Khoa học hàng tuần/23 tháng 12, 2005

Bước tới: chuyển hướng, tìm kiếm

1. Neuroscience: Genes, Speech, and Language

Learning to talk is one of the most important milestones in human development, but we still have only a limited understanding of the way in which the process occurs. It normally takes just a few years to go from babbling newborn to fluent communicator. During this period, the child learns to produce a rich array of speech sounds through intricate control of articulatory muscles, assembles a vocabulary comprising thousands of words, and deduces the complicated structural rules that permit construction of meaningful sentences. All of this (and more) is achieved with little conscious effort.

Full report at

2. Systems Biology: On Reconstruction of Genetic Circuits

Many compelling biological questions center on how interactions among genes and proteins, forming genetic circuits, give rise to specific cellular functions. Genetic and biochemical techniques have successfully identified many circuit components and their interactions. However, in many cases knowledge about these components and their interactions is not sufficient to explain the circuit mechanism. What is missing from the circuit diagram? There are several possible deficiencies: one is that the diagram may be incomplete -- interactions may have been missed. The opposite problem also exists: the diagram may be too complete, in the sense that it contains interactions that are not actively involved in the process being investigated.

Full report at

3. Cell Biology: On the Patchy Structure of Cell Membranes

Given their biological importance, membranes have been surprisingly neglected by biochemists until recently. Perhaps this is understandable in view of the technical hurdles that working with them presents. Most methods require purification and observation in aqueous environments alien to the molecular design of a membrane, and so the field had to rely on oversimplified views that still dominate the texts and teaching in this area.

But now we have a rising number of high-resolution structures, an abundance of functional data and an evolving conceptual basis for framing more pointed questions. This is leading to a great expansion of interest in the area.

Full report at

4. Paleontology: Dinosaurs and Grass

Grasses, with about 10,000 extant species, are among the largest and most ecologically dominant families of flowering plants, and today provide staple foods for much of humankind. Dinosaurs, the dominant mega-herbivores during most of the Mesozoic Era (65 to 251 million years ago), are similarly one of the largest and best known groups of organisms. However, the possible coevolution of grasses and dinosaurs has never been studied. New work reports analysis of phytoliths -- microscopic pieces of silica formed in plant cells -- in coprolites that the authors attribute to titanosaurid sauropods that lived about 65 to 71 million years ago. Their data indicate that those dinosaurs ate grasses.

Full report at

5. Geology: On Phanerozoic Global Sea-Level Change

A new study reviews Phanerozoic sea-level changes (543 million years ago (Ma) to the present) on various time scales and presents a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 +- 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10^(4)- to 10^(6)-year scale, but a link between oxygen isotope and sea level on the 10^(7)-year scale must be due to temperature changes that the authors attribute to tectonically controlled carbon dioxide variations.

Full report at

6. Chemistry: On the Nanomolecular Wheel

At the turn of the millennium, pop surveys placed the wheel as the most important invention. Upon the foundation of this basic mechanical unit, many types of macromachines have been developed.

By analogy, some researchers hope that directable nanoscale wheels will spawn nanoscale machines. Within such a mechanism the counterpart to a wheel is a molecular rotor, capable of specific directed rotation. On the molecular level, random rotors abound, but coupling specific chemical reactions to control directional rotation is rare. New work reports such a system and considers its implications for the development of molecular motors.

Full report at

Liên kết đến đây