bluuebunny/crossref_metadata_2025 huggingface dataset:
Antarctic Bottom Water production and export by tides in the Ross Sea
Authors: Whitworth T. , Orsi A. H.
Published: June 2006

Current measurements in the western Ross Sea show that Antarctic Bottom Water is produced at the outer edge of the Continental Shelf by tidal stirring of Antarctic Surface Water, Circumpolar Deep Water and Shelf Water. Current amplitudes during spring tides are greater than 1 m/s, sufficient to carry Circumpolar Deep Water onto the shelf from offshore and stir at least the lower portion of the water column to a nearly homogeneous mixture. The Antarctic Bottom Water produced every day during spring tides does not appear to have a seasonal signal. Its export rate is estimated to be 1.95 ± 1.85 × 106 m3/s.
Solar energetic particle flux enhancement as an indicator of halo coronal mass ejection geoeffectiveness
Authors: Gleisner H. , Watermann J.
Published: June 2006

Nearly all strong magnetic storms are generated by halo coronal mass ejections (CMEs), but most frontside halo CMEs are not followed by strong storms. Hence additional information is required to discriminate highly geoeffective CMEs from those less geoeffective. There is a tendency for the strongest magnetic storms to be generated by the fastest CMEs, and in the absence of detailed information on the internal structure of an observed CME, the speed is often used to evaluate the risk that a strong storm will follow. We here report on the alternative use of solar energetic particle (SEP) flux as an indicator of the geoeffectiveness of halo CMEs, addressing the question of whether SEP flux is better in this respect than CME speed. On the basis of a list of 137 frontside halo CMEs, we have investigated the relations between CME speed, SEP flux, and strong magnetic storms. We find that enhancements of the ≥10 MeV SEP flux close to CME onset can be used to indicate whether a full halo CME will be followed by Dst below −100 nT within 18 to 72 hours (our definition of a CME–strong magnetic storm association). Ranking the CMEs by speed and by SEP flux enhancement shows that the latter indicator results in a better discrimination between highly geoeffective CMEs and those less geoeffective. The results suggest that SEP flux enhancements may provide a more efficient discrimination than CME speed for any choice of discriminating thresholds, resulting in lower rates of both false alarms and missed predictions.
A study of density of states and ground states in hydrophobic-hydrophilic protein folding models by equi-energy sampling
Authors: Kou S. C. , Oh Jason , Wong Wing Hung
Published: June 2006

We propose an equi-energy (EE) sampling approach to study protein folding in the two-dimensional hydrophobic-hydrophilic (HP) lattice model. This approach enables efficient exploration of the global energy landscape and provides accurate estimates of the density of states, which then allows us to conduct a detailed study of the thermodynamics of HP protein folding, in particular, on the temperature dependence of the transition from folding to unfolding and on how sequence composition affects this phenomenon. With no extra cost, this approach also provides estimates on global energy minima and ground states. Without using any prior structural information of the protein the EE sampler is able to find the ground states that match the best known results in most benchmark cases. The numerical results demonstrate it as a powerful method to study lattice protein folding models.
Surface scanning probe microscopy investigation of solution deposited BiFeO3 thin films
Authors: Habouti S. , Solterbeck C. , Es-Souni M.
Published: June 2006

Thin films of the multiferroic perovskite-type oxide BiFeO3 were processed via solution deposition. The annealing schedule was chosen so as to give large and fine grained thin films. Microstructure, polarization, and dielectric properties are reported. It is shown that the large grained film is characterized by poor dielectric properties. Both microstructures show, however, poor polarization characteristics. Surface scanning potential microscopy reveals areas of high and low surface potentials in both specimens with a pronounced effect in the large grained films. It is thought that these areas are indirectly responsible for the poor polarization properties of the processed BiFeO3 films.
Terahertz emission profile from laser-induced air plasma
Authors: Zhong Hua , Karpowicz Nick , Zhang X.-C.
Published: June 2006

We report the characterization of the emission profile of terahertz waves generated by four-wave mixing in the presence of laser-induced plasma. Highly directional terahertz waves with a divergence angle smaller than 10° are measured in the presence of long plasmas (>10mm). Frequency-dependent interference structures in the angular distribution of the radiation are observed under tighter focusing conditions and are explained by intense self-phase modulation of the optical pulse in the plasma. This study reveals that terahertz generation from four-wave mixing in air plasmas is a promising source for spectroscopy and imaging in the terahertz range.
Sensing electric and magnetic fields with Bose-Einstein condensates
Authors: Wildermuth S. , Hofferberth S. , Lesanovsky I. , Groth S. , Krüger P. , Schmiedmayer J. , Bar-Joseph I.
Published: June 2006

We experimentally demonstrate that one-dimensional Bose-Einstein condensates brought close to microfabricated wires on an atom chip are a very sensitive sensor for magnetic and electric fields reaching a sensitivity to potential variations of ∼10−14eV at 3μm spatial resolution. We measure a two-dimensional magnetic field map 10μm above a 100-μm-wide wire and show how the transverse current-density component inside the wire can be reconstructed. The relation between the field sensitivity and the spatial resolution is discussed and further improvements utilizing Feshbach-resonances are outlined.
Diffusion mediated growth of (111) oriented silver nanoparticles in polyvinyl alcohol film under 6MeV electron irradiation
Authors: Bogle K. A. , Dhole S. D. , Bhoraskar V. N.
Published: June 2006

Silver (111) nanoparticles were synthesized by diffusing silver from a solution into polyvinyl alcohol (PVA) films under 6MeV electron irradiation at room temperature (∼25°C). The diffusion of silver in the PVA was confirmed by the Rutherford backscattering spectroscopy and scanning electron microscopy techniques. The plasmon absorption peak at ∼426nm was an evidence for the initiation of the diffusion mediated growth of silver nanoparticles. The x-ray diffraction results and the blueshift in the plasmon absorption peak reveal that the size of silver nanoparticles could be tailored in the range from 35to15nm by varying the electron fluence over the range of 1014–1015e∕cm2.
Electronic and thermodynamic properties of β-Ga2O3
Authors: He Haiying , Blanco Miguel A. , Pandey Ravindra
Published: June 2006

Electronic and thermodynamic properties of β-Ga2O3 are investigated in the framework of density functional theory. The equilibrium structural parameters and Debye temperature are obtained through fitting of the energy surface to the equation of state. Analysis of the band structure shows the valence band maximum to be degenerate at Γ and M, whereas the conduction band minimum is predicted to be at Γ. The valence band is almost flat, indicating a rather large effective mass for holes, whereas the calculated electron effective mass comes out to be about 0.12, expressed in units of the free electron mass.
Porous InP array-directed assembly of InAs nanostructure
Authors: Che Xiao-Ling , Li Lu , Liu Feng-Qi , Huang Xiu-Qi , Wang Zhan-Guo
Published: June 2006

Fascinating features of porous InP array-directed assembly of InAs nanostructures are presented. Strained InAs nanostructures are grown by molecular-beam epitaxy on electrochemical etched porous InP substrate. Identical porous substrate with different pore depths defines different growth modes. Shallow pores direct the formation of closely spaced InAs dots at the bottom. Deep pores lead to progressive covering of the internal surface of pores by epitaxial material followed by pore mouth shrinking. For any depth an obvious dot depletion feature occurs on top of the pore framework. This growth method presages a pathway to engineer quantum-dot molecules and other nanoelements for fancy physical phenomena.
Patterned field induced polymer walls for smectic A bistable flexible displays
Authors: Gheorghiu N. , West J. L. , Glushchenko A. V. , Mitrokhin M.
Published: June 2006

We have obtained a polymer wall-stabilized smectic A liquid crystal to be used for bistable flexible displays. The polymer wall structure optimally connects the two substrates together, thus providing maximum flexibility as compared to the polymer dispersed liquid crystal. Moreover, all the intrinsic bistable properties of the smectic A material are preserved. We analyzed the pixel performance and demonstrated very good electro-optical characteristics, high contrast ratio, and excellent stability of the states. The polymer wall-stabilized smectic A on flexible substrates has high potential to be used as electronic paper.
Relationship between binding site and pressure dependence for defect-hydrogen complexes in ZnO
Authors: Wardle M. G. , Goss J. P. , Briddon P. R.
Published: June 2006

The effect of hydrostatic pressure on local vibrational modes of hydrogen defects in ZnO has been studied by first-principles methods. We find that the sign and magnitude of the frequency shift rate are strongly dependent on the local environment. In the case of isolated hydrogen, the bond centered (BC) and antibonding (AB) configurations lead to positive and negative pressure shifts, in agreement with previous work. However, this result cannot be extended to defect-hydrogen complexes. In general, the sign of the shift does not indicate whether the hydrogen atom is located at a BC or AB site.
Effects of magnetic substrates on ac losses of YBa2Cu3O7 films in perpendicular ac magnetic fields
Authors: Suenaga Masaki , Li Qiang
Published: June 2006

Effects of a magnetic substrate on the ac losses of superconducting films were investigated by measuring the losses for octagonal disks of an YBa2Cu3O7 layer on a magnetic Ni–5at.% W substrate in perpendicular ac magnetic fields at 20Hz and 77K. At low fields, the losses depended on ac magnetic field amplitude B and film thickness t as ∝B3∕t instead of ∝B4∕t3 for a superconducting film on a nonmagnetic substrate. These results are described by considering the formation of a virtual infinite stack of superconducting films due to the magnetic mirror effect.
Potential for non-symbiotic N2-fixation in different agroecological zones of southern Australia
Authors: Gupta V. V. S. R. , Roper M. M. , Roget D. K.
Published: June 2006

Nitrogen fixation by symbiotic and non-symbiotic bacteria can be a significant source of nitrogen in cropping systems. However, contributions from non-symbiotic nitrogen fixation (NSNF) are dependent on available carbon in the soil and environmental conditions (soil moisture and temperature). In Australia, measurements of NSNF have been made in the field by quantifying nitrogenase activity. These studies have included determinations of the moisture and temperature requirements for NSNF and for crop residue decomposition that supplies carbon to NSNF bacteria. Other studies have determined the N input by NSNF using N budget calculations. These data together with information about carbon supply and environmental conditions were used to estimate potential NSNF in the cropping zones of southern Australia. Using the ArcviewGIS Spatial Analyst (v3.1), maps of Australia showing estimates of NSNF in different cropping zones as determined by rainfall and temperature or carbon availability were generated. In Western Australia (represented by Wongan Hills) and South Australia (represented by Avon), where summers are dry, estimates of NSNF were generally low (10–15 kg N/ha from January to June) due to limitations of soil moisture. In New South Wales, particularly in the north where summer rainfall patterns develop (represented by Gunnedah), the warm, moist conditions produced higher estimates of NSNF (totaling 32–38 kg N/ha from January to June). In this region, the majority of estimated NSNF occurred in January and February leading to the depletion of carbon supplies and reduced NSNF in autumn (March–June). Information about potential supplies of N from NSNF across the cropping zones should be useful for researchers to select and study areas that are most likely to benefit from NSNF. It should also help agronomists and extension officers explain changes in N status within paddocks or within specific farming systems and to provide more accurate advice on N fertiliser requirements, particularly in low-input farming systems.
Impact of agricultural inputs on soil organisms—a review
Authors: Bünemann E. K. , Schwenke G. D. , Van Zwieten L.
Published: June 2006

External agricultural inputs such as mineral fertilisers, organic amendments, microbial inoculants, and pesticides are applied with the ultimate goal of maximising productivity and economic returns, while side effects on soil organisms are often neglected. We have summarised the current understanding of how agricultural inputs affect the amounts, activity, and diversity of soil organisms. Mineral fertilisers have limited direct effects, but their application can enhance soil biological activity via increases in system productivity, crop residue return, and soil organic matter. Another important indirect effect especially of N fertilisation is soil acidification, with considerable negative effects on soil organisms. Organic amendments such as manure, compost, biosolids, and humic substances provide a direct source of C for soil organisms as well as an indirect C source via increased plant growth and plant residue returns. Non-target effects of microbial inoculants appear to be small and transient. Among the pesticides, few significant effects of herbicides on soil organisms have been documented, whereas negative effects of insecticides and fungicides are more common. Copper fungicides are among the most toxic and most persistent fungicides, and their application warrants strict regulation. Quality control of organic waste products such as municipal composts and biosolids is likewise mandatory to avoid accumulation of elements that are toxic to soil organisms.
The impact of crop residue amendments and lime on microbial community structure and nitrogen-fixing bacteria in the wheat rhizosphere
Authors: Nelson Darryl R. , Mele Pauline M.
Published: June 2006

Crop management practices can affect the soil microbial community, but it is not clear whether the effect of these practices is measurable at the wheat root–soil interface, where the plant exerts significant influence through root exudation. In this study, wheat plants were grown in soil amended with milled canola, lucerne, lupin, pea, and wheat residues with and without lime, to determine what changes occur to microbial community structure in the rhizosphere. Rhizosphere soil collected from wheat plants at the 5-leaf stage was assessed for overall microbial functional diversity using BIOLOG analysis and the diversity of the functional gene nifH using the polymerase chain reaction (PCR), terminal restriction fragment length polymorphism (T-RFLP), and cloning. Plant development was reduced in all residue amendments except lucerne, and a high positive correlation in the non-limited treatments between plant residue nitrogen (N) content and wheat shoot N suggested microbial competition for available N. Results from BIOLOG analysis indicated significant differences in rhizosphere microbial community structure due to lime, and to a lesser extent, residue type. Diversity, measured by the Shannon Diversity Index, was higher in limed rhizosphere soil, in addition to an increase in soils amended with lucerne, lupin, and pea residues compared with amendment with wheat, canola, and control soil. Each residue amendment promoted unique microbial communities determined by multi-dimensional scaling (MDS) and analysis of similarities (ANOSIM) of the BIOLOG data; the strongest effect was produced by addition of canola residues. N-fixing bacteria were also affected by lime, but residue effects were less apparent, especially between limed samples. The factor that correlated best with both BIOLOG and nifH T-RFLP data in non-limed soil was a combination of residue sodium (Na), copper (Cu), and manganese (Mn). In limed soil, phosphorus (P), calcium (Ca), and pH correlated well with BIOLOG data, and N, potassium (K), and iron (Fe) correlated with nifH T-RFLP data. A clone library of nifH sequences from control and limed, pea-amended soils revealed significant diversity amongst nifH sequences, most clustering with α-proteobacteria, and in some instances with Geobacter sulfurreducens. Clone distribution was significantly different for control soil and pea/lime soil, especially amongst the α-proteobacteria. The results suggest that rhizosphere microorganisms can be influenced by soil amendments, and change, depending on the type of residue applied. The addition of lime, however, produced the most significant changes in microbial community structure and nifH-containing rhizobacteria, highlighting the significant functional changes that occur when soil pH is increased.
Multiple routes lead to the native state in the energy landscape of the β-trefoil family
Authors: Chavez Leslie L. , Gosavi Shachi , Jennings Patricia A. , Onuchic José N.
Published: June 2006

In general, the energy landscapes of real proteins are sufficiently well designed that the depths of local energetic minima are small compared with the global bias of the native state. Because of the funneled nature of energy landscapes, models that lack energetic frustration have been able to capture the main structural features of the transition states and intermediates found in experimental studies of both small and large proteins. In this study we ask: Are the experimental differences in folding mechanisms among members of a particular structural family due to local topological constraints that deviate from the tertiary fold common to the family? The β-trefoil structural family members IL-1β, hisactophilin, and acidic/basic FGFs were chosen to address this question. It has been observed that the topological landscape of the β-trefoils allows for the population of diverse, geometrically disconnected routes that provide energetically similar but structurally distinct ways for this family to fold. Small changes in topology or energetics can alter the preferred route. Taken together, these results indicate that the global fold of the β-trefoil family determines the energy landscape but that the routes accessed on that landscape might differ as a result of functional requirements of the individual family members.
Butyrophilin controls milk fat globule secretion
Authors: Robenek Horst , Hofnagel Oliver , Buers Insa , Lorkowski Stefan , Schnoor Michael , Robenek Mirko J. , Heid Hans , Troyer David , Severs Nicholas J.
Published: June 2006

The molecular mechanism underlying milk fat globule secretion in mammary epithelial cells ostensibly involves the formation of complexes between plasma membrane butyrophilin and cytosolic xanthine oxidoreductase. These complexes bind adipophilin in the phospholipid monolayer of milk secretory granules, the precursors of milk fat globules, enveloping the nascent fat globules in a layer of plasma membrane and pinching them off the cell. However, using freeze-fracture immunocytochemistry, we find these proteins in locations other than those previously inferred. Significantly, butyrophilin in the residual plasma membrane of the fat globule envelope is concentrated in a network of ridges that are tightly apposed to the monolayer derived from the secretory granule, and the ridges coincide with butyrophilin labeling in the globule monolayer. Therefore, we propose that milk fat globule secretion is controlled by interactions between plasma membrane butyrophilin and butyrophilin in the secretory granule phospholipid monolayer rather than binding of butyrophilin–xanthine oxidoreductase complexes to secretory granule adipophilin.
Economic, neurobiological, and behavioral perspectives on building America’s future workforce
Authors: Knudsen Eric I. , Heckman James J. , Cameron Judy L. , Shonkoff Jack P.
Published: June 2006

A growing proportion of the U.S. workforce will have been raised in disadvantaged environments that are associated with relatively high proportions of individuals with diminished cognitive and social skills. A cross-disciplinary examination of research in economics, developmental psychology, and neurobiology reveals a striking convergence on a set of common principles that account for the potent effects of early environment on the capacity for human skill development. Central to these principles are the findings that early experiences have a uniquely powerful influence on the development of cognitive and social skills and on brain architecture and neurochemistry, that both skill development and brain maturation are hierarchical processes in which higher level functions depend on, and build on, lower level functions, and that the capacity for change in the foundations of human skill development and neural circuitry is highest earlier in life and decreases over time. These findings lead to the conclusion that the most efficient strategy for strengthening the future workforce, both economically and neurobiologically, and improving its quality of life is to invest in the environments of disadvantaged children during the early childhood years.
Endocytic vesicle scission by lipid phase boundary forces
Authors: Liu Jian , Kaksonen Marko , Drubin David G. , Oster George
Published: June 2006

Endocytosis in budding yeast is thought to occur in several phases. First, the membrane invaginates and then elongates into a tube. A vesicle forms at the end of the tube, eventually pinching off to form a “free” vesicle. Experiments show that actin polymerization is an active participant in the endocytic process, along with a number of membrane-associated proteins. Here we investigate the possible roles of these components in driving vesiculation by constructing a quantitative model of the process beginning at the stage where the membrane invagination has elongated into a tube encased in a sheath of membrane-associated protein. This protein sheath brings about the scission step where the vesicle separates from the tube. When the protein sheath is dynamin, it is commonly assumed that scission is brought about by the constriction of the sheath. Here, we show that an alternative scenario can work as well: The protein sheath acts as a “filter” to effect a phase separation of lipid species. The resulting line tension tends to minimize the interface between the tube region and the vesicle region. Interestingly, large vesicle size can further facilitate the reduction of the interfacial diameter down to a few nanometers, small enough so that thermal fluctuations can fuse the membrane and pinch off the vesicle. To deform the membrane into the tubular vesicle shape, the membrane elastic resistance forces must be balanced by some additional forces that we show can be generated by actin polymerization and/or myosin I. These active forces are shown to be important in successful scission processes as well.
Discovery of aminoacyl-tRNA synthetase activity through cell-surface display of noncanonical amino acids
Authors: Link A. James , Vink Mandy K. S. , Agard Nicholas J. , Prescher Jennifer A. , Bertozzi Carolyn R. , Tirrell David A.
Published: June 2006

The incorporation of noncanonical amino acids into recombinant proteins in
Escherichia coli
can be facilitated by the introduction of new aminoacyl-tRNA synthetase activity into the expression host. We describe here a screening procedure for the identification of new aminoacyl-tRNA synthetase activity based on the cell surface display of noncanonical amino acids. Screening of a saturation mutagenesis library of the
E. coli
methionyl-tRNA synthetase (MetRS) led to the discovery of three MetRS mutants capable of incorporating the long-chain amino acid azidonorleucine into recombinant proteins with modest efficiency. The Leu-13 → Gly (L13G) mutation is found in each of the three MetRS mutants, and the MetRS variant containing this single mutation is highly efficient in producing recombinant proteins that contain azidonorleucine.
Controlling interlayer diffusion to achieve sustained, multiagent delivery from layer-by-layer thin films
Authors: Wood Kris C. , Chuang Helen F. , Batten Robert D. , Lynn David M. , Hammond Paula T.
Published: June 2006

We present the fabrication of conformal, hydrolytically degradable thin films capable of administering sustained, multiagent release profiles. Films are constructed one molecular layer at a time by using the layer-by-layer, directed-deposition technique; the subsequent hydrolytic surface erosion of these systems results in the release of incorporated materials in a sequence that reflects their relative positions in the film. The position of each species is determined by its ability to diffuse throughout the film architecture, and, as such, the major focus of this work is to define strategies that physically block interlayer diffusion during assembly to create multicomponent, stratified films. By using a series of radiolabeled polyelectrolytes as experimental probes, we show that covalently crosslinked barriers can effectively block interlayer diffusion, leading to compartmentalized structures, although even very large numbers of ionically crosslinked (degradable or nondegradable) barrier layers cannot block interlayer diffusion. By using these principles, we designed degradable films capable of extended release as well as both parallel and serial multiagent release. The ability to fabricate multicomponent thin films with nanoscale resolution may lead to a host of new materials and applications.
Bone morphogenetic proteins 2, 4, and 9 stimulate murine hepcidin 1 expression independently of Hfe, transferrin receptor 2 (Tfr2), and IL-6
Authors: Truksa Jaroslav , Peng Hongfan , Lee Pauline , Beutler Ernest
Published: June 2006

Recently, it has been suggested that hepcidin, a peptide involved in iron homeostasis, is regulated by bone morphogenetic proteins (BMPs), apparently by binding to hemojuvelin (Hjv) as a coreceptor and signaling through Smad4. We investigate the role of Hfe, Tfr2 (transferrin receptor 2), and IL-6 in BMP2-, BMP4-, and BMP9-stimulated up-regulation of murine hepcidin, because these molecules, like Hjv, are known to be involved in hepcidin signaling. We show that the BMP signaling pathway acts independently of Hfe, Tfr2, and IL-6: The response to BMP2, BMP4, and BMP9 is similar in isolated hepatocytes of wild-type,
Hfe
−/−
,
IL-6
−/−
, and
Tfr2
m
mutant mice. The potency of different human BMPs in stimulating hepcidin transcription by murine primary hepatocytes is BMP9 > BMP4 > BMP2. However, in human HepG2 cells, BMP4 and BMP9 are equally potent, whereas BMP2 requires a higher dose to become an effective hepcidin activator. Moreover, all of the tested BMPs are more potent regulators of hepcidin than IL-6 and thus are the most potent known stimulators of hepcidin transcription.
Insights into the mechanism of microtubule stabilization by Taxol
Authors: Xiao Hui , Verdier-Pinard Pascal , Fernandez-Fuentes Narcis , Burd Berta , Angeletti Ruth , Fiser Andras , Horwitz Susan Band , Orr George A.
Published: June 2006

The antitumor drug Taxol stabilizes microtubules and reduces their dynamicity, promoting mitotic arrest and cell death. Upon assembly of the α/β-tubulin heterodimer, GTP bound to β-tubulin is hydrolyzed to GDP reaching a steady-state equilibrium between free tubulin dimers and microtubules. The binding of Taxol to β-tubulin in the polymer results in cold-stable microtubules at the expense of tubulin dimers, even in the absence of exogenous GTP. However, there is little biochemical insight into the mechanism(s) by which Taxol stabilizes microtubules. Here, we analyze the structural changes occurring in both β- and α-tubulin upon microtubule stabilization by Taxol. Hydrogen/deuterium exchange (HDX) coupled to liquid chromatography–electrospray ionization MS demonstrated a marked reduction in deuterium incorporation in both β-and α-tubulin when Taxol was present. Decreased local HDX in peptic peptides was mapped on the tubulin structure and revealed both expected and new dimer–dimer interactions. The increased rigidity in Taxol microtubules was distinct from and complementary to that due to GTP-induced polymerization. The Taxol-induced changes in tubulin conformation act against microtubule depolymerization in a precise directional way. These results demonstrate that HDX coupled to liquid chromatography–electrospray ionization MS can be effectively used to study conformational effects induced by small ligands on microtubules. The present study also opens avenues for locating drug and protein binding sites and for deciphering the mechanisms by which their interactions alter the conformation of microtubules and tubulin dimers.
Thermal fluctuations of grafted microtubules provide evidence of a length-dependent persistence length
Authors: Pampaloni Francesco , Lattanzi Gianluca , Jonáš Alexandr , Surrey Thomas , Frey Erwin , Florin Ernst-Ludwig
Published: June 2006

Microtubules are hollow cylindrical structures that constitute one of the three major classes of cytoskeletal filaments. On the mesoscopic length scale of a cell, their material properties are characterized by a single stiffness parameter, the persistence length ℓ
p
. Its value, in general, depends on the microscopic interactions between the constituent tubulin dimers and the architecture of the microtubule. Here, we use single-particle tracking methods combined with a fluctuation analysis to systematically study the dependence of ℓ
p
on the total filament length
L
. Microtubules are grafted to a substrate with one end free to fluctuate in three dimensions. A fluorescent bead is attached proximally to the free tip and is used to record the thermal fluctuations of the microtubule's end. The position distribution functions obtained with this assay allow the precise measurement of ℓ
p
for microtubules of different contour length
L
. Upon varying
L
between 2.6 and 47.5 μm, we find a systematic increase of ℓ
p
from 110 to 5,035 μm. At the same time we verify that, for a given filament length, the persistence length is constant over the filament within the experimental accuracy. We interpret this length dependence as a consequence of a nonnegligible shear deflection determined by subnanometer relative displacement of adjacent protofilaments. Our results may shine new light on the function of microtubules as sophisticated nanometer-sized molecular machines and give a unified explanation of seemingly uncorrelated spreading of microtubules' stiffness previously reported in literature.
Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea
Authors: Hall B. L. , Hoelzel A. R. , Baroni C. , Denton G. H. , Le Boeuf B. J. , Overturf B. , Töpf A. L.
Published: June 2006

We show that southern elephant seal (
Mirounga leonina
) colonies existed proximate to the Ross Ice Shelf during the Holocene, well south of their core sub-Antarctic breeding and molting grounds. We propose that this was due to warming (including a previously unrecognized period from ≈1,100 to 2,300
14
C yr B.P.) that decreased coastal sea ice and allowed penetration of warmer-than-present climate conditions into the Ross Embayment. If, as proposed in the literature, the ice shelf survived this period, it would have been exposed to environments substantially warmer than present.
CD28-stimulated ERK2 phosphorylation is required for polarization of the microtubule organizing center and granules in YTS NK cells
Authors: Chen Xi , Allan David S. J. , Krzewski Konrad , Ge Baoxue , Kopcow Hernan , Strominger Jack L.
Published: June 2006

Activation of natural killer (NK) cell cytotoxicity requires adhesion and formation of a conjugate with a susceptible target cell, followed by actin polymerization, and polarization of the microtubule organizing center (MTOC) and cytolytic granules to the NK cell immune synapse. Here, by using the YTS NK cell line as a model, CD28 is shown to be an activating receptor. It signals cytotoxicity in a process dependent on phosphoinositide-3 kinase activation, leading to sustained extracellular signal-regulated kinase 2 (ERK2) phosphorylation. ERK and phospho-ERK localize to microtubule filaments. Neither conjugation with targets nor actin polymerization is affected by blocking ERK2 activation. However, both polarization of the MTOC and cytolytic granules to the synaptic region and NK cell cytotoxicity are strongly reduced by blocking ERK2 activation. A role for the CD28/CD80 interaction in cytotoxicity of human peripheral NK cells also was established. By contrast, lymphocyte function-associated antigen 1 (LFA-1) ligation transduces only a transient ERK2 activation and fails to induce killing in YTS cells. Thus, in YTS cells, a CD28 signal is used to polarize the MTOC and cytolytic granules to the NK cell immune synapse by stimulating sustained ERK2 activation.
Pupil mobility, attainment and progress in primary school
Authors: Strand Steve , Demie Feyisa
Published: June 2006

This article presents an analysis of the association between pupil mobility and educational attainment in the 2002 national end of Key Stage 2 (KS2) tests for 11‐year‐old pupils in an inner London education authority. The results show that pupil mobility is strongly associated with low attainment in the end of key stage tests. However, the negative association with pupil mobility is reduced by half when account is taken of other pupil background factors known to be related to educational attainment (such as special educational need and socio‐economic disadvantage), and is eliminated entirely when account is also taken of pupils' prior attainment as indicated by end of KS1 test scores at age 7. Thus there is no indication that changing school has a negative impact on educational progress during primary school. Pupils who join their school during KS2 from other schools in England are more likely to be ‘at risk’ of low attainment due to higher levels of socio‐economic disadvantage, a greater need for support in relation to English as an additional language, a higher incidence and greater severity of special educational needs and pre‐existing low attainment at the end of KS1. A key factor in understanding the relationship between mobility and attainment is the reason for mobility. One‐third of mobile pupils had arrived from schools outside of England, often as refugees, asylum seekers or economic migrants, and these pupils accounted for the major part of the effect ascribed to ‘pupil mobility’. The low attainment of these pupils is the result not of ‘changing school’ but of a broad range of factors including substantial cultural, educational and social adjustment.
A curriculum without foundation
Authors: Boyle Bill , Bragg Joanna
Published: June 2006

Peter Tymms has written recently (BERJ, August 2004) on the subject of measuring whether standards are rising in English and mathematics in primary schools based on pupil outcomes from national end of key stage tests. This article takes the position that the performance data debate is an interesting one but peripheral to a far bigger issue. Whether measurable (by standardised testing at ages 7 and 11) national standards in English and mathematics have risen or not, does not justify the drastic reduction of the intended ‘broad and balanced’ curriculum which has taken place to try to achieve the national percentage targets. The curriculum data on which the authors base their findings are supplied by the Qualifications and Curriculum Authority's own longitudinal monitoring of the school curriculum which has been carried out by the authors from 1996 to 2004.
Secondary school pupils' preferences for different types of structured grouping practices
Authors: Hallam Susan , Ireson Judith
Published: June 2006

The aim of this article is to explore pupils' preferences for particular types of grouping practices, an area neglected in earlier research focusing on the personal and social outcomes of ability grouping. The sample comprised over 5000 Year 9 pupils (aged 13–14 years) in 45 mixed secondary comprehensive schools in England. The schools represented three levels of ability grouping in the lower school (Years 7 to 9). Pupils responded to a questionnaire which explored the types of grouping that they preferred and the reasons for their choices. The majority of pupils preferred setting, although this was mediated by their set placement, type of school, socio‐economic status and gender. The key reason given for this preference was that it enabled work to be matched to learning needs. The article considers whether there are other ways of achieving this, which avoid the negative social and personal outcomes of setting for some pupils.
The personal and professional selves of teachers: stable and unstable identities
Authors: Day Christopher , Kington Alison , Stobart Gordon , Sammons Pam
Published: June 2006

In much educational literature it is recognised that the broader social conditions in which teachers live and work, and the personal and professional elements of teachers' lives, experiences, beliefs and practices are integral to one another, and that there are often tensions between these which impact to a greater or lesser extent upon teachers' sense of self or identity. If identity is a key influencing factor on teachers' sense of purpose, self‐efficacy, motivation, commitment, job satisfaction and effectiveness, then investigation of those factors which influence positively and negatively, the contexts in which these occur and the consequences for practice, is essential. Surprisingly, although notions of ‘self’ and personal identity are much used in educational research and theory, critical engagement with individual teachers' cognitive and emotional ‘selves’ has been relatively rare. Yet such engagement is important to all with an interest in raising and sustaining standards of teaching, particularly in centralist reform contexts which threaten to destabilise long‐held beliefs and practices. This article addresses the issue of teacher identities by drawing together research which examines the nature of the relationships between social structures and individual agency; between notions of a socially constructed, and therefore contingent and ever‐remade, ‘self’, and a ‘self’ with dispositions, attitudes and behavioural responses which are durable and relatively stable; and between cognitive and emotional identities. Drawing upon existing research literature and findings from a four‐year Department for Education and Skills funded project with 300 teachers in 100 schools which investigated variations in teachers' work and lives and their effects on pupils (VITAE), it finds that identities are neither intrinsically stable nor intrinsically fragmented, as earlier literature suggests. Rather, teacher identities may be more, or less, stable and more or less fragmented at different times and in different ways according to a number of life, career and situational factors.
Talk as action in ‘collaborative action research’: making and taking apart teacher/researcher relationships
Authors: Frankham Jo , Howes Andy
Published: June 2006

This article considers the role of university researchers in a project aimed at developing inclusive practices in schools through collaborative action research. It tells the story of how these researchers became part of the action in one school—Beechbank Primary—through visits, the collection and reporting of data, and through the development of a relationship (particularly with the head teacher) that facilitated learning and change to take place. One of the issues highlighted is that it is in the process of setting up an action research project that many disturbances are evident and, perhaps, inevitable. We argue that it is in working with these disturbances that one might begin to establish the basis of a collaborative relationship, rather than implying that collaboration may result in such things. The approach taken in the section ‘Beechbank Story’ is a conscious departure from the investigations conducted as a consequence of audit mechanisms, where only particular measurable outcomes, designated in advance, constitute evidence of ‘progress’. We focus instead on process and hope to illustrate the small shifts and changes, documented ethnographically, which we argue are essential if change is to take place in the culture of a school.
Libya: Reforming the impossible?
Authors: Pargeter Alison
Published: June 2006

The violent protests that broke out in Libya's eastern city of Benghazi in February 2006 in response to the row over the Danish cartoons of the Prophet Mohamed came as no big surprise to Libya watchers. Although the demonstrations were sparked by Italian minister Roberto Calderoli's declaration that he intended to print t-shirts bearing the cartoons, they also reflected the simmering discontent and frustration that have long been building in the country's second city. Indeed, the protests were as much a means of expressing anger with the situation inside Libya as they were about the depiction of the Prophet and it wasn't long before protestors began shouting anti-regime slogans. Although Benghazi has traditionally been a rebellious region kept deliberately impoverished by the regime, the frustrations expressed by those in the incident are not unique to the eastern region. There is a groundswell of anger and despondency among much of the Libyan population at the regime's apparent inability or lack of will to improve living conditions and day-to-day life in the country.
Autonomy & Intifadah: New Horizons in Western Saharan Nationalism
Authors: Mundy Jacob
Published: June 2006

The Western Sahara conflict entered its thirtieth year last November. Celebrated by Moroccans and lamented by Sahrawi nationalists, the anniversary went largely unnoticed by the international community. Though it has been on the Security Council's agenda since 1988, Western Sahara has defied resolution by three successive Secretaries General and Kofi Annan's former personal envoy, former US Secretary of State James Baker. It is likely that a fourth Secretary General will take over management of the conflict next year.
Security & insecurity in North Africa
Authors: Keenan Jeremy
                      H.
Published: June 2006

The article analyses the North African security situation over the last 15 or so years, but especially since the 9/11 attacks on New York and Washington, which provided the pre-emptive basis for the launch of Washington's global ‘War on Terror’. The article explains how and why the US, in collaboration with its lead ally in the region, Algeria, and with the cognisance of France and other European powers, duplicitously fabricated a new front in the ‘war on terror’ across the Sahara and Sahel, bringing an entirely new dimension to the nature and meaning of ‘terrorism’ in North Africa. Far from furthering political stability, security and democracy, as the Bush administration has proclaimed, Washington's attempt to establish itself as the elite power in the region has taken North Africa and most of the Sahel into a dangerous spiral of increased authoritarianism and repression, increased regional instability and insecurity, increased popular resentment of both Washington and the regimes of the region and the increased threat of militant extremism. The article shows how the US has not been able to get its own way willy-nilly in the region, but has instead found itself running up against a whole raft of pressures and conflicts, many of its own making, which reflect both existing and new forms of political opposition and organisation. In focusing on labour and resource issues, especially those connected with oil and gas production, the article highlights the links between abundant oil, rents and the aggrandizement of the authoritarian state at the expense of autonomous civil society. The article concludes by suggesting that the US is unable to maintain its power and position in North Africa as a result of what is turning into a classic case of imperial over-reach.
‘Between a rock & a hard place’: North Africa as a region of emigration, immigration & transit migration
Authors: Baldwin-Edwards Martin
Published: June 2006

The prevailing Eurocentric perspective on Mediterranean migration lies almost exclusively in the security paradigm, focusing upon African illegal migration to Europe and disregarding the role of migration in the socio-economic development of the African continent. The older emigration histories of North African countries are diverse, with Morocco, Tunisia and Algeria linked to France as a destination country, Libya as an immigration country, and Egypt linked with other Arab countries for temporary migration alongside permanent migration to Anglophone countries. More recent changes include the emergence of southern Europe as destination countries for all except Libyans, and all of North Africa turned into transit countries for migrants from sub-Sahara Africa and Asia.

The ‘new migrations’ from and through North Africa are described, along with known major migration routes and data on interceptions of illegal migrants by southern European countries. North African policy responses are also identified, noting especially the failure of all countries in the region to observe international human rights standards. Finally, I outline the ‘failed policy’ of the European Union, which simply continues the securitisation approach previously pursued by Spain and Italy, neglecting the fundamental realities of Africa as a new continent of emigration. Furthermore, European policy promotes the human rights abuses of North Africa with regard to illegal migrants and asylum-seekers, yet welcomes skilled (as opposed to semiskilled) African migrants to European territory. Europe thus guarantees the continuation of African underdevelopment – seeking to avoid its negative symptom of mass emigration and asylum-seeking whilst benefiting from the migration to Europe of skilled African workers.
Contribution of Swedish moist snuff to the metabolic syndrome: A wolf in sheep's clothing?
Authors: Norberg Margareta , Stenlund Hans , Lindahl Bernt , Boman Kurt , Weinehall Lars
Published: June 2006

Aim: Combined effects of genetic and environmental factors underlie the clustering of cardiovascular risk factors in the metabolic syndrome (MetSy). The aim was to investigate associations between several lifestyle factors and MetSy, with a focus on the possible role of smokeless tobacco in the form of Swedish moist snuff (snus). Methods: A population-based longitudinal cohort study within the Västerbotten Intervention Programme in Northern Sweden. All inhabitants at the ages of 30, 40, 50, and 60 are invited to participate in a health survey that includes a questionnaire on psychosocial conditions and lifestyle and measurement of biological variables. Individuals examined in 1990—94 (n=24,230) and who also returned for follow-up after 10 years were included (total of 16,492 individuals: 46.6% men and 53.4% women). Regression analyses were performed. MetSy was the outcome and analyses were adjusted for age, sex, alcohol abuse, and family history of CVD and diabetes. Results: Ten-year development of MetSy was associated with high-dose consumption of snus at baseline (OR 1.6 [95% CI 1.26—2.15]), low education (2.2 [1.92—2.63]), physical inactivity (1.5 [1.22—1.73]) and former smoking (1.2 [1.06—1.38]). Snus was associated with separate components of MetSy, including triglycerides (1.6, 1.30—1.95), obesity (1.7 [1.36—2.18]) but not hypertension, dysglycemia and low HDL cholesterol. Conclusions: MetSy is independently associated with high consumption of snus, even when controlling for smoking status. The finding is of public health interest in societies with widespread use of snus. More research is needed to better understand the mechanisms underlying this effect.