scholarly journals Fibonacci or quasi-symmetric phyllotaxis. Part I: why?

2016 ◽  
Vol 85 (4) ◽  
Author(s):  
Christophe Golé ◽  
Jacques Dumais ◽  
Stéphane Douady
Keyword(s):  
Fibonacci Numbers ◽  
Companion Paper ◽  
Disk Accretion ◽  
Elementary Model ◽  
Data Analyses ◽  
Biological Studies ◽  
Accretion Model ◽  
Square Packing ◽  
Plant Data

The study of phyllotaxis has focused on seeking explanations for the occurrence of consecutive Fibonacci numbers in the number of helices paving the stems of plants in the two opposite directions. Using the disk-accretion model, first introduced by Schwendener and justified by modern biological studies, we observe two distinct types of solutions: the classical Fibonacci-like ones, and also more irregular configurations exhibiting nearly equal number of helices in a quasi-square packing, the quasi-symmetric ones, which are a generalization of the whorled patterns. Defining new geometric tools allowing to work with irregular patterns and local transitions, we provide simple explanations for the emergence of these two states within the same elementary model. A companion paper will provide a wide array of plant data analyses that support our view.

scholarly journals Symmetry in plants: from Bravais' lattices to an explanation of Fibonacci phyllotaxis.

2014 ◽  
Vol 70 (a1) ◽  
pp. C1420-C1420
Author(s):  
Christophe Gole
Keyword(s):  
Computer Simulations ◽  
Fibonacci Numbers ◽  
Mathematical Work ◽  
Simple Explanation ◽  
Seminal Work ◽  
Plant Samples ◽  
Golden Angle ◽  
Accretion Model

In 1837, fourteen years before publishing his seminal Etude sur la cristallographie Auguste Bravais and his brother Louis wrote an equally seminal work on the arrangement of leaves around the stem of a plant. In this paper, one of the very first truly bio-mathematical work, they introduce and analyze cylindrical lattices and conjecture that only those with the golden angle between successive leaves can exhibit the Fibonacci numbers of spirals predominant in plants. With the advent of the microscope, and following  observations of the plants growing tips by Hofmeister, botanists Schwendener and van Iterson  developed an accretion model of the plant structures. Their work use ideas of what we now would call renormalization of morphogenetic fronts to understand transitions between successive Fibonacci pairs. This gives rise to a  simple explanation of the omni-presence of Fibonacci numbers in plants, which can be verified on digitized plant samples and with systematic computer simulations. This could inform crystallographers in their study of dislocations.

scholarly journals Fu Orionis eruptions and early stellar evolution

1990 ◽  
Vol 137 ◽  
pp. 229-251
Author(s):  
Bo Reipurth
Keyword(s):  
Stellar Evolution ◽  
Accretion Rate ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Disk Accretion ◽  
Low Mass Stars ◽  
Photometric And Spectroscopic Observations ◽  
T Tauri ◽  
Accretion Model ◽  
Low Mass

The FU Orionis phenomenon has attracted increasing attention in recent years, and is now accepted as a crucial element in the early evolution of low mass stars. The general characteristics of FUors are outlined and individual members of the class are discussed. The discovery of a new FUor, BBW 76, is presented, together with a discussion of photometric and spectroscopic observations of the star. The evidence for circumstellar disks around T Tauri stars is briefly outlined, and the FUor phenomenon is discussed in the context of a disk accretion model. A large increase in the accretion rate through a circumstellar disk makes the disk self-luminous with a luminosity two or more orders larger than that of the star. Massive cool winds rise from FUors, and it is conceivable that they are related to the initiation of Herbig-Haro flows. The FUor phenomenon appears to be repetitive, and newborn low-mass stars may be cycling between the FUor state and the T Tauri state.

scholarly journals EVIDENCE FOR MAGNETO-LEVITATION ACCRETION IN LONG-PERIOD X-RAY PULSARS

2014 ◽  
Vol 28 ◽  
pp. 1460187 ◽  
Author(s):  
NAZAR IKHSANOV ◽  
NINA BESKROVNAYA ◽  
YURY LIKH
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Disk Accretion ◽  
X Ray ◽  
Accretion Flow ◽  
Long Period ◽  
Intrinsic Magnetic Field ◽  
Spin Evolution ◽  
Accretion Model

Study of observed spin evolution of long-period X-ray pulsars challenges quasi-spherical and Keplerian disk accretion scenarios. It suggests that the magnetospheric radius of the neutron stars is substantially smaller than Alfvén radius and the spin-down torque applied to the star from accreting material significantly exceeds the value predicted by the theory. We show that these problems can be avoided if the fossil magnetic field of the accretion flow itself is incorporated into the accretion model. The initially spherical flow in this case decelerates by its own magnetic field and converts into a non-Keplerian disk (magnetic slab) in which the material is confined by its intrinsic magnetic field ("levitates") and slowly moves towards the star on a diffusion timescale. Parameters of pulsars expected within this magneto-levitation accretion scenario are evaluated.

Modification of the Electron Microscope for Investigation of Fully Hydrated Biological Specimens

1969 ◽  
Vol 27 ◽  
pp. 418-419 ◽  
Author(s):  
R. C. Moretz ◽  
D. F. Parsons
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Structural Damage ◽  
Lower Percentage ◽  
Vacuum Drying ◽  
Total Removal ◽  
Total Absence ◽  
Biological Studies ◽  
Electron Microscopes ◽  
Beam Damage

Short lifetime or total absence of electron diffraction of ordered biological specimens is an indication that the specimen undergoes extensive molecular structural damage in the electron microscope. The specimen damage is due to the interaction of the electron beam (40-100 kV) with the specimen and the total removal of water from the structure by vacuum drying. The lower percentage of inelastic scattering at 1 MeV makes it possible to minimize the beam damage to the specimen. The elimination of vacuum drying by modification of the electron microscope is expected to allow more meaningful investigations of biological specimens at 100 kV until 1 MeV electron microscopes become more readily available. One modification, two-film microchambers, has been explored for both biological and non-biological studies.

Design of Sensitive Photographic Materials for the High-Voltage Electron Microscope

1975 ◽  
Vol 33 ◽  
pp. 156-157
Author(s):  
Murray Vernon King ◽  
Donald F. Parsons
Keyword(s):  
Electron Microscope ◽  
Radiation Damage ◽  
High Voltage ◽  
Radiation Sensitivity ◽  
Fast Electrons ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Biological Studies ◽  
Low Sensitivity

Effective application of the high-voltage electron microscope to a wide variety of biological studies has been restricted by the radiation sensitivity of biological systems. The problem of radiation damage has been recognized as a serious factor influencing the amount of information attainable from biological specimens in electron microscopy at conventional voltages around 100 kV. The problem proves to be even more severe at higher voltages around 1 MV. In this range, the problem is the relatively low sensitivity of the existing recording media, which entails inordinately long exposures that give rise to severe radiation damage. This low sensitivity arises from the small linear energy transfer for fast electrons. Few developable grains are created in the emulsion per electron, while most of the energy of the electrons is wasted in the film base.

Application of stereological analysis of cell volume to isolated myocytes in culture with and without adrenergic innervation

1990 ◽  
Vol 48 (3) ◽  
pp. 416-417
Author(s):  
Jane K. Rosenthal ◽  
Dianne L. Atkins ◽  
William J. Marvin ◽  
Penny A. Krumm
Keyword(s):  
Cardiac Myocytes ◽  
Structural Changes ◽  
Three Dimensional ◽  
Adrenergic Innervation ◽  
Culture Cell ◽  
Serial Sections ◽  
Newborn Rats ◽  
Primary Culture Cell ◽  
Biological Studies ◽  
Cell Volumes

To comprehend structural changes in cardiac myocytes accompanying adrenergic innervation, it is essential that a three dimensional analysis be performed. To date, biological studies which utilize stereological methods have been limited to cells in tissue and in organs. Our laboratory has utilized current stereological techniques for measuring absolute volumes of individual myocytes in primary culture. Cell volumes are calculated for two distinct groups of cells at 96 hours in culture: isolated myocytes and myocytes innervated with adrenergic neurons (Figure 1).Cardiac myocytes are cultured from the ventricular apices of newborn rats. Cells are plated directly onto tissue culture dishes with or without preplated explants from the paravertebral thoracolumbar sympathetic chain. On day four cultures are photographed and marked for one-to-one cell location. Following conventional fixation and embeddment in eponate-12, the cells are relocated and mounted for microtomy. The cells are completely sectioned at 120nm in their parallel orientation to the surface of the dish (Figure 2). Serial sections are collected on formvar coated slotted grids and are recorded in sequence.

Pilot Plant Data for Synthetic Iron Oxides

1952 ◽  
Vol 44 (3) ◽  
pp. 449-449
Author(s):  
C DeWitt ◽  
M Livingood ◽  
K Miller
Keyword(s):  
Iron Oxides ◽  
Pilot Plant ◽  
Plant Data

Compensatory Coping Through the Extension of Working Hours

2019 ◽  
Vol 63 (3) ◽  
pp. 115-128 ◽  
Author(s):  
Maie Stein ◽  
Sylvie Vincent-Höper ◽  
Nicole Deci ◽  
Sabine Gregersen ◽  
Albert Nienhaus
Keyword(s):  
Job Demands ◽  
Working Hours ◽  
Well Being ◽  
Leader Member Exchange ◽  
Workplace Health ◽  
High Quality ◽  
Data Analyses ◽  
Member Exchange ◽  
The Relationship ◽  
Advance Knowledge

Abstract. To advance knowledge of the mechanisms underlying the relationship between leadership and employees’ well-being, this study examines leaders’ effects on their employees’ compensatory coping efforts. Using an extension of the job demands–resources model, we propose that high-quality leader–member exchange (LMX) allows employees to cope with high job demands without increasing their effort expenditure through the extension of working hours. Data analyses ( N = 356) revealed that LMX buffers the effect of quantitative demands on the extension of working hours such that the indirect effect of quantitative demands on emotional exhaustion is only significant at low and average levels of LMX. This study indicates that integrating leadership with employees’ coping efforts into a unifying model contributes to understanding how leadership is related to employees’ well-being. The notion that leaders can affect their employees’ use of compensatory coping efforts that detract from well-being offers promising approaches to the promotion of workplace health.

Catechin derivatives from Parapiptadenia rigida: biological studies and conformational analysis

Planta Medica ◽  
2010 ◽  
Vol 76 (12) ◽  
Author(s):  
C Schmidt ◽  
M Fronza ◽  
R Murillo ◽  
V Wray ◽  
G Bringmann ◽  
...  
Keyword(s):  
Conformational Analysis ◽  
Biological Studies
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