31,100 research outputs found
Irradiation of Sperm Tails by Laser Microbeam
1. Sea-urchin and starfish sperm tails were irradiated at pre-selected points along the flagellum and at pre-selected phases of the beat cycle by means of a pulsed ruby laser microbeam. Multiple-exposure dark-field photomicrographs were taken immediately before and after irradiation. The flagellum usually appeared to be broken at the irradiated point.
2. The portion of a flagellum between the head and the irradiated point continued for at least a few beats if its length was at least 25% of the length of the tail, and stopped immediately if it was shorter.
3. Bends already established beyond the irradiated point continued to propagate to the tip of the flagellum. Their propagation velocity generally decreased, and there were usually changes in other bend parameters.
4. No new bends ever developed beyond the irradiated point.
5. Irradiation within a bent region often completely eliminated that region
DSN observations of Titan
When using Deep Space Station (DSS)-14 in a monostatic configuration, radar observations of Titan show that Titan is a diffuse reflector with a relative radar cross section of 0.14 +/- 0.03. No hot spots were observed
Absence of Chaos in Bohmian Dynamics
The Bohm motion for a particle moving on the line in a quantum state that is
a superposition of n+1 energy eigenstates is quasiperiodic with n frequencies.Comment: 1 pag
A stability bound for relay control systems in non-phase variable form
Stability bound for relay control systems using similarity transformation for each parameter set within parameter spac
Bi-Directional Energy Cascades and the Origin of Kinetic Alfv\'enic and Whistler Turbulence in the Solar Wind
The observed sub-proton scale turbulence spectrum in the solar wind raises
the question of how that turbulence originates. Observations of keV energetic
electrons during solar quite-time suggest them as possible source of free
energy to drive the turbulence. Using particle-in-cell simulations, we explore
how free energy in energetic electrons, released by an electron two-stream
instability drives Weibel-like electromagnetic waves that excite wave-wave
interactions. Consequently, both kinetic Alfv\'enic and whistler waves are
excited that evolve through inverse and forward magnetic energy cascades.Comment: 12 pages, 5 figures, Submitted to Physical Review Letter
Immunity to K1 killer toxin: internal TOK1 blockade.
K1 killer strains of Saccharomyces cerevisiae harbor RNA viruses that mediate secretion of K1, a protein toxin that kills virus-free cells. Recently, external K1 toxin was shown to directly activate TOK1 channels in the plasma membranes of sensitive yeast cells, leading to excess potassium flux and cell death. Here, a mechanism by which killer cells resist their own toxin is shown: internal toxin inhibits TOK1 channels and suppresses activation by external toxin
A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows
Reaction rates in turbulent, reacting flows are reviewed. Assumed probability density functions (pdf) modeling of reaction rates is being investigated in relation to a three variable pdf employing a 'most likely pdf' model. Chemical kinetic mechanisms treating hydrogen air combustion is studied. Perfectly stirred reactor modeling of flame stabilizing recirculation regions was used to investigate the stable flame regions for silane, hydrogen, methane, and propane, and for certain mixtures thereof. It is concluded that in general, silane can be counted upon to stabilize flames only when the overall fuel air ratio is close to or greater than unity. For lean flames, silane may tend to destabilize the flame. Other factors favoring stable flames are high initial reactant temperatures and system pressure
- …