This Week in Science

Science  23 Oct 1998:
Vol. 282, Issue 5389, pp. 589
  1. Truly Teleported

    Quantum states can be correlated at a distance. This effect, called entanglement, is one of the fundamental ways in which the quantum realm differs from the classical. Furusawa et al. (p. 706; see the Perspective by Caves) report that continuous quantum variables, in this case the amplitude and phase of an optical field, can be teleported (sent by classical channels) between a sending and receiving station. The signal enters and leaves the sending and receiving stations independently through a third system and is not destroyed in the measurement process. Without entanglement, the fidelity of transmission did not exceed 50%; with the use of entangled states, the authors achieve a fidelity of 58%.

  2. Core-Mantle Boundary Anomalies

    Some mixing occurs between the iron-rich liquid outer core and the silicate-rich solid lower mantle in the 1000-kilometer region (called the D” region) above the core-mantle boundary (CMB), but it has been difficult to distinguish whether the D” region is a distinctive layer or just isolated regions of anomalous material. Bréger and Romanowicz (p. 718) measured the differences in travel times of different seismic shear waves through the D” region below the central Pacific Ocean. They then perturbed the velocity structure in a model of the D” region to account for the experimental data. Their refined model shows a slow velocity zone associated with the Hawaiian hot spot plume source at the CMB and a fast velocity zone associated with chemical heterogeneity, which indicates that the D” region is not a well-defined layer but is heterogeneous.

  3. Adding Water to Temperature Records

    Much of our information on temperatures during glacial times comes from analysis of oxygen isotope records, but interpretations are complicated because the records typically reflect both the effects of temperature and the change in the composition of the oceans and precipitation as a result of storage of water in large ice sheets. Beyerle et al. (p. 731) present both a test of the relation between oxygen isotopes and temperatures and a paleoclimate record from underneath a glacier-covered region by examining groundwater changes in an aquifer in Switzerland. Groundwater moves slowly through the aquifer, and older waters record information from when they last equilibrated with the atmosphere. Combined use of noble gases dissolved in the groundwater and oxygen isotope analyses shows that glacial-age temperatures were about 5 Celsius degrees cooler in the region than they are today.

  4. Limits on Climate Predictability?

    The weather of the next few days can be predicted with reasonable accuracy, but long-term climate prediction has been thought to be almost impossible because even very small changes in the initial conditions given to models can grow exponentially after a short time. Imperfect observation quality and coverage, therefore, preclude prediction beyond 5 to 15 days. However, as the recent successful El Niño prediction shows, there are exceptions to this rule, and these exceptions extend at least to some extent beyond the tropical Pacific to higher latitudes, such as the North Pacific and North America. Shukla (p. 728) uses climate modeling case studies to demonstrate the predictability of these climatic features and to discuss some of the underlying reasons, in particular the role of sea-surface temperatures in reducing the influence of atmospheric variability on climate.

  5. Biomineralization Close-Up

    Many factors affect the growth of biominerals such as calcite (CaCO3), including surface steps and the presence of organic compounds. Teng et al. (p. 724) used atomic force microscopy to quantify the thermodynamic and kinetic controls on the growth of calcite from solution. The experiments confirm the Gibbs-Thomson connection, which relates the growth of a crystal face along a step to the oversaturation of the solution. Addition of aspartic acid greatly changed the step morphology and free energy of the system.

  6. Growing Quantum Dot Crystals

    Quantum dots, nanoscale structures that confine electrons, can form spontaneously on a surface if certain materials are deposited on an appropriate substrate; their size and shape will depend on the lattice mismatch between the two compounds. Springholz et al. (p. 734) show that if successive layers of PbSe quantum dots in a matrix of Pb1−×Eu× Te layers are deposited, the particles begin to align vertically as well as in the plane of deposition and form a three-dimensional quantum dot crystal. Such crystals may be of interest for optoelectronic nanodevices.

  7. Protein Folding over Milliseconds and Months

    Detailed simulations of protein folding are computationally intensive and are normally performed for periods corresponding to nanoseconds, but proteins typically fold on microsecond time scales. Duan and Kollman (p. 740; see the Perspective by Berendsen) have performed a millisecond simulation of a 36-residue protein starting from a fully denatured structure. The protein forms intermediate structures, one of which has a lifetime greater than 100 nanoseconds and resembles the fully folded structure. Despite the use of parallel processing, the simulation still required about 4 months of central processing unit time on Cray supercomputers.

  8. Complexities of Spore Formation

    In yeast, sporulation is a key process for reproduction that produces haploid germ cells. Because the complete genomic sequence of Saccharomyces cerevisiae is now available, Chu et al. (p. 699) were able to use DNA microarray technology to increase by an order of magnitude the number of genes associated with the sporulation process. Studies of the expression patterns and of consensus sequences in mutant and wild-type cells allowed previously unsuspected associations to be made between genes and regulatory factors.

  9. Stalking Somatostatin Agonists

    Generation of nonpeptide compounds that activate receptors that normally bind peptide hormones has proven to be difficult, although the utility of such compounds for study of the biological roles of such receptors and for the development of therapeutic drugs has long been recognized. Rohrer et al. (p. 737) identified nonpeptide agonists of high affinity that are specific for particular subtypes of the somatostatin receptor. (Somatostatin participates in control of release of other hormones from the pituitary and pancreas, and analogs have application in treatment of cancer and other cell proliferation disorders.) They screened combinatorial libraries constructed to mimic interactions determined by modeling known peptide agonists. The new compounds were used to probe the biological roles of two of the five distinct somatostatin receptor subtypes.

  10. Combating Cholesterol

    Individuals with abetalipoproteinemia have extremely low levels of plasma lipoproteins. This disorder is caused by an inherited deficiency in microsomal triglyceride transfer protein (MTP), a molecule required for assembly and secretion of lipoprotein particles. Wetterau et al. (p. 751) postulated that inhibitors of MTP might have therapeutic potential as cholesterol-lowering drugs. In a high-throughput screen of chemical compounds, they isolated an orally active MTP inhibitor that lowered plasma lipoprotein levels in several animal models, including a rabbit model of hyperlipidemia that is resistant to existing drugs. MTP inhibitors may open up a new avenue for treatment of humans who are at risk for atherosclerosis because of high cholesterol levels.

  11. Ancient Aerobatics

    Some of the oldest (paleozoic) dragonfly-like insects have “smart” structures on their wings. Wootton et al. (p. 749; see the news story by Vogel) show that these ancient insects had devices analogous to those seen in modern dragonflies that deform the wing in response to aerodynamic loading. Despite the analogies, the two types of structures are not homologs—in one case (the triangle-subtriangle complex) they are effectively built the opposite way around, thus providing a vivid illustration of adaption arriving at the same functional solution through different morphological routes.

  12. Don't Count Them Out

    Can monkeys count? Brannon and Terrace (p. 746; see the Perspective by Carey) trained two monkeys to use a touch-sensitive screen to order images on the basis of how many items were present. The monkeys would first touch the image containing one item (a geometric shape of varying color and size on a background of varying color, or even a piece of clip art), then the image containing two items, and so forth up to four items. When presented with pairs of images each containing between five and nine items, the monkeys could select the image with more items.

  13. Surprises in Chlamydia

    Chlamydia are bacterial pathogens that can cause disease in the eye and the genital tract. In reporting the sequence of the complete genome, Stephens et al. (p. 754; see the Perspective by Hatch) have found genes that no one thought Chlamydia had and did not find genes that were thought to be essential for all bacteria. They have also found candidate proteins that could be responsible for the virulence of the organism.

  14. Secreted Weapon of TB

    Three million people die each year of tuberculosis (TB), an infectious disease caused by certain strains of mycobacteria. In the host cell, these bacteria replicate in special intracellular compartments called phagosomes and are thought to escape destruction therein by secreting proteins that remodel the phagosomes. Berthet et al. (p. 759) show that a secreted mycobacterial protein called ERP (exported repetitive protein), which is found only in strains that cause TB and leprosy, is present in phagosomes and is essential for intracellular replication.

  15. Smoothly Varying Stishovite

    Stishovite is a high-pressure polymorph of silica (SiO2) in which silicon atoms are coordinated to six oxygen atoms, rather than to four as in quartz. Andrault et al. 720 determined the crystal structure of stishovite at pressures up to 120 gigapascals in a multianvil apparatus with x-ray diffraction measurements at the third-generation European synchrotron source. They confirmed the CaCl2 distortion of stishovite at 54 gigapascals and found no other significant structural changes that would signify a phase transition at higher pressure. The smooth decrease in the volume of stishovite with increasing pressure allows scientists to predict its behavior and stability throughout Earth's mantle.

  16. Getting Physical

    Physical maps of the human genome are essential aids for studies of complex genetic traits and for positional cloning of disease genes. Deloukas et al. 744 announce the release of a new map of expressed genes that is twice as dense and two to three times more accurate than has previously been available. More than 30,000 gene-based markers have been localized, which may represent nearly half of all human genes.

  17. Cellulose Biosynthesis in Arabidopsis

    T. Arioli et al. performed a “molecular analysis of cellulose biosynthesis in Arabidopsis” (wall cress plant) with the use of an “rsw1 mutant [gene with a] temperature-sensitive allele [that] is changed in one amino acid” (Reports, 30 Jan., p. 717).

    R. H. Atalla comments that the results, while “an important contribution,” do not rule out “two alternative interpretations of the soluble β-1,4-linked glucan” that accumulates in the presence of the mutant rsw1 gene. He states that “careful permethylation analyses … will be important to the full development of the implications of the observations made by Arioli et al.“The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/282/5389/591a