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Graphene has a close lattice match to the Ni(111) surface, resulting in a preference for 1 × 1 configurations. We have investigated graphene grown by chemical vapor deposition (CVD) on the nickel carbide (Ni(2)C) reconstruction of Ni(111) with scanning tunneling microscopy (STM). The presence of excess carbon, in the form of Ni(2)C, prevents graphene from adopting the preferred 1 × 1 configuration and leads to grain rotation. STM measurements show that residual Ni(2)C domains are present under rotated graphene. Nickel vacancy islands are observed at the periphery of rotated grains and indicate Ni(2)C dissolution after graphene growth. Density functional theory (DFT) calculations predict a very weak (van der Waals type) interaction of graphene with the underlying Ni(2)C, which should facilitate a phase separation of the carbide into metal-supported graphene. These results demonstrate that surface phases such as Ni(2)C can play a major role in the quality of epitaxial graphene.

Two mutants with defects in hook-associated protein 3 (HAP3) were isolated that exhibit impaired swimming only when they interact with a solid surface or a semisolid matrix. Motility and chemotaxis were normal in liquid media, even in media containing viscous agents, but cells failed to swarm in 0·28% agar. Mutants appeared to carry a full complement of flagella of normal configuration and length. However, filaments rotating counterclockwise close to a glass surface transformed from normal to straight, while filaments rotating clockwise transformed from curly to straight. Both transformations propagated from base to tip, as expected if torsionally induced. The mutations mapped to the middle of flgL, the structural gene for HAP3, and sequence analysis revealed the same coding change in both mutants: a substitution of cysteine for arginine 168. Our results show that the ability of a filament composed of normal flagellin subunits to resist mechanical stress depends on the structure of the protein (HAP3) to which is attached at its base. The N-terminal sequence of HAP3 was found to be similar to the N-terminal sequence of flagellin, and the possibility that it provides a nucleation site for the C-terminal region of flagellin is discussed.

The four transmembrane chemoreceptors of Escherichia coli sense phenol as either an attractant (Tar) or a repellent (Tap, Trg, and Tsr). In this study, we investigated the Tar determinants that mediate its attractant response to phenol and the Tsr determinants that mediate its repellent response to phenol. Tar molecules with lesions in the aspartate-binding pocket of the periplasmic domain, with a foreign periplasmic domain (from Tsr or from several Pseudomonas chemoreceptors), or lacking nearly the entire periplasmic domain still mediated attractant responses to phenol. Similarly, Tar molecules with the cytoplasmic methylation and kinase control domains of Tsr still sensed phenol as an attractant. Additional hybrid receptors with signaling elements from both Tar and Tsr indicated that the transmembrane (TM) helices and HAMP domain determined the sign of the phenol-sensing response. Several amino acid replacements in the HAMP domain of Tsr, particularly attractant-mimic signaling lesions at residue E248, converted Tsr to an attractant sensor of phenol. These findings suggest that phenol may elicit chemotactic responses by diffusing into the cytoplasmic membrane and perturbing the structural stability or position of the TM bundle helices, in conjunction with structural input from the HAMP domain. We conclude that behavioral responses to phenol, and perhaps to temperature, cytoplasmic pH, and glycerol, as well, occur through a general sensing mechanism in chemoreceptors that detects changes in the structural stability or dynamic behavior of a receptor signaling element. The structurally sensitive target for phenol is probably the TM bundle, but other behaviors could target other receptor elements.

During transmembrane signaling by Escherichia coli Tsr, changes in ligand occupancy in the periplasmic serine-binding domain promote asymmetric motions in a four-helix transmembrane bundle. Piston displacements of the signaling TM2 helix in turn modulate the HAMP bundle on the cytoplasmic side of the membrane to control receptor output signals to the flagellar motors. A five-residue control cable joins TM2 to the HAMP AS1 helix and mediates conformational interactions between them. To explore control cable structural features important for signal transmission, we constructed and characterized all possible single amino acid replacements at the Tsr control cable residues. Only a few lesions abolished Tsr function, indicating that the chemical nature and size of the control cable side chains are not individually critical for signal control. Charged replacements at I214 mimicked the signaling consequences of attractant or repellent stimuli, most likely through aberrant structural interactions of the mutant side chains with the membrane interfacial environment. Prolines at residues 214 to 217 also caused signaling defects, suggesting that the control cable has helical character. However, proline did not disrupt function at G213, the first control cable residue, which might serve as a structural transition between the TM2 and AS1 helix registers. Hydrophobic amino acids at S217, the last control cable residue, produced attractant-mimic effects, most likely by contributing to packing interactions within the HAMP bundle. These results suggest a helix extension mechanism of Tsr transmembrane signaling in which TM2 piston motions influence HAMP stability by modulating the helicity of the control cable segment.

An array of surface science measurements has revealed novel water adsorption behavior at the Fe(3)O(4)(001) surface. Following room temperature exposure to water, a low coverage of hydrogen atoms is observed, with no associated water hydroxyl group. Mild annealing of the hydrogenated surface leads to desorption of water via abstraction of surface oxygen atoms, leading to a reduction of the surface. These results point to an irreversible splitting of the water molecule. The observed phenomena are discussed in the context of recent DFT calculations (Mulakaluri, N.; Pentcheva, R.; Scheffler, M. J. Phys. Chem. C 2010, 114, 11148), which show that the Jahn-Teller distorted surface isolates adsorbed H in a geometry that could kinetically hinder recombinative desorption. In contrast, the adsorption geometry facilitates interaction between water hydroxyl species, which are concluded to leave the surface following a reactive desorption process, possibly via the creation of O(2).

Oxide surfaces, and particularly those of vanadium oxides, play a major role in heterogeneous catalysis [1], yet there have been very few quantitative experimental structure determinations. The (0001) faces of the corundum-phase structures V2O3, � -Al2O3, and Cr2O3, are particularly interesting because there are several distinctly different atomic layers at which the bulk structure might be terminated. One fundamental question is whether, in practice, these surfaces can be created in a state that is truly in equilibrium with their surroundings under preparation conditions. Starting from a bulk crystal one might anticipate difficulty in overcoming the kinetic barriers to achieve this equilibrium under conditions of temperature and oxygen partial pressure accessible to surface science experiments. Alternatively, epitaxial growth of the oxide on a suitable substrate, by deposition of metal vapor in the presence of a partial pressure of oxygen, may offer a better means of achieving this gas-solid equilibrium. Growth is intrinsically a nonequilibrium process, yet using low metal deposition rates in an excess of oxygen gas, the kinetic barriers to achieving equilibrium may be much lower than those needed to modifyan existingnonequilibrium surface. In fact, previous structural studies of the surface of bulk crystals of � -Al2O3 and Cr2O3, and of Cr2O3 produced by oxidation of metallic Cr, appear to be broadly consistent with the theoretically predicted equilibrium structure. By contrast, spectroscopic, imaging, and chemical studies of the V2O3ð0001Þ surface of epitaxial films grown in situ have been interpreted in terms of a nonequilibrium surface (e.g., [2–6]). Here we show that two independent quantitative experimental determinations of the structure of V2O3ð0001Þ, using distinctly different ion scattering methods, demonstrate that the structure does correspond to the equilibrium state predicted in density functional theory (DFT) calculations. We find this is true for the surfaces of films grown under conditions that are both similar to, and distinctly different from, those used in the earlier explorations of these surfaces. We discuss how these apparently conflicting views may be reconciled. Relative to the (0001) basal plane, the bulk structure of V2O3 comprises alternate buckled layers containing 2 metal atoms per unit mesh, and planar layers containing 3 oxygen atoms per unit mesh; this layer structure is denoted

Complementary but independent medium-energy and low-energy ion scattering studies of the (0001) surfaces of V(2)O(3) films grown on Pd(111), Au(111) and Cu(3)Au(100) reveal a reconstructed full O(3)-layer termination creating a VO(2) surface trilayer. This structure is fully consistent with previous calculations based on thermodynamic equilibrium at the surface during growth, but contrasts with previous suggestions that the surface termination comprises a complete monolayer of vanadyl (V=O) species.

The adsorption of H on the magnetite (001) surface was studied with photoemission spectroscopies, scanning tunneling microscopy, and density-functional theory. At saturation coverage the insulating $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})R45\ifmmode^\circ\else\textdegree\fi{}$ reconstruction is lifted and the surface undergoes a semiconductor--half metal transition. This transition involves subtle changes in the local geometric structure linked to an enrichment of ${\text{Fe}}^{2+}$ cations at the surface. The ability to manipulate the electronic properties by surface engineering has important implications for magnetite-based spintronic devices.

The interaction of S-2 with Ag(111) under ultra-high vacuum conditions has been investigated by medium energy ion scattering (MEIS). 100 key He+ MEIS measurements provide a direct confirmation of a previous report, based on thermal desorption, that the growth of multilayer films of Ag2S occurs through a continuous corrosion process. These films show a commensurate (root 7 x root 7)R19 degrees unit mesh in low energy electron diffraction, consistent with the epitaxial growth of (111) layers of the high-temperature F-cubic phase of Ag2S. The substantial range of co-existing film thicknesses found indicates that the growth must be in the form of variable-thickness islands. The use of 100 key H+ incident ions leads to a very rapid decrease in the sulphide film thickness with increasing exposure that we attribute to an unusual chemical leaching, with implanted H atoms interacting with S atoms and desorption of H2S from the surface.

HAMP domains mediate input-output signaling in histidine kinases, adenylyl cyclases, methyl-accepting chemotaxis proteins, and some phosphatases. HAMP subunits have two 16-residue amphiphilic helices (AS1, AS2) joined by a 14- to 15-residue connector segment. Two alternative HAMP structures in these homodimeric signaling proteins have been described: HAMP(A), a tightly packed, parallel, four-helix bundle; and HAMP(B), a more loosely packed bundle with an altered AS2/AS2′ packing arrangement. Stimulus-induced conformational changes probably modulate HAMP signaling by shifting the relative stabilities of these opposing structural states. Changes in AS2/AS2′ packing, in turn, modulate output signals by altering structural interactions between output helices through heptad repeat stutters that produce packing phase clashes. Output helices that are too tightly or too loosely packed most likely produce kinase-off output states, whereas kinase-on states require an intermediate range of HAMP stabilities and dynamic behaviors. A three-state, dynamic bundle signaling model best accounts for the signaling properties of chemoreceptor mutants and may apply to other transducers as well.

Medium energy ion scattering (MEIS), using 100 keV H+ ions, has been applied to investigate the surface relaxations involved in the Cu(4 1 0)-O phase through the measurement and simulation of a series of blocking curves. Measurements were made in six different scattering geometries that exploit the intrinsic asymmetry of the stepped surface by using the scattering plane that is perpendicular to the surface and to the [0 0 1] steps (i.e. in the [1 (4) over bar 0] azimuth). Specifically, incidence in 'up-step' and 'down-step' directions were used that are equivalent relative to the (1 0 0) terraces, but not relative to the (4 1 0) surface. A range of relaxation models were tested, investigating the influence of 16 distinct structural parameters that define surface-induced displacements perpendicular and parallel to the surface, but optimising only the eight parameters associated with movements of the outermost four Cu atom rows that lie directly at the solid/vacuum interface. Relaxations broadly similar to those found in a previous study based on X-ray diffraction and density functional theory calculations are found, although there are some significant quantitative differences. The results are also compared with relaxations previously measured on the related Cu(1 0 0)(root 2 x 2 root 2)R45 degrees-O 'missing row' structure. (C) 2010 Elsevier B.V. All rights reserved.

A control system has been designed and implemented to provide more effective energy management of low-pressure gas distribution networks. The key to this is the provision of a control scheme that maintains low pressures across a network. The work was approached from first principles and a modelling technique has been developed which provides reduced order models that adequately describe the characteristics of multi-feed gas networks. The models were then used for the control system design, which in this case also included the selection of the optimal measurement points for most effective control. Following extensive design studies a relatively straightforward control scheme resulted which has been implemented and proved to be effective.

The effect of reel speed, can size, and percent air during steam and steam/air processing in a Steritort on the heating rate of tomato concentrate (an induced convection-heating product) was investigated. A Taylor expansion equation, relating Ball process times with the above three variables, considering first order, second order, and interaction effects, was presented. A correlation equation for the Nusselt number as a function of the Reynolds and Prandtl numbers, the can length over the diameter ratio, and the steam content was also presented. Percent reduction in process lethality increased with increasing can size and air content, and decreasing reel speed and target lethality. Increase in percent air in the steam/air mixture could be compensated by an increase of the rotational speed.

To test the gearbox model of HAMP signalling in the Escherichia coli serine receptor, Tsr, we generated a series of amino acid replacements at each residue of the AS1 and AS2 helices. The residues most critical for Tsr function defined hydrophobic packing faces consistent with a four-helix bundle. Suppression patterns of helix lesions conformed to the predicted packing layers in the bundle. Although the properties and patterns of most AS1 and AS2 lesions were consistent with both proposed gearbox structures, some mutational features specifically indicate the functional importance of an x-da bundle over an alternative a-d bundle. These genetic data suggest that HAMP signalling could simply involve changes in the stability of its x-da bundle. We propose that Tsr HAMP controls output signals by modulating destabilizing phase clashes between the AS2 helices and the adjoining kinase control helices. Our model further proposes that chemoeffectors regulate HAMP bundle stability through a control cable connection between the transmembrane segments and AS1 helices. Attractant stimuli, which cause inward piston displacements in chemoreceptors, should reduce cable tension, thereby stabilizing the HAMP bundle. This study shows how transmembrane signalling and HAMP input-output control could occur without the helix rotations central to the gearbox model.

The energy spectrum associated with scattering of 100 keV H+ ions from the outermost few atomic layers of Cu(111) in different scattering geometries provides direct evidence of trajectory-dependent electronic energy loss. Theoretical simulations, combining standard Monte Carlo calculations of the elastic scattering trajectories with coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter, reproduce the effects well and provide a means for far more complete analysis of medium-energy ion scattering data.

We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy. gamma-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.5846). The optical spectrum of this object exhibits rather narrow H beta (FWHM(H beta) similar to 1500 km s(-1)), weak forbidden lines, and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at a high Eddington ratio. The radio loudness and variability of the compact radio core indicate the presence of a relativistic jet. Quasi-simultaneous radio/optical/X-ray and gamma-ray observations are presented. Both radio and gamma-ray emissions (observed over five months) are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broadband spectral energy distribution (SED) and, in particular, the gamma-ray spectrum measured by Fermi are similar to those of more powerful Flat-Spectrum Radio Quasars (FSRQs). A comparison of the radio and gamma-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and gamma-ray power with respect to other FSRQs. The physical parameters obtained from modeling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti & Ghisellini. We suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.

Effects of residual air were evaluated on the heating rates of a convectionheating product processed in a continuous rotary sterilizer. Heat penetration tests were conducted in a Steritort at various reel speeds (1-10 rpm) and air overpressures (0-69.0 kPa) using 211 × 300, 300 × 407 and 603 × 700 cans containing Washington white beans in brine. Sterilization times calculated by Ball's formula method were longer for test cans processed with overpressure than those processed with no overpressure. Maximum reduction in calculated lethality for 69.0 kPa air overpressure was 15.2% for 211 × 300 and 300 × 407 experiments and 49.4% for 603 × 700 experiments. For each can size and reel speed, average process time was a linear function of overpressure.

HAMP domains are 50-residue motifs, found in many bacterial signaling proteins, that consist of two amphiphilic helices joined by a nonhelical connector segment. The HAMP domain of Tsr, the serine chemoreceptor of Escherichia coli, receives transmembrane input signals from the periplasmic serine binding domain and in turn modulates output signals from the Tsr kinase control domain to elicit chemotactic responses. We created random amino acid replacements at each of the 14 connector residues of Tsr-HAMP to identify those that are critical for Tsr function. In all, we surveyed 179 connector missense mutants and identified three critical residues (G235, L237, and I241) at which most replacements destroyed Tsr function and another important residue (G245) at which most replacements impaired Tsr function. The region surrounding G245 tolerated 1-residue deletions and insertions of up to 10 glycines, suggesting a role as a relatively nonspecific, flexible linker. The critical connector residues are consistent with a structural model of the Tsr-HAMP domain based on the solution structure of an isolated thermophile HAMP domain (M. Hulko, F. Berndt, M. Gruber, J. U. Linder, V. Truffault, A. Schultz, J. Martin, J. E. Schultz, A. N. Lupas, and M. Coles, Cell 126:929‐940, 2006) in which G235 defines a critical turn at the C terminus of the first helix and L237 and I241 pack against the helices, perhaps to stabilize alternative HAMP signaling conformations. Most I241 lesions locked Tsr signal output in the kinase-on mode, implying that this residue is responsible mainly for stabilizing the kinase-off signaling state. In contrast, lesions at L237 resulted in a variety of aberrant output patterns, suggesting a role in toggling output between signaling states. Many signaling proteins in bacteria and archaea contain HAMP domains, a 50-residue motif named for its presence in histidine kinases, adenylyl cyclases, chemoreceptors known as methyl-accepting chemotaxis proteins (MCPs), and some phosphatases (8, 46). HAMP domains typically reside between the periplasmic sensing and cytoplasmic signaling regions of transmembrane proteins near the inner face of the cytoplasmic membrane and appear to play a central role in transmitting stimulus-induced conformational changes between the input and output domains of such signaling proteins. Their ability to mediate signaling transactions between heterologous input and output domains in chimeric proteins suggests that the mecha

Aluminium intoxication in renal failure occurred over weeks or months when dialysis fluid or parenteral solutions were heavily contaminated and over many years when the main source was oral administration of aluminium-containing phosphate binders. Encephalopathy was common during subacute intoxication but in slow aluminium poisoning the main brunt was borne by the bones. However, in both tempos of intoxication several organs or systems were involved. Encephalopathy was usually accompanied by bone disease, bone disease by parathyroid suppression and both by anaemia. The heart and the lymphocytes are probably damaged by aluminium overload. Among the many questions left unanswered 15 years after the incrimination of aluminium as the cause of this multi-system illness are: (1) does low level aluminium overload in renal failure cause gradual deterioration in cerebral function? And, if so, (2) does it resemble Alzheimer's disease or a slow-onset version of dialysis encephalopathy? The evidence we review suggests that the answer to (1) is 'yes' and to (2) 'probably the latter'.

The chemoreceptor molecules that mediate chemotactic responses in bacteria and archaea are physically clustered and operate as highly cooperative arrays. Few experimental approaches are able to investigate the structure-function organization of these chemoreceptor networks in living cells. This chapter describes chemical crosslinking methods that can be applied under normal physiological conditions to explore physical interactions between chemoreceptors and their underlying genetic and structural basis. Most of these crosslinking approaches are based on available atomic structures for chemoreceptor homodimers, the fundamental building block for higher-order networks. However, the general logic of our in vivo crosslinking approaches is readily applicable to other protein-protein interactions and other organisms, even when high-resolution structural information is not available.

The morphologies of bacterial colonies in soft agar media can provide a wealth of information about a strain's locomotor and chemotactic abilities. Photographic images are often the simplest and most effective means of documenting these behavioral phenotypes. Uniform, indirect, transmitted illumination of the plates is essential for obtaining good colony images. This brief chapter describes a simple and relatively inexpensive illumination device for viewing and photographing bacterial colonies in soft agar.

As an important model for transmembrane signaling, methyl-accepting chemotaxis proteins (MCPs) have been extensively studied by using genetic, biochemical, and structural techniques. However, details of the molecular mechanism of signaling are still not well understood. The availability of genomic information for hundreds of species enables the identification of features in protein sequences that are conserved over long evolutionary distances and thus are critically important for function. We carried out a large-scale comparative genomic analysis of the MCP signaling and adaptation domain family and identified features that appear to be critical for receptor structure and function. Based on domain length and sequence conservation, we identified seven major MCP classes and three distinct structural regions within the cytoplasmic domain: signaling, methylation, and flexible bundle subdomains. The flexible bundle subdomain, not previously recognized in MCPs, is a conserved element that appears to be important for signal transduction. Remarkably, the N- and C-terminal helical arms of the cytoplasmic domain maintain symmetry in length and register despite dramatic variation, from 24 to 64 7-aa heptads in overall domain length. Loss of symmetry is observed in some MCPs, where it is concomitant with specific changes in the sensory module. Each major MCP class has a distinct pattern of predicted methylation sites that is well supported by experimental data. Our findings indicate that signaling and adaptation functions within the MCP cytoplasmic domain are tightly coupled, and that their coevolution has contributed to the significant diversity in chemotaxis mechanisms among different organisms.

The chemoreceptor molecules that mediate chemotactic responses in bacteria and archaea are physically clustered and operate as highly cooperative arrays. Few experimental approaches are able to investigate the structure–function organization of these chemoreceptor networks in living cells. This chapter describes chemical crosslinking methods that can be applied under normal physiological conditions to explore physical interactions between chemoreceptors and their underlying genetic and structural basis. Most of these crosslinking approaches are based on available atomic structures for chemoreceptor homodimers, the fundamental building block for higher‐order networks. However, the general logic of our in vivocrosslinking approaches is readily applicable to other protein–protein interactions and other organisms, even when high‐resolution structural information is not available.

The morphologies of bacterial colonies in soft agar media can provide a wealth of information about a strain's locomotor and chemotactic abilities. Photographic images are often the simplest and most effective means of documenting these behavioral phenotypes. Uniform, indirect, transmitted illumination of the plates is essential for obtaining good colony images. This brief chapter describes a simple and relatively inexpensive illumination device for viewing and photographing bacterial colonies in soft agar.

The receptors that mediate chemotactic behaviors in E. coli and other motile bacteria and archaea are exquisite molecular machines. They detect minute concentration changes in the organism's chemical environment, integrate multiple stimulus inputs, and generate a highly amplified output signal that modulates the cell's locomotor pattern. Genetic dissection and suppression analyses have played an important role in elucidating the molecular mechanisms that underlie chemoreceptor signaling. This chapter discusses three examples of phenotypic suppression analyses of receptor signaling defects. (i) Balancing suppression can occur in mutant receptors that have biased output signals and involves second‐site mutations that create an offsetting bias change. Such suppressors can arise in many parts of the receptor and need not involve directly interacting parts of the molecule. (ii) Conformational suppression within a mutant receptor molecule occurs through a mutation that directly compensates for the initial structural defect. This form of suppression should be highly dependent on the nature of the structural alterations caused by the original mutation and its suppressor, but in practice may be difficult to distinguish from balancing suppression without high‐resolution structural information about the mutant and pseudorevertant proteins. (iii) Conformational suppression between receptor molecules involves correction of a functional defect in one receptor by a mutational change in a heterologous receptor with which it normally interacts. The suppression patterns exhibit allele‐specificity with respect to the compensatory residue positions and amino acid side chains, a hallmark of stereospecific protein–protein interactions.

The energy-loss spectrum associated with scattering of 100-keV H+ ions from K, Rb, and Cs atoms adsorbed on Al(111) has been investigated both experimentally and theoretically. Theoretical simulations were conducted based on calculations of the energy loss experienced in specific ion trajectories at the surface, using coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter. The energy losses can be attributed entirely to single atomic collisions from the alkali atoms, and the experiments reproduce the markedly increased asymmetry in scattering from Rb and Cs relative to K, attributable largely to the role of 3d and 4d excitations, respectively, and particularly the role of multiple excitations of these states. For Rb and Cs scattering, the data show excellent quantitative agreement between theory and experiment; for the K scattering, a discrepancy of a low-energy shoulder is attributed to a problem associated with the sample preparation.

$100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ ${\mathrm{H}}^{+}$ medium-energy ion scattering has been applied to investigate the surface relaxations of the clean rutile ${\mathrm{TiO}}_{2}(110)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$ surface structure. A set of blocking curves in four different incident directions show clear differences between the surface and bulk attributable to surface relaxation. Optimized values of the surface relaxation parameters to give the best fit to the surface structure are generally in quite good agreement with a recent experimental determination of this structure using quantitative low-energy electron diffraction. In particular, both solutions favor an outward relaxation of the bridging O atoms on the surface rather than the strong inward displacement favored by the only previous experimental structure determination based on surface x-ray diffraction.

Motile bacteria follow gradients of attractant and repellent chemicals with high sensitivity. Their chemoreceptors are physically clustered, which may enable them to function as a cooperative array. Although native chemoreceptor molecules are typically transmembrane homodimers, they appear to associate through their cytoplasmic tips to form trimers of dimers, which may be an important architectural element in the assembly and operation of receptor clusters. The five receptors of Escherichia coli that mediate most of its chemotactic and aerotactic behaviors have identical trimer contact residues and have been shown by in vivo crosslinking methods to form mixed trimers of dimers. Mutations at the trimer contact sites of Tsr, the serine chemoreceptor, invariably abrogate Tsr function, but some of those lesions (designated Tsr*) are epistatic and block the function of heterologous chemoreceptors. We isolated and characterized mutations (designated Tar ⋀ ) in the aspartate chemoreceptor that restored function to Tsr* receptors. The suppressors arose at or near the Tar trimer contact sites and acted in an allele-specific fashion on Tsr* partners. Alone, many Tar ⋀ receptors were unable to mediate chemotactic responses to aspartate, but all formed clusters with varying efficiencies. Most of those Tar ⋀ receptors were epistatic to WT Tsr, but some regained Tar function in combination with a suppressible Tsr* partner. Tar ⋀ –Tsr* suppression most likely occurs through compensatory changes in the conformation or dynamics of a mixed receptor signaling complex, presumably based on trimer-of-dimer interactions. These collaborative teams may be responsible for the high-gain signaling properties of bacterial chemoreceptors.

We reviewed retrospectively 45 patients (46 procedures) with bladder exstrophy treated by bilateral oblique pelvic osteotomy in conjunction with genitourinary repair. The operative technique and post-operative management with or without external fixation are described. A total of 21 patients attended a special follow-up clinic and 24 were interviewed by telephone. The mean follow-up time was 57 months (24 to 108). Of the 45 patients, 42 reported no pain or functional disability, although six had a waddling gait and two had marked external rotation of the hip. Complications included three cases of infection and loosening of the external fixator requiring early removal with no deleterious effect. Mid-line closure failed in one neonate managed in plaster. This patient underwent a successful revision procedure several months later using repeat osteotomies and external fixation. The percentage pubic approximation was measured on anteroposterior radiographs pre-operatively, post-operatively and at final follow-up. The mean approximation was 37% (12% to 76%). It varied markedly with age and was better when external fixation was used. The wide range reflects the inability of the anterior segment to develop naturally in spite of close approximation at operation. We conclude that bilateral oblique pelvic osteotomy with or without external fixation is useful in the management of difficult primary closure in bladder exstrophy, failed primary closure and secondary reconstruction.

Objectives: The goal of the research is to evaluate the application of genetic algorithms (GAs) in listener-directed optimization of audio-processing designs. We hypothesize that cochlear-implant recipients can use a GA-guided adaptive psychophysical search procedure to select useful designs from among a large number of speech processor MAPS. Design: An adaptive psychophysical procedure was developed in which a listener's preferred four out of eight speech processor MAPs were updated according to a genetic algorithm. Experiments involving cochlear-implant recipients were conducted to characterize both the convergence behavior of the adaptive procedure as well as properties of the MAPs optimized by the recipient. Results: Results from five cochlear-implant recipients indicate that the -adaptive procedure converges to useful speech processor MAPs within twenty iterations. Conclusion: The results suggest a means whereby a potentially large number of audio-processing designs can be searched efficiently by a human listener without requiring excessive amounts of feedback or prior knowledge about the listener's preferences. In the case of cochlear-implant recipients, it may be possible to use this procedure as an aid to the clinician in the fitting of a speech processor MAP.

AIM To evaluate prospectively the pattern, severity and predictive factors of pain after interventional radiological procedures. MATERIALS AND METHODS All patients undergoing non-arterial radiological interventional procedures were assessed using a visual-analogue scale (VAS) for pain before and at regular intervals for 24 h after their procedure. RESULTS One hundred and fifty patients (87 men, mean age 62 years, range 18–92 years) were entered into the study. Significant increases in VAS score occurred 8 h after percutaneous biliary procedures (+47.7 mm, SD 14.9 mm; p =0.001), 6 h after central venous access and gastrostomy insertion (+23.7 mm, SD 19.5 mm; p =0.001 and +28.4 mm, SD 9.7 mm; p =0.007, respectively) and 4 h after oesophageal stenting (+27.8 mm, SD 20.2 mm, p =0.001). Non-significant increases in VAS pain score were observed after duodenal and colonic stenting (duodenal: +5.13 mm, SD 7.47 mm; p =0.055, colonic: +23.3 mm, SD 13.10 mm, p =0.250) at a mean of 5 h (range 4–6 h). Patients reported a significant reduction in pain score for nephrostomy insertion (−28.4 mm, SD 7.11 mm, p =0.001). Post-procedural analgesia was required in 99 patients (69.2%), 40 (28.0%) requiring opiates. Maximum post-procedural VAS pain score was significantly higher in patients who had no pre-procedural analgesia ( p =0.003). CONCLUSION Post-procedural pain is common and the pattern and severity of pain between procedures is variable. Pain control after interventional procedures is often inadequate, and improvements in pain management are required.

The energy-loss spectrum associated with scattering of 100 keV H{sup +} ions from Y atoms on Si(111) has been investigated both experimentally and theoretically. Measurements were made from Y overlayers, and from the Si(111)(1x1) two-dimensional silicide phase formed by Y on this surface, in various scattering geometries and with different surface preparations. Theoretical simulations were conducted based on calculations of the energy loss experienced in specific ion trajectories through the surface, using coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter. The experimental results indicate that additional broadening contributions arise from surface inhomogeneity and roughness, but for near-normal incident and outgoing trajectories the theory and experiment agree quite well. The calculations show that, even for the ideal two-dimensional silicide phase in which the Y atoms lie just below the surface, significant energy loss arises from interaction of the ions with surrounding Si atoms, leading to a complete loss of intensity at zero energy loss.

CheA is a multidomain histidine kinase for chemotaxis in Escherichia coli. CheA autophosphorylates through interaction of its N-terminal phosphorylation site domain (P1) with its central dimerization (P3) and ATP-binding (P4) domains. This activity is modulated through the C-terminal P5 domain, which couples CheA to chemoreceptor control. CheA phosphoryl groups are donated to two response regulators, CheB and CheY, to control swimming behavior. The phosphorylated forms of CheB and CheY turn over rapidly, enabling receptor signaling complexes to elicit fast behavioral responses by regulating the production and transmission of phosphoryl groups from CheA. To promote rapid phosphotransfer reactions, CheA contains a phosphoacceptor-binding domain (P2) that serves to increase CheB and CheY concentrations in the vicinity of the adjacent P1 phosphodonor domain. To determine whether the P2 domain is crucial to CheA's signaling specificity, we constructed CheADeltaP2 deletion mutants and examined their signaling properties in vitro and in vivo. We found that CheADeltaP2 autophosphorylated and responded to receptor control normally but had reduced rates of phosphotransfer to CheB and CheY. This defect lowered the frequency of tumbling episodes during swimming and impaired chemotactic ability. However, expression of additional P1 domains in the CheADeltaP2 mutant raised tumbling frequency, presumably by buffering the irreversible loss of CheADeltaP2-generated phosphoryl groups from CheB and CheY, and greatly improved its chemotactic ability. These findings suggest that P2 is not crucial for CheA signaling specificity and that the principal determinants that favor appropriate phosphoacceptor partners, or exclude inappropriate ones, most likely reside in the P1 domain., This work was supported by research grant GM19559 from the National Institutes of Health. K.J. was supported by a Feodor Lynen postdoctoral fellowship from the Alexander von Humboldt Foundation. A.G. was supported by a postdoctoral fellowship from the Spanish Ministry of Education under the auspices of the Fulbright Program. The Protein-DNA Core Facility at the University of Utah receives support from National Cancer Institute grant CA42014 to the Huntsman Cancer Institute.

The team signaling model for bacterial chemoreceptors proposes that receptor dimers of different detection specificities form mixed trimers of dimers. These receptor “squads” then recruit the cytoplasmic signaling proteins CheA and CheW to form ternary signaling teams, which typically cluster at the poles of the cell. We devised cysteine-directed in vivo crosslinking approaches to ask whether mixed receptor squads could form in the absence of CheA and CheW and, if so, whether the underlying structural interactions conformed to trimer-of-dimers geometry. One approach used cysteine reporters at positions in the serine (Tsr) and aspartate (Tar) receptors that should form disulfide-linked Tsr≈Tar products when juxtaposed at the interface of a mixed trimer. Another approach used a cysteine reporter with trigonal geometry near the trimer contact region and a trifunctional maleimide reagent with a spacer length appropriate for capturing the three axial subunits in a trimer of dimers. Both approaches detected mixed receptor-crosslinking products in cells lacking CheA and CheW. Under these conditions, receptor methylation and ligand-binding state had no discernable effect on crosslinking efficiencies. Crosslinking with the trigonal reporter was rapid and did not increase with longer treatment times or higher reagent concentrations, suggesting that this method produces a short-exposure snapshot of the receptor population. The extent of crosslinking indicated that most of the cell's receptor molecules were organized in higher-order groups. Crosslinking in receptor trimer contact mutants correlated with their signaling behaviors, suggesting that trimers of dimers are both structural and functional precursors of chemoreceptor signaling teams in bacteria.

The design and construction of a tactile sensor that has been developed to measure the surface shape of objects held between the fingers of a robot gripper are described. A robotic tactile sensory workcell has been assembled to investigate touch-mediated grasping and object manipulation. This system requires sensors to provide surface profile information for experiments involving object manipulation and shape determination. A piezoresistive tactile sensor originally developed for the workcell proved to be generally unsuitable because its stiff sensing surface gave little surface shape information. A solution was provided by a tactile sensor designed to have a compliant structure. >

Chemoreceptors of the methyl-accepting chemotaxis protein family form clusters, typically at the cell pole(s), in both Bacteria and Archaea. To elucidate the architecture and signaling role of receptor clusters, we investigated interactions between the serine (Tsr) and aspartate (Tar) chemoreceptors in Escherichia coli by constructing Tsr mutations at the six hydrophobic and five polar residues implicated in “trimer of dimers” formation. Tsr mutants with proline replacements could not mediate serine chemotaxis, receptor clustering, or clockwise flagellar rotation. Alanine and tryptophan mutants, although also nonchemotactic, formed receptor clusters, and some produced clockwise flagellar rotation, indicating receptor-coupled activation of the signaling CheA kinase. The alanine and tryptophan mutants evidently assemble defective receptor complexes that cannot modulate CheA activity in response to serine stimuli. In cells containing wild-type Tar receptors, tryptophan replacements in Tsr interfered with Tar function, whereas four Tsr mutants with alanine replacements regained Tsr function. These epistatic and rescuable phenotypes imply interactions between Tsr and Tar dimers in higher-order signaling teams. The bulky side chain in tryptophan mutants may prevent stimulus-induced conformational changes in the team, whereas the small side chain in alanine mutants may permit signaling control when teamed with functional receptor molecules. Direct physical interactions between Tsr and Tar molecules were observed by in vivo chemical crosslinking. Wild-type Tsr crosslinked to Tar, whereas a clustering-defective proline replacement mutant did not. These findings indicate that bacterial chemoreceptor clusters are comprised of signaling teams, seemingly based on trimers of dimers, that can contain different receptor types acting collaboratively.

Publisher Summary This chapter outlines a general approach to the modelling of stochastic dynamic systems, emphasizes on the importance of stochastic methods and statistical analysis in the derivation of the models, and illustrates the various methodological issues and the philosophical approach to modeling that they underpin. This general approach is built on the assumption that the dynamic modeling of environmental systems involve two basic model types: (1) speculative and normally quite complex simulation models, which represent the current, state-of-the-art, scientific understanding of the environmental system; and (2) data-based mechanistic (DBM) models obtained initially from the analysis of observational. The DBM ideas are applied mainly to the analysis of the large Enting–Lassey (EL) global carbon cycle model. The chapter demonstrates the merits of DBM modeling and statistical methods in all aspects of environmental systems analysis, and when experimental data are available, such an approach ensures that the identifiable modes of dynamic behavior are defined and estimated objectively in the most parsimonious manner.

The CheY protein is the response regulator in bacterial chemotaxis. Phosphorylation of a conserved aspartyl residue induces structural changes that convert the protein from an inactive to an active state. The short half-life of the aspartyl-phosphate has precluded detailed structural analysis of the active protein. Persistent activation of Escherichia coli CheY was achieved by complexation with beryllofluoride (BeF(3)(-)) and the structure determined by NMR spectroscopy to a backbone r.m.s.d. of 0.58(+/-0.08) A. Formation of a hydrogen bond between the Thr87 OH group and an active site acceptor, presumably Asp57.BeF(3)(-), stabilizes a coupled rearrangement of highly conserved residues, Thr87 and Tyr106, along with displacement of beta4 and H4, to yield the active state. The coupled rearrangement may be a more general mechanism for activation of receiver domains.

In the UK, Action Levels for radon have been established at 400 Bq m(-3) for the workplace and 200 Bq m(-3) for the home. We have estimated the dose received by occupants of rooms with radon levels near or above the Action Level, using hourly radon readings, and a questionnaire to record occupancy. In the workplace, results for 73 staff suggest that doses are lower than expected, partly due to part-time working and partly due to the mobility of staff. The 75% quantile for the series, corrected to a 37 hour week, is 5.2 mSv at 400 Bq m(-3). Compared to the current annual limit for radiation workers, the Action Level could be increased, but the current Action Level is compatible with the recent EEC Directive requiring a lower dose limit. However, when raised radon levels in the workplace were reduced by remediation in the series we studied, the dose reduction to staff was consistently around half of the radon level reduction. Although it would be appropriate to study more locations, this suggests an Action Level for remediated workplaces of 200 Bq m(-3). Finally, in a limited series of dose assessments in domestic properties, we found that doses could considerably exceed 5 mSv at the 200 Bq m(-3) Action Level, primarily because the sample included an example of high occupancy, in our case several Asian wives in purdah, whose occupancy was almost total.

The activities implemented jointly (AIJ) pilot phase does not include provisions for crediting of greenhouse gas (GHG) emission reductions. The absence of crediting is a major deficiency of the AIJ pilot and has contributed to the relatively small number of projects developed. In contrast, the provisions of the Kyoto Protocol permit crediting for joint implementation (JI) or Clean Development Mechanism (CDM) projects. The issue of which entities will receive emission reduction (ER) credits is a matter of considerable analysis and negotiation. Countries that could potentially participate in the CDM may only be interested in credits if they can sell or bank them for future use. Credit sharing may raise the cost per unit of GHG reduced for investors and act like a tax on project development. Credits developed via joint implementation projects may also be traded or banked based on the mutual needs of the investor or host country entities.

Many national programs in both investor and host countries have defined criteria for selection or acceptance of activities implemented jointly (AIJ) projects. In many countries the criteria far exceed the standards of the criteria defined in Decision 5 of the UN Framework Convention on Climate Change (FCCC) First Conference of the Parties (COP-1). In some counties these criteria have been uniformly and rigidly applied while in others the AIJ pilot has been a period of learning and criteria evaluation. Some criteria, some as those dealing with additionality and greenhouse gas (GHG) emissions baseline determination have been the subject of considerable analysis and debate. Project reporting has been uneven and among the Parties in spite of the establishment of a Uniform Reporting Format (URF). Lessons learned regarding the Ali pilot criteria can be applied to the development of the Clean Development Mechanism (CDM).

The aim of this study was to assess the feasibility of providing i.v. antibiotic therapy outside hospital. The main outcome measures were the direct costs of providing i.v. antibiotic therapy in the community compared with standard hospital treatment and the perceptions of patients and General Practitioners (GPs). A total of 29 patients entered the study, of whom 15 received teicoplanin and 14 ceftriaxone. The costs of drugs exceeded the cost of the estimated alternative treatments (median Pound Sterling 208 and Pound Sterling 126 respectively) and this was only partially compensated for by a small reduction in costs of consumables. The staff time required to train patients was compensated for by savings in drug preparation and administration. Sensitivity analysis showed that these conclusions were sensitive to drug and patient selection, and that treatment of skin and soft tissue infections outside hospital with ceftriaxone was likely to have similar variable costs to treatment in hospital with drugs such as flucloxacillin. Non-inpatient i.v. (NIPIV) therapy was estimated to save a total of 532 bed days in the year of the study. Patients strongly preferred non-inpatient treatment to hospital treatment. GPs identified a number of potential disadvantages, mainly concerning safety and lack of support for patients at home. Following the study a strategy for development of NIPIV services in Tayside has been developed with local GPs and a plan has been agreed for funding a community liaison nurse based on the impact of NIPIV therapy on future bed requirements in Dundee Teaching Hospitals Trust.

Sixteen experienced cochlear implant patients with a wide range of speechperception abilities received the SPEAK processing strategy in the Nucleus Spectra-22 cochlear implant. Speech perception was assessed in quiet and in noise with SPEAK and with the patients' previous strategies (for most, Multipeak) at the study onset, as well as after using SPEAK for 6 months. Comparisons were made within and across the two test sessions to elucidate possible learning effects. Patients were also asked to rate the strategies on seven speech recognition and sound quality scales. After 6 months' experience with SPEAK, patients showed significantly improved mean performance on a range of speech recognition measures in quiet and noise. When mean subjective ratings were compared over time there were no significant differences noted between strategies. However, many individuals rated the SPEAK strategy better for two or more of the seven subjective measures. Ratings for "appreciation of music" and "quality of my own voice" in particular were generally higher for SPEAK. Improvements were realized by patients with a wide range of speech perception abilities, including those with little or no open-set speech recognition.