1,090 research outputs found
Computer Simulation of Cytoskeleton-Induced Blebbing in Lipid Membranes
Blebs are balloon-shaped membrane protrusions that form during many
physiological processes. Using computer simulation of a particle-based model
for self-assembled lipid bilayers coupled to an elastic meshwork, we
investigated the phase behavior and kinetics of blebbing. We found that blebs
form for large values of the ratio between the areas of the bilayer and the
cytoskeleton. We also found that blebbing can be induced when the cytoskeleton
is subject to a localized ablation or a uniform compression. The results
obtained are qualitatively in agreement with the experimental evidence and the
model opens up the possibility to study the kinetics of bleb formation in
detail.Comment: To appear in Physical Review
Mass spectrometers and atomic oxygen
The likely role of atmospheric atomic oxygen in the recession of spacecraft surfaces and in the shuttle glow has revived interest in the accurate measurement of atomic oxygen densities in the upper atmosphere. The Air Force Geophysics Laboratory is supplying a quadrupole mass spectrometer for a materials interactions flight experiment being planned by the Johnson Space Center. The mass spectrometer will measure the flux of oxygen on test materials and will also identify the products of surface reactions. The instrument will be calibrated at a new facility for producing high energy beams of atomic oxygen at the Los Alamos National Laboratory. The plans for these calibration experiments are summarized
Interstellar Scintillation Observations of 146 Extragalactic Radio Sources
From 1979--1996 the Green Bank Interferometer was used by the Naval Research
Laboratory to monitor the flux density from 146 compact radio sources at
frequencies near 2 and 8 GHz. We filter the ``light curves'' to separate
intrinsic variations on times of a year or more from more rapid interstellar
scintilation (ISS) on times of 5--50 d. Whereas the intrinsic variation at 2
GHz is similar to that at 8 GHz (though diminished in amplitude), the ISS
variation is much stronger at 2 than at 8 GHz. We characterize the ISS
variation by an rms amplitude and a timescale and examine the statistics of
these parameters for the 121 sources with significant ISS at 2 GHz. We model
the scintillations using the NE2001 Galactic electron model assuming the
sources are brightness-limited.
We find the observed rms amplitude to be in general agreement with the model,
provided that the compact components of the sources have about 50% of their
flux density in a component with maximum brightness temperatures
--K. Thus our results are consistent with cm-wavelength VLBI
studies of compact AGNs, in that the maximum brightness temperatures found are
consistent with the inverse synchrotron limit at K, boosted
in jet configurations by Doppler factors up to about 20. The average of the
observed 2 GHz ISS timescales is in reasonable agreement with the model at
Galactic latitudes above about 10\de. At lower latitudes the observed
timescales are too fast, suggesting that the transverse plasma velocity
increases more than expected beyond about 1 kpc.Comment: 32 pages, 16 figures. Submitted to Ap
Streamer Wave Events Observed in Solar Cycle 23
In this paper we conduct a data survey searching for well-defined streamer
wave events observed by the Large Angle and Spectrometric Coronagraph (LASCO)
on-board the Solar and Heliospheric Observatory (SOHO) throughout Solar Cycle
23. As a result, 8 candidate events are found and presented here. We compare
different events and find that in most of them the driving CMEs ejecta are
characterized by a high speed and a wide angular span, and the CME-streamer
interactions occur generally along the flank of the streamer structure at an
altitude no higher than the bottom of the field of view of LASCO C2. In
addition, all front-side CMEs have accompanying flares. These common
observational features shed light on the excitation conditions of streamer wave
events.
We also conduct a further analysis on one specific streamer wave event on 5
June 2003. The heliocentric distances of 4 wave troughs/crests at various
exposure times are determined; they are then used to deduce the wave properties
like period, wavelength, and phase speeds. It is found that both the period and
wavelength increase gradually with the wave propagation along the streamer
plasma sheet, and the phase speed of the preceding wave is generally faster
than that of the trailing ones. The associated coronal seismological study
yields the radial profiles of the Alfv\'en speed and magnetic field strength in
the region surrounding the streamer plasma sheet. Both quantities show a
general declining trend with time. This is interpreted as an observational
manifestation of the recovering process of the CME-disturbed corona. It is also
found that the Alfv\'enic critical point is at about 10 R where the
flow speed, which equals the Alfv\'en speed, is 200 km s
Plasma Electronics
Contains reports on eight research projects.National Science Foundation (Grant G-24073)United States Atomic Energy Commission (Contract AF(30-1)-3285)Lincoln Laboratory (Purchase Order DDL BB-107)United States Air Force (Contract AF19(628)-500)United States Atomic Energy Commission (Contract AT(30-1)-3221
Parametric instabilities in magnetized multicomponent plasmas
This paper investigates the excitation of various natural modes in a
magnetized bi-ion or dusty plasma. The excitation is provided by parametrically
pumping the magnetic field. Here two ion-like species are allowed to be fully
mobile. This generalizes our previous work where the second heavy species was
taken to be stationary. Their collection of charge from the background neutral
plasma modifies the dispersion properties of the pump and excited waves. The
introduction of an extra mobile species adds extra modes to both these types of
waves. We firstly investigate the pump wave in detail, in the case where the
background magnetic field is perpendicular to the direction of propagation of
the pump wave. Then we derive the dispersion equation relating the pump to the
excited wave for modes propagating parallel to the background magnetic field.
It is found that there are a total of twelve resonant interactions allowed,
whose various growth rates are calculated and discussed.Comment: Published in May 2004; this is a late submission to the archive. 14
pages, 8 figure
Towards a Simple Model of Compressible Alfvenic Turbulence
A simple model collisionless, dissipative, compressible MHD (Alfvenic)
turbulence in a magnetized system is investigated. In contrast to more familiar
paradigms of turbulence, dissipation arises from Landau damping, enters via
nonlinearity, and is distributed over all scales. The theory predicts that two
different regimes or phases of turbulence are possible, depending on the ratio
of steepening to damping coefficient (m_1/m_2). For strong damping
(|m_1/m_2|<1), a regime of smooth, hydrodynamic turbulence is predicted. For
|m_1/m_2|>1, steady state turbulence does not exist in the hydrodynamic limit.
Rather, spikey, small scale structure is predicted.Comment: 6 pages, one figure, REVTeX; this version to be published in PRE. For
related papers, see http://sdphpd.ucsd.edu/~medvedev/papers.htm
The Ursinus Weekly, February 13, 1961
Jun Kawashima to study at U.C. this semester • Cub and Key asks junior men to apply • Dr. G. S. Pancoast seeks State Assembly position • Dr. Miller begins new TV series on WFIL-TV • Mrs. Rice addresses Collegeville club on Swedish decor • IRC Club to participate in Model UN meeting in N.Y. • Art museum presents series of art programs • Pancoast, Sanders appear on radio; Discuss politics • Spring Festival replaces May Day • Mr. H. Lloyd Jones helps plan conference at Lafayette College • Mr. Jordania to play his own piano pieces for French Club • Rev. Mrs. Kriebel will speak at annual Color Day • Lorelei will be held on Feb. 17 • Y to sponsor Ash Wed. candlelight service • Dean Rothenberger talks to Bible class on European tours • Dr. Harold K. Schilling to address Forum at 8 • Ford, Genter to direct annual senior show • Ardith Mumbauer to show her Costa Rican slides on Feb. 20 • Editorial: Policies • Letters to the editor • Chapel commentary • Seven weeks abroad at music festivals • Village of the damned • Consideration of costs • Tribute for Dr. Dooley • Book review: Herman Wouk\u27s This is my God • Snowbound thoughts • On the theory and practice of in-class sleeping • Spanish sketchbook: The marriage situation • Poomer • On the movie scene • Thoughts at Broad and Locust • Meal time mess • Man over beasts • Wrestlers score another victory, defeat E-Town • Lassies topple strong crusaders; Downed by Grads • Varsity five overpower Johns Hopkins, Fords • Greek gleanings • Cindy Benner is R&B contest rep • Dean\u27s listhttps://digitalcommons.ursinus.edu/weekly/1332/thumbnail.jp
Plasma Electronics
Contains reports on nine research projects.National Science Foundation (Grant G-24073)United States NavyUnited States Navy, Office of Naval Research (Contract Nonr-1841(78))United States Air Force (Contract AF19(604)-7400)Lincoln Laboratory (Purchase Order DDL B-00368)United States Arm
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