38,982 research outputs found
Influence of organic films on the evaporation and condensation of water in aerosol
Uncertainties in quantifying the kinetics of evaporation and condensation of water from atmospheric aerosol are a significant contributor to the uncertainty in predicting cloud droplet number and the indirect effect of aerosols on climate. The influence of aerosol particle surface composition, particularly the impact of surface active organic films, on the condensation and evaporation coefficients remains ambiguous. Here, we report measurements of the influence of organic films on the evaporation and condensation of water from aerosol particles. Significant reductions in the evaporation coefficient are shown to result when condensed films are formed by monolayers of long-chain alcohols [C(n)H((2n+1))OH], with the value decreasing from 2.4 × 10(−3) to 1.7 × 10(−5) as n increases from 12 to 17. Temperature-dependent measurements confirm that a condensed film of long-range order must be formed to suppress the evaporation coefficient below 0.05. The condensation of water on a droplet coated in a condensed film is shown to be fast, with strong coherence of the long-chain alcohol molecules leading to islanding as the water droplet grows, opening up broad areas of uncoated surface on which water can condense rapidly. We conclude that multicomponent composition of organic films on the surface of atmospheric aerosol particles is likely to preclude the formation of condensed films and that the kinetics of water condensation during the activation of aerosol to form cloud droplets is likely to remain rapid
On the absence of Shapiro-like steps in certain mesoscopic S-N-S junctions
In DC transport through mesoscopic S-N-S junctions, it is known that the
Josephson coupling decreases exponentially with increasing temperature, but the
phase dependence of the conductance persists to much higher temperatures and
decreases only as 1/T. It is pointed out here that, despite the fact that such
a phase-dependent conductance does bring about an AC current for a pure DC
voltage, it cannot, by itself, lead to the formation of Shapiro steps.Comment: 1 page, to be published in PRL (as Comment
Accelerations in Flight
This report deals with the accelerations obtained in flight on various airplanes at Langley Field for the purpose of obtaining the magnitude of the load factors in flight and to procure information on the behavior of an airplane in various maneuvers. The instrument used in these tests was a recording accelerometer of a new type designed by the technical staff of the National Advisory Committee for Aeronautics. The instrument consists of a flat steel spring supported rigidly at one end so that the free end may be deflected by its own weight from its neutral position by any acceleration acting at right angles to the plane of the spring. This deflection is measured by a very light tilting mirror caused to rotate by the deflection of the spring, which reflected the beam of light onto a moving film. The motion of the spring is damped by a thin aluminum vane which rotates with the spring between the poles of an electric magnet. Records were taken on landings and takeoffs, in loops, spins, spirals, and rolls
Control in Circling Flight
This investigation was undertaken for the purpose of developing instruments that would record the forces and positions of all three controls, and to obtain data on the behavior of an airplane in turns. All the work was done on a standard rigged JN4H (airplane no. 2 of National Advisory Committee for Aeronautics, report no. 70). It was found that the airplane was longitudinally unstable and nose heavy; that it was laterally unstable, probably due to too little dihedral; and that it was directionally unstable, due to insufficient fin area, this last being very serious, for in case of a loss of rudder control the airplane immediately whips into a spin from which there is no way of getting it out. On the other hand, it was found possible to fly quite satisfactorily with the rudder locked, and safely, though not so well, with the ailerons locked
Quantum Spinodal Decomposition
We study the process of spinodal decomposition in a scalar quantum field
theory that is quenched from an equilibrium disordered initial state at to a final state at . The process of formation and growth
of correlated domains is studied in a Hartree approximation. We find an
approximate scaling law for the size of the domains at long times for weakly coupled theories, with the zero
temperature correlation length.Comment: REVTEX 13 pages(2 figures not included),PITT 93-0
Charged State of a Spherical Plasma in Vacuum
The stationary state of a spherically symmetric plasma configuration is
investigated in the limit of immobile ions and weak collisions. Configurations
with small radii are positively charged as a significant fraction of the
electron population evaporates during the equilibration process, leaving behind
an electron distribution function with an energy cutoff. Such charged plasma
configurations are of interest for the study of Coulomb explosions and ion
acceleration from small clusters irradiated by ultraintense laser pulses and
for the investigation of ion bunches propagation in a plasma
Rabi oscillations under ultrafast excitation of graphene
We study coherent nonlinear dynamics of carriers under ultrafast interband
excitation of an intrinsic graphene. The Rabi oscillations of response appear
with increasing of pumping intensity. The photoexcited distribution is
calculated versus time and energy taking into account the effects of energy
relaxation and dephasing. Spectral and temporal dependencies of the response on
a probe radiation (transmission and reflection coefficients) are considered for
different pumping intensities and the Rabi oscillations versus time and
intensity are analyzed.Comment: 6 pages, 6 figure
Implications of reflectance measurements on the mechanism for superconductivity in MgB
Recent optical studies in c-axis oriented superconducting MgB films
indicate that the electron-phonon coupling is weak [tu01]. We reinforce this
conclusion by examining the raw reflectance data; its frequency dependence is
incompatible with strong electron-phonon scattering. This is further
strengthened by analysis of the real part of the conductivity, and by the
temperature dependence of the effective Drude scattering rate. Using a
realistic electron-phonon spectral shape [kong01], we find , in agreement with Tu et al. [tu01]. To the extent that
, this disagrees sharply with model
calculations [kong01,kortus01,an01], and is far too low to provide the means
for K. A simple model is constructed with coupling to a high
frequency excitation, which is consistent with both the low frequency optical
data and the high .Comment: 4 pages, 4 figure
Stripped Spiral Galaxies as Promising Targets for the Determination of the Cepheid distance to the Virgo Cluster
The measurement of precise galaxy distances by Cepheid observations out to
the distance of the Virgo cluster is important for the determination of the
Hubble constant (). The Virgo cluster is thereby often used as an
important stepping stone. The first HST measurement of the distance of a Virgo
galaxy (M100) using Cepheid variables provided a value for
km/s/Mpc (Freedman et al. 1994). This measurement was preceeded by a ground
based study of the Virgo spiral NGC4571 (Pierce et al. 1994) formally providing
km/s/Mpc. These determinations rely on the accuracy with which
the position of this observed spiral galaxy can be located with respect to the
Virgo cluster center. This uncertainty introduces a major error in the
determination of , together with the uncertainty in the adopted Virgo
infall velocity of the Local Group. Here we propose the use of spiral galaxies
which show clear signs of being stripped off their interstellar medium by the
intracluster gas of the Virgo cluster as targets for the Cepheid distance
measurements. We show that the stripping process and the knowledge of the
intracluster gas distribution from ROSAT X-ray observations allow us to locate
these galaxies with an at least three times higher precision with respect to
M87 than in the case of other spirals like M100. The X-ray observations further
imply that M87 is well centered within the intracluster gas halo of the Virgo
cluster and that M86 is associated with a group of galaxies and a larger dark
matter halo. The combination of these informations could enable us to locate
the two stripped spiral galaxies quite precisely within the Virgo cluster and
could greatly improve the determination of the Virgo cluster distance.Comment: 21 pages, Latex(aaspp.sty), including 6 figures, accepted for
publication in ApJL (shortened abstract:
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