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PubMed2005

Extreme winds and waves in the aftermath of a Neoproterozoic glaciation.

The most severe excursions in the Earth's climatic history are thought to be associated with Proterozoic glaciations. According to the 'Snowball Earth' hypothesis, the Marinoan glaciation, which ended about 635 million years ago, involved global or nearly global ice cover. At the termination of this glacial period, rapid melting of continental ice sheets must have caused a large rise in sea level. Here we show that sediments deposited during this sea level rise contain remarkable structures that we interpret as giant wave ripples. These structures occur at homologous stratigraphic levels in Australia, Brazil, Canada, Namibia and Svalbard. Our hydrodynamic analysis of these structures suggests maximum wave periods of 21 to 30 seconds, significantly longer than those typical for today's oceans. The reconstructed wave conditions could only have been generated under sustained high wind velocities exceeding 20 metres per second in fetch-unlimited ocean basins. We propose that these extraordinary wind and wave conditions were characteristic of the climatic transit, and provide observational targets for atmospheric circulation models.

Journal Article↗
PubMed2006

Isotopic enhancements of 17O and 18O from solar wind particles in the lunar regolith.

Differences in isotopic abundances between meteorites and rocks on Earth leave unclear the true composition of the gas out of which the Solar System formed. The Sun should have preserved in its outer layers the original composition, and recent work has indicated that the solar wind is enriched in 16O, relative to Earth, Mars and bulk meteorites. This suggests that self-shielding of CO due to photo-dissociation, which is a well understood process in molecular clouds, also led to evolution in the isotopic abundances in the early Solar System. Here we report measurements of oxygen isotopic abundances in lunar grains that were recently exposed to the solar wind. We find that 16O is underabundant, opposite to an earlier finding based on studies of ancient metal grains. Our result, however, is more difficult to understand within the context of current models, because there is no clear way to make 16O more abundant in Solar System rocks than in the Sun.

Journal Article↗
PubMed2002

NCX-701 (nitroparacetamol) is an effective antinociceptive agent in rat withdrawal reflexes and wind-up.

1. Non-steroidal anti-inflammatory drugs (NSAIDs) are effective anti-inflammatory and analgesic drugs although they also induce unwanted side effects due to the inhibition of the physiological effects regulated by prostaglandins. This has led to the search for new compounds with fewer side effects, such as the nitro-NSAIDs (NO-NSAIDs). Paracetamol is an analgesic drug devoid of some of the side effect of the NSAIDs but without anti-inflammatory activity. NCX-701 is a nitric oxide releasing version of paracetamol with anti-inflammatory and analgesic properties. 2. We have tested, in the single motor unit technique, the antinociceptive actions of intravenous cumulative doses of NCX-701 vs paracetamol, studying their antinociceptive effects in responses to noxious mechanical and electrical stimulation (wind-up). 3. Paracetamol did not induce any significant effect at the doses tested (maximum of 480 micromol kg(-1), 72.5 mg kg(-1)). NCX-701 however was very effective in reducing responses to noxious mechanical stimulation (32+/-10% of control response) and wind-up (ED(50) of 147+/-1 micromol kg(-1), 41.5+/-0.3 mg kg(-1)). The inhibition was not reversed by 1 mg kg(-1) of the opioid antagonist naloxone. In control experiments performed with either the vehicle or the NO donor NOC-18, no significant changes were observed in the nociceptive responses studied. 4. We conclude that NCX-701 is a very effective non-opioid antinociceptive agent in normal animals and its action is located mainly at central areas. The antinociceptive effect was not due solely to the release of NO.

Acetaminophen↗
PubMed1994

Successes and failures of shallow-water interpretations of Voyager wind data.

Studying the dynamics of Jupiter's atmosphere is a rewarding experience, in part because the planet's cloud-top circulations are easy to track from space, the jet streams flow in straight lines eastward or westward, and there is enough room for the vortices to usually keep out of each other's way. Earth, in contrast, is a planet with global circulations that are not easy to track from space, with jet streams that make wide, fluctuating arcs as they negotiate mountain ranges, and with vortices that are constantly jostling against each other in a cramped environment. But we know a great deal more about the vertical structure of Earth's atmosphere than of Jupiter's. In order to make headway on the Jovian problem, researchers have turned to the shallow-water model as a guide to interpreting the Voyager wind data. The shallow-water model matches the character of the data because it combines high-resolution horizontal dynamics with low-resolution vertical structure, but there is no guarantee that it captures the character of Jupiter's atmosphere itself. Remarkably, the model does well at reproducing the Great Red Spot, and it has revealed that Jupiter is clever about how it manages its vorticity by arranging its zonal winds to be neutrally stable with respect to Arnol'd's second stability theorem. We discuss reasons why the shallow-water model works for Jupiter and point out the limitations that are motivating researchers to develop more realistic models.

Journal Article↗
PubMed1969

Wind directions aloft and effects of seeding on precipitation in the whitetop experiment.

The subdivision of all the experimental days of the Whitetop project into two approximately equal groups, group W with predominantly westerly winds aloft and group E with frequent easterly winds, shows a remarkable difference in the apparent effect of seeding. On W days there was no detectable effect of seeding on rainfall. On E days with seeding, the average 24 hour precipitation in an area of about 100,000 square miles was significantly less than that without seeding by 46 per cent of the latter. The decrease resulted from a "decapitation" of the usual afternoon rise in rainfall. It may be significant that the afternoon maximum of natural precipitation on E days occurs some two hours later than on W days. If the actual cause of the differences in rainfall was seeding, then the loss of water resulting from operational, rather than experimental, seeding would have averaged eight million acre-feet per summer.

Journal Article↗
PubMed1982

Simulated and empiric wind pollination patterns of conifer ovulate cones.

Wind tunnel analyses of conifer ovulate cones indicate that the total geometry of the cone enhances the probability of pollen entrapment. Aerodynamic characteristics of cone scale-bract complexes are such that suspended pollen is directed toward the micropyles of attached ovules. Within the taxa examined, there appears to be a preferential entrapment by ovulate cones of pollen of the same species. The data are interpreted as evidence for an aerodynamic reciprocity between wind-suspended pollen and the structure of ovulate cones which increases the frequency of pollination and the potential for fertilization.

Journal Article↗
PubMed1999

Bipolar Molecular Outflows Driven by Hydromagnetic Protostellar Winds.

We demonstrate that magnetically collimated protostellar winds will sweep ambient material into thin, radiative, momentum-conserving shells whose features reproduce those commonly observed in bipolar molecular outflows. We find that the typical position-velocity and mass-velocity relations occur in outflows in a wide variety of ambient density distributions, regardless of the time histories of their driving winds.

Journal Article↗
PubMed2000

Identification of the Coronal Sources of the Fast Solar Wind.

The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on 1996 April 6-9 with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory spacecraft, identifies the interplume lanes and background coronal hole regions as the channels in which the fast solar wind is preferentially accelerated. In interplume lanes, at heliocentric distance 1.7 R middle dot in circle, the corona expands at a rate between 105 and 150 km s-1, that is, much faster than in plumes in which the outflow velocity is between 0 and 65 km s-1. The wind velocity is inferred from the Doppler dimming of the O vi lambdalambda1032, 1037 lines, within a range of values, whose lower and upper limit corresponds to anisotropic and isotropic velocity distribution of the oxygen coronal ions, respectively.

Journal Article↗
PubMed1986

The second wind phenomenon in McArdle's disease.

Three patients with McArdle's disease exercised for 2 h at 30% VO2max. During exercise two phases occurred. During the first 15 min they experienced progressive fatigue and weakness of exercised muscles, with a rapid and complete recovery (adaptation phase). Following this, all 3 patients were able to continue exercise without difficulty ('second wind' phase). During the adaptation phase, patients have to cope with their inability to use muscle glycogen as a fuel. Processes occurring during this phase are as follows. An increase in cardiac output. This might be expected to increase muscle blood flow in order to supply exercising muscle with substrates that can substitute for muscle glycogen (free fatty acids (FFA), bloodborne glucose). Changes in the metabolic pathways. These cause a sufficient amount of hexose phosphates to be present to overcome the first 2.5 min of exercise, and FFA and bloodborne glucose to play a major role in energy supply at an earlier stage in exercise than in control subjects. An increase in EMG activity. This is most probably caused by the recruitment of more motor units to compensate for a failure of force generation in the muscle fibres. Central command seems to play an important role in the regulation of cardiovascular processes during the adaptation phase. Despite these compensatory mechanisms, metabolic stress occurs during the adaptation phase. During the 'second wind' phase there are no important differences between the metabolism of exercising muscle of patients with McArdle's disease and that of control subjects.

Adaptation, Physiological↗
PubMed1999

Effects of entropy inhomogeneity on density-temperature correlation in solar wind.

Compressive fluctuations in solar wind slow speed streams are studied by means of a magnetohydrodynamics (MHD) model, which represents the plasma in the vicinity of the heliospheric current sheet. The model contains a current sheet, as well as density and temperature variations, corresponding to a large scale modulation of the specific entropy. Alfvénic fluctuations are initially superimposed on the background equilibrium and compressive fluctuations are consequently generated during the time evolution. The resulting correlation between density and temperature fluctuations at various spatial scales is interpreted in terms of both generation of magnetosonic fluctuations and of an "entropy cascade." The latter phenomenon arises as a consequence of the interaction between the MHD turbulence and the underlying large scale entropy structure. In particular, it is responsible for anticorrelated density and temperature fluctuations detected at various scales. The results of the model are compared with the proton density-temperature correlation calculated during several crossings of solar wind slow speed streams by the Helios spacecraft. The model reproduces to a good extent the main observed features, in particular the dependence of the correlation coefficient on location (close to or far from the current sheet) and on the fluctuation scale. The results show that large scale inhomogeneities, in particular, that of specific entropy, are important ingredients in the dynamics of the MHD turbulence in slow speed streams.

Journal Article↗
PubMed2000

Power law distributions of burst duration and interburst interval in the solar wind: turbulence or dissipative self-organized criticality?

We calculate the probability density functions P of burst energy e, duration T, and interburst interval tau for a known turbulent system in nature. Bursts in the Earth-Sun component of the Poynting flux at 1 AU in the solar wind were measured using the MFI and SWE experiments on the NASA WIND spacecraft. We find P(e) and P(T) to be power laws, consistent with self-organized criticality (SOC). We find also a power-law form for P(tau) that distinguishes this turbulent cascade from the exponential P(tau) of ideal SOC, but not from some other SOC-like sandpile models. We discuss the implications for the relation between SOC and turbulence.

Journal Article↗
PubMed2002

Mean wind and its reversal in thermal convection.

Properties of the mean wind in thermal convection, especially the abrupt reversal of its direction at high Rayleigh numbers, are studied. Measurements made in a closed cylindrical container of aspect ratio 1 are analyzed, and both the long-term and short-term behaviors of the direction reversals are discussed. A first look at the data suggests a Brownian-type process in action, but a closer look suggests the existence of hierarchical features with time scales extending roughly over a decade and a half. A physical model consistent with experimental observations is presented, and the origin of the cutoff scales is discussed. It appears that the generation of the wind as well as the reversal of its direction can be understood in terms of the imbalance between buoyancy effects and friction.

Journal Article↗
PubMed2003

Fluctuations of the winding number of a directed polymer in a random medium.

For a directed polymer in a random medium lying on an infinite cylinder that is in 1+1 dimensions with finite width and periodic boundary conditions on the transverse direction, the winding number is simply the algebraic number of turns the polymer does around the cylinder. This paper presents exact expressions of the fluctuations of this winding number due to, first, the thermal noise of the system and, second, the different realizations of the disorder in the medium.

Journal Article↗
PubMed2005

Directed polymers with constrained winding angle.

In this paper we study from a nonperturbative point of view the entanglement of two directed polymers subjected to repulsive interactions given by a Dirac delta-function potential. An exact formula of the so-called second moment of the winding angle is derived. This result is used to provide a thorough analysis of entanglement phenomena in the classical system of two polymers subjected to repulsive interactions and related problems. No approximation is made in treating the constraint on the winding angle and the repulsive forces. In particular, we investigate how repulsive forces influence the entanglement degree of the two-polymer system. In the limit of ideal polymers, in which the interactions are switched off, we show that our results are in agreement with those of previous works.

Journal Article↗
PubMed2005

Mean wind in convective turbulence of mercury.

The large-scale circulation, often called "wind," in the confined thermal turbulence of mercury is studied experimentally. The instantaneous velocity profile at 128 points is directly measured using ultrasonic velocimetry. The periodic velocity oscillation is observed in the case of the aspect-ratio Gamma = 1,2 but not in Gamma = 0.5. Its peak frequency is scaled by f(c) proportional Ra(gamma(c)), where Ra is the Rayleigh number and gamma(c) = 0.43,0.45 for Gamma = 1,2. f(c) is close to the wind circulation frequency f(p), and has the same order of transit time from the bottom to the top of the convection cell. A single roll circulation is expected in Gamma = 1; however, axisymmetric toroidal rings may exist near the upper and lower plate for Gamma = 0.5, which are stable up to Ra = 7 x 10 (10).

Journal Article↗
PubMed2006

Structural elucidation of the PDI-related chaperone Wind with the help of mutants.

The structures of the PDI-related protein Wind (with a C-terminal His(6) tag) and the mutants Y53S, Y53F and Y55K have been determined and compared with the wild-type structure with the His(6) tag at the N-terminus. All five structures show the same mode of dimerization, showing that this was not an artefact introduced by the nearby N-terminal His(6) tag and suggesting that this dimer may also be the biologically active form. Although the mutants Y53S and Y55K completely abrogate transport of the protein Pipe (which appears to be the primary function of Wind in the cell), only subtle differences can be seen in the putative Pipe-binding region. The Pipe binding in the active forms appears to involve hydrophobic interactions between aromatic systems, whereas the inactive mutants may be able to bind more strongly with the help of hydrogen bonds, which could disturb the delicate equilibrium required for effective Pipe transport.

Amino Acid Substitution↗
PubMed2002

Breaking wind waves as a source of ambient noise.

A theoretical model for the prediction of ambient noise level due to collective oscillations of air bubbles under breaking wind waves is presented. The model uses a budget of the energy flux from the breaking waves to quantify acoustic power radiation by a bubble cloud. A shift of the noise spectra to lower frequency due to collective bubble oscillation is assumed. The model derives good estimates of the magnitude, slope, and frequency range of the noise spectra using the wind speed or height of breaking waves.

Journal Article↗
PubMed2004

Satellite measurements reveal persistent small-scale features in ocean winds.

Four-year averages of 25-kilometer-resolution measurements of near-surface wind speed and direction over the global ocean from the QuikSCAT satellite radar scatterometer reveal the existence of surprisingly persistent small-scale features in the dynamically and thermodynamically important curl and divergence of the wind stress. Air-sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields, as are the influences of islands and coastal mountains. Ocean currents such as the Gulf Stream generate distinctive patterns in the curl field. These previously unresolved features have important implications for oceanographic and air-sea interaction research.

Journal Article↗