS tunneling diode biased at the inversion region is used as a photodetector. The ultrathin gate oxide film used in the MIS tunneling diode was grown by liquid phase deposition at 50 °C to lower the thermal budget. A Ge light-emitting diode has a higher quantum efficiency than a similar Si device (at least one order of magnitude stronger) due to the higher radiative recombination coefficient. With the detection of the Ge MIS photodetector, the data communication in free space is reported and demonstrated for the first time.
An induction heating diamond anvil cell for high pressure and temperature micro-Raman spectroscopic measurements
Authors: Shinoda Keiji , Noguchi Naoki
Published: January 2008

A new external heating configuration is presented for high-temperature diamond anvil cell instruments. The supporting rockers are thermally excited by induction from an externally mounted copper coil passing a 30kHz alternating current. The inductive heating configuration therefore avoids the use of breakable wires, yet is capable of cell temperatures of 1100K or higher. The diamond anvil cell has no resistive heaters, but uses a single-turn induction coil for elevating the temperature. The induction coil is placed near the diamonds and directly heats the tungsten carbide rockers that support the diamond. The temperature in the cell is determined from a temperature-power curve calibrated by the ratio between the intensities of the Stokes and anti-Stokes Raman lines of silicon. The high-pressure transformation of quartz to coesite is successfully observed by micro-Raman spectroscopy using this apparatus. The induction heating diamond anvil cell is thus a useful alternative to resistively heated diamond anvil cells.
The field symmetry breaking effects in microwave-vortex structures originated by ferrite disks in a cavity
Authors: Sigalov Michael , Kamenetskii E. O. , Shavit Reuven
Published: January 2008

For a microwave resonator with an enclosed ferrite disk, one has the electromagnetic resonant fields which are not the fields of standing waves. This leads to very specific topological-phase characteristics. In such a nonintegrable system with time-reversal symmetry breaking, one obtains the Poynting-vector microwave vortices and intensive field localization in a region of a disk. The purpose of this paper is to give detailed explanations of physics of the electromagnetic-vortex phenomena shown in our recently published paper [E. O. Kamenetskii et al., Phys. Rev. E 74, 0366620 (2006)]. Based on numerical simulation, we show that for a thin ferrite disk with positive permeability parameters and negligibly small material losses, the Poynting-vector microwave vortices in a cavity are accompanied with topological magnetic currents and topological magnetic charges. Such topological sources create very unique field structures with evident symmetry breaking properties. The observed vortex phenomena open an exciting prospect in novel applications of ferrite-based microwave devices.
Plasma mechanisms of resonant terahertz detection in a two-dimensional electron channel with split gates
Authors: Ryzhii V. , Satou A. , Otsuji T. , Shur M. S.
Published: January 2008

We analyze the operation of a resonant detector of terahertz (THz) radiation based on a two-dimensional electron gas (2DEG) channel with split gates. The side gates are used for the excitation of plasma oscillations by incoming THz radiation and control of the resonant plasma frequencies. The central gate provides the potential barrier separating the source and drain portions of the 2DEG channel. Two possible mechanisms of the detection are considered: (1) modulation of the ac potential drop across the barrier and (2) heating of the 2DEG due to the resonant plasma-assisted absorption of THz radiation followed by an increase in thermionic dc current through the barrier. Using the device model, we calculate the frequency and temperature dependences of the detector responsivity associated with both dynamic and heating (bolometric) mechanisms. It is shown that the dynamic mechanism dominates at elevated temperatures, whereas the heating mechanism provides larger contribution at low temperatures, T≲35−40 K.
Softening of nickel in the vicinity of its Curie point
Authors: Zaretsky E.
Published: January 2008

The dynamic yield strength of commercially pure nickel (99.5% Ni), as determined by planar impact experiments, shows a fivefold decrease in the close (±50°C) vicinity of its Curie point. The effect is attributed to the enhanced adsorption of impurity atoms by stacking fault ribbons (Suzuki atmosphere) that takes place in a narrow temperature interval.
Optical Thomson scatter from laser-ablated plumes
Authors: Delserieys A. , Khattak F. Y. , Lewis C. L. S , Riley D. , Pedregosa Gutierrez J.
Published: January 2008

We have obtained density and temperature informations on an expanding KrF laser-ablated magnesium plume via optical Thomson scatter with a frequency doubled Nd:YAG laser. The electron temperature was found to decay with the expected Te∝t−1 dependence. However, we have found the electron density to have a time dependence ne∝t−4.95 which can be explained by strong recombination processes. We also observed atomic Raman satellites originating from transitions between the different angular momentum levels of the metastable P03 term in MgI.
Spatially localized one-dimensional porous silicon photonic crystals
Authors: Park H. , Dickerson J. H. , Weiss S. M.
Published: January 2008

The authors report a straightforward method to achieve spatially localized photonic band-gap structures in porous silicon. This photonic band-gap lithography technique consists of local photo-oxidation followed by exposure to methanol solvent. Reflectance measurements show that the oxidized porous silicon regions maintain their photonic band structure with only a slight blueshift while there is significant spectral degradation in the nonoxidized regions. Fourier transform infrared spectroscopy and scanning electron microscopy were performed to investigate this phenomenon. The significant spectral change in the nonoxidized regions is attributed to chemical modification of the porous silicon.
Dependence of the structures and properties on LaAlO3 cap layer in LaAlO3∕BaTiO3 superlattices
Authors: Zuo Changming , Lu Shengbo , Zhou Xun , Zhang Yu
Published: January 2008

The LaAlO3∕BaTiO3 artificial superlattices were fabricated on (001)-oriented Nb-doped SrTiO3 substrates by laser molecular-beam epitaxy. The structures of the superlattice were analyzed by normal θ-2θ scan mode x-ray diffraction analysis, high-resolution reciprocal space mapping measurement, and x-ray reflectivity measurement. The use of a LaAlO3 cap layer could effectively reduce dislocation formation at the interface, which released the strain induced by the lattice misfit between the sublayers. The surface and interface were also smoothed by the use of a LaAlO3 cap layer. Therefore, the strain was maintained in the film and the ferroelectric property of the superlattice was significantly enhanced.
Rudolph Minkowski: Observational Astrophysicist
Authors: Osterbrock Donald E.
Published: January 2008

Rudolph Minkowski was born in Germany near the end of the last century and died in California during the final quarter of this century. He was trained as a laboratory physicist, but worked most of his life as an observational astronomer. Using the largest optical telescopes in the world, he made important contributions to nearly every branch of nebular and extragalactic astronomy, but his most important contribution was to the identification and interpretation of cosmic radio sources. His monument is the National Geographic Society-Palomar Observatory Sky Survey. He guided, encouraged and counseled a generation of radio and optical astronomers.
Small-Angle X-Ray Scattering and Structural Biology
Authors: Doniach Sebastian
Published: January 2008

It has been 25 years since Max Perutz and John Kendrew, working in Cambridge, England, used x-ray crystallography to determine in three dimensions the molecular structure of the oxygen-transport proteins hemoglobin and myoglobin. Their technique—xray diffraction from crystallized samples—continues to be one of the central sources of structural information for biology at the molecular level. Now, however, the advent of powerful new synchrotron x-ray sources based on multi-GeV electron storage rings is opening up new ways in which one can probe biological structure at the subcellular level.
High-School Physics: Progress and Continuing Challenge
Authors: Clark Robert Beck
Published: January 2008

In September 1983, PHYSICS TODAY devoted a special issue to the crisis in US high-school physics education. That issue was prepared in the wake of a series of well-publicized reports from a number of prominent national commissions and committees that documented the severity of the crisis. Of particular interest to the physics community was the shortage of qualified high-school physics instructors across the nation and the low level of high-school physics enrollment.
The SSC: A Machine for the Nineties
Authors: Glashow Sheldon L. , Lederman Leon M.
Published: January 2008

In July of 1983, the High Energy Physics Advisory Panel of the Department of Energy recommended that the highest priority be given to construction of a very large accelerator, the Superconducting Super Collider. The recommended energy per beam of this accelerator is 20 TeV, or 20 000 GeV—this is a macroscopic energy of about 32 ergs for each proton in the beam. Head-on collisions of protons against protons will thus make 40 TeV available in the center of mass, more than 60 times the energy available at the present CERN collider and 20 times that to become available at the Fermi National Accelerator Laboratory in the near future. The committee urged, moreover, that this facility be completed and available for physics research within about a decade. The solemnity of the advice was underscored by the simultaneous recommendations that all other proposals for high-energy accelerators not be approved. This included both the Colliding Beam Accelerator, in which the Brookhaven National Laboratory had invested considerable effort, and the Dedicated Collider, a proposed expansion of the Fermilab complex.
Major Facilities for Nuclear Physics
Authors: Baym Gordon
Published: January 2008

Nuclear physics is now entering one of the most challenging and interesting periods in the half century since the discovery of the neutron. With the simple picture of the nucleus in terms of the single-nucleon shell model well understood, nuclear physicists are turning to focus on nuclei as finite, saturating, many-body systems. The dominant theme promises to be the rich physics generated by the extensive array of nuclear degrees of freedom—from pure nucleonic states, as in the shell model, to mesonic and excited hadronic states, through to quarkgluon degrees of freedom.
Bringing the News of Fission to America
Authors: Stuewer Roger H.
Published: January 2008

In January 1939 the news of the discovery of nuclear fission burst in America, sending physicists into their laboratories to try to confirm the startling new discovery. Some aspects of the story of how this news reached America are well known. Others, however, are not; they have remained hidden in private correspondence and other unpublished documents. By examining these materials in conjunction with the published literature, one can reconstruct the circumstances that converged to produce this historic event.
Niels Bohr, the Man
Authors: Wheeler John Archibald
Published: January 2008

The fall of wartime 1944. Connecticut Avenue in downtown Washington. A broad sidewalk. One physicist from the du Pont plant at Hanford, Washington, producer of plutonium, walking alongside two from Los Alamos, customer for that plutonium. From Los Alamos, Aage Bohr, the son, and Niels Bohr, the father: an immensely impressive figure, widely regarded as the world's most responsible man of science. A few days before, thanks to the friendly offices of Supreme Court Justice Felix Frankfurter, the deeply concerned Bohr had had his long and historic discussion with President Franklin D. Roosevelt on weapons control, the higher politics of international relations in the coming nuclear age and the ideal of the open world. “How can such a man as I,” Bohr said early in that long walk, “speak about these issues to the leader of such a country in the midst of such a war? But I put it simply to him as man to man; what other way is there?”
Ammonia emissions from rough cattle slurry and from derived solid and liquid fractions applied to alfalfa pasture
Authors: Balsari P. , Dinuccio E. , Santoro E. , Gioelli F.
Published: January 2008

A field trial was conducted to assess the emission of ammonia from rough cattle slurry and solid and liquid fractions (generated from its mechanical separation) applied to alfalfa pasture. Three materials (rough slurry, liquid fraction and solid fraction) were applied on alfalfa over two seasons (summer and autumn), with two application rates (40 and 70 kg N/ha) and with two air velocities (0–0.6 m/s) at the soil surface. Ammonia losses were measured either by a set of wind tunnels (adjusting the air velocity at 0.6 m/s) or by a funnel system, allowing measurements to be recorded at an air speed close to 0 m/s. Each trial lasted 5 days with daily sampling of the gaseous emissions. Trial results showed that the rough slurry substrate had the highest level of ammonia emissions, followed by the liquid and solid fractions. Up to 35% of the applied total Kjeldahl nitrogen was lost as ammonia from the rough slurry in 5 days in summer conditions and with an air velocity of 0.6 m/s. No effect due to the application rate was observed, however, a significant effect of the temperature and air velocity on ammonia emissions was measured. Ammonia emissions after the spreading of the rough slurry were up to 26% higher when compared with those generated after application of the two fractions (solid + liquid).
Changes in methane emission and rumen fermentation parameters induced by refaunation in sheep
Authors: Morgavi D. P. , Jouany J. -P. , Martin C.
Published: January 2008

Elimination of protozoa or defaunation is known to reduce methane emission by ruminants. However, the long-term efficacy of this practice is not well documented. In this work methane and other end products of fermentation were monitored in five adult, rumen-cannulated wethers that had been kept defaunated for two years (Def1) and successively refaunated (Fau, 12 weeks) and defaunated (Def2) during a 6-month-long experiment. Methane was measured for periods of 4 days at about 4-weekly intervals using the SF6 tracer technique, and rumen content samples were taken regularly throughout the experiment. Refaunation was performed by single administration of a mixed protozoal inoculum (103 cells). A noticeable protozoal population was observed at 12 days after inoculation, which was followed by an exponential increase that peaked at 12 ± 3 × 105 cells/mL rumen fluid at 4 weeks and decreased thereafter to 8 ± 4 × 105 cells/mL at the end of the 12-week Fau period. Production of methane, which was 33 ± 8 L/animal.day in Def1, increased (P < 0.05) up to 42 ± 5 L at the end of the Fau period and dropped back at the end of Def2 to 35 ± 7 L (Def1 v. Def2, P > 0.05). Even though protozoal numbers were comparable to conventional animals 20 days after inoculation, the increase in methane production was observed later, at 8 weeks, suggesting that protozoa are not the only microbial factor favouring methanogenesis and that the ecosystem needs a relatively long adaptation time following protozoal introduction to optimise this function. The presence of protozoa did not affect total volatile fatty acids and acetate concentration in the rumen but increased butyrate, while decreasing propionate concentration (Fau v. Def1, Def2, P < 0.05). These results show that the decrease in methane emissions induced by defaunation in sheep was stable for a period of up to 2 years. In the absence of protozoa, methane decreased by ~20% in both short- and long-term defaunated animals.
The effect of level of intake and forage quality on methane production by sheep
Authors: Molano G. , Clark H.
Published: January 2008

In an experiment to determine the effect of level and quality of forage intake on methane (CH4) emissions, 16 wether lambs were allocated over two periods to two dietary treatments consisting of ryegrass at two stages of physiological maturity: an advanced stage of flowering and seeding (reproductive phase) and before flowering (vegetative phase). Additionally, in each period the lambs were divided into four groups and fed differing levels of food, from three-quarters maintenance to twice maintenance, to ensure a range of dry matter intakes amongst lambs. Apparent in vivo digestibility was measured and the mean values were 62.5% and 75.3% (s.e.d. = 0.84) for reproductive and vegetative ryegrass, respectively. Methane emissions were measured with the sulfur hexafluoride tracer technique. Daily methane emission was highly correlated with the amount of dry matter intake (DMI) (R2 = 0.83) and the regression was similar for both types of feed. Mean CH4 emissions per unit of DMI were 23.7 and 22.9 g/kg DMI (s.e.d. = 0.59) for reproductive and vegetative phases of ryegrass, respectively. The CH4 emissions per unit of DMI were not related to either level of DMI or diet quality.
The effectiveness of dicyandiamide in reducing nitrous oxide emissions from a cattle-grazed, winter forage crop in Southland, New Zealand
Authors: Smith L. C. , de Klein C. A. M. , Monaghan R. M. , Catto W. D.
Published: January 2008

A study was conducted in Southland, New Zealand to: (i) measure nitrous oxide (N2O) emissions and nitrate (NO3–-N) leaching losses from a cattle-grazed, winter forage crop; and (ii) quantify the effect of dicyandiamide (DCD) in reducing these losses. Drainage losses were measured for 12 months (December 2005–November 2006) from a December-sown kale crop using 12 hydrologically isolated drainage plots at the Woodlands Research Station. N2O emissions were measured for 6 months (June–November) following simulated grazing of the crop in mid-June. N2O emissions from the bare ground following grazing of the crop amounted to 3.6 kg nitrogen (N)/ha for the winter–spring period. This figure is higher than that measured for pasture on the same soil type over a similar period. DCD application significantly reduced N2O emissions for the whole crop area by 25% over this period and reduced the N2O emission factor for urine by 54%. DCD application increased the length of time mineral N (0–10 cm soil depth) was maintained in the ammonium form and significantly reduced soil NO3–-N levels for 6 weeks following the simulated grazing. Annual NO3–-N losses in drainage under this winter forage crop were relatively high at 79 kg N/ha.year, with the majority of this (67%) being lost over the wet summer months (December–January rainfall 434 mm or 200% of normal) during crop growth. The application of DCD following the grazing resulted in a 47% decrease in NO3–-N leached over the winter–spring period (26 kg N/ha v. 14 kg N/ha) with this equating to a 29% decrease over the full 12-month measurement period. This study suggested that winter forage crops are major contributors to N losses from livestock farming systems in Southland and that DCD application following the grazing of such crops by cattle can significantly reduce N2O emissions and leaching N losses.
Required sample size and nonreplicability thresholds for heterogeneous genetic associations
Authors: Moonesinghe Ramal , Khoury Muin J. , Liu Tiebin , Ioannidis John P. A.
Published: January 2008

Many gene–disease associations proposed to date have not been consistently replicated across different populations. Nonreplication often reflects false positives in the original claims. However, occasionally, nonreplication may be due to heterogeneity due to biases or even genuine diversity of the genetic effects in different populations. Here, we propose methods for estimating the required sample size to replicate an association across many studies with different amounts of between-study heterogeneity, when data are summarized through metaanalysis. We demonstrate thresholds of between-study heterogeneity (τ02) above which one cannot reach adequate power to replicate a proposed association at a specified level of statistical significance whenkstudies are performed (regardless of how large these studies are). Based on empirical evidence from 91 proposed gene–disease associations (50 on candidate genes and 41 from genome-wide association efforts), the observed between-study heterogeneity is often close to or even surpasses nonreplicability thresholds. With more modest between-study heterogeneity, the required sample size increases considerably compared with when no between-study heterogeneity exists. Increases are steep as τ02is approached. Therefore, some true associations may not be practically possible to replicate with consistency, no matter how large studies are conducted. Efforts should be made to minimize between-study heterogeneity in targeted genetic effects.
A predisposition for biological motion in the newborn baby
Authors: Simion Francesca , Regolin Lucia , Bulf Hermann
Published: January 2008

An inborn predisposition to attend to biological motion has long been theorized, but had so far been demonstrated only in one animal species (the domestic chicken). In particular, no preference for biological motion was reported for human infants of <3 months of age. We tested 2-day-old babies' discrimination after familiarization and their spontaneous preferences for biological vs. nonbiological point-light animations. Newborns were shown to be able to discriminate between two different patterns of motion (Exp. 1) and, when first exposed to them, selectively preferred to look at the biological motion display (Exp. 2). This preference was also orientation-dependent: newborns looked longer at upright displays than upside-down displays (Exp. 3). These data support the hypothesis that detection of biological motion is an intrinsic capacity of the visual system, which is presumably part of an evolutionarily ancient and nonspecies-specific system predisposing animals to preferentially attend to other animals.
Instability in pipe flow
Authors: Cotrell D. L. , McFadden G. B. , Alder B. J.
Published: January 2008

The long-puzzling, unphysical result that linear stability analyses lead to no transition in pipe flow, even at infinite Reynolds number, is ascribed to the use of stick boundary conditions, because they ignore the amplitude variations associated with the roughness of the wall. Once that length scale is introduced (here, crudely, through a corrugated pipe), linear stability analyses lead to stable vortex formation at low Reynolds number above a finite amplitude of the corrugation and unsteady flow at a higher Reynolds number, where indications are that the vortex dislodges. Remarkably, extrapolation to infinite Reynolds number of both of these transitions leads to a finite and nearly identical value of the amplitude, implying that below this amplitude, the vortex cannot form because the wall is too smooth and, hence, stick boundary results prevail.