On the Amount of Dust in the Asteroid Belt

1971 ◽  
Vol 12 ◽  
pp. 389-393
Author(s):  
Fred L. Whipple
Keyword(s):  
Solar Radiation ◽  
Particle Density ◽  
Asteroid Belt ◽  
Space Vehicles ◽  
The Sun ◽  
Small Particles ◽  
Zodiacal Cloud ◽  
Upper Limit ◽  
Upper Limits

Calculations of upper limits to the quantity of small particles in the asteroid belt are based on (1) the brightness of the counterglow coupled with observations and theory for the zodiacal cloud near Earth's orbit and (2) the destruction and erosion of asteroidal particles as they spiral toward the Sun because of solar radiation via the Poynting-Robertson effect. These calculations place the likely upper limit on asteroidal space particle density at the order of 5 to 10 times and the hazard to space vehicles at 2 to 4 times those near Earth's orbit. No such evidence indicates, however, that the hazard from small particles is actually much greater in the asteroid belt.

2.1.8 Sources of Interplanetary Dust: Asteroids

1976 ◽  
Vol 31 ◽  
pp. 187-205 ◽  
Author(s):  
J. S. Dohnanyi
Keyword(s):  
Interplanetary Dust ◽  
Asteroid Belt ◽  
The Sun ◽  
Number Density ◽  
Zodiacal Cloud ◽  
Relative Contribution ◽  
Potential Source ◽  
Asteroidal Belt ◽  
Pioneer 10

AbstractThe asteroid belt is examined as a potential source of interplanetary dust. Using results from the Pioneer-10 experiments the relative contribution of asteroidal and cometary particles to the Zodiacal cloud is estimated using methods developed in earlier studies of meteoroidal collisions (collisional model). It is found that the contribution of asteroidal particles to dust in the asteroidal belt is small compared with the number density of cometary type particles. Similar conclusions apply to the Zodiacal cloud between the sun and the asteroid belt. When definitive criteria for differentiating between comets and asteroids become available, a reexamination of some of our conclusions may become necessary.The distribution of asteroidal rotations is analyzed; it is found that the gross features of the distribution can be reproduced using the collisional model.

The Effects of Hyperbolic Meteoroids from Parker Solar Probe to the Moon

2020 ◽  
Author(s):  
Jamey Szalay ◽  
Petr Pokorny ◽  
Mihaly Horanyi ◽  
Stuart Bale ◽  
Eric Christian ◽  
...  
Keyword(s):  
Solar System ◽  
Solar Radiation ◽  
Radiation Pressure ◽  
Solar Radiation Pressure ◽  
The Sun ◽  
The Moon ◽  
Zodiacal Cloud ◽  
Impact Ejecta ◽  
Density Enhancement ◽  
Small Grains

<p>The zodiacal cloud in the inner solar system undergoes continual evolution, as its dust grains are collisionally ground and sublimated into smaller and smaller sizes. Sufficiently small (~<500 nm) grains known as beta-meteoroids are ejected from the inner solar system on hyperbolic orbits under the influence of solar radiation pressure. These small grains can reach significantly larger speeds than those in the nominal zodiacal cloud and impact the surfaces of airless bodies. Since the discovery of the Moon's asymmetric ejecta cloud, the origin of its sunward-canted density enhancement has not been well understood. We propose impact ejecta from beta-meteoroids that hit the Moon's sunward side could explain this unresolved asymmetry. The proposed hypothesis rests on the fact that beta-meteoroids are one of the few truly asymmetric meteoroid sources in the solar system, as unbound grains always travel away from the Sun and lack a symmetric inbound counterpart. This finding suggests beta-meteoroids may also contribute to the evolution of other airless surfaces in the inner solar system as well as within other exo-zodiacal disks. We will also highlight recent observations from the Parker Solar Probe (PSP) spacecraft, which suggest it is being bombarded by the very same beta-meteoroids. We discuss how observations by PSP, which lacks a dedicated dust detector, can be used to inform the structure and variability of beta-meteoroids in the inner solar system closer to the Sun than ever before.</p>

scholarly journals Measurements of X-ray radiation of the Sun on the heliogeophysical measuring equipment of spacecraft of the Russian Hydrometheorological Service

2019 ◽  
Vol 30 ◽  
pp. 15009
Author(s):  
Anatoly Nusinov ◽  
Vladimir Minligareev ◽  
Andrey Repin ◽  
Igor Shirokov
Keyword(s):  
Solar Radiation ◽  
Measuring Equipment ◽  
Experimental Studies ◽  
Calibration Procedure ◽  
Space Vehicles ◽  
The Sun ◽  
X Ray ◽  
Reference Base ◽  
Geostationary Satellites ◽  
Technological Sample

The characteristics of the equipment for monitoring X-ray solar radiation onboard geostationary satellites. A reference base for X-ray flux meters of the DIR-E was developed and experimental studies of the characteristics on the technological sample of the device were carried out. The calibration procedure of DIR-E for use in measurements on perspective space vehicles was also developed.

scholarly journals A search for millimeter emission from the coldest and closest brown dwarf with ALMA

2020 ◽  
Vol 642 ◽  
pp. A96
Author(s):  
Dirk Petry ◽  
Valentin D. Ivanov
Keyword(s):  
Magnetic Field ◽  
Calibration Procedure ◽  
The Sun ◽  
Brown Dwarf ◽  
Astronomical Observations ◽  
Link Type ◽  
Upper Limit ◽  
Unique Object ◽  
Upper Limits ◽  
Low Mass

Context. WISE J085510.83−071442.5 (W0855) is a unique object: with Teff ≈ 250 K it is the coldest known brown dwarf (BD), located at only ≈2.2 pc form the Sun. It is extremely faint, which makes any astronomical observations difficult. However, at least one remotely similar ultra-low-mass object, the M9 dwarf TVLM 513-46546, has been shown to be a steady radio emitter at frequencies up to 95 GHz with superimposed active states where strong, pulsed emission is observed. Aims. Our goal is to determine the millimeter radio properties of W0855 with deep observations around 93 GHz (3.2 mm) in order to investigate whether radio astrometry of this object is feasible and to measure or set an upper limit on its magnetic field. Methods. We observed W0855 for 94 min at 85.1–100.9 GHz on 24 December 2019 using 44 of the Atacama Large millimeter Array (ALMA) 12 m antennas. We used the standard ALMA calibration procedure and created the final image for our analysis by accommodating the Quasar 3C 209, the brightest nearby object by far. Furthermore, we created a light curve with a 30 s time resolution to search for pulsed emission. Results. Our observations achieve a noise RMS of 7.3 μJy beam−1 for steady emission and of 88 μJy for 30 s pulses in the aggregated bandwidth (Stokes I). There is no evidence for steady or pulsed emission from the object at the time of the observation. We derive 3σ upper limits of 21.9 μJy on the steady emission and of 264 μJy on the pulsed emission of W0855 between 85 GHz and 101 GHz. Conclusions. Together with the recent non-detection of W0855 at 4–8 GHz, our constraints on the steady and pulsed emission from W0855 confirm that the object is neither radio-loud nor magnetospherically particularly active.

Vitamin-A-Exzess durch Pferdefleischprodukte mit hohen Leberanteilen

2013 ◽  
Vol 41 (01) ◽  
pp. 31-36
Author(s):  
E. Kienzle ◽  
N. Becker
Keyword(s):  
Vitamin A ◽  
Eine Analyse ◽  
Upper Limit ◽  
Upper Limits

ZusammenfassungIm Rahmen einer Eliminationsdiät wird regelmäßig Pferdefleisch eingesetzt. Aus Gründen der Praktikabilität verwenden Tierbesitzer häufig kommerziell erhältliches Pferdefleisch aus der Dose. Aufgrund eines Berichts von Zervikalspondylosen bei einer auf Futtermittel allergischen Katze erfolgte eine Analyse verschiedener auf Pferdefleisch basierender Produkte hinsichtlich des Vitamin-AGehalts.In 14 Pferdefleischerzeugnissen wurde der Vitamin-A-Gehalt (Retinol) analysiert. Der Gehalt an umsetzbarer Energie wurde mithilfe von Schätzformeln auf Basis der Deklaration berechnet.In Produkten mit deklarierten Anteilen von Leber, Innereien oder tierischen Nebenprodukten konnten zum Teil erhebliche Vitamin-A-Gehalte festgestellt werden. Bei alleiniger Verfütterung eines dieser Produkte (Deckung des durchschnittlichen Energiebedarfs) würde die Vitamin-A-Versorgung nur knapp unter dem Safe Upper Limit der Katze sowie oberhalb des Safe Upper Limits beim Hund liegen.Bei All-Meat-Produkten sollte nicht nur die Deklaration, sondern auch der Inhalt näher betrachtet werden, um einen Hinweis auf eventuell hohe Leberanteile zu erhalten.Aufgrund der Ergebnisse ist eine exzessive Vitamin-A-Aufnahme bei langfristiger Verfütterung von Pferdefleischprodukten mit hohen Leberanteilen nicht auszuschließen.

scholarly journals Search for π0 decays to invisible particles

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
E. Cortina Gil ◽  
◽  
A. Kleimenova ◽  
E. Minucci ◽  
S. Padolski ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Confidence Level ◽  
Branching Ratio ◽  
Standard Model Higgs Boson ◽  
Scalar Mixing ◽  
Upper Limit ◽  
Upper Limits ◽  
The Standard Model ◽  
Model Independent

Abstract The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 109 tagged π0 mesons from K+ → π+π0(γ), searching for the decay of the π0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 10−9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K+ → π+X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

scholarly journals Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Matthew O. Clarkson ◽  
Timothy M. Lenton ◽  
Morten B. Andersen ◽  
Marie-Laure Bagard ◽  
Alexander J. Dickson ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Global Scale ◽  
Uranium Isotopes ◽  
Biogeochemical Model ◽  
Emission Scenarios ◽  
Isotope Data ◽  
Upper Limit ◽  
Thermal Maximum ◽  
Upper Limits ◽  
Anoxic Events

AbstractThe Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering <2% of seafloor area.

Particle regularity on thylakoid fracture faces is influenced by storage conditions

1995 ◽  
Vol 73 (10) ◽  
pp. 1676-1682 ◽  
Author(s):  
Galina A. Semenova
Keyword(s):  
Particle Density ◽  
Freeze Fracture ◽  
Storage Conditions ◽  
Medium Composition ◽  
Prolonged Storage ◽  
Particle Sizes ◽  
Fracture Face ◽  
Small Particles ◽  
Mean Size ◽  
Regular Arrays

Specific temperature, storage times, and medium composition enable initiation of regular arrays of intramembranous particles on the exoplasmic fracture face during prolonged storage of isolated chloroplasts at 4 °C, producing about 2 – 10 regular arrays with 2 – 30 particles in each array, with a period of about 36 nm, oriented in 1 – 4 directions. The particle sizes do not change throughout the time of storage (1 – 4 weeks). The second type of particle regularity arises during prolonged storage of chloroplasts in greater than 1 M sucrose at −18 °C. Rounded areas of small particles tightly packed into paracrystalline arrays are found among less densely packed particles. The density of small particles is 4700 particles/μm2, and the mean size is 11 nm, whereas the particle density of the background is 1600 particles/μm2 with a mean particle size of 13 nm compared with 1200 particles/μm2 and mean size 16 nm in fresh chloroplasts. Based on the reduction of particle sizes and manner of packing on the fracture face, it is proposed that the small particles are a light-harvesting complex, separate from photosystem II and aggregated into paracrystalline arrays. The thylakoid lipids may participate in formation of particle regularity. Key words: thylakoid membrane, freeze fracture, particle regularity, low temperatures.

scholarly journals Reactive quenching of electronically excited NO<sub>2</sub><sup>∗</sup> and NO<sub>3</sub><sup>∗</sup> by H<sub>2</sub>O as potential sources of atmospheric HO<sub><i>x</i></sub> radicals

2018 ◽  
Vol 18 (19) ◽  
pp. 14005-14015 ◽  
Author(s):  
Terry J. Dillon ◽  
John N. Crowley
Keyword(s):  
Gas Phase ◽  
Laser Excitation ◽  
Pulsed Laser ◽  
Work Rate ◽  
Rate Coefficients ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Upper Limit ◽  
Upper Limits ◽  
Electronically Excited

Abstract. Pulsed laser excitation of NO2 (532–647 nm) or NO3 (623–662 nm) in the presence of H2O was used to initiate the gas-phase reaction NO2∗+H2O → products (Reaction R5) and NO3∗+H2O → products (Reaction R12). No evidence for OH production in Reactions (R5) or (R12) was observed and upper limits for OH production of k5b/k5<1×10-5 and k12b/k12<0.03 were assigned. The upper limit for k5b∕k5 renders this reaction insignificant as a source of OH in the atmosphere and extends the studies (Crowley and Carl, 1997; Carr et al., 2009; Amedro et al., 2011) which demonstrate that the previously reported large OH yield by Li et al. (2008) was erroneous. The upper limit obtained for k12b∕k12 indicates that non-reactive energy transfer is the dominant mechanism for Reaction (R12), though generation of small but significant amounts of atmospheric HOx and HONO cannot be ruled out. In the course of this work, rate coefficients for overall removal of NO3∗ by N2 (Reaction R10) and by H2O (Reaction R12) were determined: k10=(2.1±0.1)×10-11 cm3 molecule−1 s−1 and k12=(1.6±0.3)×10-10 cm3 molecule−1 s−1. Our value of k12 is more than a factor of 4 smaller than the single previously reported value.

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