This Week in Science

Science  15 Aug 1997:
Vol. 277, Issue 5328, pp. 879
  1. Connect the quantum dots

    Semiconductor devices use transistors to switch the flow of electrons, but difficulties with leakage currents limit the ultimate size of even field-effect transistors. A quantum-mechanical approach is to encode logic states by the position of individual electrons on interconnected quantum dots (quantum-dot cellular automata, or QCAs). Orlov et al. (p. 928; see the news story by Glanz, p. 898 experimentally constructed a basic QCA cell from four aluminum quantum dots. Each pair is connected by tunneling barriers, and the two pairs are capacitively coupled. Transfer of an electron between the input pair of dots switches the position of an electron on the output pair.

  2. Ocean plumbing

    A key control on Earth's climate is the pattern of flow and mixing in the oceans; understanding how mixing varied in the past is critical for interpreting causes of past climate change. Christensen et al. (p. 913; see the Perspective by Alberéde, p. 908) present detailed records of lead isotopes in the ocean extending back to about 50 million years ago obtained from two iron-manganese crusts in the Pacific Ocean. Changes in the lead isotope values seem to correspond to broad changes in the oxygen isotope composition of foraminifera (which reflect climate changes) and may reflect the pattern or intensity of ocean mixing.

  3. Tiny gas cylinders

    Fullerenes can be synthesized so that they trap rare gas atoms. Now carbon fibers, when subjected to high pressures and temperatures, can also irreversibly trap inert gases. Gadd et al. (p. 933) show that when carbon fibers are exposed to argon gas at high pressure and appropriate temperature conditions, the tubes seal after the gas has entered. The gas remains trapped in the tubes at high pressures, even after the outside pressure is released to atmospheric pressure. These fibers, which have an outer diameter of about 0.1 micrometer, thus form very small, high-pressure gas cylinders.

  4. Readily resolving chiral compounds

    Pure enantiomeric compounds (all right- or left-handed versions of the same molecule) are important building blocks for organic synthesis. Synthetic methods, however, often produce both forms, and separations can be time-consuming and waste material. Tokunaga et al. (p. 936) report on a catalytic method for resolving enantiomers of an important class of compounds, terminal epoxides. A recyclable chiral cobalt catalyst was used to resolve racemic mixtures of these molecules into epoxides and 1,2-diols of nearly a single handedness (usually greater than 98 percent resolution). The only reagent consumed was water.

  5. Insulin-like signals in worms

    In Caenorhabditis elegans, harsh conditions can cause the worms to halt the normal reproductive development and enter a “resting” or dauer state. This process is controlled by a neuroendocrine pathway consisting of genes from the DAF family. Mutations in these genes causes abnormal dauer formation or, in some cases, longevity. Kimura et al. (p. 942; see the news story by Roush, p. 897) have now shown that one of the daf genes, daf-2, is an insulin receptor-like molecule. Such homology has not been seen before in worms and indicates that this insulin-like signaling pathway cooperates with the other daf pathway (which is a transforming growth factor-β-like signaling pathway) to control this fundamental developmental process.

  6. No place to hide

    Identifying factors that regulate fish populations has proven difficult, in part because of problems in obtaining accurate catch data. Hixon and Carr (p. 946) have approached the question experimentally: They translocated live coral reef heads to new locations to construct 32 similar habitats. These were populated with different densities of damselfish, exposed to two types of predators, reef-resident and transient piscivores, and the mortality rates of the damselfish assessed. In the presence of either one of the predator types, damselfish mortality was not density-dependent but both predators together caused density-dependent mortality. Transient predators attack in the waters above the reef, while resident predators attack within the reef structure.

  7. Genetics and AIDS

    A major endeavor in HIV (human immunodeficiency virus) research has been to discover the underlying mechanisms that allow some “long-term survivors” to resist disease 10 to 20 years after HIV-1 infection or to allow some highly exposed individuals to remain uninfected. Although a deletion in the chemokine receptor molecule CCR5 and certain human leukocyte antigen haplotypes have been associated with survival, they can only explain a small proportion of the cases. Smith et al. (p. 959) have found a mutation in another chemokine receptor, CCR2, that, when considered with the deletion in CCR5, explains the ability of about 25 percent of long-term survivors to avoid AIDS.

  8. Making M cells

    Most of a mammal's immune system is not in the bloodstream and its associated lymph nodes, but rather, it is intimately associated with the gut. Regions of the gut that contact this tissue contain specialized transport cells called M cells. Kernéis et al. (p. 949; see the cover and the Perspective by Madara, p. 910) established an in vitro culture system to convert gut epithelium into M cells by coculture with lymphocytes, particularly B cells.

  9. Pinpointing pain

    How do we feel pain? Rainville et al. (p. 968) dissociate and monitor the physical aspects of exposure to hot water from the affective response by functional brain imaging. Under conditions where the somatosensory cortex is unaltered, activation in the anterior cingulate cortex is modulated by hypnotic suggestion, linking this frontal lobe pathway to the emotional reaction to pain.

  10. Telomerase family tree

    Telomerase, a ribonucleoprotein enzyme, replicates chromosome ends, or telomeres. The catalytic protein subunit, recently identified in a ciliate and in bakers' yeast, contains reverse transcriptase (RT) motifs. Nakamura et al. (p. 955; see the Perspective by Eickbush, p. 911) show that this subunit is conserved in fission yeast and humans. From building evolutionary trees, they conclude that telomerases form a discrete subgroup of RTs, probably of ancient origin.

  11. Stemming violence

    What factors are particularly important in reducing violence in society, particularly in cities? Sampson et al. conducted a survey of more than 8000 residents in 343 neighborhoods in Chicago and analyzed the results with respect to a variety of demographic and violence data. The results suggest that one of the key factors in reducing violence in neighborhoods is the cooperative social action and cohesion of neighbors.

  12. Connecting El Niño and monsoons

    Two of the most important climatic interactions between the ocean and atmosphere are the Asian monsoon in the Indian Ocean and the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean. Several climatic links have been proposed between these two phenomena; understanding the connection is important for modeling and predicting both. Charles et al. show that the oxygen isotopic compositions from banded coral in the western Indian Ocean (which primarily reflect sea-surface temperature) seem to respond to both of these climate systems. The data, which extend back to 150 years, thus suggest that these phenomena have been linked despite the variation, in particular, in the frequency of the ENSO.

  13. No xenon in the core

    Earth's atmosphere is depleted in xenon relative to known meteoritic and solar abundances, creating a missing Xe conundrum. Some researchers think that the missing, highly chemically inert Xe is alloyed with iron in Earth's core, but little is known about the characteristics of Xe or such alloys, under such extremes of pressure and temperature. Caldwell et al. combined laser-heated diamond anvil cell experiments with extrapolated, thermodynamic calculations to conclude that Xe is unlikely to alloy with iron at pressures of at least 100 to 150 gigapascals, so another source or mechanism for sequestering (or depleting) Xe some place in Earth's interior is needed.

  14. Transport sans membranes

    Transport of proteins through the membrane of the endoplasmic reticulum requires both the transmembrane Sec complex and the Kar2p protein, an adenosine triphosphatase. Matlack et al. show, in a completely solubilized system with purified components, that this translocation (movement of the protein from the cytosolic face to the lumenal face of the Sec complex) requires Kar2p but is not dependent on having the membrane itself present.

  15. Animal models of cognitive deficits

    Although many animal models are available to study physical illnesses, models for mental illness are less common. Certain drugs, such as phencyclidine (PCP), are known to induce symptoms of schizophrenia in humans. Jentsch et al. show that repeated administration of PCP in vervet monkeys adversely affected function of the prefrontal cortex function, an area associated with cognitive functions; dopamine utilization was reduced in the dorsolateral prefrontal cortex, and the monkeys performed poorly on a task associated with prefrontal cortex activity. These effects continued long after administration of the drug, which indicates that the deficits were not a direct effect of PCP administration. [See the news story by Pennisi.]

  16. Gene amplification and breast cancer

    In breast cancer, several chromosome regions are amplified, including a region of chromosome 20. Anzick et al. used chromosome microdissection of that region and hybrid selection techniques to identify a gene (AIB1) that occurs in increased copy number and shows elevated levels of transcription in primary breast cancer specimens. The protein encoded by this gene interacted with the estrogen receptor and enhanced estrogen-dependent transcription in vitro. Overexpression of AIB1 might affect signal transduction pathways and thus be involved in the dysregulation underlying tumor growth.