This Week in Science

Science  06 Nov 1998:
Vol. 282, Issue 5391, pp. 1005
  1. Improving Holographic Materials

    Although holography can be used to store huge amounts of digital data, the process of reading the hologram also erases it unless the material is “fixed” in some way, just as development fixes photographic film. Hesselink et al. (p. 1089) recently described an all-optical fixing method in which the energy from two light beams is used to write holograms. The weaker infrared beam, used in the reading mode, is too weak to erase the material. They now describe the underlying mechanism of this approach and ways to optimize the composition of the storage material, lithium niobate, to improve its sensitivity, gated recording efficiency, and dark-condition storage times.

  2. The Birth of Brown Dwarfs

    Since the discovery of the first bona fide brown dwarf, Gliese 229B, observers have searched for other candidate brown dwarfs to determine how they form and to characterize their mass and age. Tamura et al. (p. 1095) conducted two near-infrared wavelength surveys of the nearby (about 500 light years away) molecular clouds, Taurus and Chamaeleon, and found a dozen brown dwarf candidates. Some of these candidates had inferred masses as low as 0.012 solar masses, and some were also inferred to be as young as 1 million years old. Thus, the low mass and young age of these brown dwarf candidates suggest that these images captured brown dwarfs just after birth and that, like stars, brown dwarfs can form in molecular clouds.

  3. Particle Ballet in Neptune's Ring

    Neptune has four arcs of concentrated dusty, subkilometer-sized particles confined within a diffuse ring of particles that orbits about 63,000 kilometers away from the planet. It has been difficult to understand how this arc-ring system can be maintained over long periods of time. Salo and Hänninen (p. 1102) have developed a numerical model that reproduces several key structures of the arc-ring system that are stable for long time scales. They show that gravitational attraction between particles within the arcs actually keeps them from impacting each other under the influence of the major confining forces applied by Neptune and Neptune's moon, Galatea. Thus particle self-gravity allows the arcs to maintain their shape. This unexpected result removes an assumed source of dust (by particle-particle impacts) for the arcs, however. The authors suggest that kilometer-sized particles between the arcs are impacted by smaller particles. The subtle gravitational presence of the larger particles then confines the dusty ejecta into specific regions, and simulations show that multiple regions may intersect one arc. Thus, the large particles help to explain the width and high concentration of dust in the arcs.

  4. Harnessing Human Stem Cells

    The early embryo contains cells that have unlimited growth and differentiation potential. In mice, these embryonic stem (ES) cells have been cloned and used to generate mice with specific genetic changes. Thomson et al. (p. 1145; see the editorial, news story by Marshall, and the Perspective by Gearhart) generated long-term cell lines from early human embryos. Although the cells remain undifferentiated in culture and express primate ES cell markers, they can be induced both in vitro and in vivo to differentiate into recognizable tissue from all three major lineages: ectoderm, mesoderm, and endoderm. Cell lines such as these may be useful for generating replacement human cells and tissues.

  5. Fields of Nanotubes

    Carbon nanotubes are receiving much attention as components in nanoscale electronic devices. A key requirement for such applications is the synthesis of highly ordered arrays of the tubes and to use the synthesis conditions and substrates that are compatible with the intended applications. For example, flat panel displays use glass substrates, which constrains the highest temperatures that can be used in the nanotube synthesis. Ren et al. (p. 1105) show that nanotube arrays of high regularity and wide spatial extent (several square millimeters) can be grown directly on glass substrates at low enough temperatures (below 700°C) so that the glass properties were not affected.

  6. Early Foil Fashioning

    Metalworking, including the fashioning of intricate copper and gold ornaments, has been well known since about 2500 years ago in Andean civilizations, but the origins of this culture have been uncertain. Burger and Gordon (p. 1108; see the Perspective by Quilter) now describe simple copper and gold artifacts dating to about 3400 years ago from Mina Perdida, Peru. The foil artifacts seem to have been produced by shaping native metal and indicate that metalworking significantly predated ore smelting.

  7. Trauma Response in the Brain

    What is the capacity for long-term change in the primate brain? Two reports provide anatomical and physiological results from monkeys that have suffered trauma to an upper limb, thus altering the sensory input to the brain (see the Perspective by Merzenich). Jones and Pons (p. 1121) find that the thalamus, the first station through which sensory input passes, experienced massive reorganization that resulted in the sensory representations of the face and trunk coming together along with an expansion of the corresponding areas. Florence et al. (p. 1117) find that similarly large-scale changes of representation and neuronal expansion occurred in the somatosensory cortex.

  8. Clues from the Malaria Parasite Genome

    The complete sequence of a chromosome of the malaria parasite, Plasmodium falciparum, is presented by Gardner et al. (p. 1126). Chromosome 2 is 945 kilobases in length and contains 209 predicted genes. Its highly A+T-rich (80.2 %) nature had suggested that established procedures for whole-genome “shotgun” strategies would not work; however, accurate assembly was accomplished. Several Plasmodium-specific genes, including a family of rifins that may be involved in antigenic variation, were identified.

  9. Underpinnings of Adaptive Mutability

    In 1988, Cairns described a series of experiments, which seemed to show that an organism could respond to stress by increasing the rate of mutation in one or more genes that would help it to deal with that stress. This “adaptive mutability” hypothesis itself has created a large increase in the amount of seeking to confirm or refute the premise. Andersson et al. (p. 1133) present experiments to show that there can be selective amplification of a mutant gene that is partly functional. This selective amplification increases the number of targets and makes it appear like the mutation rate has increased after exposure to stress, when, in reality, the mutability of locus is unchanged.

  10. Building the Bite

    Tooth development in mammals depends on finely regulated interactions between the ectoderm and the underlying mesenchyme. Further specifications must define the particular type of tooth and the order relative to other teeth, placing incisors in the front of the mouth and molars in the rear. Tucker et al. (p. 1136) have identified the peptide signal BMP4 and the homeobox gene Barx-1 as some of the components that determine tooth identity in the mouse. Fine differences in structure between members of an array of otherwise similar structures can be specified and adjusted by the timing and balance of relevant peptide signals and homeobox gene expression.

  11. Energy and Excitation

    In many tissues, potassium (K+) channels are modulated by adenosine triphosphate (ATP). The metabolism of the cell can thus control the membrane resting potential and hence its excitability. The mismatch between ATP sensitivity of these K+channels and the ATP concentration found in many cells suggests that other endogenous factors influence this modulation. Baukrowitz et al. (p. 1141) and Shyng et al. (p. 1138) show that the phospholipids PIP and PIP2 strongly control ATP and K+channel interaction (see the Perspective by Ashcroft). This finding may be another example for the fine-tuning of cellular excitability by its metabolic state.

  12. Layered Shells

    Hollow micro- or nanoparticles have potential uses in areas such as drug delivery and catalysis. Synthesis methods include fabrication of a coated sphere followed by removal of the core by calcination or chemical dissolution. Caruso et al 1111 used a recently developed technique to make inorganic-polymer composite multilayer assemblies on colloidal particles. They subsequently removed the colloid to leave hollow spheres with multilayered shells. Submicrometer-sized hollow shells with wall thicknesses of tens to hundreds of nanometers were obtained. The method should allow the tuning of shell size, topology, and composition, as different shapes of the underlying colloidal particle could be used. The deposition technique for the layers should allow incorporation of a wide range of compounds, including biological macromolecules, dyes, or nanoparticles.

  13. Dating Early Earthquakes

    Assessing earthquake hazards often requires knowledge of the time and magnitude of several previous quakes. Large earthquakes typically recur hundreds of years apart or longer, but most historic records extend for at most a few centuries, so methods of dating early earthquake events are needed. Zreda and Noller 1097 show that bedrock fault scarps can be dated directly by examination of the accumulation of cosmogenic nuclides in the exposed rocks. Their study of the Hebgen Lake fault, Wyoming, shows that it ruptured in five large earthquakes since 24,000 years ago. The repeat time between events is irregular, that is, strain seems to be released in discrete intervals.

  14. Auxin Response in Plants

    The plant hormone auxin regulates many aspects of plant growth and physiology. The auxin-binding protein 1 (ABP1), localized in the endoplasmic reticulum, is a candidate for the auxin receptor. Jones et al. 1114 now show that when ABP1 is expressed in tissue culture cells, or overexpressed in whole plants, an additional auxin-responsive phenotype is conferred. Thus, ABP1 is a key component of the novel auxin response pathway.

  15. Natural Impact Detector

    The detection of small particles in the outer solar system has usually been accomplished by satellites such as Pioneer 11 and Galileo, which record a signal each time they are hit by a small particle. Showalter 1099 analyzed three clumps in Saturn's F ring that formed, brightened, and then faded over about a 2-week period in Voyager images taken in 1980 and 1981. These clumps were caused by impacts of small meteoroids (about 2 to 40 centimeters in radius) from outside the Saturn system into the F ring. Further analysis of Voyager images and future observations by Hubble Space Telescope and Cassini should refine the impact models to distinguish whether the meteoroids are coming from asteroids or comets and how these impacts affect the dynamics and structure of planetary ring systems.

  16. Calcineurin Inhibition and Cardiac Hypertrophy

    M. A. Sussman et al. (Reports, 11 Sept., p. 1690) found that “administration of the calcineurin inhibitors cyclosporin and FK506 prevented disease in mice that were genetically predisposed to develop hypertrophic cardiomyopathy.” “Cyclosporin had a similar effect in a rat model of pressure-overload hypertrophy.” J. G. Müller et al. comment that, in their experiments, with high serum concentrations of cyclosporin in a mouse model of pressure-overload hypertrophy, “all treated animals developed hypertrophy within 3 weeks.” They conclude that “activated calcineurin is sufficient, but not necessary, for the induction of cardiac hypertrophy.” In response, J. D. Molkentin (Sussman et al.) agrees “that calcineurin is not necessary for the induction of pressure-overload hypertrophy.” The original report was a 6-day study. Molkentin now observes that “rats treated with cyclosporin for longer periods, 21 days, did not show a significant prevention of the pathologic response.” The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/282/5391/1007a

  17. Detecting Strain in the Yucca Mountain Area, Nevada

    B. Wernicke et al. (Reports, 27 Mar., p. 2096) used data from Global Positioning System (GPS) satellite surveys and from trilateration surveys to measure the rate of strain in the Earth's crust in the Yucca Mountain area, which is under consideration as a site for the permanent disposal of highly radioactive waste. The strain rates they found were “at least an order of magnitude higher than would be predicted from the Quaternary volcanic and tectonic history of the area.” J. C. Savage comments that Wernicke et al. “did not include the effects of monument instability in their error budget” and “did not give proper weight to the coseismic and postseismic effects of the Little Skull Mountain earthquake” of 1992. C. B. Connor et al. state that high-precision isotopic dates of Lathrop Wells basalts indicate an age much older than that cited by Wernicke et al. They propose “three alternatives to the suggestion by Wernicke et al.” that the GPS-derived strain rates indicate that the area is experiencing an anomalous strain accumulation. In response to Savage, J. L. Davis et al. give details of their “four different solutions for the rate of strain using different methods” to account for coseismic effects. Davis et al. state that the “several alternatives” offered by Connor et al. are “plausible, but also speculative.” (Davis et al. also correct a value of one of the trilateration measurements.) The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/282/5391/1007b

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