scholarly journals The Sextanid Meteor Stream

1964 ◽  
Vol 17 (1) ◽  
pp. 158 ◽  
Author(s):  
CS Nilsson
Keyword(s):  
Meteor Shower ◽  
Peak Activity ◽  
Meteor Stream ◽  
Time Plot

The Sextanid meteor shower was first reported by Weiss (1960), who matched theoretical envelopes to the echo range-time plot from a directive radar rate equipment to find the radiant = 155�8�, S = 0�1O�. The peak activity persisted from September 29 to October 3, but was noticeable only in 1957. No trace of activity due to this shower could be found in previous surveys.

scholarly journals 44. Investigation of perturbed motion of the leonid meteor stream

1968 ◽  
Vol 33 ◽  
pp. 449-475 ◽  
Author(s):  
E. I. Kazimirčak-Polonskaja ◽  
N. A. Beljaev ◽  
I. S. Astapovič ◽  
A. K. Terenteva
Keyword(s):  
Maximum Activity ◽  
Meteor Shower ◽  
Meteor Stream ◽  
Outer Planets ◽  
The Earth ◽  
Meteor Body ◽  
Action At A Distance ◽  
Last 300 Years ◽  
The Times ◽  
Made In

The investigation is based on a system of elements, obtained from the best observations made in England during the maximum of the meteor shower 1866. This system represents the most probable orbit of that part of the stream, which passed perihelion during the years 1864–67 and was later given the name of Ortho-Leonids. Seventeen points (meteor groups) have been chosen on this orbit, and differential equations of their motion have been integrated on the electronic computer BESM-2 by Cowell's method of quadratures, taking account of perturbations from eight planets (Venus–Pluto), with a variable step from 0·001 to 40 days and taking account of differences through to the 4th order. The motions of two groups (XI and XII) have been investigated in an interval of 300 years (1700–2000), and the motions of the rest of the groups for a space of 135 years (1866–2000). All the close approaches of these groups to the Earth, Jupiter, Saturn and Uranus have been determined. The results of integration are given in the tables, which clearly represent the evolution of the orbit of every group. It has been found that the basic factors determining the evolution of separate groups, and of the stream as a whole, are the close approaches to the outer planets. The perturbations by these planets, especially by Jupiter and Saturn, determine the conditions for an encounter of the meteor groups with the Earth, and cause a change in the activity of the Leonid shower at different apparitions. Apparitions of the Leonids have been investigated for the last millennium, and in more detail for the last 180 years. It has been stated that the orbit of the Ortho-Leonid stream remained stable over the interval of 1000 years; its stability has been confirmed by calculations during the last 300 years, and the limits of changes of its elements have been computed. The perturbing influence of the Earth on the motion of meteor bodies in its sphere of action has been investigated. It turns out that at exceptionally deep penetrations of meteor bodies into this sphere of action, at a distance of some 1000 km from the Earth, its perturbations can essentially transform the orbit of a meteor body, e.g. reduce its period of revolution by some years, and materially change the eccentricity of the orbit, its inclination, etc. Conditions for an encounter of the stream with the Earth in the period 1898–2000 have been clarified, and forecasts have been made for the times of maximum activity of the shower in the years 1966–68. In 1967 the maximum activity of the Leonids is predicted to occur from November 17, 18h to November 18, 1h UT.

scholarly journals On the Relationship Between Comet P/Machholz and the Quadrantid Meteor Stream

1992 ◽  
Vol 152 ◽  
pp. 325-327 ◽  
Author(s):  
R. Gonczi ◽  
H. Rickman ◽  
C. Froeschlé
Keyword(s):  
Three Dimensional ◽  
Extensive Study ◽  
Meteor Shower ◽  
Meteor Stream ◽  
Orbital Inclination ◽  
Meteor Streams ◽  
Protection Mechanisms ◽  
The Subject ◽  
The Relationship

The Quadrantid meteor shower has been recognized for more than 150 years. The dynamics of the corresponding stream is peculiar due to the high orbital inclination and, for some particles, the closeness of the 2/1 mean motion resonance with Jupiter. It has been the subject of many investigations relating to the structure of the stream and its nodal retrogression as well as its long-term history and its likely cometary origin. Thus Hamid and Youssef (1963) found that the jovian secular perturbations lead to very large changes in the inclination and perihelion distance of typical stream particles with a period around 4000 yrs. From a more extensive study by Williamset al.(1979) it was obvious that this period is not unique but may vary considerably between different particles. Related to this behaviour is also the investigation by Froeschlé and Scholl (1982) who performed an extensive study of three-dimensional orbits at the 2/1 resonance. The orbits remain confined in the resonance zone and are stable in Hill's sense. Close encounters with Jupiter are avoided through the action of three main protection mechanisms:σlibration around 0,ωlibration aroud 90°, ande–ωcoupling, although most orbits exhibit large variations in inclination and eccentricity. Investigating in more detail a Quadrantid-like meteor stream, Froeschlé and Scholl (1986) also found a nonuniform nodal retrogression and an unusual progression. This behaviour causes a formation of arcs which was not found for other meteor streams in resonance with Jupiter – however, almost never having large inclinations.

scholarly journals 8. Quadrantid Meteor Shower: Eleven Years of Radar Observations

1977 ◽  
Vol 39 ◽  
pp. 171-174
Author(s):  
B. A. McIntosh
Keyword(s):  
International Cooperation ◽  
Cross Section ◽  
Meteor Shower ◽  
Continuous Series ◽  
Meteor Stream ◽  
Radar Observations ◽  
Meteor Streams ◽  
The Cross

In studying the evolution of meteor streams from cometary debris it is desirable to know the distribution of particles both around the orbit and in the cross section perpendicular to the orbit. Earth-based observations are limited to a once-per-year sample and also limited by the position of the observer on earth as it crosses the meteor stream. A continuous series, 11 years, of records of the Quadrantid meteor shower illustrates the problems and the results that can be achieved. International cooperation would greatly assist such studies.

VARIATIONS IN THE INTRINSIC STRENGTH OF THE 1956 QUADRANTID METEOR SHOWER

1957 ◽  
Vol 35 (6) ◽  
pp. 703-711 ◽  
Author(s):  
C. O. Hines ◽  
E. L. Vogan
Keyword(s):  
Incidence Rate ◽  
Detection Rate ◽  
Meteor Shower ◽  
New Technique ◽  
Occurrence Rate ◽  
Meteor Stream ◽  
Forward Scatter ◽  
Scatter Theory ◽  
Intrinsic Strength

The occurrence rate of meteoric signals, detected on a V.H.F. forward-scatter path, is analyzed for the time of the 1956 Quadrantid shower. The detection rate of the shower meteors is converted to an incidence rate, by use of the appropriate forward-scatter theory. The variation in the intrinsic strength of the shower is thereby determined, on an hour-to-hour basis, and it is compared with variations which have been obtained in other years by other methods. The comparison reveals a distinct secular shifting of the orbit of the Quadrantid meteor stream. It also illustrates the marked advantage of the new technique in assessing variations in the strengths of short-lived showers.

scholarly journals η Lyrid Meteor Stream Associated with Comet Iras-Araki-Alcock, 1983 VII

1991 ◽  
Vol 126 ◽  
pp. 315-318
Author(s):  
K. Ohtsuka
Keyword(s):  
Meteor Shower ◽  
Meteor Stream

AbstractThe probable association of Comet IRAS-Araki-Alcock with theηLyrid meteor stream is suggested, and the possible relation of the radio meteor shower on 1983 May 10 is also discussed.

A history of botanical collections in the Luangwa Valley, Zambia

1998 ◽  
Vol 25 (2) ◽  
pp. 283-291
Author(s):  
P.S.M. PHIRI ◽  
D.M. MOORE
Keyword(s):  
Eighteenth Century ◽  
Environmental Impact ◽  
Impact Assessment ◽  
Vascular Plants ◽  
Central Africa ◽  
Peak Activity ◽  
Historical Account ◽  
History Of ◽  
The 1960S ◽  
Made In

Central Africa remained botanically unknown to the outside world up to the end of the eighteenth century. This paper provides a historical account of plant explorations in the Luangwa Valley. The first plant specimens were collected in 1897 and the last serious botanical explorations were made in 1993. During this period there have been 58 plant collectors in the Luangwa Valley with peak activity recorded in the 1960s. In 1989 1,348 species of vascular plants were described in the Luangwa Valley. More botanical collecting is needed with a view to finding new plant taxa, and also to provide a satisfactory basis for applied disciplines such as ecology, phytogeography, conservation and environmental impact assessment.

Radio Geminid meteor shower of 1994

1996 ◽  
Vol 19 (3) ◽  
pp. 451-454 ◽  
Author(s):  
G. Cevolani ◽  
V. Porubčan ◽  
A. Hajduk ◽  
M. F. Gabucci ◽  
G. Grassi ◽  
...  
Keyword(s):  
Meteor Shower

Respiratory response to partial paralysis in anesthetized dogs

1984 ◽  
Vol 56 (6) ◽  
pp. 1583-1588 ◽  
Author(s):  
A. Oliven ◽  
E. C. Deal ◽  
S. G. Kelsen ◽  
N. S. Cherniack
Keyword(s):  
Motor Activity ◽  
Respiratory Muscle ◽  
Respiratory Muscles ◽  
Peak Activity ◽  
Inspiratory Time ◽  
Muscle Paralysis ◽  
Anesthetized Dogs ◽  
Spontaneously Breathing ◽  
Partial Paralysis

The ability to maintain alveolar ventilation is compromised by respiratory muscle weakness. To examine the independent role of reflexly mediated neural mechanisms to decreases in the strength of contraction of respiratory muscles, we studied the effects of partial paralysis on the level and pattern of phrenic motor activity in 22 anesthetized spontaneously breathing dogs. Graded weakness induced with succinylcholine decreased tidal volume and prolonged both inspiratory and expiratory time causing hypoventilation and hypercapnia. Phrenic peak activity as well as the rate of rise of the integrated phrenic neurogram increased. However, when studied under isocapnic conditions, increases in the severity of paralysis, as assessed from the ratio of peak diaphragm electromyogram to peak phrenic activity, produced progressive increases in inspiratory time and phrenic peak activity but did not affect its rate of rise. After vagotomy, partial paralysis induced in 11 dogs with succinylcholine also prolonged the inspiratory burst of phrenic activity, indicating that vagal reflexes were not solely responsible for the alterations in respiratory timing. Muscle paresis was also induced with gallamine or dantrolene, causing similar responses of phrenic activity and respiratory timing. Thus, at constant levels of arterial CO2 in anesthetized dogs, respiratory muscle partial paralysis results in a decrease in breathing rate without changing the rate of rise of respiratory motor activity. This is not dependent solely on vagally mediated reflexes and occurs regardless of the pharmacological agent used. These observations in the anesthetized state are qualitatively different from the response to respiratory muscle paralysis or weakness observed in awake subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals CELL-MEDIATED CYTOTOXICITY DURING REJECTION AND ENHANCEMENT OF ALLOGENEIC SKIN GRAFTS IN RATS

1972 ◽  
Vol 135 (6) ◽  
pp. 1301-1315 ◽  
Author(s):  
Hans-Hartmut Peter ◽  
Joseph D. Feldman
Keyword(s):  
Lymph Nodes ◽  
Thoracic Duct ◽  
Lymphoid Cells ◽  
Target Cells ◽  
Skin Grafts ◽  
Peak Activity ◽  
Adult Rats ◽  
Background Levels

Cell-mediated cytotoxicity (CMC) in spleens and lymph nodes of allografted rats was determined by release of 51Cr from labeled target cells incubated with aggressor lymphoid cells. CMC was first detected in grafted adult rats on day 5, peaked on days 7 and 8, and declined rapidly to background levels by days 9 to 11. In allografted neonates and in cyclophosphamide-treated or neonatally thymectomized adults CMC was a fraction of that observed in normal adult rats. Enhancing antibodies deferred in vivo peak activity of CMC in allografted neonates for 3–4 days, and blocked in vitro the action of aggressor lymphocytes by binding to target cells. Enhancing antibodies had no effect on the cytotoxicity of aggressor cells, but horse antibodies to rat thoracic duct cells inhibited in vitro CMC of aggressor cells.

Sign in / Sign up

Export Citation Format

Share Document