bluuebunny/crossref_metadata_2025 huggingface dataset:
Melanocortins and agouti‐related protein modulate the excitability of two arcuate nucleus neuron populations by alteration of resting potassium conductances
Authors: Smith Mark A. , Hisadome Kazunari , Al‐Qassab Hind , Heffron Helen , Withers Dominic J. , Ashford Michael L. J.
Published: October 2006

The hypothalamic melanocortin system is crucial for the control of appetite and body weight. Two of the five melanocortin receptors, MC3R and MC4R are involved in hypothalamic control of energy homeostasis, with the MC4R having the major influence. It is generally thought that the main impact of the melanocortin system on hypothalamic circuits is external to the arcuate nucleus, and that any effect locally in the arcuate nucleus is inhibitory on proopiomelanocortin‐expressing (POMC) neurons. In contrast, using current‐ and voltage‐clamp recordings from identified neurons, we demonstrate that MC3R and MC4R agonists depolarize arcuate POMC neurons and a separate arcuate neuronal population identified by the rat insulin 2 promoter (RIPCre) transgene expression. Furthermore, the endogenous MC3R and MC4R antagonist, agouti‐related protein (AgRP), hyperpolarizes POMC and RIPCre neurons in the absence of melanocortin agonist, consistent with inverse agonism at the MC4R. A decreased transient outward (IA) potassium conductance, and to a lesser extent the inward rectifier (KIR) conductance, underlies neuronal depolarization, whereas an increase in IA mediates AgRP‐induced hyperpolarization. Accordingly, POMC and RIPCre neurons may be targets for peptide transmitters that are possibly released locally from AgRP‐expressing and POMC neurons in the arcuate nucleus, adding further previously unappreciated complexity to the arcuate system.
Ozone Destruction by Chlorine: The Impracticality of Mitigation Through Ion Chemistry
Authors: Viggiano A. A. , Morris R. A. , Gollinger K. , Arnold F.
Published: October 2006

The feasibility of using negative ion chemistry to mitigate stratospheric ozone depletion by chlorine-containing radicals, as proposed recently, is addressed here. Previous in situ measurements of the negative ion composition of the stratosphere show that chlorine-containing ions represent only a small fraction of total ions. New measurements of the negative ion temporal evolution in the stratosphere show that the fractional abundance of chlorine-containing ions is never greater than 1 percent at any time in the ion evolution. On the basis of these and other arguments, using negative ion chemistry to mitigate ozone depletion by chlorine-containing compounds is not feasible.
Synthesis of Linear Acetylenic Carbon: The "
sp
" Carbon Allotrope
Authors: Lagow Richard J. , Kampa Joel J. , Wei Han-Chao , Battle Scott L. , Genge John W. , Laude David A. , Harper Carla J. , Bau Robert , Stevens Raymond C. , Haw James F. , Munson Eric
Published: October 2006

A carbon allotrope based on "
sp
" hybridization containing alternating triple and single bonds (an acetylenic or linear carbon allotrope) has been prepared. Studies of small (8 to 28 carbon atoms) acetylenic carbon model compounds show that such species are quite stable (130° to 140°C) provided that nonreactive terminal groups or end caps (such as tert-butyl or trifluoromethyl) are present to stabilize these molecules against further reactions. In the presence of end capping groups, laser-based synthetic techniques similar to those normally used to generate fullerenes, produce thermally stable acetylenic carbon species capped with trifluoromethyl or nitrile groups with chain lengths in excess of 300 carbon atoms. Under these conditions, only a negligible quantity of fullerenes is produced. Acetylenic carbon compounds are not particularly moisture or oxygen sensitive but are moderately light sensitive.
A Neutral Templating Route to Mesoporous Molecular Sieves
Authors: Tanev Peter T. , Pinnavaia Thomas J.
Published: October 2006

A neutral templating route for preparing mesoporous molecular sieves is demonstrated based on hydrogen-bonding interactions and self-assembly between neutral primary amine micelles (S°) and neutral inorganic precursors (1°). The S° 1° templating pathway produces ordered mesoporous materials with thicker framework walls, smaller x-ray scattering domain sizes, and substantially improved textural mesoporosities in comparison with M41S materials templated by quaternary ammonium cations of equivalent chain length. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods. The S° 1° templating route provides for the synthesis of other oxide mesostructures (such as aluminas) that may be less readily accessible by electrostatic templating pathways.
Simultaneous Studies of Reaction Kinetics and Structure Development in Polymer Processing
Authors: Bras W. , Derbyshire G. E. , Bogg D. , Cooke J. , Elwell M. J. , Komanschek B. U. , Naylor S. , Ryan A. J.
Published: October 2006

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.
Optical Properties of the South Pole Ice at Depths Between 0.8 and 1 Kilometer
Authors: Askebjer P. , Barwick S. W. , Bergström L. , Bouchta A. , Carius S. , Coulthard A. , Engel K. , Erlandsson B. , Goobar A. , Gray L. , Hallgren A. , Halzen F. , Hulth P. O. , Jacobsen J. , Johansson S. , Kandhadai V. , Liubarsky I. , Lowder D. , Miller T. , Mock P. C. , Morse R. , Porrata R. , Price P. B. , Richards A. , Rubinstein H. , Schneider E. , Sun Q. , Tilav S. , Walck C. , Yodh G.
Published: October 2006

The optical properties of the ice at the geographical South Pole have been investigated at depths between 0.8 and 1 kilometer. The absorption and scattering lengths of visible light (∼515 nanometers) have been measured in situ with the use of the laser calibration setup of the Antarctic Muon and Neutrino Detector Array (AMANDA) neutrino detector. The ice is intrinsically extremely transparent. The measured absorption length is 59 ± 3 meters, comparable with the quality of the ultrapure water used in the Irvine-Michigan-Brookhaven and Kamiokande proton-decay and neutrino experiments and more than twice as long as the best value reported for laboratory ice. Because of a residual density of air bubbles at these depths, the trajectories of photons in the medium are randomized. If the bubbles are assumed to be smooth and spherical, the average distance between collisions at a depth of 1 kilometer is about 25 centimeters. The measured inverse scattering length on bubbles decreases linearly with increasing depth in the volume of ice investigated.
The Elemental Composition of the Corona of Procyon: Evidence for the Absence of the FIP Effect
Authors: Drake Jeremy J. , Laming J. Martin , Widing Kenneth G. , Schmitt Jürgen H. M. M. , Haisch Bernhard , Bowyer Stuart
Published: October 2006

The chemical composition of the solar corona is not the same as that of the underlying photosphere. In the corona, elements with a first ionization potential (FIP) of ≤10 electron volts (for example, iron, magnesium, silicon, and calcium) are overabundant relative to those with an FIP of ≥10 electron volts (for example, oxygen, neon, and sulfur) by factors of 3 to 10 with respect to the photosphere. The origin of this FIP effect is unknown. The launch of the Extreme Ultraviolet Explorer Satellite (EUVE) opened up the spectroscopic capability required to determine elemental abundances in the coronae of other stars. Spectroscopic observations of the corona of the nearby F5 IV star Procyon obtained with EUVE have yielded estimates of the relative abundances of high- and low-FIP species. The results provide evidence that Procyon, unlike the sun, does not exhibit the FIP effect. Whether the sun or Procyon is more typical of the general late-type stellar population is of fundamental interest to the physics of stellar outer atmospheres and has a bearing on the origin of cosmic rays.
Properties of Metallic Nanowires: From Conductance Quantization to Localization
Authors: Pascual J. I. , Méndez J. , Gómez-Herrero J. , Baró A. M. , Garcia N. , Landman Uzi , Luedtke W. D. , Bogachek E. N. , Cheng H. -P.
Published: October 2006

Material structures of reduced dimensions exhibit electrical and mechanical properties different from those in the bulk. Measurements of room-temperature electronic transport in pulled metallic nanowires are presented, demonstrating that the conductance characteristics depend on the length, lateral dimensions, state and degree of disorder, and elongation mechanism of the wire. Conductance during the elongation of short wires (length ℓ ∼ 50 angstroms) exhibits periodic quantization steps with characteristic dips, correlating with the order-disorder states of layers of atoms in the wire predicted by molecular dynamics simulations. The resistance
R
of wires as long as ℓ ∼ 400 angstroms exhibits localization characteristics with In
R
(ℓ) ∼ ℓ
2
.
Spontaneous Magnetic Ordering in the Fullerene Charge-Transfer Salt (TDAE)C
60
Authors: Lappas A. , Prassides K. , Vavekis K. , Arcon D. , Blinc R. , Cevc P. , Amato A. , Feyerherm R. , Gygax F. N. , Schenck A.
Published: October 2006

The zero-field muon spin relaxation technique has been used in the direct observation of spontaneous magnetic order below a Curie temperature (
T
c
) of ∼16.1 kelvin in the fullerene charge-transfer salt (tetrakisdimethylaminoethylene)C
60
[(TDAE)C
60
]. Coherent ordering of the electronic magnetic moments leads to a local field of 68(1) gauss at the muon site at 3.2 kelvin (parentheses indicate the error in the last digit). Substantial spatially inhomogeneous effects are manifested in the distribution of the local fields, whose width amounts to 48(2) gauss at the same temperature. The temperature evolution of the internal magnetic field below the freezing temperature mirrors that of the saturation magnetization, closely following the behavior expected for collective spin wave (magnon) excitations. The transition to a ferromagnetic state with a
T
c
higher than that of any other organic material is now authenticated.
Physics Festival Brightens Rainy San Jose
Authors: Travis John
Published: October 2006

A week after floodwaters surged through parts of San Jose's downtown, a flood tide of physicists—almost 6000 of them—appeared for the annual March meeting of the American Physical Society (APS). Gloom and drizzle continued for the first 4 days of the gathering, but there were plenty of bright spots inside the hall.
In from the Cold: Prospects for Conversion of the Defense Industrial Base
Authors: Kelley Maryellen R. , Watkins Todd A.
Published: October 2006

At the end of the Cold War, the manufacturing operations involved in making military equipment and commercial goods are commonly believed to intersect hardly at all. Our analyses of 1991 survey data from a large sample of establishments in the machining-intensive durable goods sector show that there are few technical and competitive conditions separating the defense and commercial industrial spheres. Commercial-military integration of production is now the normal practice among the majority of defense contractors in this sector. Moreover, we find little difference between defense and commercial producers in the competitive conditions they face or in the diversity of their customers. However, defense contractors have an advantage over their strictly commercial counterparts because of their greater use of productivity-enhancing technologies.
Interlayer Tunneling Mechanism for High-
T
c
Superconductivity: Comparison with
c
Axis Infrared Experiments
Authors: Anderson P. W.
Published: October 2006

Recent
c
axis-polarized infrared measurements in the high-transition temperature (high-
T
c
) cuprate superconductor (La,Sr)
2
CuO
4
can be interpreted on the basis that the entire condensation energy comes from the interlayer Josephson coupling. This gives a parameter-free determination of penetration depth λ and coherence length ξ for this superconductor that are in agreement with experiment.
Pressure-Tuned Fermi Resonance in Ice VII
Authors: Aoki K. , Yamawaki H. , Sakashita M.
Published: October 2006

Fermi resonance was observed between the OH stretch and the overtone of the OH bending modes of HDO molecules contaminated in phase VII of D
2
O ice over the pressure range from 17 to 30 gigapascals. An anharmonic coupling constant, which is related to the potential energy surface on which hydrogen-bonded protons oscillate, was found to range around 50 wave numbers through the resonant pressure range. Its experimentally obtained magnitude and pressure-insensitive behavior will be useful for theoretical studies of the potential energy surface and hence of the nature of hydrogen bonding in ice.
The Photoreactivity of Chlorine Dioxide
Authors: Vaida Veronica , Simon John D.
Published: October 2006

Determining the detailed photoreactivity of radicals that are of importance in atmospheric processes requires information from both laboratory and field measurements and theoretical calculations. Laboratory experiments and quantum calculations have been used to develop a comprehensive understanding of the photoreactivity of chlorine dioxide (OCIO). The photoreactivity is strongly dependent on the medium (gas phase, liquid solution, or cryogenic matrix). These data reveal details of the complex chemistry of OCIO. The potential role of this radical in stratospheric ozone depletion is discussed in accord with these laboratory measurements.
Growth of
Prochlorococcus
, a Photosynthetic Prokaryote, in the Equatorial Pacific Ocean
Authors: Vaulot Daniel , Marie Dominique , Olson Robert J. , Chisholm Sallie W.
Published: October 2006

The cell cycle of
Prochlorococcus
, a prokaryote that accounts for a sizable fraction of the photosynthetic biomass in the eastern equatorial Pacific, progressed in phase with the daily light cycle. DNA replication occurred in the afternoon and cell division occurred at night. Growth rates were maximal (about one doubling per day) at 30 meters and decreased toward the surface and the bottom of the ocean. Estimated
Prochlorococcus
production varied between 174 and 498 milligrams of carbon per square meter per day and accounted for 5 to 19 percent of total gross primary production at the equator. Because
Prochlorococcus
multiplies close to its maximum possible rate, it is probably not severely nutrient-limited in this region of the oceans.
Hubble Space Telescope Imaging of Neptune's Cloud Structure in 1994
Authors: Hammel H. B. , Lockwood G. W. , Mills J. R. , Barnet C. D.
Published: October 2006

Images of Neptune taken at six wavelengths with the Hubble Space Telescope in October and November 1994 revealed several atmospheric features not present at the time of the Voyager spacecraft encounter in 1989. Furthermore, the largest feature seen in 1989, the Great Dark Spot, was gone. A dark spot of comparable size had appeared in the northern hemisphere, accompanied by discrete bright features at methane-band wavelengths. At visible wavelengths, Neptune's banded structure appeared similar to that seen in 1989.
A Helical Polymer with a Cooperative Response to Chiral Information
Authors: Green Mark M. , Peterson Norman C. , Sato Takahiro , Teramoto Akio , Cook Robert , Lifson Shneior
Published: October 2006

Polyisocyanates, long studied as theoretical models for wormlike chains in dilute solution and liquid crystals, differ from their biological helical analogs in the absence of a predetermined helical sense. These polymers have an unusual sensitivity to chiral effects that arises from a structure in which alternating right- and left-handed long helical blocks are separated by infrequent and mobile helical reversals. Statistical thermodynamic methods yield an exact description of the polymer and the cooperative nature of its chiral properties. Minute energies that favor one of the helical senses drive easily measurable conformational changes, even though such energies may be extremely difficult to calculate from structural theory. In addition, the chiral nature of the polymer can be used to test theoretical ideas concerned with cholesteric liquid crystals, one of which solves the problem of assigning the helical sense.
Dissecting Amazonian Biodiversity
Authors: Tuomisto Hanna , Ruokolainen Kalle , Kalliola Risto , Linna Ari , Danjoy Walter , Rodriguez Zoila
Published: October 2006

Biogeographical and biodiversity studies in lowland Amazonian rain forests typically refer to observed or postulated distribution barriers such as past unfavorable climates, mountains, rivers, and river floodplains that divide the uniform tierra firme (noninundated) forest. Present-day ecological heterogeneity within tierra firme has hardly been discussed in this context, although edaphic differences are known to affect species distribution patterns in both inundated areas and tierra firme. Quantification of landscape heterogeneity in Peruvian lowland Amazonia (500,000 kilometers squared), based on field studies and satellite image analysis, shows that Peruvian Amazonia is considerably more heterogeneous than previously reported. These observations have implications for the research, management, and conservation of Amazonian biodiversity.
Experimental Studies and Theoretical Predictions for the H + D
2
→ HD + D Reaction
Authors: Schnieder L. , Seekamp-Rahn K. , Borkowski J. , Wrede E. , Welge K. H. , Aoiz F. J. , Bañiares L. , D'Mello M. J. , Herrero V. J. , Rábanos V. Sáez , Wyatt R. E.
Published: October 2006

The H + H
2
exchange reaction constitutes an excellent benchmark with which to test dynamical theories against experiments. The H + D
2
(vibrational quantum number
v
= 0, rotational quantum number
j
= 0) reaction has been studied in crossed molecular beams at a collision energy of 1.28 electron volts, with the use of the technique of Rydberg atom time-of-flight spectroscopy. The experimental resolution achieved permits the determination of fully rovibrational state-resolved differential cross sections. The high-resolution data allow a detailed assessment of the applicability and quality of quasi-classical trajectory (QCT) and quantum mechanical (QM) calculations. The experimental results are in excellent agreement with the QM results and in slightly worse agreement with the QCT results. This theoretical reproduction of the experimental data was achieved without explicit consideration of geometric phase effects.
Climate Records Covering the Last Deglaciation
Authors: Sowers Todd , Bender Michael
Published: October 2006

The oxygen-18/oxygen-16 ratio of molecular oxygen trapped in ice cores provides a time-stratigraphic marker for transferring the absolute chronology for the Greenland Ice Sheet Project (GISP) II ice core to the Vostok and Byrd ice cores in Antarctica. Comparison of the climate records from these cores suggests that, near the beginning of the last deglaciation, warming in Antarctica began approximately 3000 years before the onset of the warm Bølling period in Greenland. Atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in Greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the Northern Hemisphere.
Diurnal Changes in the Partial Pressure of Carbon Dioxide in Coral Reef Water
Authors: Kayanne Hajime , Suzuki Atsushi , Saito Hiroshi
Published: October 2006

Coral reefs are considered to be a source of atmospheric carbon dioxide because of their high calcium carbonate production and low net primary production. This was tested by direct measurement of diurnal changes in the partial pressure of carbon dioxide (
P

co
2

) in reef waters during two 3-day periods, one in March 1993 and one in March 1994, on Shiraho reef of the Ryukyu Islands, Japan. Although the
P

co
2

values in reef waters exhibited large diurnal changes ranging from 160 to 520 microatmospheres, they indicate that the reef flat area is a net sink for atmospheric carbon dioxide. This suggests that the net organic production rate of the reef community exceeded its calcium carbonate production rate during the observation periods.
Late Miocene Tidal Deposits in the Amazonian Foreland Basin
Authors: Räsänen Matti E. , Linna Ari M. , Santos José C. R. , Negri Francisco R.
Published: October 2006

Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the western Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota.
Urban Ozone Control and Atmospheric Reactivity of Organic Gases
Authors: Russell A. , Milford J. , Bergin M. S. , McBride S. , McNair L. , Yang Y. , Stockwell W. R. , Croes B.
Published: October 2006

Control strategies for urban ozone traditionally have been based on mass reductions in volatile organic compounds (VOCs). Studies show, however, that some organic gas species (such as alkanes and alcohols) form an order of magnitude less ozone than equal mass emissions of others (such as alkenes and aldehydes). Chemically detailed photochemical models are used to assess uncertainty and variability in reactivity quantification. VOC control strategies based on relative reactivity appear to be robust with respect to nationwide variations in environmental conditions and uncertainties in the atmospheric chemistry. Control of selective organic gas species on the basis of reactivity can offer cost savings over traditional strategies.
Direct Observation of Dislocation Core Structures in CdTe/GaAs(001)
Authors: McGibbon A. J. , Pennycook S. J. , Angelo J. E.
Published: October 2006

A strategy is presented for determining sublattice polarity at defects in compound semiconductors. Core structures of 60-degree and Lomer dislocations in the CdTe/GaAs(001) system have been obtained by the application of maximum-entropy analysis to
Z
-contrast images (
Z
is atomic number) obtained in a 300-kilovolt scanning transmission electron microscope. Sixty-degree dislocations were observed to be of the glide type, whereas in the case of Lomer dislocations, both a symmetric (Hornstra-like) core and an unexpected asymmetric structure made up of a fourfold ring were seen.
Two-Dimensional Imaging of Potential Waves in Electrochemical Systems by Surface Plasmon Microscopy
Authors: Flätgen Georg , Krischer Katharina , Pettinger Bruno , Doblhofer Karl , Junkes Heinz , Ertl Gerhard
Published: October 2006

The potential dependence of resonance conditions for the excitation of surface plasmons was exploited to obtain two-dimensional images of the potential distribution of an electrode with high temporal resolution. This method allows the study of spatiotemporal patterns in electrochemical systems. Potential waves traveling across the electrode with a speed on the order of meters per second were observed in the bistable regime of an oscillatory electrochemical reaction. This velocity is close to that of excitation waves in nerve fibers and is far greater than the velocity of reaction-diffusion waves observed in other chemical systems.
Molecular Diffuse Interstellar Band Carriers in the Red Rectangle
Authors: Sarre P. J. , Miles J. R. , Scarrott S. M.
Published: October 2006

High-resolution optical spectroscopic observations of unidentified emission bands from the unusual biconical nebula known as the Red Rectangle are reported. The peak wavelengths and the widths of prominent bands near 5799, 5853, and 6616 angstroms decrease with increasing offset from the central A0-type star HD 44179 and, in the limit of large distance from the star, are shown to converge toward the known values for some of the narrower diffuse interstellar absorption bands at 5797, 5850, and 6614 angstroms. The same carriers give rise to both Red Rectangle emission and corresponding diffuse interstellar absorption bands, and these particular bands arise from electronic transitions in gas-phase molecules.
Polar Standstill of the Mid-Cretaceous Pacific Plate and Its Geodynamic Implications
Authors: Tarduno John A. , Sager William W.
Published: October 2006

Paleomagnetic data from the Mid-Cretaceous Mountains suggest that Pacific plate motion during the Early to mid-Cretaceous was slow, less than 0.3 degree per year, resembling the polar standstill observed in coeval rocks of Eurasia and North America. There is little evidence for a change in plate motion that could have precipitated the major volcanic episode of the early Aptian that is marked by the formation of the Ontong Java Plateau. During the volcanism, oceanic plates bordering the Pacific plate moved rapidly. Large-scale northward motion of the Pacific plate began after volcanism ceased. This pattern suggests that mantle plume volcanism exerted control on plate tectonics in the Cretaceous Pacific basin.
Scanning Interferometric Apertureless Microscopy: Optical Imaging at 10 Angstrom Resolution
Authors: Zenhausern F. , Martin Y. , Wickramasinghe H. K.
Published: October 2006

Interferometric near-field optical microscopy achieving a resolution of 10 angstroms is demonstrated. The scattered electric field variation caused by a vibrating probe tip in close proximity to a sample surface is measured by encoding it as a modulation in the optical phase of one arm of an interferometer. Unlike in regular near-field optical microscopes, where the contrast results from a weak source (or aperture) dipole interacting with the polarizability of the sample, the present form of imaging relies on a fundamentally different contrast mechanism: sensing the dipole-dipole coupling of two externally driven dipoles (the tip and sample dipoles) as their spacing is modulated.
Population Dynamics of Exploited Fish Stocks at Low Population Levels
Authors: Myers R. A. , Barrowman N. J. , Hutchings J. A. , Rosenberg A. A.
Published: October 2006

Models of population dynamics in which per capita reproductive success declines at low population levels (variously known as depensation, the Allee effect, and inverse density-dependence) predict that populations can have multiple equilibria and may suddenly shift from one equilibrium to another. If such depensatory dynamics exist, reduced mortality may be insufficient to allow recovery of a population after abundance has been severely reduced by harvesting. Estimates of spawner abundance and number of surviving progeny for 128 fish stocks indicated only 3 stocks with significant depensation. Estimates of the statistical power of the tests strengthen the conclusion that depensatory dynamics are not apparent for fish populations at the levels studied.
Physicists Polish One Model While Looking to the Next
Authors: Hellemans Alexander
Published: October 2006

BRUSSELS, BELGIUM—High-energy physicists' current explanation for the behavior of subatomic particles and forces, known as the Standard Model, is doing just fine. That was the take-home message for the 800 delegates who gathered here from 27 July to 2 August for the International Europhysics Conference on High-Energy Physics. "Mainly this was a conference of consolidation, steady progress, many very beautiful and detailed results," Christopher Llewellyn Smith, director general of CERN, the European particle physics laboratory, told
Science
. But while a multitude of presentations described ever more accurate tests and confirmations of the model, physicists also discussed hints that a whole new range of phenomena beyond the Standard Model is lurking just above the energies of current accelerators—and within range of the next generation of experiments.
Modeling Ocean Circulation
Authors: Semtner Albert J.
Published: October 2006

Ocean numerical models have become quite realistic over the past several years as a result of improved methods, faster computers, and global data sets. Models now treat basin-scale to global domains while retaining the fine spatial scales that are important for modeling the transport of heat, salt, and other properties over vast distances. Simulations are reproducing observed satellite results on the energetics of strong currents and are properly showing diverse aspects of thermodynamic and dynamic ocean responses ranging from deep-water production to EI Niño. Now models can represent not only currents but also the consequences for climate, biology, and geochemistry over time spans of months to decades. However, much remains to be understood from models about ocean circulation on longer time scales, including the evolution of the dominant water masses, the predictability of climate, and the ocean's influence on global change.
Dependence of Peptide Binding by MHC Class I Molecules on Their Interaction with TAP
Authors: Grandea Andres G. , Androlewicz Matthew J. , Athwal Raghbir S. , Geraghty Daniel E. , Spies Thomas
Published: October 2006

Major histocompatibility complex (MHC) class I molecules bind peptides that are delivered from the cytosol into the endoplasmic reticulum by the MHC-encoded transporter associated with antigen processing (TAP). Peptide capture by immature heterodimers of class I heavy chains and β
2
-microglobulin may be facilitated by their physical association with TAP. A genetic defect in a human mutant cell line causes the complete failure of diverse class I heterodimers to associate with TAP. This deficiency impairs the ability of the class I heterodimers to efficiently capture peptides and results from loss of function of an unidentified gene or genes linked to the MHC.
A Business Blueprint: How to Build a Better Ph.D.
Authors: Kaiser Jocelyn
Published: October 2006

Traditional Ph.D. training ill meets industry's needs for versatility and the ability to move a research project rapidly to a commercial payoff, business leaders have long complained. Here's a roundup of what they think it takes to make in their job market.
Scientists Enjoy Life in the Not-So-Fast Lanes
Authors: Fox Karen Celia
Published: October 2006

Even hot-shot Ph.D.s who end up in academia are increasing unlikely to be working at research powerhouses. But small schools offer tremendous opportunities as well as vigorous challenges, as can be seen in these interviews with some big fish in small academic ponds.
Bax-Deficient Mice with Lymphoid Hyperplasia and Male Germ Cell Death
Authors: Knudson C. Michael , Tung Kenneth S. K. , Tourtellotte Warren G. , Brown Gary A. J. , Korsmeyer Stanley J.
Published: October 2006

BAX, a heterodimeric partner of BCL2, counters BCL2 and promotes apoptosis in gain-of-function experiments. A
Bax
knockout mouse was generated that proved viable but displayed lineage-specific aberrations in cell death. Thymocytes and B cells in this mouse displayed hyperplasia, and
Bax-
deficient ovaries contained unusual atretic follicles with excess granulosa cells. In contrast,
Bax
-deficient males were infertile as a result of disordered seminiferous tubules with an accumulation of atypical premeiotic germ cells, but no mature haploid sperm. Multinucleated giant cells and dysplastic cells accompanied massive cell death. Thus, the loss of
Bax
results in hyperplasia or hypoplasia, depending on the cellular context.
How the Glucocorticoids Suppress Immunity
Authors: Marx Jean
Published: October 2006

Glucocorticoids have been used for decades as immune suppressants to treat allergic reactions, reduce inflammation, and prevent rejection of transplanted organs. But how they work has been something of a mystery. Now, two teams of researchers report in
Science
that they appear to work by stimulating cells to produce a protein, which in turn binds and inactivates a second protein normally involved in turning on genes that orchestrate an immune response.
Lofty Flashes Come Down to Earth
Authors: Kerr Richard A.
Published: October 2006

Mystery solved? Two teams of physicists believe they have fingered the source of puzzling flashes that can sometimes be seen in the atmosphere high above giant thunderclouds. The culprit: molecular nitrogen excited by electron collisions. Lightning strokes power the whole process, they believe, by sending pulses of energy into the upper atmosphere and causing slower changes in the atmosphere's electric field.
Quantum Computation
Authors: DiVincenzo David P.
Published: October 2006

If the bits of computers are someday scaled down to the size of individual atoms, quantum mechanical effects may profoundly change the nature of computation itself. The wave function of such a quantum computer could consist of a superposition of many computations carried out simultaneously; this kind of parallelism could be exploited to make some important computational problems, like the prime factoring of large integers, tractable. However, building such a quantum computer would place undreamed of demands on the experimental realization of highly quantum-coherent systems; present-day experimental capabilities in atomic physics and other fields permit only the most rudimentary implementation of quantum computation.
Crystal Structure of the MATa1/MATα2 Homeodomain Heterodimer Bound to DNA
Authors: Li Thomas , Stark Martha R. , Johnson Alexer D. , Wolberger Cynthia
Published: October 2006

The
Saccharomyces cerevisiae
MATa1 and MATα2 homeodomain proteins, which play a role in determining yeast cell type, form a heterodimer that binds DNA and represses transcription in a cell type-specific manner. Whereas the α2 and a1 proteins on their own have only modest affinity for DNA, the a1/α2 heterodimer binds DNA with high specificity and affinity. The three-dimensional crystal structure of the a1/α2 homeodomain heterodimer bound to DNA was determined at a resolution of 2.5 Å. The a1 and α2 homeodomains bind in a head-to-tail orientation, with heterodimer contacts mediated by a 16-residue tail located carboxyl-terminal to the α2 homeodomain. This tail becomes ordered in the presence of a1, part of it forming a short amphipathic helix that packs against the a1 homeodomain between helices 1 and 2. A pronounced 60° bend is induced in the DNA, which makes possible protein-protein and protein-DNA contacts that could not take place in a straight DNA fragment. Complex formation mediated by flexible protein-recognition peptides attached to stably folded DNA binding domains may prove to be a general feature of the architecture of other classes of eukaryotic transcriptional regulators.
Immunosuppression by Glucocorticoids: Inhibition of NF-κB Activity Through Induction of IκB Synthesis
Authors: Auphan Nathalie , DiDonato Joseph A. , Rosette Caridad , Helmberg Arno , Karin Michael
Published: October 2006

Glucocorticoids are among the most potent anti-inflammatory and immunosuppressive agents. They inhibit synthesis of almost all known cytokines and of several cell surface molecules required for immune function, but the mechanism underlying this activity has been unclear. Here it is shown that glucocorticoids are potent inhibitors of nuclear factor kappa B (NF-κB) activation in mice and cultured cells. This inhibition is mediated by induction of the IκBα inhibitory protein, which traps activated NF-κB in inactive cytoplasmic complexes. Because NF-κB activates many immunoregulatory genes in response to pro-inflammatory stimuli, the inhibition of its activity can be a major component of the anti-inflammatory activity of glucocorticoids.
From Genome to Proteome: Looking at a Cell's Proteins
Authors: Kahn Patricia
Published: October 2006

Heidelberg, Germany—It sounds like
Mission Impossible:
Follow the changes taking place in a cell by identifying the thousands of different proteins the cell produces and watching how they ebband flow over time. But a growing band of researchers believes that improved analytical techniques may soon make such an approach feasible, and they haveeven coined a new term for it: proteome research. Prototype systems that screen and analyze thousands of proteins at a time look promising.
Lithoautotrophic Microbial Ecosystems in Deep Basalt Aquifers
Authors: Stevens Todd O. , McKinley James P.
Published: October 2006

Bacterial communities were detected in deep crystalline rock aquifers within the Columbia River Basalt Group (CRB). CRB ground waters contained up to 60 μM dissolved H
2
and autotrophic microorganisms outnumbered heterotrophs. Stable carbon isotope measurements implied that autotrophic methanogenesis dominated this ecosystem and was coupled to the depletion of dissolved inorganic carbon. In laboratory experiments, H
2
, a potential energy source for bacteria, was produced by reactions between crushed basalt and anaerobic water. Microcosms containing only crushed basalt and ground water supported microbial growth. These results suggest that the CRB contains a lithoautotrophic microbial ecosystem that is independent of photosynthetic primary production.
Role of Yeast Insulin-Degrading Enzyme Homologs in Propheromone Processing and Bud Site Selection
Authors: Adames Neil , Blundell Kelly , Ashby Matthew N. , Boone Charles
Published: October 2006

The
Saccharomyces cerevisiae AXL1
gene product Axl1p shares homology with the insulin-degrading enzyme family of endoproteases. Yeast
axl1
mutants showed a defect in a-factor pheromone secretion, and a probable site of processing by Axl1p was identified within the a-factor precursor. In addition, Axl1p appears to function as a morphogenetic determinant for axial bud site selection. Amino acid substitutions within the presumptive active site of Axl1p caused defects in propheromone processing but failed to perturb bud site selection. Thus, Axl1p has been shown to participate in the dual regulation of distinct signaling pathways, and a member of the insulinase family has been implicated in propeptide processing.
Serial Analysis of Gene Expression
Authors: Velculescu Victor E. , Zhang Lin , Vogelstein Bert , Kinzler Kenneth W.
Published: October 2006

The characteristics of an organism are determined by the genes expressed within it. A method was developed, called serial analysis of gene expression (SAGE), that allows the quantitative and simultaneous analysis of a large number of transcripts. To demonstrate this strategy, short diagnostic sequence tags were isolated from pancreas, concatenated, and cloned. Manual sequencing of 1000 tags revealed a gene expression pattern characteristic of pancreatic function. New pancreatic transcripts corresponding to novel tags were identified. SAGE should provide a broadly applicable means for the quantitative cataloging and comparison of expressed genes in a variety of normal, developmental, and disease states.
Antisense Has Growing Pains
Authors: Gura Trisha
Published: October 2006

Antisense compounds once seemed the answer to drug designers' dreams: molecules precisely tailoredto block specific genes. But researchers have run into unexpected difficulties, and they are no longer sure what antisense drugs are doing inside the body. Are clinical trials premature?
Imaging Pattern Formation in Surface Reactions from Ultrahigh Vacuum up to Atmospheric Pressures
Authors: Rotermund H. H. , Haas G. , Franz R. U. , Tromp R. M. , Ertl G.
Published: October 2006

Two optical methods that allow pattern formation to be investigated at an arbitrary pressure are here applied to image concentration patterns of adsorbed species associated with heterogeneous catalytic reactions. In contrast to most surface physical techniques, these methods are not restricted to high vacuum conditions and thus bridge the “pressure gap.” With carbon monoxide oxidation on a (110) surface of platinum as an example, the coupling mechanisms responsible for spatiotemporal self-organization in surface reactions were followed from reaction-diffusion control to the thermokinetic region, associated with phenomena not previously observed in pattern formation.
"Super" Japanese Site Gears Up to Solve Neutrino Puzzle
Authors: Normile Dennis
Published: October 2006

Kamioka, Japan—In an old lead mine, 1 kilometer underground, Japanese physicists are about to put 50,000 tons of water into a giant tank lined with 11,200 photomultiplier tubes. Their quarry: Unprecedented numbers of the elusive particles called neutrinos. Their goal: An answer to the burning question, Do neutrinos have mass?
Were Dinos Cold-Blooded After All? The Nose Knows
Authors: Fischman Joshua
Published: October 2006

The debate over the origins of endothermy—and whether or not dinosaurs were warm-blooded—has blown hot and cold for years, hampered by the lack of clear-cut evidence. But bones in the nose that are essential for conserving water and heat in endotherms seem completely lacking in dinosaurs, and many researchers say this indicates the extinct animals couldn't have been warm-blooded.
Development and Plasticity of Cortical Processing Architectures
Authors: Singer Wolf
Published: October 2006

One of the basic functions of the cerebral cortex is the analysis and representation of relations among the components of sensory and motor patterns. It is proposed that the cortex applies two complementary strategies to cope with the combinatorial problem posed by the astronomical number of possible relations: (i) the analysis and representation of frequently occurring, behaviorally relevant relations by groups of cells with fixed but broadly tuned response properties; and (ii) the dynamic association of these cells into functionally coherent assemblies. Feedforward connections and reciprocal associative connections, respectively, are thought to underlie these two operations. The architectures of both types of connections are susceptible to experience-dependent modifications during development, but they become fixed in the adult. As development proceeds, feedforward connections also appear to lose much of their functional plasticity, whereas the synapses of the associative connections retain a high susceptibility to use-dependent modifications. The reduced plasticity of feedforward connections is probably responsible for the invariance of cognitive categories acquired early in development. The persistent adaptivity of reciprocal connections is a likely substrate for the ability to generate representations for new perceptual objects and motor patterns throughout life.
On the Origins of Spontaneous Polarization in Tilted Smectic Liquid Crystals
Authors: Photinos Demetri J. , Samulski Edward T.
Published: October 2006

The rapid electrooptic response of ferroelectric liquid crystals-stratified (smectic) melts exhibiting spontaneous electric polarization-makes them candidates for the next generation of electrooptic shutters and liquid crystal displays. The model advanced here suggests that polarity is indigenous to tilted smectics and that spontaneous polarization derives from the packing constraints mesogens experience, a tilt-dependent correlation of molecular conformation with orientation. First-rank orientational order parameters (
C
xX
) are nonzero with a tilt- (temperature-) dependent magnitude, and under certain packing conditions, the sign of
C
xX
varies with tilt. These results have a direct bearing on experimental observations because most ferroelectric liquid crystals exhibit a tilt-dependent spontaneous polarization and some show an inversion of the sign of the polarization.
The Yin and Yang of T Cell Costimulation
Authors: Allison James P. , Krummel Matthew F.
Published: October 2006

The Perspective by J. Allison and M. Krummel discusses a paper in this issue of
Science
by Waterhouse
et al
. (
p. 985
), which reports the lymphoproliferative phenotype of mice lacking the T cell antigen CTLA-4. The function of this molecule has been elusive, but the pronounced lymphadenopathy of these knockout mice provides strong evidence that it works in opposition to the positive signal generated by the costimulatory T cell antigen receptor-peptide and CD28-B7 interactions.
Optical Microfabrication of Chalcogenide Glasses
Authors: Hisakuni H. , Tanaka K.
Published: October 2006

It was found that chalcogenide glasses can be shaped by stressing the glass under light illumination because light illumination enhances the fluidity of the glass. The mechanism of photoinduced fluidity was found to be photoelectronic, that is, athermal. The process can be applied to microfabrication of optical fibers and glassy films with a typical dimension of 10 to 100 micrometers.
A Left-Handed Parallel β Helix in the Structure of UDP-
N-
Acetylglucosamine Acyltransferase
Authors: Raetz Christian R. H. , Roderick Steven L.
Published: October 2006

UDP-
N
-acetylglucosamine 3-
O
-acyltransferase (LpxA) catalyzes the transfer of (
R
)-3-hydroxymyristic acid from its acyl carrier protein thioester to UDP-
N
-acetylglucosamine. LpxA is the first enzyme in the lipid A biosynthetic pathway and is a target for the design of antibiotics. The x-ray crystal structure of LpxA has been determined to 2.6 angstrom resolution and reveals a domain motif composed of parallel β strands, termed a left-handed parallel β helix (LβH). This unusual fold displays repeated violations of the protein folding constraint requiring right-handed crossover connections between strands of parallel β sheets and may be present in other enzymes that share amino acid sequence homology to the repeated hexapeptide motif of LpxA.
Will NASA's Research Reforms Fly?
Authors: Lawler Andrew
Published: October 2006

The U.S. space agency is trying to reform its science portfolio at the same time its budget and staff are shrinking. Officials have big plans, but researchers say that it would be a mistake to move too quickly.
New Clues Found to Huntington's
Authors: Barinaga Marcia
Published: October 2006

San Diego—The function of huntingtin, the protein encoded by the gene defective in Huntington's disease, has been a mystery. But the discovery that huntingtin has a partner protein, coupled with the finding that the partner binds the mutated form of huntingtin more tightly than the normal form, may give researchers the handle they need to solve the mystery
Nanotubes Show Image-Display Talent
Authors: Service Robert F.
Published: October 2006

Many schemes have been proposed for using tiny all-carbon nanotubes since the unusual structures were discovered 4 years ago. Now, results reported in this issue (p.
p. 1179
) suggest that one scheme stands a chance of becoming real: Nanotubes can form the basis of tiny electron emission devices, used to paint images on flat screen displays used in laptop computers
Annual Genetics Meeting: Some Puzzles, Some Answers
Authors: Nowak Rachel
Published: October 2006

Minneapolis—Participants in the 45th Annual Meeting of the American Society for Human Genetics learned about the possible solution of another genetic mystery: how a defect in a single gene might bring about the many symptoms of myotonic dystrophy (DM). The RNA produced by the mutant DM gene somehow interferes with the cell's handling of RNAs made by other genes, giving it the potential to expand its reach into several different systems. Researchers also reported tracing the origin of the “sporadic” mutations that cause Apert's syndrome to the patients' fathers. That's no surprise, but the method they used has the potential to help identify the origins of other sporadic genetic disorders.
The Right Ties Can Save Lives and Move Mountains
Authors: Mervis Jeffrey
Published: October 2006

Shanghai—In the past few years, Chinese researchers have been establishing fruitful connections with colleagues abroad. Such collaborations can provide much-needed funds and equipment, international exposure, and more access to publishing in the top journals. For overseas collaborators, they can provide partnerships with topflight scientists and access to a unique research environment.