bluuebunny/crossref_metadata_2025 huggingface dataset:
White Light Sunspot Observations from the Solar Optical Universal Polarimeter on Spacelab-2
Authors: Shine R. A. , Title A. M. , Tarbell T. D. , Topka K. P.
Published: October 2006

The flight of the Solar Optical Universal Polarimeter on Spacelab-2 provided the opportunity for the collection of time sequences of diffraction-limited (0.5 arc second) solar images with excellent pointing stability (0.003 arc second) and with freedom from the distortion that plagues ground-based images. A series of white-light images of active region 4682 were obtained on 5 August 1985, and the area containing the sunspot has been analyzed. These data have been digitally processed to remove noise and to separate waves from low-velocity material motions. The results include (i) proper motion measurements of a radial outflow in the photospheric granulation pattern just outside the penumbra; (ii) discovery of occasional bright structures ("streakers") that appear to be ejected outward from the penumbra; (iii) broad dark "clouds" moving outward in the penumbra, in addition to the well-known bright penumbral grains moving inward; (iv) apparent extensions and contractions of penumbral filaments over the photosphere; and (v) observation of a faint bubble or looplike structure that seems to expand from two bright penumbral filaments into the photosphere.
A Mouse Macrophage Factor Induces Head Structures and Organizes a Body Axis in
Xenopus
Authors: Sokol S. , Wong G. G. , Melton D. A.
Published: October 2006

Soluble peptide factors have been implicated as the agents responsible for embryonic inductions in vertebrates. Here, a protein (PIF) secreted by a mouse macrophage cell line is shown to change the developmental fate of
Xenopus
embryonic cells. Exposure to PIF causes presumptive ectodermal explants to form anterior neural and mesodermal tissues, including brain and eye, instead of ciliated epidermis. In addition, the induced tissues are organized into a rudimentary embryonic axis. These results suggest that PIF or a closely related molecule is involved in inducing anterior structures and organizing the frog body plan.
Superconductivity—The State That Came in from the Cold
Authors: Geballe T. H. , Hulm J. K.
Published: October 2006

The exploration of high transition temperature copper-oxide-based superconductors has proceeded vigorously and internationally during the first year following the initial publication of the work of Bednorz and Müller. Progress in understanding the physics that underlies the phenomena has been slowed by difficulties resulting from the delicate and complex crystal chemistry of the material. Reports of superconducting behavior well above 100 kelvin have not been confirmed to date, although there is some suggestive evidence. A survey of the present state of the science and the possibilities for electronic and electrical power technologies is given.
Electronic Structure and Valence-Bond Band Structure of Cuprate Superconducting Materials
Authors: Guo Yuejin , Langlois Jean-Marc , Goddard William A.
Published: October 2006

From ab initio calculations on various clusters representing the La

2-
x

Sr

x

Cu
1
O
4
and Y
1
Ba
2
Cu
3
O
7
classes of high-temperature superconductors, it is shown that (i) all copper sites have a Cu
II
(
d
9
)oxidation state with one unpaired spin that is coupled antiferromagnetically to the spins of adjacent Cu
II
sites; (ii) oxidation beyond the cupric (Cu
II
) state leads not to Cu
III
but rather to oxidized oxygen atoms, with an oxygen
p
π hole bridging two Cu
II
sites; (iii) the oxygen
p
π hole at these oxidized sites is ferromagnetically coupled to the adjacent Cu
II
d
electrons despite the fact that this is opposed by the direct
dd
exchange; and (iv) the hopping of these oxygen
p
π holes (in CuO sheets or chains) from site to site is responsible for the conductivity in these systems (
N
-electron band structures are reported for the migration of these localized charges).
Molecular-Level Control over Surface Order in Self-Assembled Monolayer Films of Thiols on Gold
Authors: Bain Colin D. , Whitesides George M.
Published: October 2006

Long-chain ω-hydroxyalkanethiols [HS(CH
2
)

n

OH] coordinate to gold surfaces through the sulfur atom and produce ordered, hydrophilic monolayers in which the hydroxyl groups are exposed at the outer surface. Coadsorption of two ω-hydroxyalkanethiols of different chain lengths
n
resulted in the formation of a monolayer having a disordered surface region that was markedly less hydrophilic than the homogeneous, hydroxylic surface formed from either pure compound. By controlling the composition of the monolayer, it was also possible to control simultaneously the degree of order in the surface and its hydrophilicity. In the monolayers containing a mixture of alkanethiol components, these components apparently did not phase-segregate into macroscopic islands, but were dispersed on a molecular scale.
Analysis of T-Cell Receptor Gene Rearrangement and Expression in Human Natural Killer Clones
Authors: Ritz Jerome , Campen Thomas J. , Schmidt Reinhold E. , Royer Hans Dieter , Hercend Thierry , Hussey Rebecca E. , Reinherz Ellis L.
Published: October 2006

A series of clones of human natural killer (NK) cells was characterized with respect to expression of the Ti α and Ti β genes of the T-cell receptor. T11
+
T3
+
NK clones contained Ti α and Ti β RNA transcripts and expressed disulfide-linked heterodimers, demonstrating the presence of a functional T-cell receptor. In contrast, T11
+
T3
-
NK clones expressed only 1.0-kilobase truncated Ti β transcripts, without a Ti α transcript and no detectable surface Ti protein. Since previous studies demonstrated that Ti β gene activation precedes Ti α gene activation in thymic ontogeny, the T11
+
T3
-
NK cells appear to be derived from T-lineage precursors.
Hemispherical Color Differences on Pluto and Charon
Authors: Binzel Richard P.
Published: October 2006

Time-resolved multicolor photometric observations of Pluto-Charon mutual events have been used to derive individual colors for these two bodies and to investigate the degree of color differences between their synchronous facing and opposite hemispheres. Pluto is significantly redder than Charon, where direct measurements of the anti-Charon hemisphere of Pluto and the Pluto-facing hemisphere of Charon yield B-V magnitudes of 0.867 ± 0.008 and 0.700 ± 0.010, respectively. Both Pluto and Charon are found to have relatively uniform longitudinal color distributions with 1σ upper limits of 2% and 5%, respectively, for any large-scale hemispherical color asymmetries. Thus, a previous suspicion of a significant color asymmetry on Charon is not confirmed. Instead the data may be attributed to a direct detection of polar caps on Pluto.
Olmec Settlement Data from La Venta, Tabasco, Mexico
Authors: Rust William F. , Sharer Robert J.
Published: October 2006

Research at La Venta, a major Olmec center on a low salt dome 12 kilometers from the Gulf Coast has revealed evidence of initial occupation (about 1750 to 1400 B.C.) along levees of the silted-in Río Barí, north of the site core in a transitional estuarine-riverine environment. Between 1400 and 1150 B.C. settlement expanded to nearby La Venta itself, which between 1150 and 800 B.C. developed into a major temple-town complex. Local development peaked at La Venta and along the river levees between 800 and 500 B.C. In this span La Venta headed a local three-tiered site hierarchy as social distinctions expanded to the peripheral Río Barí sites. New excavations show that growth in population size and density at La Venta preceded the development of sociopolitical complexity. These data contradict the traditional organizational reconstruction of Olmec society, the "vacant ceremonial center" model, and provide qualified support for a model that presents riverine resource concentration as a significant factor in the evolution of Olmec civilization.
Observations of Stratospheric NO
2
and O
3
at Thule, Greenland
Authors: Mount G. H. , Solomon S. , Sanders R. W. , Jakoubek R. O. , Schmeltekopf A. L.
Published: October 2006

Scattered sunlight and direct light from the moon was used in two wavelength ranges to measure the total column abundances of stratospheric ozone (O
3
) and nitrogen dioxide (NO
2
) at Thule, Greenland (76.5°N), during the period from 29 January to 16 February 1988. The observed O
3
column varied between about 325 and 400 Dobson units, and the lower values were observed when the center of the Arctic polar vortex was closest to Thule. This gradient probably indicates that O
3
levels decrease due to dynamical processes near the center of the Arctic vortex and should be considered in attempts to derive trends in O
3
levels. The observed NO
2
levels were also lowest in the center of the Arctic vortex and were sometimes as low as 5 × 10
14
molecules per square centimeter, which is even less than comparable values measured during Antarctic spring, suggesting that significant heterogeneous photochemistry takes place during the Arctic winter as it does in the Antarctic.
Origins of the 1988 North American Drought
Authors: Trenberth Kevin E. , Branstator Grant W. , Arkin Phillip A.
Published: October 2006

The 1988 summer drought in the United States was the most extensive in many years. Because the drought developed in different places at different times, not all regional effects can be traced to the same cause. Along the West Coast and in the northwestern United States drought conditions developed during 1987 in association with the 1986 to 1987 El Niño in the tropical Pacific Ocean. Record low rainfalls from April to June 1988 led to rapid development of drought in the North Central United States. Strong anticyclonic conditions and a northward displaced jet stream in the upper atmosphere over North America throughout this period were only part of a pronounced and distinctive wavetrain of anomalies in the atmospheric circulation that appeared to emanate from the tropical Pacific. Below average sea surface temperatures along the equator in the Pacific in the northern spring of 1988, combined with warmer than normal water from 10° to 20°N, led to a northward displaced but still active intertropical convergence zone (ITCZ) southeast of Hawaii. Results from a steady-state planetary-wave atmospheric model indicate that the atmospheric heating anomalies associated with the displaced ITCZ can force an anomalous wavetrain across North America similar to that observed. Land surface processes probably contributed to the severity and persistence of the drought; however, the large-scale atmospheric circulation perturbations associated with natural variations in the coupled atmosphere-ocean system in the tropical Pacific were most likely the primary cause.
Gravitational Separation of Gases and Isotopes in Polar Ice Caps
Authors: Craig H. , Horibe Y. , Sowers T.
Published: October 2006

Atmospheric gases trapped in polar ice at the firn to ice transition layer are enriched in heavy isotopes (nitrogen-15 and oxygen-18) and in heavy gases (O
2
/N
2
and Ar/N
2
ratios) relative to the free atmosphere. The maximum enrichments observed follow patterns predicted for gravitational equilibrium at the base of the firn layer, as calculated from the depth to the transition layer and the temperature in the firn. Gas ratios exhibit both positive and negative enrichments relative to air: the negative enrichments of heavy gases are consistent with observed artifacts of vacuum stripping of gases from fractured ice and with the relative values of molecular diameters that govern capillary transport. These two models for isotopic and elemental fractionation provide a basis for understanding the initial enrichments of carbon-13 and oxygen-18 in trapped CO
2
, CH
4
, and O
2
in ice cores, which must be known in order to decipher ancient atmospheric isotopic ratios.
Changing Composition of the Global Stratosphere
Authors: McElroy Michael B. , Salawitch Ross J.
Published: October 2006

The current understanding of stratospheric chemistry is reviewed with particular attention to the influence of human activity. Models are in good agreement with measurements for a variety of species in the mid-latitude stratosphere, with the possible exception of ozone (O
3
) at high altitude. Rates calculated for loss of O
3
exceed rates for production by about 40 percent at 40 kilometers, indicating a possible but as yet unidentified source of high-altitude O
3
. The rapid loss of O
3
beginning in the mid-1970s at low altitudes over Antarctica in the spring is due primarily to catalytic cycles involving halogen radicals. Reactions on surfaces of polar stratospheric clouds play an important role in regulating the abundance of these radicals. Similar effects could occur in northern polar regions and in cold regions of the tropics. It is argued that the Antarctic phenomenon is likely to persist: prompt drastic reduction in the emission of industrial halocarbons is required if the damage to stratospheric O
3
is to be reversed.
The Axial Oxygen Atom and Superconductivity in YBa
2
Cu
3
O
7
Authors: Conradson S. D. , Raistrick I. D.
Published: October 2006

Changes in the copper K-edge x-ray absorption spectrum of YBa
2
Cu
3
O
7
across the critical temperature indicate that, accompanying the superconducting transition, the mean square relative displacement of some fraction of the Cu2-O4 bonds becomes smaller or more harmonic (or both), that there may be a slight increase in the associated Cu1-O4 distance, and that electronic states involving these atom pairs become more atomic-like. If there is an association between the superconductivity and this lattice instability, then the bridging axial oxygen is of central importance in determining the high transition temperature of YBa
2
Cu
3
O
7
. Because this structural perturbation will affect the dynamic polarizability of the copper oxygen sublattice, it is consistent with an excitonic pairing mechanism in these materials.
Global Positioning System Measurements for Crustal Deformation: Precision and Accuracy
Authors: Prescott William H. , Davis James L. , Svarc Jerry L.
Published: October 2006

Analysis of 27 repeated observations of Global Positioning System (GPS) position-difference vectors, up to 11 kilometers in length, indicates that the standard deviation of the measurements is 4 millimeters for the north component, 6 millimeters for the east component, and 10 to 20 millimeters for the vertical component. The uncertainty grows slowly with increasing vector length. At 225 kilometers, the standard deviation of the measurement is 6, 11, and 40 millimeters for the north, east, and up components, respectively. Measurements with GPS and Geodolite, an electromagnetic distance-measuring system, over distances of 10 to 40 kilometers agree within 0.2 part per million. Measurements with GPS and very long baseline interferometry of the 225-kilometer vector agree within 0.05 part per million.
Autoreactive Epitope Defined as the Anticodon Region of Alanine Transfer RNA
Authors: Bunn Christopher C. , Mathews Michael B.
Published: October 2006

Autoantibodies to aminoacyl-transfer RNA (tRNA) synthetases are common in the human autoimmune diseases polymyositis and dermatomyositis. Sera of the PL-12 specificity contain separate antibodies reacting with alanyl-tRNA synthetase and alanine tRNA (tRNA
Ala
). The antibodies to tRNA recognize at least six distinguishable human tRNA
Ala
species grouped into two sequence families. The antibody-reactive determinants on the tRNA were identified through ribonuclease protection and oligonucleotide binding experiments. The antibody binding site is a seven- to nine-nucleotide sequence containing the anticodon loop and requires an intact anticodon. No requirement for anticodon stem structure or sequence is observed, although the 5′ portion of the stem is protected from nuclease attack. Antibodies from several patients appear to share the same specificitym, indicating that the antibodies are induced by a unique sequence feature in the immunogen.
Synthesis of Organic Salts with Large Second-Order Optical Nonlinearities
Authors: Marder Seth R. , Perry Joseph W. , Schaefer William P.
Published: October 2006

A series of organic salts, in which the cation has been designed to have a large molecular hyperpolarizability, has been prepared. Variation of the counterion (anion) in many cases leads to materials with large powder second harmonic generation efficiencies, the highest of which is roughly 1000 times that of a urea reference.
Modulation of Acetylcholine Receptor Desensitization by Forskolin Is Independent of cAMP
Authors: Wagoner P. Kay , Pallotta Barry S.
Published: October 2006

Biochemical and electrophysiological studies suggest that adenosine 3′,5′-monophosphate (cAMP)-dependent phosphorylation of the nicotinic acetylcholine receptor channel is functionally significant because it modifies the receptor's rate of desensitization to acetylcholine. In studies that support this conclusion researchers have used forskolin to stimulate cAMP-dependent phosphorylation in intact muscle. It is now shown that although forskolin facilitated desensitization in voltage-clamped rat muscle, this effect was not correlated with the abilities of forskolin and forskolin analogs to activate adenylate cyclase or phosphorylate the receptor. Furthermore, elevation of intracellular cAMP or addition of the catalytic subunit of A-kinase failed to alter desensitization. Therefore, in intact skeletal muscle, cAMP-dependent phosphorylation does not modulate desensitization.
A Monoclonal Antibody to the α Subunit of G
k
Blocks Muscarinic Activation of Atrial K
+
Channels
Authors: Yatani Atsuko , Hamm Heidi , Codina Juan , Mazzoni Maria R. , Birnbaumer Lutz , Brown Arthur M.
Published: October 2006

The activated heterotrimeric guanine nucleotide binding (G) protein G
k
, at subpicomolar concentrations, mimics muscarinic stimulation of a specific atrial potassium current. Reconstitution studies have implicated the α and βγ subunits as mediators, but subunit coupling by the endogenous G protein has not been analyzed. To study this process, a monoclonal antibody (4A) that binds to α
k
but not to βγ was applied to the solution bathing an inside-out patch of atrial membrane; the antibody blocked carbachol-activated currents irreversibly. The state of the endogenous G
k
determined its susceptibility to block by the antibody. When agonist was absent or when activation by muscarinic stimulation was interrupted by withdrawal of guanosine triphosphate (GTP) in the presence or absence of guanosine diphosphate (GDP), the effects of the antibody did not persist. Thus, monoclonal antibody 4A blocked muscarinic activation of potassium channels by binding to the activated G protein in its holomeric form or by binding to the dissociated α subunit.
Effects of Fish and Plankton on Lake Temperature and Mixing Depth
Authors: Mazumder A. , Taylor W. D. , McQueen D. J. , Lean D. R.S.
Published: October 2006

A comparative study of small temperate lakes (<20 square kilometers) indicates that the mixing depth or epilimnion is directly related to light penetration measured as Secchi depth. Clearer lakes have deeper mixing depths. This relation is the result of greater penetration of incident solar radiation in lakes and enclosures with high water clarity. Data show that light penetration is largely a function of size distribution and biomass of algae as indicated by a relation between the index of plankton size distribution (slope) and Secchi depth. Larger or steeper slopes (indicative of communities dominated by small plankton) are associated with shallower Secchi depth. In lakes with high abundances of planktivorous fish, water clarity or light penetration is reduced because large zooplankton, which feed on small algae, are reduced by fish predation. The net effect is a shallower mixing depth, lower metalimnetic temperature and lower heat content in the water column. Consequently, the biomass and size distribution of plankton can change the thermal structure and heat content of small lakes by modifying light penetration.
The Strange Periodic Comet Machholz
Authors: Green Daniel W. E. , Rickman Hans , Porter Alain C. , Meech Karen J.
Published: October 2006

The recently discovered periodic comet Machholz 1986 VIII (1986e) travels closer to the sun than any known planet and any known comet with an orbital period of less than 150 years, thus providing astronomers with a unique object for studying cometary evolution. The comet is spiraling steadily closer to the sun, from perihelion distance
q
≃ 0.9 astronomical unit at about A.D. 700 to
q
≃ 0.13 at present (orbital period, 5.25 years), to an expected
q
≃ 0.03 by about 2450; should the comet survive such increasingly close perihelion passages,
q
will begin steadily to increase shortly thereafter. A review of observations made since discovery is presented, together with a discussion of numerical investigations of the comet's orbit over 4000 years and prospects for observing the upcoming return to perihelion in 1991.
Arachidonic Acid and Other Fatty Acids Directly Activate Potassium Channels in Smooth Muscle Cells
Authors: Ordway Richard W. , Walsh John V. , Singer Joshua J.
Published: October 2006

Arachidonic acid, as well as fatty acids that are not substrates for cyclooxygenase and lipoxygenase enzymes, activated a specific type of potassium channel in freshly dissociated smooth muscle cells. Activation occurred in excised membrane patches in the absence of calcium and all nucleotides. Therefore signal transduction pathways that require such soluble factors, including the NADPH-dependent cytochrome P450 pathway, do not mediate the response. Thus, fatty acids directly activate potassium channels and so may constitute a class of signal molecules that regulate ion channels.
Nuclear Resonance Properties of YBa
2
Cu
3
O
6+x
Superconductors
Authors: Walstedt R. E. , Warren W. W.
Published: October 2006

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) results for copper-63, oxygen-17, and yttrium-89 nuclei in the superconducting composition range of YBa
2
Cu
3
O

6+
x

(0.4 ≤ x ≤ 1.0) are reviewed and interpreted. Copper NMR shift and susceptibility data, combined with a simple ionic model of local magnetic properties, yield a comprehensive analysis of the normal-state anisotropic susceptibility components and full characterization of the copper spin and orbital hyperfine couplings. Data on the spin-lattice relaxation time of these three nuclear species serve to characterize the highly correlated fermion dynamics in this system. Relaxation data from YBa
2
Cu
3
O
7
(superconducting transition temperature
T
c
= 90 K) and oxygen-deficient samples of this material (
T
c
∼60 K) have been analyzed in terms of mean-field models incorporating short-range antiferromagnetic order, giving a quantitative account of (planar) relaxation for these three nuclei in terms of a single dynamical susceptibility.
Chemosynthetic Mussels at a Brine-Filled Pockmark in the Northern Gulf of Mexico
Authors: MacDonald I. Rosman , Reilly James F. , Guinasso Norman L. , Brooks James M. , Carney Robert S. , Bryant William A. , Bright Thomas J.
Published: October 2006

A large (540 square meters) bed of
Bathymodiolus
n. sp. (Mytilidae: Bivalvia) rings a pool of hypersaline (121.35 practical salinity units) brine at a water depth of 650 meters on the continental slope south of Louisiana. The anoxic brine (dissolved oxygen ≤0.17 milliliters per liter) contains high concentrations of methane, which nourishes methanotrophic symbionts in the mussels. The brine, which originates from a salt-cored diapir that penetrates to within 500 meters of the sea floor, fills a depression that was evidently excavated by escaping gas. The spatial continuity of the mussel bed indicates that the brine level has remained fairly constant; however, demographic differences between the inner and outer parts of the bed record small fluctuations.
Histidine Transfer RNA Levels in Friend Leukemia Cells: Stimulation by Histidine Deprivation
Authors: Litt Michael , Weiser Kristina
Published: October 2006

Friend leukemia cells incubated with sublethal concentrations of histidinol for 5 to 6 days show up to twofold increases in their relative concentrations of histidine transfer RNA and no change in the relative concentrations of leucine transfer RNA. A similar effect is seen when cells are grown to stationary phase in the presence of 0.2 times the amount of histidine in Eagle's minimum essential medium. These observations support the theory that the concentrations of specific transfer RNA's are regulated by a mechanism that is sensitive to the extent of their aminoacylation.
Peptide and Protein Synthesis by Segment Synthesis-Condensation
Authors: Kaiser Emil Thomas , Mihara Hisakazu , Laforet Genevieve A. , Kelly Jeffery W. , Walters Lee , Findeis Mark A. , Sasaki Tomikazu
Published: October 2006

The chemical synthesis of biologically active peptides and polypeptides can be achieved by using a convergent strategy of condensing protected peptide segments to form the desired molecule. An oxime support increases the ease with which intermediate protected peptides can be synthesized and makes this approach useful for the synthesis of peptides in which secondary structural elements have been redesigned. The extension of these methods to large peptides and proteins, for which folding of secondary structures into functional tertiary structures is critical, is discussed. Models of apolipoproteins, the homeo domain from the developmental protein encoded by the
Antennapedia
gene of
Drosophila
, a part of the Cro repressor, and the enzyme ribonuclease T
1
and a structural analog have been synthesized with this method.
Perineurium Originates from Fibroblasts: Demonstration in Vitro with a Retroviral Marker
Authors: Bunge Mary Bartlett , Wood Patrick M. , Tynan Laura B. , Bates Margaret L. , Sanes Joshua R.
Published: October 2006

A cellular sheath, the perineurium, forms a protective barrier around fascicles of nerve fibers throughout the peripheral nervous system. In a study to determine the cellular origin of perineurium, a culture system was used in which perineurium forms after purified populations of sensory neurons, Schwann cells, and fibroblasts are recombined. Before recombination, the Schwann cells or the fibroblasts were labeled by infection with a defective recombinant retrovirus whose gene product, β-galactosidase, is histochemically detectable in the progeny of infected cells. Perineurial cells were labeled when fibroblasts had been infected but not when Schwann cells had been infected. Thus, perineurium arises from fibroblasts in vitro and, by implication, in vivo as well.
Leucine Repeats and an Adjacent DNA Binding Domain Mediate the Formation of Functional cFos-cJun Heterodimers
Authors: Turner Richard , Tjian Robert
Published: October 2006

The discovery that the AP-1 family of enhancer binding factors includes a complex of the cellular Fos (cFos) and cellular Jun (cJun) proteins established a direct and important link between oncogenesis and transcriptional regulation. Homodimeric cJun protein synthesized in vitro is capable of binding selectively to AP-1 recognition sites, whereas the cFos polypeptide is not. When cotranslated, the cFos and cJun proteins can form a stable, heterodimeric complex with the DNA binding properties of AP-1/cJun. The related proteins Jun B and vJun are also able to form DNA binding complexes with cFos. Directed mutagenesis of the cFos protein reveals that a leucine repeat structure is required for binding to cJun, in a manner consistent with the proposed function of the "leucine zipper." A novel domain adjacent to, but distinct from, the leucine repeat of cFos is required for DNA binding by cFos-cJun heterodimers. Thus experimental evidence is presented that leucine repeats can mediate complex formation between heterologous proteins and that promotes further understanding of the molecular mechanisms underlying the function of two proto-oncogene products.
A G Protein γ Subunit Shares Homology with ras Proteins
Authors: Gautam Narasimhan , Baetscher Manfred , Aebersold Ruedi , Simon Melvin I.
Published: October 2006

Guanine nucleotide binding proteins (G proteins) that transduce signals from cell surface receptors to effector molecules are made up of three subunits, α, β, and γ. A complementary DNA clone that encodes a 71-amino acid protein was isolated from bovine brain; this protein contains peptide sequences that were derived from the purified γ subunit of G
i
and G
o
. The primary sequence of this G protein γ subunit (Gγ) has 55 percent homology to the γ subunit of transducin (Tγ) and also has homology to functional domains of mammalian ras proteins. The probe for isolating the clone was generated with the use of the polymerase chain reaction (PCR). The extent of divergence between Tγ and Gγ, the isolation of homologous PCR-generated fragments, and the differences between the predicted amino acid sequence of Gγ and that derived from the γ subunit of G
i
and G
o
indicate that γ subunits are encoded by a family of genes.
Hybrid Ferromagnetic-Semiconductor Structure
Authors: Prinz Gary A.
Published: October 2006

Ultrahigh-vacuum growth techniques are now being used to grow single-crystal films of magnetic materials. These growth procedures, carried out in the same molecular beam epitaxy systems commonly used for the growth of semiconductor films, have yielded a variety of new materials and structures that may prove useful for integrated electronics and integrated optical device applications. Examples are given for growth on GaAs and ZnSe, including magnetic sandwiches and patterned structures.
Models for Material Failure and Deformation
Authors: Meakin Paul
Published: October 2006

Simple computer models have been used to investigate a variety of pattern formation processes associated with material failure and deformation. These models reproduce surprisingly well the characteristic morphologies observed in a wide range of real systems. They provide a sound basis for the development of more realistic models that can be used to develop a better understanding of the mechanical properties of real materials. The present algorithms are adequate for some purposes, but substantial improvements are needed if simulation results are to make a major contribution to our theoretical understanding of the asymptotic fractal scaling and universality properties of patterns generated by failure and deformation phenomena.
Spectroscopic Observations of Bright and Dark Emission Features on the Night Side of Venus
Authors: Bell J. F. , Crisp D. , Lucey P. G. , Ozoroski T. A. , Sinton W. M. , Willis S. C. , Campbell B. A.
Published: October 2006

Near-infrared spectra of a bright and a dark thermal emission feature on the night side of Venus have been obtained from 2.2 to 2.5 micrometers (μm) at a spectral resolution of 1200 to 1500. Both bright and dark features show numerous weak absorption bands produced by CO
2
, CO, water vapor, and other gases. The bright feature (hot spot) emits more radiation than the dark feature (cold spot) throughout this spectral region, but the largest contrasts occur between 2.21 and 2.32 μm, where H
2
SO
4
clouds and a weak CO
2
band provide the only known sources of extinction. The contrast decreases by 55 to 65 percent at wavelengths longer than 2.34 μm, where CO, clouds, and water vapor also absorb and scatter upwelling radiation. This contrast reduction may provide direct spectroscopic evidence for horizontal variations in the water vapor concentrations in the Venus atmosphere at levels below the cloud tops.
Observations of Extreme Upwelling Filaments in the Southeast Atlantic Ocean
Authors: Lutjeharms J. R. E. , Shillington F. A. , Duncombe Rae C. M.
Published: October 2006

Cold oceanic water upwells along the western coastline of most major continents. The thermal front that demarcates the farthest seaward extent of this upwelled water is sometimes characterized by extensive whisps or cross-frontal filaments. These may play an important role in the functioning of the upwelling ecosystem as a whole. Satellite observations on filaments of the Benguela upwelling system show filaments that exceed 1000 kilometers in length. Two mechanisms that may produce the exceptional length of these filaments are interaction with Agulhas rings and the effect of intense berg winds.
Galileo Infrared Imaging Spectroscopy Measurements at Venus
Authors: Carlson R. W. , Baines K. H. , Encrenaz TH. , Taylor F. W. , Drossart P. , Kamp L. W. , Pollack J. B. , Lellouch E. , Collard A. D. , Calcutt S. B. , Grinspoon D. , Weissman P. R. , Smythe W. D. , Ocampo A. C. , Danielson G. E. , Fanale F. P. , Johnson T. V. , Kieffer H. H. , Matson D. L. , McCord T. B. , Soderblom L. A.
Published: October 2006

During the 1990 Galileo Venus flyby, the Near Infrared Mapping Spectrometer investigated the night-side atmosphere of Venus in the spectral range 0.7 to 5.2 micrometers. Multispectral images at high spatial resolution indicate substantial cloud opacity variations in the lower cloud levels, centered at 50 kilometers altitude. Zonal and meridional winds were derived for this level and are consistent with motion of the upper branch of a Hadley cell. Northern and southern hemisphere clouds appear to be markedly different. Spectral profiles were used to derive lower atmosphere abundances of water vapor and other species.
The Neuron-Specific Protein PGP 9.5 Is a Ubiquitin Carboxyl-Terminal Hydrolase
Authors: Wilkinson Keith D. , Lee Keunmyoung , Deshpande Seema , Duerksen-Hughes Penelope , Boss Jeremy M. , Pohl Jan
Published: October 2006

A complementary DNA (cDNA) for ubiquitin carboxyl-terminal hydrolase isozyme L3 was cloned from human B cells. The cDNA encodes a protein of 230 amino acids with a molecular mass of 26.182 daltons. The human protein is very similar to the bovine homolog, with only three amino acids differing in over 100 residues compared. The amino acid sequence deduced from the cDNA was 54% identical to that of the neuron-specific protein PGP 9.5. Purification of bovine PGP 9.5 confirmed that it is also a ubiquitin carboxyl-terminal hydrolase. These results suggest that a family of such related proteins exists and that their expression is tissue-specific.
Amplification and Molecular Cloning of HTLV-I Sequences from DNA of Multiple Sclerosis Patients
Authors: Reddy E. Premkumar , Sandberg-Wollheim Magnhild , Mettus Richard V. , Ray Phillip E. , DeFreitas Elaine , Koprowski Hilary
Published: October 2006

Techniques of gene amplification, molecular cloning, and sequence analysis were used to test for the presence of sequences related to human T-lymphotropic virus type I (HTLV-I) in peripheral blood mononuclear cells of six patients with multiple sclerosis (MS) and 20 normal individuals. HTLV-I sequences were detected in all six MS patients and in one individual from the control group by DNA blot analysis and molecular cloning of amplified DNAs. The viral sequences in MS patients were associated with adherent cell populations consisting predominantly of monocytes and macrophages. Molecular cloning and nucleotide sequence analysis indicated that these amplified viral sequences were related to the HTLV-I proviral genome.
Coordinate Regulation and Sensory Transduction in the Control of Bacterial Virulence
Authors: Miller Jeff F. , Mekalanos John J. , Falkow Stanley
Published: October 2006

Genes and operons that encode bacterial virulence factors are often subject to coordinate regulation. These regulatory systems are capable of responding to various environmental signals that may be encountered during the infectious cycle. For some pathogens, proteins that mediate sensory transduction and virulence control are similar to components of other bacterial information processing systems. Understanding the molecular mechanisms governing global regulation of pathogenicity is essential for understanding bacterial infectious diseases.
Scanning Tunneling Microscopy of Galena (100) Surface Oxidation and Sorption of Aqueous Gold
Authors: Eggleston Carrick M. , Hochella Michael F.
Published: October 2006

Scanning tunneling microscopy was used to characterize the growth of oxidized areas on galena (100) surfaces and the formation of gold islands by the reductive adsorption of AuCl
4
–
from aqueous solution. The gold islands and galena substrate were distinguished by atomic resolution imaging and tunneling spectroscopy. Oxidized areas on galena have [110]-trending boundaries; gold islands elongate along [110] directions. However, there are no obvious structural registry considerations that would lead to elongation of gold islands in a [110] direction. Instead, it is probable that a direct coupling of gold reduction and sulfide surface oxidation controls the initial formation of gold islands. Gold islands grow less quickly on preoxidized galena surfaces and show no preferred direction of growth.
New Quantum Structures
Authors: Sundaram Mani , Chalmers Scott A. , Hopkins Peter F. , Gossard Arthur C.
Published: October 2006

Structures in which electrons are confined to move in two dimensions (quantum wells) have led to new physical discoveries and technological applications. Modification of these structures to confine the electrons to one dimension (quantum wires) or release them in the third dimension, are predicted to lead to new electrical and optical properties. This article discusses techniques to make quantum wires, and quantum wells of controlled size and shape, from compound semiconductor materials, and describes some of the properties of these structures.
Studies of Inositol Phospholipid-Specific Phospholipase C
Authors: Rhee Sue Goo , Suh Pann-Ghill , Ryu Sung-Ho , Lee Sang Yeol
Published: October 2006

Inositol phospholipid-specific phospholipase C is the enzyme that generates phosphoinositide-derived messenger molecules. Mammalian cells contain at least five immunologically distinct phospholipase C enzymes that appear to be separate gene products. Complete amino acid sequences of four of these isozymes have been established. The overall sequence similarity is surprisingly low for enzymes catalyzing the same chemical reaction: three of them show limited amino acid sequence similarity to each other in two narrow regions, and the fourth enzyme is completely different. The diversity in primary structure together with different regional and cellular expression of the isozymes suggests that each isozyme has a defined function in processing the physiological response of different cell types to a variety of external stimuli and that each is regulated differently.
In What Sense Is Turbulence an Unsolved Problem?
Authors: Nelkin Mark
Published: October 2006

Turbulence can be narrowly defined as a property of incompressible fluid flow at very high Reynolds number, and thus an attempt can be made to specify what is and what is not understood about it. The applicability of the Navier-Stokes equations of hydrodynamics to real turbulent flows and the successes and limitations of direct numerical simulation are considered. A discussion is presented of universality, and mention is made of the remarkable success of Kolmogorov's 1941 scaling ideas despite uncertainties about basic underlying assumptions such as local isotropy. Extensions of this scaling to the multifractal picture of dissipation fluctuations are discussed, but this picture remains phenomenological. Turbulence as defined above remains "unsolved" in the sense that a clear physical understanding of the observed phenomena does not exist.
Rectification of STM Current to Graphite Covered with Phthalocyanine Molecules
Authors: Pomerantz M. , Aviram A. , McCorkle R. A. , Li L. , Schrott A. G.
Published: October 2006

The scanning tunneling microscope (STM) can be used to measure current-voltage characteristics on an atomic scale. The attachment of copper phthalocyanine molecules, in contrast to a variety of other molecules, to graphite changes the electrical characteristics of the STM from relatively symmetric to highly asymmetric or rectifying. Evidence is presented to show that the asymmetry arises because of the electronic energy levels of the copper phthalocyanine. The organic molecules were bonded to the graphite by an acid-base reaction that may have wide applicability.
LIGO: The Laser Interferometer Gravitational-Wave Observatory
Authors: Abramovici Alex , Althouse William E. , Drever Ronald W. P. , Gürsel Yekta , Kawamura Seiji , Raab Frederick J. , Shoemaker David , Sievers Lisa , Spero Robert E. , Thorne Kip S. , Vogt Rochus E. , Weiss Rainer , Whitcomb Stanley E. , Zucker Michael E.
Published: October 2006

The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics of gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGO's gravitational-wave searches will begin in 1998.
Cnidocyte Mechanoreceptors Are Tuned to the Movements of Swimming Prey by Chemoreceptors
Authors: Watson Glen M. , Hessinger David A.
Published: October 2006

Cnidocytes, the stinging cells of cnidarians, discharge nematocysts in response to physical contact accompanied by the stimulation of specific chemoreceptors. Cnidocytes in fishing tentacles of a sea anemone are now found to discharge nematocysts preferentially into targets vibrating at 30, 55, and 65 to 75 hertz. Moreover, in the presence of submicromolar concentrations of known chemosensitizers, such as N-acetylated sugars and mucin, these optima shift to 5, 15, 30, and 40 hertz, frequencies that correspond to the movements of swimming prey. Hence, chemoreceptors for these substances tune cnidocyte mechanoreceptors to frequencies that match the movements of the prey.
Ulysses Radio and Plasma Wave Observations in the Jupiter Environment
Authors: Stone R. G. , Pedersen B. M. , Harvey C. C. , Canu P. , Cornilleau-Wehrlin N. , Desch M. D. , de Villedary C. , Fainberg J. , Farrell W. M. , Goetz K. , Hess R. A. , Hoang S. , Kaiser M. L. , Kellogg P. J. , Lecacheux A. , Lin N. , MacDowall R. J. , Manning R. , Meetre C. A. , Meyer-Vernet N. , Moncuquet M. , Osherovich V. , Reiner M. J. , Tekle A. , Thiessen J. , Zarka P.
Published: October 2006

The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of auroral-like hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the Io plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the Io torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.
Ulysses Radio Occultation Observations of the Io Plasma Torus During the Jupiter Encounter
Authors: Bird M. K. , Asmar S. W. , Brenkle J. P. , Edenhofer P. , Funke O. , Pätzold M. , Volland H.
Published: October 2006

Radio signals from Ulysses were used to probe the Io plasma torus (IPT) shortly after the spacecraft's closest approach to Jupiter. The frequencies of the two downlinks at S-band (2.3 gigahertz) and X-band (8.4 gigahertz) were recorded, differenced, and integrated in order to derive the columnar electron density of the IPT. The measurements agree qualitatively with contemporary models of the IPT based on Voyager data, but significant differences are apparent as well. The overall level of the IPT electron density is approximately the same as the prediction, implying that the amount of gas (or plasma) injected from Io is similar to that observed during the Voyager era. On the other hand, the IPT seems to be less extended out of the centrifugal equator, implying a smaller plasma temperature than predicted.
Quasars, Blazars, and Gamma Rays
Authors: Dermer Charles D. , Schlickeiser Reinhard
Published: October 2006

Before the launch of the Compton Gamma Ray Observatory (CGRO), the only source of >100-megaelectron volt (MeV) gamma radiation known outside our galaxy was the quasar 3C 273. After less than a year of observing, 13 other extragalactic sources have been discovered with the Energetic Gamma Ray Experiment Telescope (EGRET) on CGRO, and it is expected that many more will be found before the full sky survey is complete. All 14 sources show evidence of blazar properties at other wavelengths; these properties include high optical polarization, extreme optical variability, flat-spectrum radio emission associated with a compact core, and apparent superluminal motion. Such properties are thought to be produced by those few, rare extragalactic radio galaxies and quasars that are favorably aligned to permit us to look almost directly down a relativistically outflowing jet of matter expelled from a supermassive black hole. Although the origin of the gamma rays from radio jets is a subject of much controversy, the gamma-ray window probed by CGRO is providing a wealth of knowledge about the central engines of active galactic nuclei and the most energetic processes occurring in nature.
Sulfate Cooling Effect on Climate Through In-Cloud Oxidation of Anthropogenic SO
2
Authors: Lelieveld Jos , Heintzenberg Jost
Published: October 2006

Anthropogenic SO
2
emissions may exert a significant cooling effect on climate in the Northern Hemisphere through backscattering of solar radiation by sulfate particles. Earlier estimates of the sulfate climate forcing were based on a limited number of sulfate-scattering correlation measurements from which a high sulfate-scattering efficiency was derived. Model results suggest that cloud processing of air is the underlying mechanism. Aqueous phase oxidation of SO
2
into sulfate and the subsequent release of the dry aerosol by cloud evaporation render sulfate a much more efficient scatterer than through gas-phase SO
2
oxidation.
Room-Temperature, Electric Field-Induced Creation of Stable Devices in CulnSe
2
Crystals
Authors: Cahen David , Gilet Jean-Marc , Schmitz Claus , Chernyak Leonid , Gartsman Konstantin , Jakubowicz Abram
Published: October 2006

Multiple-junction structures were formed, on a microscopic scale, at room temperature, by the application of a strong electric field across originally homogeneous crystals of the ternary chalcopyrite semiconductor CuInSe
2
. After removal of the electric field, the structures were examined with electron beam-induced current microscopy and their current-voltage characteristics were measured. Bipolar transistor action was observed, indicating that sharp bulk junctions can form in this way at low ambient temperatures. The devices are stable under normal (low-voltage) operating conditions. Possible causes for this effect, including electromigration and electric field-assisted defect reactions, are suggested.