bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties and magnetoresistance in small iron oxide cluster assemblies
Authors: Peng D. L. , Asai T. , Nozawa N. , Hihara T. , Sumiyama K.
Published: December 2002

We report the magnetic properties and magnetoresistance (MR) in small iron oxide (Fe3−xO4 and Fe3O4) cluster assemblies. Half-metallic Fe3O4 cluster assembly with grain size of 10–15 nm is shown to exhibit a MR value of about 8% at T=30 K and a peak around the Verwey transition temperature Tv=115 K which is a little lower than the Tv value (∼120 K) of single crystal specimens. Even at T=5 K, the magnetization is not saturated in fields up to 50 kOe. The MR behaviors of a Fe3−xO4-coated iron cluster assembly and a sample which was prepared by embedding the Fe3−xO4-coated iron clusters into a MgO matrix are also studied for comparison. The MR value of the latter is over one time larger than that of the former and is also larger than those of the Fe3O4 cluster assembly at various temperatures. It suggests that the barrier layer is important for enhancing the MR effect at high temperatures.
Extraction of height–height correlation function of random surfaces from the average intensity of image speckles
Authors: Cheng Chuanfu , Teng Shuyun , Liu Man , Gong Shangqing , Li Ruxin , Xu Zhizhan
Published: December 2002

We present a method for the extraction of the height–height correlation function of random surfaces from the average intensity of image speckles. The setup of a Fourier transforming and imaging system with a variable aperture is used for both the theoretical analysis and experimental performances. Based on the analytical expression of the image intensity, an algorithm is developed to formulate numerically the intensity data versus the aperture radius into the pair of Bessel–Fourier transform and the inversion, from which the height–height correlation function is reconstructed. Three samples of Gaussian correlation are used for the experimental demonstration. The extracted height–height correlation function and the random surface parameters obtained thereby conform with those obtained by atomic force microscopy.
Supermode-noise suppression using a nonlinear Fabry–Pérot filter in a harmonically mode-locked fiber ring laser
Authors: Zhao Donghui , Lai Yicheng , Shu Xuewen , Zhang Lin , Bennion Ian
Published: December 2002

A simple efficient method for stabilizing a harmonically mode-locked fiber ring laser is proposed. In this method, a linear optical filter and a nonlinear Fabry–Pérot filter in which the refractive index is optical intensity dependent are located in the laser cavity. The linear filter is used to select a fixed lasing wavelength, and the Fabry–Pérot filter introduces a negative all-optical feedback mechanism that is able to suppress pulse-to-pulse amplitude fluctuations in the laser cavity. The scheme was experimentally demonstrated using a fiber Bragg grating as the linear filter and a laser diode biased below threshold as the nonlinear Fabry–Pérot, and stable harmonically mode-locked pulses with a supermode noise suppression ratio >55 dB were obtained.
Dropping of electromagnetic waves through localized modes in three-dimensional photonic band gap structures
Authors: Bayindir Mehmet , Ozbay E.
Published: December 2002

We experimentally demonstrate trapping and dropping of photons through localized cavity modes in three-dimensional layer-by-layer photonic crystal structures. By creating acceptor- and donor-like cavities which are coupled to a highly confined waveguide (HCW), we drop selected frequencies from the waveguide mode. Tunability of the demultiplexing structures can be achieved by changing the properties of cavities and the coupling between the cavity and the HCW.
Images of dopant profiles in low-energy scanning transmission electron microscopy
Authors: Merli P. G. , Corticelli F. , Morandi V.
Published: December 2002

A scanning electron microscope is used in transmission mode. The image is formed with secondary electrons, collected by the standard detector, resulting from the conversion of transmitted electrons on a circular disk, covered with MgO smoke, located below the thinned specimen, and centered on the optical axis. Operating in this mode, bright-field images of As dopant profiles in Si, having a peak concentrations of 5 and 2.5 at. % and a spatial extension of about 40 nm, have been observed in cross sectioned specimens. The description of the dopant profiles has a resolution of 6 nm as defined by the spot size of the microscope, equipped with a LaB6 tip, and operating at 30 keV.
Simple catalyst for the growth of small-diameter carbon nanotubes
Authors: Campbell P. M. , Snow E. S. , Novak J. P.
Published: December 2002

We describe a simple technique to grow small (approximately 1–4 nm) diam carbon nanotubes both in and out of the plane of a silicon substrate using the decomposition of ethylene and a nickel–iron thin film catalyst. This procedure can be used to produce nanotubes for ultrasharp atomic force microscope probes as well as for nanotube-based electronic devices. The technique is compatible with the patterned growth of nanotubes and with standard device microfabrication processes.
Highly-bright white organic light-emitting diodes based on a single emission layer
Authors: Chuen C. H. , Tao Y. T.
Published: December 2002

A very bright white organic light-emitting diode (OLED) was fabricated with a thin layer of 4-{4-[N-(1-naphthyl)-N-phenylaminophenyl]}-1,7-diphenyl-3,5-dimethyl-1,7-dihydro-dipyrazolo [3,4-b;4′3′-e]pyridine (PAP-NPA) doped with rubrene as the source of the white emission. Thus, with a simple three-layer structure of ITO/NPB(40 nm)/PAP-NPA:0.5% rubrene(20 nm)/TPBI(40 nm)/Mg:Ag, a white light with Commission Internationale de l’Eclairage (CIE) coordinates of (0.31, 0.33) were generated. The device gave a maximum brightness of ∼42 000 cd/m2 at 14 V, and maximum luminance efficiencies of 2.92 lm/W at 6.5 V and 6.11 cd/A at 7.0 V. The CIE coordinates stayed virtually constant when the voltage increased from 8 to 12 V. Furthermore, with a two-layer structure of ITO/PAP-NPA:0.4%rubrene(40 nm)/TPBI(40 nm)/Mg:Ag, the device also reached a stable white color with maximum brightness of ∼37 000 cd/m2 and maximum luminance efficiencies of 2.51 lm/W at 6.5 V and 5.57 cd/A at 8.5 V. The stability of the white color is attributed to the confinement of charge recombination zone in a single layer.
Switchable organic electroluminescence
Authors: Gao Xi-Cun , Zou De-Chun , Fujita Katsuhiko , Tsutsui Tetsuo
Published: December 2002

The vacuum deposited amorphous organic thin film melamine cyanurate (MC) is found to possess an electrical switching property. The as-fabricated fresh thin film is at a semiconductor state and shows a rectification property in a range of several voltages. Under a higher applied voltage, the resistance of the film changes to a lower value, and shows linearity in its current–voltage relationship. After the application of a negative driving voltage for no more than 100 s, the MC film returns from the resistor state to the semiconductor state with a higher impedance. Based on this reproducible switching phenomenon, a type of voltage-controlled switchable organic electroluminescence device was fabricated by inserting the MC layer between the anode indium tin oxide (ITO) and the hole transport layer N,N′-bis (3-methylphenyl)-N,N′-diphenyl-benzidine (TPD). In the forward driving voltage scan (for example, increasing the driving voltage from 0 to 16 V), the impedance is higher and the current density is lower; then the scan is backward (decreasing the driving voltage from 16 to 0 V), the impedance becomes lower and the current density becomes higher. Corresponding to the two different current density states at the same driving voltage, the device luminance also reaches two different states, one is lower and another is higher. This transition from a high (ON) to low luminance (OFF) renders a prototype to realize a switchable organic electroluminescence.
Gustation: Intersensory Experience Par Excellence
Authors: Stillman Jennifer A
Published: December 2002

On the face of it, basic tactile sensation might seem the only essential sensory requirement for the delivery of foods and beverages to the digestive system. In practice, however, the appropriate delivery of raw materials for the maintenance and repair of the body requires complex sensory and cognitive processes, such that flavour sensation arguably constitutes the pre-eminent example of an integrated multicomponent perceptual experience. To raise the profile of the chemical senses amongst researchers in other perceptual domains, I review here the contribution of various sense modalities to the flavour of foods and beverages. Further, in the light of these multisensory inputs, the physiological and psychophysical research summarised in this paper invites optimism that novel ways will be found to intervene when nutritional status is compromised either by specific dietary restraints, or by taste and smell disorders.
Large-Scale Visual Frontoparallels under Full-Cue Conditions
Authors: Koenderink Jan J , van Doorn Andrea J , Kappers Astrid M L , Lappin Joseph S
Published: December 2002

We determined the curvature of apparent frontoparallels in a natural scene (a large lawn in broad daylight). Data on frontoparallels in these conditions are very sparse and reveal idiosyncratic curvatures of frontoparallels and irregular variation with distance. We used a method of bisection of linear segments indicated through pairs of stakes at angular separations (from the vantage point) of up to 120 deg. Distances of 2 m and 10 m (in the forward direction) were used. The bisection was carried out by the observer through maneuvering a radio-controlled vehicle carrying a third stake. Four observers participated in the experiment; they had no problems with the task and yielded mutually consistent results. We found that the frontoparallels are significantly curved and are concave towards the observer. Surprisingly, the sign of the curvature is opposite to that found when the frontoparallels are defined through an exocentric pointing task. Available theory (Luneburg's) does not predict this, but the theory is hardly applicable to the case of vision in natural scenes. This interesting discrepancy has not been reported before.
The Difference between Flipping Strategy and Spinning Strategy in Mental Rotation
Authors: Kanamori Nobuhiro , Yagi Akihiro
Published: December 2002

Murray (1997 Memory & Cognition25 96–105) showed that, when an inverted object was mentally rotated to upright, the reaction time (RT) of flipping strategy (rotating in depth about the horizontal axis) was shorter than that of spinning strategy (rotating in the picture plane). We hypothesised the absence of representation at the intermediate position between the inverted and the upright representations in the flipping strategy, and investigated this hypothesis by a priming paradigm that included prime and probe tasks within one trial. In the prime task, participants were asked to mentally rotate an inverted object to upright. In the probe task, they were asked to judge whether two objects simultaneously presented were the same or different. The flipping strategy in the prime task did not prime the probe task, whereas the spinning strategy did. The present results suggest that there is no intermediate representation in the flipping strategy: the difference in RT between the flipping strategy and the spinning strategy may be attributed to whether there is an intermediate representation or not, which could explain why depth rotation is faster.
Perception of Self-Tilt in a True and Illusory Vertical Plane
Authors: Groen Eric L , Jenkin Heather L , Howard Ian P
Published: December 2002

A tilted furnished room can induce strong visual reorientation illusions in stationary subjects. Supine subjects may perceive themselves upright when the room is tilted 90° so that the visual polarity axis is kept aligned with the subject. This ‘upright illusion’ was used to induce roll tilt in a truly horizontal, but perceptually vertical, plane. A semistatic tilt profile was applied, in which the tilt angle gradually changed from 0° to 90°, and vice versa. This method produced larger illusory self-tilt than usually found with static tilt of a visual scene. Ten subjects indicated self-tilt by setting a tactile rod to perceived vertical. Six of them experienced the upright illusion and indicated illusory self-tilt with an average gain of about 0.5. This value is smaller than with true self-tilt (0.8), but comparable to the gain of visually induced self-tilt in erect subjects. Apparently, the contribution of nonvisual cues to gravity was independent of the subject's orientation to gravity itself. It therefore seems that the gain of visually induced self-tilt is smaller because of lacking, rather than conflicting, nonvisual cues. A vector analysis is used to discuss the results in terms of relative sensory weightings.
Dynamics of Attention in Depth: Evidence from Multi-Element Tracking
Authors: Viswanathan Lavanya , Mingolla Ennio
Published: December 2002

We examined the allocation of attention in depth using a multi-element tracking paradigm. Observers were required to track a predefined subset of from two to eight elements in displays containing up to sixteen identical moving elements. We first show that depth cues, such as binocular disparity and occlusion through T-junctions, improve performance in a multi-element tracking task in the case where element boundaries are allowed to intersect in the depiction of motion in a single frontoparallel plane. We also show that the allocation of attention across two perceptually distinguishable planar surfaces, either frontoparallel or receding at a slanting angle and defined by coplanar elements, is easier than allocation of attention within a single surface. The same result was not found when attention was required to be deployed across items of two-color populations rather than across items of a single color. Our results suggest that, when surface information does not suffice to distinguish between targets and distractors that are embedded in these surfaces, division of attention across two surfaces aids in tracking moving targets. A final experiment with populations of elements moving within distinct volumes produced similar results, suggesting that spatial separation in three dimensions, rather than confinement to surfaces as such, may explain the improved performance for the two-surface case.
Influences of Motion and Depth on Brightness Induction: An Illusory Transparency Effect?
Authors: Morikawa Kazunori , Papathomas Thomas V
Published: December 2002

Two experiments were performed to investigate whether motion and binocular disparity influence brightness induction, and whether the effects of motion and binocular disparity, if any, interact with each other. In order to introduce motion, textured backgrounds were used as the inducing field. The results showed that motion and/or crossed disparity reduce brightness induction, whereas uncrossed disparity increases it. The effect of motion and the effect of disparity are independent of each other and additive, which suggests that, to the extent that brightness induction reflects segmentation of objects, motion and binocular disparity serve independently to segment objects from their background. The difference between the effects of crossed and uncrossed disparity can be explained by what we call ‘illusory transparency’.
Seeing Stereoscopic Depth from Disparity between Kinetic Edges
Authors: Poom Leo
Published: December 2002

Traditionally, it is assumed that stereovision operates only on the positional difference (disparity) between luminance-defined features in the images in the left and the right eye. Here, I show that stereoscopic depth can be seen from disparity between edges created by relative motion of texture elements, and between edges created by correlated flicker of stationary texture elements. Luminance-based stereopsis was impossible since the texture was binocularly uncorre-lated. Positional disparity of the centre of revolving patterns was not an efficient depth cue. Stereopsis from the stimuli presented here was possible even without binocular overlap of textured areas. The results provide evidence that positional disparity of kinetic edges, defined by correlated flicker or motion contrast alone, can be used as matching features to recover stereoscopic depth.
The insulation of genes from external enhancers and silencing chromatin
Authors: Burgess-Beusse Bonnie , Farrell Catherine , Gaszner Miklos , Litt Michael , Mutskov Vesco , Recillas-Targa Felix , Simpson Melanie , West Adam , Felsenfeld Gary
Published: December 2002

Insulators are DNA sequence elements that can serve in some cases as barriers to protect a gene against the encroachment of adjacent inactive condensed chromatin. Some insulators also can act as blocking elements to protect against the activating influence of distal enhancers associated with other genes. Although most of the insulators identified so far derive from
Drosophila
, they also are found in vertebrates. An insulator at the 5′ end of the chicken β-globin locus marks a boundary between an open chromatin domain and a region of constitutively condensed chromatin. Detailed analysis of this element shows that it possesses both enhancer blocking activity and the ability to screen reporter genes against position effects. Enhancer blocking is associated with binding of the protein CTCF; sites that bind CTCF are found at other critical points in the genome. Protection against position effects involves other properties that appear to be associated with control of histone acetylation and methylation. Insulators thus are complex elements that can help to preserve the independent function of genes embedded in a genome in which they are surrounded by regulatory signals they must ignore.
Heritable chromatin structure: Mapping “memory” in histones H3 and H4
Authors: Smith Christine M. , Haimberger Zara W. , Johnson Catherine O. , Wolf Alex J. , Gafken Philip R. , Zhang Zhongli , Parthun Mark R. , Gottschling Daniel E.
Published: December 2002

Telomeric position effect in
Saccharomyces cerevisiae
is a chromatin-mediated phenomenon in which telomere proximal genes are repressed (silenced) in a heritable, but reversible, fashion. Once a transcriptional state (active or silenced) is established, however, there is a strong tendency for that state to be propagated. Twenty-five years ago, H. Weintraub and colleagues suggested that such heritability could be mediated by posttranslational modification of chromatin [Weintraub, H., Flint, S. J., Leffak, I. M., Groudine, M. & Grainger, R. M. (1977)
Cold Spring Harbor Symp. Quant. Biol.
42, 401–407]. To identify potential sites within the chromatin that might act as sources of “memory” for the heritable transmission, we performed a genetic screen to isolate mutant alleles of the histones H3 and H4 genes that would “lock” telomeric marker genes into a silenced state. We identified mutations in the NH
2
-terminal tail and core of both histones; most of the amino acid changes mapped adjacent to lysines that are known sites of acetylation or methylation. We developed a method using MS to quantify the level of acetylation at each lysine within the histone H4 NH
2
-terminal tail in these mutants. We discovered that each of these mutants had a dramatic reduction in the level of acetylation at lysine 12 within the histone H4 tail. We propose that this lysine serves as a “memory mark” for propagating the expression state of a telomeric gene: when it is unacetylated, silent chromatin will be inherited; when it is acetylated an active state will be inherited.
Induction and maintenance of nonsymmetrical DNA methylation in
Neurospora
Authors: Selker Eric U. , Freitag Michael , Kothe Gregory O. , Margolin Brian S. , Rountree Michael R. , Allis C. David , Tamaru Hisashi
Published: December 2002

One can imagine a variety of mechanisms that should result in self-perpetuating biological states. It is generally assumed that cytosine methylation is propagated in eukaryotes by enzymes that specifically methylate hemimethylated symmetrical sites (e.g.,
5′
CpG/GpC
5′
or
5′
CpNpG/GpNpC
5′
). Although there is wide support for this model, we and others have found examples of methylation that must be propagated by a different mechanism. Most methylated regions of the
Neurospora
genome that have been examined are products of repeat-induced point mutation, a premeiotic genome defense system that litters duplicated sequences with C⋅G to T⋅A mutations and typically leaves them methylated at remaining cytosines. In general, such relics of repeat-induced point mutation are capable of triggering methylation
de novo
. Nevertheless, some reflect a mechanism that can propagate heterogeneous methylation at nonsymmetrical sites. We propose that
de novo
and maintenance methylation are manifestations of a single mechanism in
Neurospora
, catalyzed by the DIM-2 DNA methyltransferase. The action of DIM-2 is controlled by the DIM-5 histone H3 Lys-9 methyltransferase, which in turn is influenced by other modifications of histone H3. DNA methylation indirectly recruits histone deacetylases, providing the framework of a self-reinforcing system that could result in propagation of DNA methylation and the associated silenced chromatin state.
Sequence-dependent denaturation energetics: A major determinant in amyloid disease diversity
Authors: Hammarström Per , Jiang Xin , Hurshman Amy R. , Powers Evan T. , Kelly Jeffery W.
Published: December 2002

Several misfolding diseases commence when a secreted folded protein encounters a partially denaturing microenvironment, enabling its self assembly into amyloid. Although amyloidosis is modulated by numerous environmental and genetic factors, single point mutations within the amyloidogenic protein can dramatically influence disease phenotype. Mutations that destabilize the native state predispose an individual to disease; however, thermodynamic stability alone does not reliably predict disease severity. Here we show that the rate of transthyretin (TTR) tetramer dissociation required for amyloid formation is strongly influenced by mutation (V30M, L55P, T119M, V122I), with rapid rates exacerbating and slow rates reducing amyloidogenicity. Although these rates are difficult to predict
a priori
, they notably influence disease penetrance and age of onset. L55P TTR exhibits severe pathology because the tetramer both dissociates quickly and is highly destabilized. Even though V30M and L55P TTR are similarly destabilized, the V30M disease phenotype is milder because V30M dissociates more slowly, even slower than wild type (WT). Although WT and V122I TTR have nearly equivalent tetramer stabilities, V122I cardiomyopathy, unlike WT cardiomyopathy, has nearly complete penetrance—presumably because of its 2-fold increase in dissociation rate. We show that the T119M homotetramer exhibits kinetic stabilization and therefore dissociates exceedingly slowly, likely explaining how it functions to protect V30M/T119M compound heterozygotes from disease. An understanding of how mutations influence both the kinetics and thermodynamics of misfolding allows us to rationalize the phenotypic diversity of amyloid diseases, especially when considered in concert with other genetic and environmental data.
Transgenic barley grain overexpressing thioredoxin shows evidence that the starchy endosperm communicates with the embryo and the aleurone
Authors: Wong Joshua H. , Kim Yong-Bum , Ren Pei-Hsien , Cai Nick , Cho Myeong-Je , Hedden Peter , Lemaux Peggy G. , Buchanan Bob B.
Published: December 2002

Homozygous lines of barley overexpressing a wheat thioredoxin
h
transgene (up to 30-fold) were generated earlier by using a B
1
-hordein promoter with a signal peptide sequence for targeting to the protein body and found to be enriched in starch debranching enzyme (pullulanase). Here, we describe the effect of biochemically active, overexpressed thioredoxin
h
on germination and the onset of α-amylase activity. Relative to null segregant controls lacking the transgene, homozygotes overexpressing thioredoxin
h
effected (
i
) an acceleration in the rate of germination and appearance of α-amylase activity with a 1.6- to 2.8-fold increase in gibberellin A
1
(GA
1
) content; (
ii
) a similar acceleration in the appearance of the α-amylase activity in deembryonated transgenic grain incubated with gibberellic acid; (
iii
) a 35% increase in the ratio of relative reduction (abundance of SH) of the propanol soluble proteins (hordein I fraction); and (
iv
) an increase in extractable and soluble protein of 5–12% and 11–35%, respectively. Thioredoxin
h
, which was highly reduced in the dry grain, was degraded in both the null segregant and homozygote after imbibition. The increase in α-amylase activity and protein reduction status was accompanied by a shift in the distribution of protein from the insoluble to the soluble fraction. The results provide evidence that thioredoxin
h
of the starchy endosperm communicates with adjoining tissues, thereby regulating their activities, notably by accelerating germination of the embryo and the appearance of α-amylase released by the aleurone.
Probing the folding free energy landscape of the src-SH3 protein domain
Authors: Shea Joan-Emma , Onuchic José N. , Brooks Charles L.
Published: December 2002

The mechanism and thermodynamics of folding of the Src homology 3 (SH3) protein domain are characterized at an atomic level through molecular dynamics with importance sampling. This methodology enables the construction of the folding free energy landscape of the protein as a function of representative reaction coordinates. We observe that folding proceeds in a downhill manner under native conditions, with early compaction and structure formation in the hydrophobic sheet consisting of the three central β strands of the protein. This state bears considerable resemblance to the experimentally determined transition state for folding. Folding proceeds further with the formation of the second hydrophobic sheet consisting of the terminal strands and the RT loop. The final stages of folding appear to involve the formation of the hydrophobic core through the expulsion of water molecules bridging the two hydrophobic sheets. This work sheds new light on the complementary roles of sequence and topology in governing the folding mechanism of small proteins and provides further support for the role of water in facilitating the late stages in folding.
Prion and doppel proteins bind to granule cells of the cerebellum
Authors: Legname Giuseppe , Nelken Peter , Guan Zhengyu , Kanyo Zoltan F. , DeArmond Stephen J. , Prusiner Stanley B.
Published: December 2002

We reported that expression of the cellular prion protein (PrP
C
) rescues doppel (Dpl)-induced cerebellar degeneration in mice. To search for protein(s) that mediate this process, we fused the C-termini of mouse (Mo) PrP and Dpl to the Fc portion of an IgG. Although both MoPrP-Fc and MoDpl-Fc bound to many regions of the brain, we observed restricted binding to granule cells in the cerebellum, suggesting a scenario in which granule cells express a protein that mediates Dpl-induced neurodegeneration. Because granule cells do not express PrP
C
, it seems unlikely that MoPrP-Fc binding reflects a ligand that is involved in the conversion of PrP
C
into PrP
Sc
, the disease-causing isoform. In contrast, the dominant-negative MoPrP(Q218K)-Fc not only binds to granule cells but also binds to neurons of the molecular layer where PrP
C
is expressed. These findings raise the possibility that the cells of the molecular layer express an auxiliary protein, provisionally designated protein X, which is involved in prion formation and is likely to be distinct from the protein that mediates Dpl-induced degeneration. Although the binding of the dominant-negative MoPrP(Q218K)-Fc to cells in the molecular layer expressing PrP
C
is consistent with a scenario for the binding of MoPrP(Q218K)-Fc to protein X, the absence of PrP
Sc
deposition in the molecular layer requires that PrP
Sc
, once formed there, be readily transported to the cerebellar white matter where PrP
Sc
is found. Identifying the ligands to which PrP-Fc, Dpl-Fc, and dominant-negative PrP bind may provide new insights into the functions of PrP
C
and Dpl as well as the mechanism of PrP
Sc
formation.
Molecular basis of cell migration in the fish lateral line: Role of the chemokine receptor CXCR4 and of its ligand, SDF1
Authors: David Nicolas B. , Sapède Dora , Saint-Etienne Laure , Thisse Christine , Thisse Bernard , Dambly-Chaudière Christine , Rosa Frédéric M. , Ghysen Alain
Published: December 2002

Cell migration plays an essential role in many morphogenetic processes, and its deregulation has many dramatic consequences. Yet how migration is controlled during normal development is still a largely unresolved question. We examined this process in the case of the posterior lateral line (PLL), a mechanosensory system present in fish and amphibians. In zebrafish, the embryonic PLL comprises seven to eight sense organs (neuromasts) aligned from head to tail along the flank of the animal and is formed by a primordium that originates from a cephalic placode. This primordium migrates along a stereotyped pathway toward the tip of the tail and deposits in its wake discrete groups of cells, each of which will become a neuromast. We show that a trail of SDF1-like chemokine is present along the pathway of the primordium and that a CXCR4-like chemokine receptor is expressed by the migrating cells. The inactivation of either the ligand or its receptor blocks migration, whereas in mutants in which the normal SDF1 trail is absent, the primordium path is redirected to the next, more ventral
sdf1
expression domain. In all cases, the sensory axons remain associated to the primordium, indicating that the extension of the neurites to form the PLL nerve depends on the movement of the primordium. We conclude that both the formation and the innervation of this system depend on the SDF1-CXCR4 system, which has also been implicated in several migration events in humans, including metastasis formation and lymphocyte homing.
Information optimization in coupled audio-visual cortical maps
Authors: Kardar Mehran , Zee A.
Published: December 2002

Barn owls hunt in the dark by using cues from both sight and sound to locate their prey. This task is facilitated by topographic maps of the external space formed by neurons (e.g., in the optic tectum) that respond to visual or aural signals from a specific direction. Plasticity of these maps has been studied in owls forced to wear prismatic spectacles that shift their visual field. Adaptive behavior in young owls is accompanied by a compensating shift in the response of (mapped) neurons to auditory signals. We model the receptive fields of such neurons by linear filters that sample correlated audio-visual signals and search for filters that maximize the gathered information while subject to the costs of rewiring neurons. Assuming a higher fidelity of visual information, we find that the corresponding receptive fields are robust and unchanged by artificial shifts. The shape of the aural receptive field, however, is controlled by correlations between sight and sound. In response to prismatic glasses, the aural receptive fields shift in the compensating direction, although their shape is modified due to the costs of rewiring.
Identification of specific HIV-1 reverse transcriptase contacts to the viral RNA:tRNA complex by mass spectrometry and a primary amine selective reagent
Authors: Kvaratskhelia Mamuka , Miller Jennifer T. , Budihas Scott R. , Pannell Lewis K. , Le Grice Stuart F. J.
Published: December 2002

We have devised a high-resolution protein footprinting methodology to dissect HIV-1 reverse transcriptase (RT) contacts to the viral RNA:tRNA complex. The experimental strategy included modification of surface-exposed lysines in RT and RT-viral RNA:tRNA complexes by the primary amine selective reagent NHS-biotin, SDS/PAGE separation of p66 and p51 polypeptides, in gel proteolysis, and comparative mass spectrometric analysis of peptide fragments. The lysines modified in free RT but protected from biotinylation in the nucleoprotein complex were readily revealed by this approach. Results of a control experiment examining the RT-DNA:DNA complex were in excellent agreement with the crystal structure data on the identical complex. Probing the RT-viral RNA:tRNA complex revealed that a majority of protein contacts are located in the primer-template binding cleft in common with the RT-DNA:DNA and RT-RNA:DNA species. However, our footprinting data indicate that the p66 fingers subdomain makes additional contacts to the viral RNA:tRNA specific for this complex and not detected with DNA:DNA. The protein footprinting method described herein has a generic application for high-resolution solution structural studies of multiprotein-nucleic acid contacts.
Near-neutrality in evolution of genes and gene regulation
Authors: Ohta Tomoko
Published: December 2002

The nearly neutral theory contends that the interaction of drift and selection is important and occurs at various levels, including synonymous and nonsynonymous substitutions in protein coding regions and sequence turnover of regulatory elements. Recent progress of the theory is reviewed, and the interaction between drift and selection is suggested to differ at these different levels. Weak selective force on synonymous changes is stable, whereas its consequence on nonsynonymous changes depends on environmental factors. Selection on differentiation of regulatory elements is even more dependent on environmental factors than on amino acid changes. Of particular significance is the role of drift in the evolution of gene regulation that directly participates in morphological evolution. The range of near neutrality depends on the effective size of the population that is influenced by selected linked loci. In addition to the effective population size, molecular chaperones such as heat shock protein 90 have significant effects on the range of near neutrality.
Microtubule release from the centrosome in migrating cells
Authors: Abal Miguel , Piel Matthieu , Bouckson-Castaing Veronique , Mogensen Mette , Sibarita Jean-Baptiste , Bornens Michel
Published: December 2002

In migrating cells, force production relies essentially on a polarized actomyosin system, whereas the spatial regulation of actomyosin contraction and substrate contact turnover involves a complex cooperation between the microtubule (MT) and the actin filament networks (Goode, B.L., D.G. Drubin, and G. Barnes. 2000. Curr. Opin. Cell Biol., 12:63–71). Targeting and capture of MT plus ends at the cell periphery has been described, but whether or not the minus ends of these MTs are anchored at the centrosome is not known. Here, we show that release of short MTs from the centrosome is frequent in migrating cells and that their transport toward the cell periphery is blocked when dynein activity is impaired. We further show that MT release, but not MT nucleation or polymerization dynamics, is abolished by overexpression of the centrosomal MT-anchoring protein ninein. In addition, a dramatic inhibition of cell migration was observed; but, contrary to cells treated by drugs inhibiting MT dynamics, polarized membrane ruffling activity was not affected in ninein overexpressing cells. We thus propose that the balance between MT minus-end capture and release from the centrosome is critical for efficient cell migration.
Essential role of the G-domain in targeting of the protein import receptor atToc159 to the chloroplast outer membrane
Authors: Bauer Jörg , Hiltbrunner Andreas , Weibel Petra , Vidi Pierre-Alexandre , Alvarez-Huerta Mayte , Smith Matthew D. , Schnell Danny J. , Kessler Felix
Published: December 2002

Two homologous GTP-binding proteins, atToc33 and atToc159, control access of cytosolic precursor proteins to the chloroplast. atToc33 is a constitutive outer chloroplast membrane protein, whereas the precursor receptor atToc159 also exists in a soluble, cytosolic form. This suggests that atToc159 may be able to switch between a soluble and an integral membrane form. By transient expression of GFP fusion proteins, mutant analysis, and biochemical experimentation, we demonstrate that the GTP-binding domain regulates the targeting of cytosolic atToc159 to the chloroplast and mediates the switch between cytosolic and integral membrane forms. Mutant atToc159, unable to bind GTP, does not reinstate a green phenotype in an albino mutant (ppi2) lacking endogenous atToc159, remaining trapped in the cytosol. Thus, the function of atToc159 in chloroplast biogenesis is dependent on an intrinsic GTP-regulated switch that controls localization of the receptor to the chloroplast envelope.
Guidelines for the Prevention of Intravascular Catheter–Related Infections
Authors: O'Grady Naomi P. , Alexander Mary , Dellinger E. Patchen , Gerberding Julie L. , Heard Stephen O. , Maki Dennis G. , Masur Henry , McCormick Rita D. , Mermel Leonard A. , Pearson Michele L. , Raad Issam I. , Randolph Adrienne , Weinstein Robert A.
Published: December 2002

These guidelines have been developed for practitioners who insert catheters and for persons responsible for surveillance and control of infections in hospital, outpatient, and home health-care settings. This report was prepared by a working group comprising members from professional organizations representing the disciplines of critical care medicine, infectious diseases, health-care infection control, surgery, anesthesiology, interventional radiology, pulmonary medicine, pediatric medicine, and nursing. The working group was led by the Society of Critical Care Medicine (SCCM), in collaboration with the Infectious Disease Society of America (IDSA), Society for Healthcare Epidemiology of America (SHEA), Surgical Infection Society (SIS), American College of Chest Physicians (ACCP), American Thoracic Society (ATS), American Society of Critical Care Anesthesiologists (ASCCA), Association for Professionals in Infection Control and Epidemiology (APIC), Infusion Nurses Society (INS), Oncology Nursing Society (ONS), Society of Cardiovascular and Interventional Radiology (SCVIR), American Academy of Pediatrics (AAP), and the Healthcare Infection Control Practices Advisory Committee (HICPAC) of the Centers for Disease Control and Prevention (CDC) and is intended to replace the Guideline for Prevention of Intravascular Device–Related Infections published in 1996. These guidelines are intended to provide evidence-based recommendations for preventing catheter-related infections. Major areas of emphasis include 1) educating and training health-care providers who insert and maintain catheters; 2) using maximal sterile barrier precautions during central venous catheter insertion; 3) using a 2% chlorhexidine preparation for skin antisepsis; 4) avoiding routine replacement of central venous catheters as a strategy to prevent infection; and 5) using antiseptic/antibiotic impregnated short-term central venous catheters if the rate of infection is high despite adherence to other strategies (i.e., education and training, maximal sterile barrier precautions, and 2% chlorhexidine for skin antisepsis). These guidelines also identify performance indicators that can be used locally by health-care institutions or organizations to monitor their success in implementing these evidence-based recommendations.
Assessing a controversial medical technology: Canadian public consultations on xenotransplantation
Authors: Einsiedel Edna F.
Published: December 2002

A policy question was posed in 2001 to Canadian publics: should Canada proceed with clinical trials on xenotransplantation and if so, under what conditions? As part of its development of policy and regulations on this medical technology, Health Canada and the Canadian Public Health Association implemented a public consultation process that included a public opinion survey and deliberative citizen fora modeled along the citizens' jury. This study focuses on the citizen fora and describes an assessment of effectiveness based on an evaluation framework developed on the basis of concepts from constructive technology assessment and deliberative democracy.
Creating identity with biotechnology: the xenotransplanted body as the norm
Authors: Lundin Susanne
Published: December 2002

One of today's great issues is how an advanced medical technology like xenotransplantation should be applied. It is well known that medicine brings not only potential but also risk. On the cultural level, xenotransplantations are equally complicated; they arouse thoughts about whether our outlook on humanity will be influenced now that modern techniques can “correct” our defective bodies. The article asks whether xenotransplantation creates new cultural meanings. That is, how do newly emerging ideas of a technologically created normality raise a set of moral questions about nature and culture, mind and body? The discussion is based on interview studies with patients suffering from diabetes and Parkinson's disease. The former have been given porcine islets, while the others have had human fetal cells transplanted into the brain; the latter are also potential recipients of xenotransplants. This empirical material becomes the basis for discussing how diseases can lead to a crisis in which it is essential—on a concrete, everyday level—to find strategies for dealing with the consequences. In this process of identity and normalization, advanced biomedicine is an important factor.
Japanese attitudes toward xenotransplantation
Authors: Macer Darryl , Inaba Masakazu , Maekawa Fumi , Ng Maryann Chen , Obata Hiroko
Published: December 2002

The reasons given by the Japanese public, scientists, and school and university students toward xenotransplantation were assessed by questionnaire surveys and by respondents' written comments. Between 1997 and 2000, there was an increase in the number of people who said they had heard of xenotransplant research, from 43 percent to 67 percent. In 2000, three in ten among the public said that it should be encouraged, while half said that it should not. In contrast, just less than half of the scientists said they supported the technology. The major reasons given in all groups were to save human life, versus safety and ethical concerns. More of the general public and school students considered xenotransplants to be unnatural compared with the scientists and university students. The reasons given are discussed in light of Japanese culture and the situation regarding organ transplants. Some in all groups, including young people, expressed both benefits and risks of this technology, and sophisticated arguments were used, suggesting that a number of people are able to consider moral dilemmas, such as those posed by the use of genetically engineered animals for xenotransplants. Still there remain a number of even educated persons who argue on only one side of the debate over the use of xenotransplants.
Public preferences for informed choice under conditions of risk uncertainty
Authors: Frewer Lynn J. , Miles Susan , Brennan Mary , Kuznesof Sharon , Ness Mitchell , Ritson Christopher
Published: December 2002

It has been assumed that the general public is unable to conceptualize information about risk uncertainties, and so communication about food risk has tended to avoid this type of information. However, recent societal and political pressure to increase transparency in risk management practices will result in the uncertainties inherent in risk analysis becoming subject to public scrutiny. Best practice regarding risk communication must address how to communicate risk uncertainty. A questionnaire was developed that aimed to assess how the general public characterized uncertainty associated with food risks. The results indicated that people wanted to be provided with information about food risk uncertainty as soon as the uncertainty was identified. People were more accepting of uncertainty associated with the scientific process of risk management than they were of uncertainty due to lack of action or lack of interest on the part of the government. The findings indicate that the focus of risk communication should be on “what is being done to reduce the uncertainty.” Recommendations are made regarding best practice for communicating risk uncertainty.
Lay understandings of the relationship between race and genetics: Development of a collectivized knowledge through shared discourse
Authors: Condit Celeste Michelle , Parrott Roxanne , Harris Tina M.
Published: December 2002

Throughout the past century, research into human genetics revealed the relationships between biochemistry and various human characteristics in increasing detail. At each step of this path of discovery, social critics warned that knowledge of genetics, and especially social attention to genetics, might heighten racist attitudes. In light of these warnings and the recent sequencing of the Human Genome, it is important to inquire into the interpretations laypersons might hold of the relationship between race and genetics. A variety of recent efforts have described the insufficiency of public opinion polls for arriving at sophisticated understandings of such complex attitudinal structures. Therefore, this essay offers a sketch of some lay understandings of race and genetics in the United States based on a series of focus group sessions. In order to interpret the responses, the analysis employs a novel template for interpreting focus group research based on the theoretical concept of rhetorical formations. This approach reveals the way in which the knowledge of individual members is brought to bear upon collective decision-making through the social process of discussion to produce a pool of information that is similar to expert knowledge, although phrased in a popular vocabulary. Differences in the ways in which cultural groups negotiate this knowledge are discussed.
Role of Secretory Carrier Membrane Protein SCAMP2 in Granule Exocytosis
Authors: Liu Lixia , Guo Zhenheng , Tieu Quyen , Castle Anna , Castle David
Published: December 2002

In secretory carrier membrane proteins (SCAMPs), the most conserved structural segment is between transmembrane spans 2 and 3, facing the cytosol. A synthetic peptide, CWYRPIYKAFR (E peptide), from this segment of SCAMP2 potently inhibits exocytosis in permeabilized neuroendocrine (PC12) cells. E peptide blocked discharge of35S-labeled secretogranin with the same structural selectivity and potency as observed for hexosaminidase secretion in mast cells. SCAMPs 1 and 2 are concentrated primarily on intracellular membranes in PC12 cells. Both, however, are found on plasma membranes, but neither is present on large dense-core vesicles. Yet, large dense-core vesicles marked by secretogranin attach to plasma membranes at foci containing SCAMP2 along with syntaxin1 and complexin at putative cell-surface docking/fusion sites. Regulated overexpression of SCAMP2 with point mutations in its E peptide but not of normal SCAMP2 caused dose-dependent inhibition of depolarization-induced secretion. The SCAMP2 mutants also inhibited secretion stimulated by elevated calcium. Inhibition was largely overcome by adding lysophosphatidylcholine to the medium at concentrations that do not otherwise affect secretion. Although overexpression of normal or mutant SCAMP2 slightly inhibits endocytosis, this effect does not appear to be related to the specific effect of the mutant SCAMP on stimulated exocytosis. Thus, SCAMP2 not only colocalizes with fusion sites but also appears to have an essential function in granule exocytosis through actions mediated by its E peptide–containing domain.