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21.
L. A. Fisk 《Space Science Reviews》1996,78(1-2):129-136
Recent observations from the Voyager spacecraft have suggested that the spectrum of the anomalous cosmic ray component is relatively steep at the termination shock, which is believed to be responsible for accelerating these particles. This conclusion argues that the termination shock must be weak, which in turn requires that the upstream Mach number in the solar wind must be quite low, 2.4. It is pointed out that such conditions are unlikely to prevail at all locations along the shock front. However, it is possible for such conditions to exist at the interface between high speed streams at high heliographic latitudes and the region at low latitudes where high and low speed streams have interacted and come into equilibrium. This discussion suggests a preferred location for the injection of the anomalous component into the shock acceleration process. 相似文献
22.
On Earth, the functional stretch reflex is an important component in the maintenance of posture and muscle tone. In parabolic flight experiments, we evaluated whether the functional stretch reflex, as reflected in the tonic vibration reflex, adjusts appropriately for changes in background gravitoinertial force level. Virtually immediate alterations of appropriate sign occurred. 相似文献
23.
H. Kunow M.A. Lee L.A. Fisk R.J. Forsyth B. Heber T.S. Horbury E. Keppler J. Kóta Y.-Q. Lou R.B. McKibben C. Paizis M.S. Potgieter E.C. Roelof T.R. Sanderson G.M. Simnett R. Von Steiger B.T. Tsurutani R.F. Wimmer-Schweingruber J.R. Jokipii 《Space Science Reviews》1999,89(1-2):221-268
Ulysses observed a stable strong CIR from early 1992 through 1994 during its first journey into the southern hemisphere. After
the rapid latitude scan in early 1995, Ulysses observed a weaker CIR from early 1996 to mid-1997 in the northern hemisphere
as it traveled back to the ecliptic at the orbit of Jupiter. These two CIRs are the observational basis of the investigation
into the latitudinal structure of CIRs. The first CIR was caused by an extension of the northern coronal hole into the southern
hemisphere during declining solar activity, whereas the second CIR near solar minimum activity was caused by small warps in
the streamer belt. The latitudinal structure is described through the presentation of three 26-day periods during the southern
CIR. The first at ∼24°S shows the full plasma interaction region including fast and slow wind streams, the compressed shocked
flows with embedded stream interface and heliospheric current sheet (HCS), and the forward and reverse shocks with associated
accelerated ions and electrons. The second at 40°S exhibits only the reverse shock, accelerated particles, and the 26-day
modulation of cosmic rays. The third at 60°S shows only the accelerated particles and modulated cosmic rays. The possible
mechanisms for the access of the accelerated particles and the CIR-modulated cosmic rays to high latitudes above the plasma
interaction region are presented. They include direct magnetic field connection across latitude due to stochastic field line
weaving or to systematic weaving caused by solar differential rotation combined with non-radial expansion of the fast wind.
Another possible mechanism is particle diffusion across the average magnetic field, which includes stochastic field line weaving.
A constraint on connection to a distant portion of the CIR is energy loss in the solar wind, which is substantial for the
relatively slow-moving accelerated ions. Finally, the weaker northern CIR is compared with the southern CIR. It is weak because
the inclination of the streamer belt and HCS decreased as Ulysses traveled to lower latitudes so that the spacecraft remained
at about the maximum latitudinal extent of the HCS.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
24.
微波天线阵面的热变形是影响在轨指向精度的关键因素,如何解决大功率器件的散热问题至关重要。某微波天线热耗峰值近万瓦,在近20 m2的全阵面内,需要保证收发(TR)组件的温升和补偿加热器的功耗不能过高。针对某微波天线特有的工作模式和外热流情况,提出了机械泵驱动流体回路(MPFL)、双面散热和相变热管 3种热控方案,并分析了各自的特点和适用性。为解决天线内部狭小空间的辐射传导耦合问题,开展了单模块热阻实验分析与优化,并得到了在轨测试的验证。 相似文献
25.
M. Scholer G. Mann S. Chalov M.I. Desai L.A. Fisk J.R. Jokipii R. Kallenbach E. Keppler J. Kóta H. Kunow M.A. Lee T.R. Sanderson G.M. Simnett 《Space Science Reviews》1999,89(1-2):369-399
On the basis of the observational picture established in the report of Mason, von Steiger et al. (1999) the status of theoretical models on origin, injection, and acceleration of particles associated with Corotating Interaction
Regions (CIRs) is reviewed. This includes diffusive or first-order Fermi acceleration at oblique shocks, adiabatic deceleration
in the solar wind, stochastic acceleration in Alfvén waves and oblique propagating magnetosonic waves, and shock surfing as
possible injection mechanism to discriminate pickup ions from solar wind ions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
26.
Johannes Geiss is a world leader and foremost expert on measurements and interpretation of the composition of matter that
reveals the history, present state, and future of astronomical objects. With his Swiss team he was first to measure the composition
of the noble gases in the solar wind when in the late 1960s he flew the brilliant solar wind collecting foil experiments on
the five Apollo missions to the moon. Always at the forefront of the art of composition measurements, he with his colleagues
determined the isotopic and elemental composition of the solar wind using instruments characterized by innovative design that
have provided the most comprehensive record of the solar wind composition under all solar wind conditions at all helio-latitudes.
He discovered heavy interstellar pickup ions, from which the composition of the neutral gas of the Local Interstellar Cloud
is determined, and the “Inner Source” of pickup ions. Johannes Geiss played a key role both in the in-situ measurements and
modeling of molecular ions in comets, and the interpretation of these data. He and co-workers measured the composition of
plasmas in the magnetospheres of Earth and Jupiter. Here we highlight Johannes Geiss’ many discoveries and seminal contributions
to our knowledge of the composition of matter of the Sun, solar wind, interstellar gas, early universe, comets and magnetospheres. 相似文献
27.
Iron-magnesium silicate bioweathering on Earth (and Mars?) 总被引:1,自引:0,他引:1
We examined the common, iron-magnesium silicate minerals olivine and pyroxene in basalt and in mantle rocks to determine if they exhibit textures similar to bioweathering textures found in glass. Our results show that weathering in olivine may occur as long, narrow tunnels (1-3 microm in diameter and up to 100 microm long) and as larger irregular galleries, both of which have distinctive characteristics consistent with biological activity. These weathering textures are associated with clay mineral by-products and nucleic acids. We also examined olivine and pyroxene in martian meteorites, some of which experienced preterrestrial aqueous alteration. Some olivines and pyroxenes in the martian meteorite Nakhla were found to contain tunnels that are similar in size and shape to tunnels in terrestrial iron-magnesium silicates that contain nucleic acids. Though the tunnels found in Nakhla are similar to the biosignatures found in terrestrial minerals, their presence cannot be used to prove that the martian alteration features had a biogenic origin. The abundance and wide distribution of olivine and pyroxene on Earth and in the Solar System make bioweathering features in these minerals potentially important new biosignatures that may play a significant role in evaluating whether life ever existed on Mars. 相似文献
28.
The boundary between ice and basalt on Earth is an analogue for some near-surface environments of Mars. We investigated neutrophilic iron-oxidizing microorganisms from the basalt-ice interface in a lava tube from the Oregon Cascades with perennial ice. One of the isolates (Pseudomonas sp. HerB) can use ferrous iron Fe(II) from the igneous mineral olivine as an electron donor and O(2) as an electron acceptor. The optimum growth temperature is ~12-14°C, but growth also occurs at 5°C. Bicarbonate is a facultative source of carbon. Growth of Pseudomonas sp. HerB as a chemolithotrophic iron oxidizer with olivine as the source of energy is favored in low O(2) conditions (e.g., 1.6% O(2)). Most likely, microbial oxidation of olivine near pH 7 requires low O(2) to offset the abiotic oxidation of iron. The metabolic capabilities of this bacterium would allow it to live in near-surface, icy, volcanic environments of Mars in the present or recent geological past and make this type of physiology a prime candidate in the search for life on Mars. 相似文献
29.
The Energetic Particle and Plasma Spectrometer Instrument on the MESSENGER Spacecraft 总被引:1,自引:0,他引:1
G. Bruce Andrews Thomas H. Zurbuchen Barry H. Mauk Horace Malcom Lennard A. Fisk George Gloeckler George C. Ho Jeffrey S. Kelley Patrick L. Koehn Thomas W. LeFevere Stefano S. Livi Robert A. Lundgren Jim M. Raines 《Space Science Reviews》2007,131(1-4):523-556
The Energetic Particle and Plasma Spectrometer (EPPS) package on the MErcury Surface, Space ENvironment, GEochemistry, and
Ranging (MESSENGER) mission to Mercury is composed of two sensors, the Energetic Particle Spectrometer (EPS) and the Fast
Imaging Plasma Spectrometer (FIPS). EPS measures the energy, angular, and compositional distributions of the high-energy components
of the in situ electrons (>20 keV) and ions (>5 keV/nucleon), while FIPS measures the energy, angular, and compositional distributions
of the low-energy components of the ion distributions (<50 eV/charge to 20 keV/charge). Both EPS and FIPS have very small
footprints, and their combined mass (∼3 kg) is significantly lower than that of comparable instruments. 相似文献
30.
G.M. Mason R. Von Steiger R.B. Decker M.I. Desai J.R. Dwyer L.A. Fisk G. Gloeckler J.T. Gosling M. Hilchenbach R. Kallenbach E. Keppler B. Klecker H. Kunow G. Mann I.G. Richardson T.R. Sanderson G.M. Simnett Y.-M. Wang R.F. Wimmer-Schweingruber M. Fränz J.E. Mazur 《Space Science Reviews》1999,89(1-2):327-367
This report emphasizes new observational aspects of CIR ions revealed by advanced instruments launched on the Ulysses, WIND,
SOHO, and ACE spacecraft, and by the unique vantage point of Ulysses which carried out the first survey of Corotating Interaction
Region (CIR) properties over a very wide range of heliolatitudes. With this more complete observational picture established,
this review is the basis to consider the status of theoretical models on origin, injection, and acceleration of CIR particles
reported by Scholer, Mann et al. (1999) in this volume.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献