bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrate Losses from Disturbed Ecosystems
Authors: Vitousek Peter M. , Gosz James R. , Grier Charles C. , Melillo Jerry M. , Reiners William A. , Todd Robert L.
Published: October 2006

A systematic examination of nitrogen cycling in disturbed forest ecosystems demonstrates that eight processes, operating at three stages in the nitrogen cycle, could delay or prevent solution losses of nitrate from disturbed forests. An experimental and comparative study of nitrate losses from trenched plots in 19 forest sites throughout the United States suggests that four of these processes (nitrogen uptake by regrowing vegetation, nitrogen immobilization, lags in nitrification, and a lack of water for nitrate transport) are the most important in practice. The net effect of all of these processes except uptake by regrowing vegetation is insufficient to prevent or delay losses from relatively fertile sites, and hence such sites have the potential for very high nitrate losses following disturbance.
Atmospheric Burnup of the Cosmos-954 Reactor
Authors: Krey P. W. , Leifer R. , Benson W. K. , Dietz L. A. , Hendrikson H. C. , Coluzza J. L.
Published: October 2006

On 24 January 1978 the Russian satellite Cosmos-954 reentered the atmosphere over northern Canada. By use of high-altitude balloons, the atmosphere was sampled during 1978 up to an altitude of 39 kilometers to detect particulate debris from the reactor on board the satellite. Enriched uranium-bearing aerosols at concentrations and particle sizes compatible with partial burnup of the Cosmos-954 reactor were detected only in the high polar stratosphere.
Nitrous Oxide Emissions from an Irrigated Cornfield
Authors: Hutchinson G. L. , Mosier A. R.
Published: October 2006

During the 1978 growing season, nitrous oxide (N
2
O) emissions from a typical well-managed northern Colorado field of corn (
Zea mays
L.) totaled approximately 2.6 kilograms of nitrogen per hectare, or about 1.3 percent of the applied fertilizer nitrogen. Thirty percent of the loss occurred during the 3 weeks following fertilization while ammonia was being rapidly nitrified, and 59 percent was emitted during the week after the field's first irrigation, when restricted oxygen diffusion favored denitrification. Considering the large spatial and temporal variability of N
2
O emissions from soil, micrometeorological estimates of vertical N
2
O flux density compared favorably with estimates based on a simple soil cover method.
Nondestructive Evaluation
Authors: Kino Gordon S.
Published: October 2006

Nondestructive evaluation is a technique for determining the presence, type, and size of flaws in mechanical structures without destroying them. A description of various types of nondestructive evaluation methods is given in this article. Particular attention is paid to acoustic wave probing techniques. Major advances have been made in the development of the theory of acoustic wave scattering from flaws and in the development of methods for determining the nature of a flaw from the variation of the scattered acoustic wave amplitude with frequency and angle. Several new types of acoustic imaging methods have been developed; prime examples are the acoustic microscope and electronically focused and scanned acoustic wave imaging systems. New acoustic measurement techniques for determining the fields in materials and predicting their breaking stress are discussed, as is the development of new types of eddy current techniques and electromagnetic transducers.
Injuries from the Wichita Falls Tornado: Implications for Prevention
Authors: Glass Roger I. , Craven Robert B. , Bregman Dennis J. , Stoll Barbara J. , Horowitz Neil , Kerndt Peter , Winkle Joe
Published: October 2006

We examined the circumstances of death and injury among victims of the tornado that struck Wichita Falls, Texas, on 10 April 1979. We also assessed the protective measures taken by a representative sample of community residents who suffered no major injury in order to estimate the relative risk of injury to people directly in the tornado's path. Twenty-six (60 percent) of the 43 traumatic deaths and 30 (51 percent) of the 59 serious injuries occurred in people who, despite ample warning, went to their cars to drive out of the storm's path. These people had a risk of serious or fatal injury of 23 per 1000. People who remained indoors and in stationary homes were at relatively low risk (3 per 1000) if they took simple precautions; people in mobile homes were at greatest risk (85 per 1000). Current safety recommendations and housing codes for single family homes and mobile homes need to be amended to decrease the impact of future tornadoes on human health.
An Interface Phase Transition: Complete to Partial Wetting
Authors: Moldover M. R. , Cahn John W.
Published: October 2006

When two fluid phases are near a critical point, one of them will be excluded from contact with any third phase that happens to be present by a wetting film of the other critical phase. A simple and quite general strategy that may be used to induce a phase transition from complete wetting of the third phase to incomplete wetting is to add a new component to the fluid phases chosen to drive the two phases away from their critical point. This strategy is illustrated for methanol-cyclohexane mixtures.
Acute Effects of Alcohol on Auditory Brainstem Potentials in Humans
Authors: Squires Kenneth C. , Chu Nai-Shin , Starr Arnold
Published: October 2006

Auditory brainstem potentials were recorded from human subjects before and after an intoxicating dose of alcohol. Following alcohol ingestion there were significant, progressive increases in the latencies of brainstem potential peaks III through VII. No changes in peak amplitudes were found. The results indicate that alcohol has a depressive effect on neural transmission within the primary auditory brainstem pathway.
Science and Technology in the White House, 1977 to 1980: Part 1
Authors: Press Frank
Published: October 2006

This is the first half of a two-part article on science and technology policy in the Carter White House. Written from the perspective of the President's Office of Science and Technology Policy (OSTP), the article describes specific activities and accomplishments in the context of the overall policy framework and institutional structure within which the office operates. This part of the article addresses policy issues related to strengthening the U.S. science and technology enterprise, fostering industrial innovation, enhancing relationships among government, industry, and universities, and improving the regulatory process. Part 2 will focus on OSTP activities related to national security and foreign policy, space, energy and the environment, health, and agriculture, and will discuss OSTP advisory mechanisms and planning efforts.
Coral Snake Mimicry: Does It Occur?
Authors: Greene Harry W. , McDiarmid Roy W.
Published: October 2006

Field observations and experimental evidence refute previous objections to the coral snake mimicry hypothesis. Concordant color pattern variation spanning hundreds of miles and several presumed venomous models strongly suggests that several harmless or mildly venomous colubrid snakes are indeed mimics of highly venomous elapids.
Prehistoric Irrigation Systems in the Salt River Valley, Arizona
Authors: Masse W. Bruce
Published: October 2006

This article discusses prehistoric irrigation canals recently excavated near Phoenix, Arizona. The canals were constructed by the Hohokam Indians between A.D. 850 and 1450. Several aerial photographs taken at various times in the past five decades clearly show the paths of hundreds of the canals, including some of those recently excavated. These data provide new insights on Hohokam irrigation technology and society. Despite the destructive inroads of modern development, much significant archeological information can still be retrieved both by conventional excavation methods and by the archival study of aerial photographs.
Random Peptide Libraries: a Source of Specific Protein Binding Molecules
Authors: Devlin James J. , Panganiban Lucy C. , Devlin Patricia E.
Published: October 2006

Libraries of random peptide sequences were constructed and screened to identify peptides that specifically bind to proteins. In one of these about 2 × 10
7
different 15-residue peptide sequences were expressed on the surface of the coliphage M13. Each phage encoded a single random sequence and expressed it as a fusion complex with pIII, a minor coat protein present at five molecules per phage. Phage encoding nine different streptavidin-binding peptide sequences were isolated from this library. The core consensus sequence was His-Pro-Gln and binding of these phage to streptavidin was inhibited by biotin. This type of library makes it possible to identify peptides that bind to proteins (or other macromolecules) that have no previously known affinity for peptides.
Intraspecific Vertical Stratification as a Mate-Finding Mechanism in Tropical Cockroaches
Authors: Schal Coby
Published: October 2006

Cockroaches in a tropical forest stratify vertically both inter- and intraspecifically along micrometeorological gradients. At night, low wind speeds and unstable atmospheric conditions result in efficient vertical mixing of the air near the ground. Convective ascent of warm air imparts directionality to the pheromone- dispersion process. The occurrence of males at greater heights than pheromone- emitting conspecific females appears to be a mate-finding strategy.
Growth Rates of Phosphate Nodules from the Continental Margin Off Peru
Authors: Burnett William C. , Beers Michael J. , Roe Kevin K.
Published: October 2006

Modern sea-floor phosphorite nodules sampled from off the coast of Peru are shown to grow at rates of millimeters per thousand years in spite of the fact that the measured accumulation rates of the underlying sediment are two to four orders of magnitude faster. Phosphate nodules grow downward into soft sediment, and the rates of phosphorus accumulation into nodules are approximately equal to the upward diffusive flux of dissolved phosphate inferred from pore water profiles. These results demonstrate that phosphorus in nodules originates from regeneration in sediments rather than as a result of direct precipitation from bottom waters.
Subcellular Calcium Transients Visualized by Confocal Microscopy in a Voltage-Clamped Vertebrate Neuron
Authors: Hernández-Cruz Arturo , Sala Francisco , Adams Paul R.
Published: October 2006

Confocal laser-scanned microscopy and long-wavelength calcium (Ca
2+
) indicators were combined to monitor both sustained and rapidly dissipating Ca
2+
gradients in voltage-clamped sympathetic neurons isolated from the bullfrog. After a brief activation of voltage-dependent Ca
2+
channels, Ca
2+
spreads inwardly, and reaches the center of these spherical cells in about 300 milliseconds. Although the Ca
2+
redistribution in the bulk of the cytosol could be accounted for with a radial diffusion model, local nonlinearities, suggesting either nonuniform Ca
2+
entry or spatial buffering, could be seen. After electrical stimulation, Ca
2+
signals in the nucleus were consistently larger and decayed more slowly than those in the cytosol. A similar behavior was observed when release of intracellular Ca
2+
was induced by caffeine, suggesting that in both cases large responses originate from Ca
2+
release sites near or within the nucleus. These results are consistent with an amplification mechanism involving Ca
2+
-induced Ca
2+
release, which could be relevant to activity-dependent, Ca
2+
-regulated nuclear events.
Mercury Content of
Equisetum
Plants Around Mount St. Helens One Year After the Major Eruption
Authors: Siegel B. Z. , Siegel S. M.
Published: October 2006

The mercury content of young
Equisetum
plants collected around Mount St. Helens was higher in the direction of Yakima and Toppenish, Washington (northeast to east-northeast), than at any other compass heading and was about 20 times that measured around Portland, Oregon. The increase in substratum mercury was not as pronounced as that in plants but was also higher toward the northeast, the direction taken by the May 1980 volcanic plume.
Flight Interneurons in the Locust and the Origin of Insect Wings
Authors: Robertson R. M. , Pearson K. G. , Reichert H.
Published: October 2006

Interneurons involved in the generation of motor activity for flight in the locust were found in the first three abdominal ganglia as well as in thoracic ganglia. The evidence that sets of homologous flight interneurons occur in abdominal and thoracic ganglia supports theories that insect wings originated from movable appendages which were serially distributed along the thorax and abdomen and which were under central nervous control.
Entropy in an Expanding Universe
Authors: Frautschi Steven
Published: October 2006

The question of how the observed evolution of organized structures from initial chaos in the expanding universe can be reconciled with the laws of statistical mechanics is studied, with emphasis on effects of the expansion and gravity. Some major sources of entropy increase are listed. An expanding "causal" region is defined in which the entropy, though increasing, tends to fall further and further behind its maximum possible value, thus allowing for the development of order. The related questions of whether entropy will continue increasing without limit in the future, and whether such increase in the form of Hawking radiation or radiation from positronium might enable life to maintain itself permanently, are considered. Attempts to find a scheme for preserving life based on solid structures fail because events such as quantum tunneling recurrently disorganize matter on a very long but fixed time scale, whereas all energy sources slow down progressively in an expanding universe. However, there remains hope that other modes of life capable of maintaining themselves permanently can be found.
Coding Channels in the Taste System of the Rat
Authors: Scott Thomas R. , Giza Barbara K.
Published: October 2006

Basic taste qualities are thought to be perceived independently, yet discrete neural coding channels have not been demonstrated in the central nervous system. The response profiles of taste cells in the nucleus tractus solitarius (NTS) of the rat were categorized into four groups, and the effects of amiloride, a passive sodium channel blocker, on each were determined. NTS neurons that responded specifically to sodium chloride (NaCl) or to NaCl and sugars were suppressed by amiloride; those broadly sensitive to salts, acids, and bitter stimuli were unaffected. Moreover, the response profile evoked by NaCl lost its distinctiveness after treatment with amiloride, becoming similar to those evoked by acids and quinine. Receptors that respond to sodium must relay their information through independent coding channels to identifiable subgroups of NTS neurons, the activity of which is responsible for the perception of saltiness.
Dynamical Consequences of Orthohydrogen-Parahydrogen Disequilibrium on Jupiter and Saturn
Authors: Gierasch Peter J.
Published: October 2006

The Voyager observation of high zonal flow speeds (about 400 meters per second) in the atmosphere of Saturn has raised fundamental questions about the flow on both Jupiter and Saturn. One possibility is that the flow is extremely deep, perhaps extending through the planet. Another is that the flow is confined near the cloud tops and is associated with very strong buoyancy contrasts. It is demonstrated that the heat of conversion from parahydrogen to orthohydrogen can provide buoyancy contrasts of the required magnitude, and a feedback mechanism is proposed to couple the heat of conversion to the flow dynamics.
Induction of CD4
+
Human Cytolytic T Cells Specific for HIV-Infected Cells by a Gp160 Subunit Vaccine
Authors: Orentas Rimas J. , Hildreth James E. K. , Obah Eugene , Polydefkis Michael , Smith Gale E. , Clements Mary Lou , Siliciano Robert F.
Published: October 2006

Cytolytic T lymphocyte (CTL) responses were evaluated in humans immunized with recombinant human immunodeficiency virus type 1 (HIV) envelope glycoprotein gp160. Some vaccinees had gp160-specific CTLs that were shown by cloning to be CD4
+
. Although induced by exogenous antigen, most gp160-specific CTL clones also recognized gp160 synthesized endogenously in target cells. These clones lysed autologous CD4
+
T lymphoblasts infected with HIV. Of particular interest were certain vaccine-induced clones that lysed HIV-infected cells, recognized gp160 from diverse HIV isolates, and did not participate in "innocent bystander" killing of noninfected CD4
+
T cells that had bound gp120.
Sucrose: A Constitutive Elicitor of Phytoalexin Synthesis
Authors: Cooksey Christopher J. , Garratt Peter J. , Dahiya Jagroop S. , Strange Richard N.
Published: October 2006

Extracts of seeds and leaves of the tropical legume
Cajanus cajan
(L.) Millsp. (the pigeon pea) elicited the accumulation of three phytoalexins when applied as droplets to superficially wounded leaves of the plant. The active component was purified and identified as sucrose. Phytoalexin accumulation was proportional to the logarithm of the concentration of sucrose applied, with maxima ranging from 338 to 455 micrograms per gram (fresh weight) of leaf tissue. The sucrose concentrations required to elicit half these amounts ranged from 20 to 35 micrograms per milliliter, but other sugars had little effect even at 1000 micrograms per milliliter. The elicitor activity of sucrose was abolished by actinomycin D, puromycin, and cycloheximide at a concentration of 10 micrograms per milliliter or greater, suggesting that gene derepression is required for expression of the phytoalexin response.
"Frozen" Transition States: Pentavalent Carbon
et al.
Authors: Martin J. C.
Published: October 2006

Organic ligands have been designed for the stabilization of specific geometries of compounds of nonmetallic elements. These ligands have made possible the isolation, or direct observation, of large numbers of trigonal bipyramidal organo-nonmetallic species. Many of these species are analogs of transition states for nucleophilic displacement reactions and have been stabilized by the ligands to such a degree that they have become ground-state energy minima. Ideas derived from research on these species have been applied to carbon species to generate a molecule that is an analog of the transition state for the associative nucleophilic displacement reaction. The molecule is a pentavalent carbon species that has been observed by nuclear magnetic resonance spectroscopy.
Predicting Eruptions at Mount St. Helens, June 1980 Through December 1982
Authors: Swanson D. A. , Casadevall T. J. , Dzurisin D. , Malone S. D. , Newhall C. G. , Weaver C. S.
Published: October 2006

Thirteen eruptions of Mount St. Helens between June 1980 and December 1982 were predicted tens of minutes to, more generally, a few hours in advance. The last seven of these eruptions, starting with that of mid-April 1981, were predicted between 3 days and 3 weeks in advance. Precursory seismicity, deformation of the crater floor and the lava dome, and, to a lesser extent, gas emissions provided telltale evidence of forthcoming eruptions. The newly developed capability for prediction reduced risk to life and property and influenced land-use decisions.
Fossils of Hydrothermal Vent Worms from Cretaceous Sulfide Ores of the Samail Ophiolite, Oman
Authors: Haymon Rachel M. , Koski Randolph A. , Sinclair Colin
Published: October 2006

Fossil worm tubes of Cretaceous age preserved in the Bayda massive sulfide deposit of the Samail ophiolite, Oman, are apparently the first documented examples of fossils embedded in massive sulfide deposits from the geologic record. The geologic setting of the Bayda deposit and the distinctive mineralogic and textural features of the fossiliferous samples suggest that the Bayda sulfide deposit and fossil fauna are remnants of a Cretaceous sea-floor hydrothermal vent similar to modern hot springs on the East Pacific Rise and the Juan de Fuca Ridge.
Analysis of Junctional Diversity During B Lymphocyte Development
Authors: Meek Katheryn
Published: October 2006

Immunoglobulin rearrangement is central to generating antibody diversity because of heterogeneity generated during recombination by deletion or addition of nucleotides at coding joints by the recombinase machinery. Examination of these junctional modifications revealed that the addition of nongermline-encoded nucleotides was more prevalent in adult versus fetal B cells, thus partially limiting the fetal antibody repertoire. In contrast, deletion of nucleotides occurs equivalently in B cells at different stages of development and at different points in B cell ontogeny. Finally, the bias in murine immunoglobulins for one D
H
segment reading frame occurs at the D
H
J
H
intermediate.
Energy Scaling in Marsupials and Eutherians
Authors: Hinds David S. , MacMillen Richard E.
Published: October 2006

Marsupials have been shown to have basal metabolic rates below those of eutherian mammals. Now metabolic rates below thermoneutrality are found to be equivalent in both taxa. Two models are proposed to explain the observed metabolic patterns: in one, marsupials differ only in having reduced basal metabolic rates; in the other, the reduced marsupial basal metabolic rates combined with a reduced body temperature and elevated conductance. The metabolic costs of existence below thermoneutrality appear to be similar for both taxa. The difference in basal metabolic rate may be of energetic significance or merely a phylogenetic coincidence.
Far Red Bioluminescence from Two Deep-Sea Fishes
Authors: Widder Edith A. , Latz Michael I. , Herring Peter J. , Case James F.
Published: October 2006

Spectral measurements of red bioluminescence were obtained from the deep-sea stomiatoid fishes
Aristostomias scintillans
(Gilbert) and
Malacosteus niger
(Ayres). Red luminescence from suborbital light organs extends to the near infrared, with peak emission at approximately 705 nanometers in the far red. These fishes also have postorbital light organs that emit blue luminescence with maxima between 470 and 480 nanometers. The red bioluminescence may be due to an energy transfer system and wavelength-selective filtering.
The Enzymic Nature of Antibody Catalysis: Development of Multistep Kinetic Processing
Authors: Benkovic Stephen J. , Adams Joseph A. , Borders C. L. , Janda Kim D. , Lerner Richard A.
Published: October 2006

Detailed kinetic investigations of a catalytic antibody that promotes the hydrolyses of an anilide and phenyl ester show that this catalyst uses a multistep kinetic sequence resembling that found in serine proteases to hydrolyze its substrates, although antibody was elicited to a single transition-state analog. Like the serine proteases the antibody catalyzes the hydrolysis reactions through a putative covalent intermediate, but unlike the enzymes it may use hydroxide ion to cleave the intermediates. Nevertheless, the antibody is a potent catalyst with turnover at higher pH values rivaling that of chymotrypsin. This analysis also reveals that turnover by the antibody is ultimately limited by product desorption, suggesting that improvements in catalytic efficiency may be achieved by judicious changes in the structure of the substrate, so that it is not superimposable on that of the eliciting hapten.
Prophenoloxidase Activation: Nonself Recognition and Cell Cooperation in Insect Immunity
Authors: Ratcliffe Norman A. , Leonard Catherine , Rowley Andrew F.
Published: October 2006

The mechanism of nonself recognition by the immune system of insects is unknown. In this report the activation of the prophenoloxidase system in the wax moth
Galleria mellonella
by a microbial product is shown to enhance the recognition of nonself material. These results explain previous observations of the interaction of two different blood cell populations in the cellular defense reactions of insects.
Pavoninins: Shark-Repelling Ichthyotoxins from the Defense Secretion of the Pacific Sole
Authors: Tachibana Kazuo , Sakaitani Masahiro , Nakanishi Koji
Published: October 2006

A series of ichthyotoxic and hemolytic steroid aminoglycosides, pavoninins-1 to -6, has been isolated from the defense secretion of the sole
Pardachirus pavoninus
, and their respective chemical structures have been established by spectroscopic studies and chemical conversions. The pavoninins exert repellent activity against sharks and are considered to be the factors responsible for the predator-repelling property of the sole.
Volume and Heat Transports of the Florida Current: April 1982 Through August 1983
Authors: Molinari Robert L. , Wilson William D. , Leaman Kevin
Published: October 2006

Absolute velocity and temperature profiles are used to estimate the volume transport through the Straits of Florida and, in combination with historical midbasin data, to estimate the total meridional heat flux through a section at 27°N. The mean annual volume transport of the Florida Current from April 1982 through August 1983 is 30.5 (± 1) × 10
6
cubic meters per second. The net northward heat flux through the 27°N section is 1.2 (± 0.1) × 10
15
watts. The volume transport is characterized by high values in the late spring and early summer and low values in the late fall and early winter. There is a similar cycle in total heat flux.
Individual and Population Shifts in Flower Color by Scarlet Gilia: A Mechanism for Pollinator Tracking
Authors: Paige Ken N. , Whitham Thomas G.
Published: October 2006

Individual plants and populations of scarlet gilia (
Ipomopsis aggregate
) shift from darker to lighter corolla colors during the flowering season. Shifts to lighter color coincide with emigration of hummingbirds from the system. In the absence of hummingbirds, lighter colors attract the remaining pollinator, a hawkmoth. Comparison of plants that shift to lighter colors with those that fail to shift shows that shifting is adaptive in that it enhances reproductive success because of the preference of hawkmoths for lighter colored flowers. Color shifting therefore provides a mechanism for plants to track changing pollinator abundances.
Role of Chemotaxis in Establishing a Specific Nitrogen-Fixing Cyanobacterial-Bacterial Association
Authors: Paerl Hans W. , Gallucci Kathleen K.
Published: October 2006

A specific association with the cyanobacterium
Anabaena oscillarioides
was established by positive bacterial (pseudomonad) chemotaxis to
Anabaena oscillarioides
heterocysts. This association enhanced nitrogen fixation in
A. oscillarioides
, and positive chemotaxis was particularly strong during periods of active nitrogen fixation. Addition of compounds known to elicit positive chemotaxis in pseudomonads interfered with the establishment of the association, while removal of these compounds led to reestablishment of the association.
Anabaena oscillarioides
excretion products, some of which are exuded from heterocyst-vegetative cell junctions, are likely to be responsible for positive chemotactic responses. Chemotaxis-controlled associations such as this one explain in part why aquatic bacterial-algal and bacterial-particle associations occur sporadically and are heterogeneously distributed in time and space.
Geologic Youth of Galápagos Islands Confirmed by Marine Stratigraphy and Paleontology
Authors: Hickman Carole S. , Lipps Jere H.
Published: October 2006

Six distinctive types of fossiliferous marine deposits occur on the Galápagos Islands that provide evidence for the age of emergence of the islands above sea level and hence a maximum age for the islands' terrestrial biota. These subtidal to supratidal deposits include (i) volcanic tuffs with fossils, (ii) limestones and sandstones interbedded with basalt, (iii) terrace deposits, (iv) beach rock, (v) supratidal talus deposits, and (vi) recently uplifted tidal and subtidal rocks and sand. With the exception of (vi), the deposits were previously assigned ages varying from Miocene to Pleistocene, but all are less than about 2 million years old. This age, together with independently determined geologic ages, indicate that the islands emerged from the sea relatively recently and that all evolution of the islands' unique terrestrial biota occurred within the past 3 to 4 million years.
Intrathecal Capsaicin Depletes Substance P in the Rat Spinal Cord and Produces Prolonged Thermal Analgesia
Authors: Yaksh Tony L. , Farb David H. , Leeman Susan E. , Jessell Thomas M.
Published: October 2006

A single intrathecal injection of capsaicin depletes substance P from primary sensory neurons and causes a prolonged increase in the thermal and chemical pain thresholds of the rat but no apparent change in responses to noxious mechanical stimuli.
Opportunities in Magnetic Materials
Authors: White R. M.
Published: October 2006

Recent discoveries of new magnetic materials may greatly improve the performance of devices containing such materials and may lead to entirely new applications. For example, boron-based temary compounds for permanent magnets make new compact motor designs practical; amorphous transformer materials show greatly reduced losses at high frequencies; and thin magnetic alloy films offer increased data storage densities. The major technical issues associated with the new magnetic materials are identified.
The Crystallization of Ultralong Normal Paraffins: The Onset of Chain Folding
Authors: Ungar G. , Stejny J. , Keller A. , Bidd I. , Whiting M. C.
Published: October 2006

The nature of chain folding in polymers and the determination of the chain length at which folding occurs have been central questions in polymer science. The study of the formation of lamellar polymer crystals through chain folding has received a new impetus as a result of the recent synthesis of normal alkanes of strictly uniform chain lengths up to C
390
H
782
. Chain folding is found in all such paraffins starting with C
150
H
302
. As with polyethylenes obtained by conventional polymerization, the fold length in the normal alkanes varies with crystallization temperature, but it is always an integral reciprocal of the full chain length. This behavior indicates that the methyl end groups are located at the lamellar surface and that the fold itself must be sharp and adjacently reentrant.
A Cellular Automaton Model of Excitable Media Including Curvature and Dispersion
Authors: Gerhardt Martin , Schuster Heike , Tyson John J.
Published: October 2006

Excitable media are spatially distributed systems characterized by their ability to propagate signals undamped over long distances. Wave propagation in excitable media has been modeled extensively both by continuous partial differential equations and by discrete cellular automata. Cellular automata are desirable because of their intuitive appeal and efficient digital implementation, but until now they have not served as reliable models because they have lacked two essential properties of excitable media. First, traveling waves show dispersion, that is, the speed of wave propagation into a recovering region depends on the time elapsed since the preceding wave passed through that region. Second, wave speed depends on wave front curvature: curved waves travel with normal velocities noticeably different from the plane-wave velocity. These deficiencies of cellular automaton models are remedied by revising the classical rules of the excitation and recovery processes. The revised model shows curvature and dispersion effects comparable to those of continuous models, it predicts rotating spiral wave solutions in quantitative accord with the theory of continuous excitable media, and it is parameterized so that the spatial step size of the automaton can be adjusted for finer resolution of traveling waves.
Neuronal Circuits: An Evolutionary Perspective
Authors: Dumont James P. C. , Robertson R. Meldrum
Published: October 2006

To understand neural circuits completely, it is necessary to know not only how they work, but also why they work that way. Answers to the latter question have been almost teleological in their assumption of optimal design. However, close examination of certain systems has revealed features that apparently lack adaptive value. Their existence can be understood only if the evolution of these circuits is considered and, in particular, how nonadaptive determinants have guided that evolution.
Interannual Variability of Global Dust Storms on Mars
Authors: Haberle Robert M.
Published: October 2006

Global dust storms on Mars occur in some years but not in others. If the four Mars years of Viking data are representative, some distinguishing characteristics can be inferred. In years with global dust storms, dust is raised in the southern hemisphere and spread over much of the planet by an intensified Hadley circulation. In years without global dust storms, dust is raised in the northern hemisphere by relatively active mid-latitude storm systems but does not spread globally. In both cases the dusty season is winter in the north. Assuming that the cross-equatorial Hadley circulation plays a key role in the onset of global dust storms, it is shown from numerical simulations that a northern hemisphere dust haze weakens its intensity and, hence, its contribution to the surface stress in the southern hemisphere. This, in turn, reduces the possibility of global dust storm development. The interannual variability is therefore the result either of a competition between circulations in opposite hemispheres, in which case the variability has a random component, or it is the result of the cycling of dust between hemispheres, in which case the variability is related to the characteristics of global dust storms themselves.
Human CD4 Binds Immunoglobulins
Authors: Lenert Petar , Kroon Daniel , Spiegelberg Hans , Golub Edward S. , Zanetti Maurizio
Published: October 2006

T cell glycoprotein CD4 binds to class II major histocompatibility molecules and to the human immunodeficiency virus (HIV) envelope protein gp120. Recombinant CD4 (rCD4) bound to polyclonal immunoglobulin (Ig) and 39 of 50 (78%) human myeloma proteins. This binding depended on the Fab and not the Fc portion of Ig and was independent of the light chain. Soluble rCD4, HIV gp120, and sulfated dextrans inhibited the CD4-Ig interaction. With the use of a panel of synthetic peptides, the region critical for binding to Ig was localized to amino acids 21 to 38 of the first extracellular domain of CD4. CD4-bound antibody (Ab) complexed with antigen approximately 100 times better than Ab alone. This activity may contribute to the Ab-mediated enhancement of cellular HIV interaction that appears to depend on a trimolecular complex of HIV, antibodies to gp120, and CD4.
Fossil Mycorrhizae: A Case for Symbiosis
Authors: Stubblefield Sara P. , Taylor T. N. , Trappe James M.
Published: October 2006

Vesicular-arbuscular mycorrhizae are significant in the physiology and ecology of extant vascular plants, and they may also have played a major role in the origin of the vascular land flora. The case for fossil vesicular-arbuscular mycorrhizae rests upon hyphae and chlamydospore-like bodies in several Paleozoic taxa, but fossil arbuscles are unknown to date. Specimens from the Triassic of Antarctica represent the first known occurrence of arbuscles in the fossil record.
Organic Matter on Asteroid 130 Elektra
Authors: Cruikshank D. P. , Brown R. H.
Published: October 2006

Infrared absorption spectra of a low-albedo water-rich asteroid appear to show a weak 3.4-micrometer carbon-hydrogen stretching mode band, which suggests the presence of hydrocarbons on asteroid 130 Elektra. The organic extract from the primitive carbonaceous chondritic Murchison meteorite shows similar spectral bands.
Conserved Sequence and Structural Elements in the HIV-1 Principal Neutralizing Determinant
Authors: LaRosa Gregory J. , Davide Joseph P. , Weinhold Kent , Waterbury Julie A. , Profy Albert T. , Lewis John A. , Langlois Alphonse J. , Dreesman Gordon R. , Boswell R. Neal , Shadduck Phillip , Holley L. Howard , Karplus Martin , Bolognesi Dani P. , Matthews Thomas J. , Emini Emilio A. , Putney Scott D.
Published: October 2006

The principal neutralizing determinant (PND) of human immunodeficiency virus HIV-1 is part of a disulfide bridged loop in the third variable region of the external envelope protein, gp120. Analysis of the amino acid sequences of this domain from 245 different HIV-1 isolates revealed that the PND is less variable than thought originally. Conservation to better than 80 percent of the amino acids in 9 out of 14 positions in the central portion of the PND and the occurrence of particular oligopeptide sequences in a majority of the isolates suggest that there are constraints on PND variability. One constraining influence may be the structural motif (β strand—type II β turn—β strand—α helix) predicted for the consensus PND sequence by a neural network approach. Isolates with a PND similar to the commonly investigated human T cell lymphoma virus III
B
(HTLV-III
B
) and LAV-1 (BRU) strains were rare, and only 14 percent of sera from 86 randomly selected HIV-1 seropositive donors contained antibodies that recognized the PND of these virus isolates. In contrast, over 65 percent of these sera reacted with peptides containing more common PND sequences. These results suggest that HIV vaccine immunogens chosen because of their similarity to the consensus PND sequence and structure are likely to induce antibodies that neutralize a majority of HIV-1 isolates.
Role of the Gastropod Shell and Operculum in Inhibiting Predation by Fishes
Authors: Norton Stephen F.
Published: October 2006

In contrast to the diets of other cottid fishes and most teleosts, the diet of
Asemichthys taylori
is dominated by gastropod mollusks. Access to this underused prey appears to be made possible by morphological specializations of the neurocranium that allow
Asemichthys
to puncture the shells of its prey during mastication. Unpunched, the shell and operculum act as a barrier to digestion; more than 40% of the unpunched gastropods emerged alive in the feces.
Asemichthys
adjusted its punching behavior in an apparently adaptive way; other prey lacking such barriers to digestion were rarely punched. The ability of some shelled invertebrates to avoid digestion may make them less desirable as prey for many fishes that cannot masticate this kind of prey. The ability of shelled mollusks to survive in the digestive tracts of vertebrates may provide a dispersal mechanism for otherwise sedentary species.
Observations of the Nighttime Abundance of OClO in the Winter Stratosphere Above Thule, Greenland
Authors: Solomon S. , Mount G. H. , Sanders R. W. , Jakoubek R. O. , Schmeltekopf A. L.
Published: October 2006

Observations at Thule, Greenland, that made use of direct light from the moon on 2,3, 4,5, and 7 February 1988 revealed nighttime chlorine dioxide (OClO) abundances that were less than those obtained in Antarctica by about a factor of 5, but that exceeded model predictions based on homogeneous (gas-phase) photochemistry by about a factor of 10. The observed time scale for the formation of OClO after sunset strongly supports the current understanding of the diurnal chemistry of OClO. These data suggest that heterogeneous (surface) reactions due to polar stratospheric clouds can occur in the Arctic, providing a mechanism for possible Arctic ozone depletion.
Xenopus
Oocytes Injected with Rat Uterine RNA Express Very Slowly Activating Potassium Currents
Authors: Boyle M. B. , Azhderian E. M. , MacLusky N. J. , Naftolin F. , Kaczmarek L. K.
Published: October 2006

Under the influence of estrogen, uterine smooth muscle becomes highly excitable, generating spontaneous and prolonged bursts of action potentials. In a study of the mechanisms by which this transition in excitability occurs, polyadenylated RNA from the uteri of estrogen-treated rats was injected into
Xenopus
oocytes. The injected oocytes expressed a novel voltage-dependent potassium current. This current was not observed in oocytes injected with RNA from several other excitable tissues, including rat brain and uterine smooth muscle from ovariectomized rats not treated with estrogen. The activation of this current on depolarization was exceptionally slow, particularly for depolarizations from relatively negative membrane potentials. Such a slowly activating channel may play an important role in the slow, repetitive bursts of action potentials in the myometrium.
A Chicken Transferrin Gene in Transgenic Mice Escapes X-Chromosome Inactivation
Authors: Goldman Michael A. , Stokes Karen R. , Idzerda Rejean L. , McKnight G. Stanley , Hammer Robert E. , Brinster Ralph L. , Gartler Stanley M.
Published: October 2006

Mammalian X-chromosome inactivation involves a coordinate shutting down of physically linked genes. Several proposed models require the presence of specific sequences near genes to permit the spread of inactivation into these regions. If such models are correct, one might predict that heterologous genes transferred onto the X chromosome might lack the appropriate signal sequences and therefore escape inactivation. To determine whether a foreign gene inserted into the X chromosome is subject to inactivation, transgenic mice harboring 11 copies of the complete, 17-kilobase chicken transferrin gene on the X chromosome were used. Male mice hemizygous for this insert were bred with females bearing Searle's translocation, an X-chromosome rearrangement that is always active in heterozygous females (the unrearranged X chromosome is inactive). Female offspring bearing the Searle's translocation and the chicken transferrin gene had the same amount of chicken transferrin messenger RNA in liver as did transgenic male mice or transgenic female mice lacking the Searle's chromosome. This result shows that the inserted gene is not subject to X-chromosome inactivation and suggests that the inactivation process cannot spread over 187 kilobases of DNA in the absence of specific signal sequences required for inactivation.
Identification of a Neuropeptide Hormone That Regulates Sex Pheromone Production in Female Moths
Authors: Raina A. K. , Jaffe H. , Kempe T. G. , Keim P. , Blacher R. W. , Fales H. M. , Riley C. T. , Klun J. A. , Ridgway R. L. , Hayes D. K.
Published: October 2006

A pheromone biosynthesis activating neuropeptide (PBAN) hormone that controls sex pheromone production in female moths was identified from the brain-subesophageal ganglion complexes of the adult corn earworm,
Heliothis zea.
PBAN has 33 amino acid residues and a molecular weight of 3900. Its amino acid sequence has no significant homology with any of the fully characterized peptide hormones. The synthetic peptide, at a dose of between 2 and 4 picomoles, induced production of a normal quantity of sex pheromone in ligated
H. zea
females. The peptide also induced pheromone production in six other species of moths, thus indicating that this or similar peptides may be responsible for the regulation of pheromone production in moths.
In Situ Transcription: Specific Synthesis of Complementary DNA in Fixed Tissue Sections
Authors: Tecott Laurence H. , Barchas Jack D. , Eberwine James H.
Published: October 2006

A technique, in situ transcription, is described, in which reverse transcription of mRNAs is achieved within fixed tissue sections. An oligonucleotide complementary to proopiomelanocortin (POMC) mRNA was used as a primer for the specific synthesis of radiolabeled POMC cDNA in fixed sections of rat pituitary, thus permitting the rapid anatomical localization of POMC mRNA by autoradiography. Intermediate lobe signal intensities were sensitive to dopaminergic drugs, demonstrating that the method can be used for studies of mRNA regulation. The transcripts may also be eluted from tissue sections for a variety of uses, including the identification and cloning of autoradiographically localized cDNAs from small amounts of tissue.
Direct Observation of Structural Defects in Laser-Deposited Superconducting Y-Ba-Cu-O Thin Films
Authors: Ramesh R. , Hwang D. M. , Venkatesan T. , Ravi T. S. , Nazar L. , Inam A. , Wu X. D. , Dutta B. , Thomas G. , Marshall A. F. , Geballe T. H.
Published: October 2006

The defect structure of in situ pulsed, laser-deposited, thin films of the high—transition temperature superconductor Y-Ba-Cu-O has been observed directly by atomic resolution electron microscopy. In a thin film with the nominal composition YBa
2
Cu
3
O
7
(123), stacking defects corresponding to the cationic stoichiometry of the 248, 247, and 224 compounds have been observed. Other defects observed include edge dislocations and antiphase boundaries. These defects, which are related to the nonequilibrium processing conditions, are likely to be responsible for the higher critical currents observed in these films as compared to single crystals.
Fluid Dynamics in Suspension-Feeding Blackfish
Authors: Sanderson S. Laurie , Cech Joseph J. , Patterson Mark R.
Published: October 2006

Measurements of flow patterns and water velocities inside the oral cavity of blackfish (
Orthodon microlepidotus
), made with a fiberoptic endoscope and thermistor flow probe, revealed that gill-arch structures act in blackfish as barriers that direct particle-laden water to the mucus-covered roof of the oral cavity, where particles are retained. Gill-arch structures have previously been assumed to be the site of particle retention in suspension-feeding fishes. Water does not pass between these structures in blackfish, and they do not serve as filters that separate particles from the water. These results emphasize the importance of directly assessing flow velocity and direction inside the oral cavity of vertebrate suspension feeders, particularly at the level of the filtering elements.
Energetics of Caterpillar Locomotion: Biomechanical Constraints of a Hydraulic Skeleton
Authors: Casey Timothy M.
Published: October 2006

Power input increased linearly with speed and was closely associated with changes in cycle frequency. Minimum cost of transport of gypsy moth caterpillars was 4.5 times as high as predicted for vertebrates and arthropods with jointed framework skeletons. Reduced locomotor economy was associated with stride length only one-third or less than that for animals with solid skeletons.
Thermal Maps of Jupiter: Spatial Organization and Time Dependence of Stratospheric Temperatures, 1980 to 1990
Authors: Orton Glenn S. , Friedson A. James , Baines Kevin H. , Martin Terry Z. , West Robert A. , Caldwell John , Hammel Heidi B. , Bergstralh Jay T. , Malcom Michael E. , Golisch William F. , Griep David M. , Kaminski Charles D. , Tokunaga Alan T. , Baron Richard , Shure Mark
Published: October 2006

The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH
4
band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and mid-latitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm mid-latitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than ∼30,000 kilometers. The amplitudes of the waves vary on a time scale of ∼1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than ±30 meters per second.
40
Ar/
39
Ar Age of the Lathrop Wells Volcanic Center, Yucca Mountain, Nevada
Authors: Turrin Brent D. , Champion Duane , Fleck Robert J.
Published: October 2006

Paleomagnetic and
40
Ar/
39
Ar analyses from the Lathrop Wells volcanic center, Nevada, indicate that two eruptive events have occurred there. The ages (136 ± 8 and 141 ± 9 thousand years ago) for these two events are analytically indistinguishable. The small angular difference (4.7°) between the paleomagnetic directions from these two events suggests they differ in age by only about 100 years. These ages are consistent with the chronology of the surficial geological units in the Yucca Mountain area. These results contradict earlier interpretations of the cinder-cone geomorphology and soil-profile data that suggest that at least five temporally discrete eruptive events occurred at Lathrop Wells approximately 20,000 years ago.