Étude biométrique du développement des folioles de Parkinsonia aculeata (Leguminosae)

1983 ◽  
Vol 61 (1) ◽  
pp. 87-92 ◽  
Author(s):  
B. Jeune
Keyword(s):  
Initial Phase ◽  
Parkinsonia Aculeata ◽  
Specific Location ◽  
Organ Formation ◽  
Differentiation Zone ◽  
Close Proximity ◽  
Median Zone ◽  
Zoning Effect ◽  
Proximal Zone

There are three successive phases to foliolar development in Parkinsonia aculeata: (i) an initial phase during which primordium formation occurs; (ii) a morphogenic phase, with foliole formation; (iii) a histogenic and differentiation phase, with foliole development. Foliolar shape is determined during the basic morphogenic phase; a longer phase in which a zoning effect analogous to that seen in branches has been observed: (i) a zone of distal organ formation where folioles appear in constant succession, in a specific location, and in close proximity of each other along each border (these are the three criteria which define intrafoliolar generation centres); (ii) a histogenic median zone; and if the foliole is old enough (iii) a subproximal differentiation zone; (iv) an adult proximal zone.

Juvenile behaviour and dispersal of chuditch (Dasyurus geoffroii) (Marsupialia : Dasyuridae)

2000 ◽  
Vol 48 (5) ◽  
pp. 551 ◽  
Author(s):  
Todd R. Soderquist ◽  
Melody Serena
Keyword(s):  
Home Range ◽  
Social Cohesion ◽  
Initial Phase ◽  
Movement Patterns ◽  
Social Play ◽  
Second Phase ◽  
Radio Tracking ◽  
Close Proximity ◽  
Limited Scale ◽  
Range Observation

We examined the dispersal chronology and movement patterns of wild juvenile chuditch (Dasyurus geoffroii) using radio-tracking and trapping. Juveniles first began exploring outside the natal den when 17 weeks old and rapidly increased their foraging duration and distance. By the time weaning was completed during Weeks 22–24, at least 6 h was devoted to the initial foraging bout and juveniles were travelling over 500 m from their dens each night. The initial phase of dispersal occurred soon after weaning, with juveniles denning separately from their mothers yet remaining in the maternal home range. Mothers sometimes instigated this phase by abandoning their litters in the natal den. The second phase of dispersal away from the natal area was strongly male-biased, occurring when juveniles were 25 weeks old on average and covering long distances (>10 km). Most females were philopatric or settled in vacant areas near the maternal home range. Observation of captive chuditch during the weaning period provided further insights on dispersal, indicating that social play among littermates may be an important factor at this time. Aggressive wrestling rapidly escalated during the initial weeks of weaning, when wild juveniles were active yet in close proximity for most of the night. The intensity of wrestling declined before weaning was complete. Wild juveniles apparently participated in similar wrestling bouts, although possibly on a more limited scale than captives. This play behaviour potentially facilitates social cohesion among the litter at a time when juveniles are first capable of harming each other, and provides practice for fighting techniques used by adults to defend territories and secure mates.

Development of the tentacles and food groove in the jellyfish Aurelia aurita (Cnidaria: Scyphozoa)

2001 ◽  
Vol 79 (4) ◽  
pp. 623-632 ◽  
Author(s):  
David M Chapman
Keyword(s):  
Particulate Matter ◽  
Initial Phase ◽  
Aurelia Aurita ◽  
Lower Side ◽  
Differentiation Zone ◽  
Food Groove ◽  
Bearing Part

The development of the tentacle-bearing part of the rim of the jellyfish Aurelia aurita is described. The newly liberated ephyra lacks appendages at the bell rim between the rhopalial arms (null stage). The next stage (bump stage) has a subumbrellar bump near the rim. The bump then forms a tongue process (tongue stage) on its adoral side. The aboral part of the bump becomes the primordium of the tentacle. The tongue process elongates and spreads circumferentially, finally melding with the lappets of the rhopalial arms. Next the tongue process develops a groove that spreads laterally. The epithelium of the groove becomes glandular and serves as a food groove where particulate matter such as plankton is concentrated and undergoes the initial phase of digestion. The "upper" side of the split tongue process becomes the floor of the tentacle chambers, while the "lower" side becomes the pseudovelarium. The growth and differentiation zone for the medusa's rim is at the junction of the tentaculate part of the rim with the rhopalial region. It is here that tentacle buds form, followed by intertentacular lappets (partitions).

Microbulldozing and Microchiseling

1969 ◽  
Vol 27 ◽  
pp. 134-135
Author(s):  
J.N. Ramsey ◽  
D.P. Cameron ◽  
F.W. Schneider
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Material Handling ◽  
Microprobe Analysis ◽  
Foreign Matter ◽  
Specific Location ◽  
Potential Problems ◽  
Knoop Indenter ◽  
Scanning Electron ◽  
Microhardness Tester

As computer components become smaller the analytical methods used to examine them and the material handling techniques must become more sensitive, and more sophisticated. We have used microbulldozing and microchiseling in conjunction with scanning electron microscopy, replica electron microscopy, and microprobe analysis for studying actual and potential problems with developmental and pilot line devices. Foreign matter, corrosion, etc, in specific locations are mechanically loosened from their substrates and removed by “extraction replication,” and examined in the appropriate instrument. The mechanical loosening is done in a controlled manner by using a microhardness tester—we use the attachment designed for our Reichert metallograph. The working tool is a pyramid shaped diamond (a Knoop indenter) which can be pushed into the specimen with a controlled pressure and in a specific location.

Effects of Vincristine on Endothelial Microtubules in the Spinal Cord

1976 ◽  
Vol 34 ◽  
pp. 58-59
Author(s):  
John L. Beggs ◽  
John D. Waggener ◽  
Wanda Miller
Keyword(s):  
Spinal Cord ◽  
Biological Activity ◽  
Horseradish Peroxidase ◽  
Transport Mechanism ◽  
Vasogenic Edema ◽  
Vesicular Transport ◽  
Close Proximity

Microtubules (MT) are versatile organelles participating in a wide variety of biological activity. MT involvement in the movement and transport of cytoplasmic components has been well documented. In the course of our study on trauma-induced vasogenic edema in the spinal cord we have concluded that endothelial vesicles contribute to the edema process. Using horseradish peroxidase as a vascular tracer, labeled endothelial vesicles were present in all situations expected if a vesicular transport mechanism was in operation. Frequently,labeled vesicles coalesced to form channels that appeared to traverse the endothelium. The presence of MT in close proximity to labeled vesicles sugg ested that MT may play a role in vesicular activity.

Experiments with a scanning tunneling microscope (STM) mounted in a scanning electron microscope (SEM)

1986 ◽  
Vol 44 ◽  
pp. 636-639
Author(s):  
Oliver C. Wells ◽  
Mark E. Welland
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Mechanical Stability ◽  
Tunneling Current ◽  
Feedback System ◽  
Scanning Tunneling ◽  
Surface Profiling ◽  
Close Proximity ◽  
Metal Tip ◽  
Scanning Electron

Scanning tunneling microscopes (STM) exist in two versions. In both of these, a pointed metal tip is scanned in close proximity to the specimen surface by means of three piezos. The distance of the tip from the sample is controlled by a feedback system to give a constant tunneling current between the tip and the sample. In the low-end STM, the system has a mechanical stability and a noise level to give a vertical resolution of between 0.1 nm and 1.0 nm. The atomic resolution STM can show individual atoms on the surface of the specimen.A low-end STM has been put into the specimen chamber of a scanning electron microscope (SEM). The first objective was to investigate technological problems such as surface profiling. The second objective was for exploratory studies. This second objective has already been achieved by showing that the STM can be used to study trapping sites in SiO2.

Ultrastructure and Senescence in an Achloroplastic Mutant of Hordeum vulgare L. cv. Dyan

1992 ◽  
Vol 50 (1) ◽  
pp. 844-845
Author(s):  
R.H.M. Cross ◽  
C.E.J. Botha ◽  
A.K. Cowan ◽  
B.J. Hartley
Keyword(s):  
Cell Wall ◽  
Hordeum Vulgare ◽  
Leaf Tissue ◽  
Ultrastructural Changes ◽  
Hordeum Vulgare L ◽  
Mesophyll Cells ◽  
Lethal Mutant ◽  
Cytoplasmic Matrix ◽  
Close Proximity ◽  
Pinocytotic Vesicles

Senescence is an ordered degenerative process leading to death of individual cells, organs and organisms. The detection of a conditional lethal mutant (achloroplastic) of Hordeum vulgare has enabled us to investigate ultrastructural changes occurring in leaf tissue during foliar senescence.Examination of the tonoplast structure in six and 14 day-old mutant tissue revealed a progressive degeneration and disappearance of the membrane, apparently starting by day six in the vicinity of the mitochondria associated with the degenerating proplastid (Fig. 1.) where neither of the plastid membrane leaflets is evident (arrows, Fig. 1.). At this stage there was evidence that the mitochondrial membranes were undergoing retrogressive changes, coupled with disorganization of cristae (Fig. 2.). Proplastids (P) lack definitive prolamellar bodies. The cytoplasmic matrix is largely agranular, with few endoplasmic reticulum (ER) cisternae or polyribosomal aggregates. Interestingly, large numbers of actively-budding dictysomes, associated with pinocytotic vesicles, were observed in close proximity to the plasmalemma of mesophyll cells (Fig. 3.). By day 14 however, mesophyll cells showed almost complete breakdown of subcellular organelle structure (Fig. 4.), and further evidence for the breakdown of the tonoplast. The final stage of senescence is characterized by the solubilization of the cell wall due to expression and activity of polygalacturonase and/or cellulose. The presence of dictyosomes with associated pinocytotic vesicles formed from the mature face, in close proximity to both the plasmalemma and the cell wall, would appear to support the model proposed by Christopherson for the secretion of cellulase. This pathway of synthesis is typical for secretory glycoproteins.

Localization of DNA in chromatin using ESI and osmium ammine staining

1990 ◽  
Vol 48 (3) ◽  
pp. 116-117
Author(s):  
C.L. Woodcock ◽  
R.A. Horowitz ◽  
D. P. Bazett-Jones ◽  
A.L. Olins
Keyword(s):  
Spectroscopic Imaging ◽  
Energy Losses ◽  
Electron Spectroscopic Imaging ◽  
Feulgen Reaction ◽  
Specific Location ◽  
Eukaryotic Nucleus ◽  
Chromatin Fibers ◽  
Patiria Miniata ◽  
Model Structures

In the eukaryotic nucleus, DNA is packaged into nucleosomes, and the nucleosome chain folded into ‘30nm’ chromatin fibers. A number of different model structures, each with a specific location of nucleosomal and linker DNA have been proposed for the arrangment of nucleosomes within the fiber. We are exploring two strategies for testing the models by localizing DNA within chromatin: electron spectroscopic imaging (ESI) of phosphorus atoms, and osmium ammine (OSAM) staining, a method based on the DNA-specific Feulgen reaction.Sperm were obtained from Patiria miniata (starfish), fixed in 2% GA in 150mM NaCl, 15mM HEPES pH 8.0, and embedded In Lowiciyl K11M at -55C. For OSAM staining, sections 100nm to 150nm thick were treated as described, and stereo pairs recorded at 40,000x and 100KV using a Philips CM10 TEM. (The new osmium ammine-B stain is available from Polysciences Inc). Uranyl-lead (U-Pb) staining was as described. ESI was carried out on unstained, very thin (<30 nm) beveled sections at 80KV using a Zeiss EM902. Images were recorded at 20,000x and 30,000x with median energy losses of 110eV, 120eV and 160eV, and a window of 20eV.

Some changes during the initial phase of the unit system in a large mental hospital

1966 ◽  
Author(s):  
Robert P. Barrell ◽  
Alan S. DeWolfe ◽  
Fred E. Spaner
Keyword(s):  
Initial Phase ◽  
Mental Hospital ◽  
Unit System

Entrainment and Annihilation of Reentrant Excitation in a Periodically Stimulated Ring of Excitable Media

1997 ◽  
Vol 36 (04/05) ◽  
pp. 290-293
Author(s):  
L. Glass ◽  
T. Nomura
Keyword(s):  
Cardiac Arrhythmias ◽  
Initial Phase ◽  
Human Heart ◽  
Periodic Wave ◽  
Excitable Media ◽  
One Dimensional ◽  
Clinical Observations ◽  
Periodic Stimulation ◽  
Reentrant Excitation ◽  
Stimulation Of

Abstract:Excitable media, such as nerve, heart and the Belousov-Zhabo- tinsky reaction, exhibit a large excursion from equilibrium in response to a small but finite perturbation. Assuming a one-dimensional ring geometry of sufficient length, excitable media support a periodic wave of circulation. As in the periodic stimulation of oscillations in ordinary differential equations, the effects of periodic stimuli of the periodically circulating wave can be described by a one-dimensional Poincaré map. Depending on the period and intensity of the stimulus as well as its initial phase, either entrainment or termination of the original circulating wave is observed. These phenomena are directly related to clinical observations concerning periodic stimulation of a class of cardiac arrhythmias caused by reentrant wave propagation in the human heart.

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