Hydraulic Resistance of Plants. I. Constant or Variable?

1984 ◽  
Vol 11 (5) ◽  
pp. 333 ◽  
Author(s):  
JB Passioura
Keyword(s):  
Hydrostatic Pressure ◽  
Water Potential ◽  
Flow Rate ◽  
Single Cells ◽  
The Other ◽  
Published Data ◽  
Ohm’S Law ◽  
Composite Equation ◽  
Ohm's Law ◽  
The Difference

Two popular equations for describing the flow of water through plants are discussed and criticized. They are the Ohm's Law analogue, in which the flow rate is assumed to be proportional to the difference in water potential across the plant, between leaf and soil; and an equation, used widely to describe transmembrane fluxes of single cells, in which the flow rate is assumed to be the sum of two components, one proportional to the difference in hydrostatic pressure, the other proportional to the difference in osmotic pressure, between specified points in the plant. The well-established theoretical inadequacies of the Ohm's Law analogue are reviewed, especially the poorly recognized fact that it is of little use if substantial amounts of solutes are flowing with the water. The other, composite, equation does not have the same grave theoretical inadequacies, but its failure to agree with published data is highlighted.

scholarly journals XXI. On the rate at which electricity leaks through liquids which are bad conductors of electricity

1887 ◽  
Vol 42 (251-257) ◽  
pp. 410-429 ◽  
Keyword(s):  
Ohm’S Law ◽  
Ohm's Law ◽  
The Difference

The experiments here described were undertaken to test whether the rate at which electricity leaks through a liquid which conducts electricity badly, does or does not follow Ohm’s law. The method used is described later on; it consists in establishing by a battery a difference of potential of about 100 volts between the plates of a condenser, in which the dielectric is the faulty insulator to be experimented on, then disconnecting the battery, and measuring with an electrometer the rate at which the difference of potential dies away.

scholarly journals DIFFERING RATES OF DEATH AT INNER AND OUTER SURFACES OF THE PROTOPLASM

1944 ◽  
Vol 28 (1) ◽  
pp. 23-36 ◽  
Author(s):  
W. J. V. Osterhout
Keyword(s):  
Hydrostatic Pressure ◽  
Partition Coefficient ◽  
The Other ◽  
Protoplasmic Surface ◽  
Inner Surface ◽  
Potassium Effect ◽  
Outer Protoplasmic Surface ◽  
The Difference

When protoplasm dies it becomes completely and irreversibly permeable and this may be used as a criterion of death. On this basis we may say that when 0.2 M formaldehyde plus 0.001 M NaCl is applied to Nitella death arrives sooner at the inner protoplasmic surface than at the outer. If, however, we apply 0.17 M formaldehyde plus 0.01 M KCl death arrives sooner at the outer protoplasmic surface. The difference appears to be due largely to the conditions at the two surfaces. With 0.2 M formaldehyde plus 0.001 M NaCl the inner surface is subject to a greater electrical pressure than the outer and is in contact with a higher concentration of KCl. In the other case these conditions are more nearly equal so that the layer first reached by the reagent is the first to become permeable. The outer protoplasmic surface has the ability to distinguish electrically between K+ and Na+ (potassium effect). Under the influence of formaldehyde this ability is lost. This is chiefly due to a falling off in the partition coefficient of KCl in the outer protoplasmic surface. At about the same time the inner protoplasmic surface becomes completely permeable. But the outer protoplasmic surface retains its ability to distinguish electrically between different concentrations of the same salt, showing that it has not become completely permeable. After the potential has disappeared the turgidity (hydrostatic pressure inside the cell) persists for some time, probably because the outer protoplasmic surface has not become completely permeable.

Effect of Elongation on the Electrical Anisotropy of Natural Rubber and SBR Vulcanizates Containing ISAF Carbon Black

1962 ◽  
Vol 35 (2) ◽  
pp. 317-325 ◽  
Author(s):  
R. Chasset ◽  
P. Thirion
Keyword(s):  
Mechanical Properties ◽  
Electrical Resistivity ◽  
Carbon Black ◽  
Natural Rubber ◽  
The Other ◽  
Electrical Anisotropy ◽  
Ohm’S Law ◽  
Carbon Blacks ◽  
Ohm's Law ◽  
Current Flows

Abstract The electrical resistivity of testpieces under different elongations, both parallel and at right-angles to the axis of elongation, was measured for two vulcanizates, i.e. one of natural rubber and the other of SBR, compounded with 20 volume per cent of ISAF black (Vulcan 6). Within the range of validity of Ohm's law, the main results of this study are as follows: a) the resistivities of both vulcanizates increase considerably with elongation, in both directions. b) on the whole, both vulcanizates are electrically anisotropic, since current flows more easily longitudinally than it does transversely. The anisotropy increases at the start with elongation, then becomes practically constant. However, the latter level is much higher with natural rubber, for which it corresponds to an anisotropy of about 1,000 and an elongation of around 150%. For SBR this level is only 20 to 30 and is reached at only 50% elongation. Owing to the complexity of the problem, no interpretation can yet be given for these differences. It will first be necessary to examine other elastomers and carbon blacks. For the time being, it may merely be stated that the electrical anisotropy of natural rubber and SBR reinforced vulcanizates differs as much as their mechanical properties, especially their tearing behavior.

Effects of Osmotica Around the Roots on Water Uptake by Maize Plants

1980 ◽  
Vol 7 (1) ◽  
pp. 27 ◽  
Author(s):  
RA Nulsen ◽  
GW Thurtell
Keyword(s):  
Polyethylene Glycol ◽  
Water Potential ◽  
Nutrient Solution ◽  
Leaf Water Potential ◽  
Flow Rate ◽  
Osmotic Potential ◽  
Leaf Water ◽  
Maize Plants ◽  
The Difference ◽  
Osmotic Potentials

Nutrient solutions with osmotic potentials of -70, -190 and -380 kPa were supplied to maize plants whose roots were enclosed in a pressure chamber. The plants were stressed and then rewatered with the same nutrient solution. Sap flow rate from the detopped root system was measured at 400 kPa applied pressure. The lower was the osmotic potential of the pretreatment solution, the lower was the initial flow rate. Flow rates rapidly decreased to zero and did not recover for up to 90 min. Different responses in leaf water potential of unstressed, intact plants occurred when the nutrient solution bathing the root was replaced by either a more concentrated nutrient solution or a solution of sucrose or polyethylene glycol 6000. For nutrient solution replacement the change in leaf water potential was less than the difference in solution osmotic potentials; for sucrose the difference was greater, and for polyethylene glycol the change was equal to the osmotic potential difference. Osmotic effects observed were due to differential accumulations at different barriers in the root. The zero-flow periods seen during recovery of severely stressed plants may have been due to a decrease in the osmotic potential of the solution external to the plasmalemma of root cortical cells.

scholarly journals Formulation of root water uptake in a multi-layer soil-plant model: does van den Honert's equation hold?

1998 ◽  
Vol 2 (1) ◽  
pp. 31-39 ◽  
Author(s):  
J.-P. Lhomme
Keyword(s):  
Water Potential ◽  
Soil Water ◽  
Water Uptake ◽  
Transpiration Rate ◽  
Plant Resistance ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Layer Model ◽  
Ohm’S Law ◽  
Ohm's Law

Abstract. The withdrawal of water from soil by vegetation, which in steady state conditions is equivalent to the transpiration rate, can be written in terms of water potential in the form of an Ohm's law analogy, known as van den Honert's equation: The difference between an effective soil water potential and the bulk canopy water potential is divided by an effective soil-plant resistance. This equation is commonly used, but little is known about the precise definition of its parameters. The issue of this paper is to bridge the gap between the bulk approach and a multi-layer description of soil-plant water transfer by interpreting the bulk parameters in terms of the characteristics of the multi-layer approach. Water flow through an elementary path within the soil or the root is assumed to follow an Ohm's law analogy, and the soil and root characterisics are allowed to vary with depth. Starting from the basic equations of the multi-layer approach, it is proved that the total rate of transpiration can also be expressed in the form of an Ohm's law analogy. This means that van den Honert's equation holds at canopy scale, insofar as the assumptions made on the physics of root water uptake hold. In the bulk formulation derived, the effective soil-plant resistance appears as a combination of the elementary resistances making up the multi-layer model; and the effective soil water potential is a weighted mean of the water potentials in each soil layer, the weighting system involving the complete set of elementary resistances. Simpler representations of soil-plant interaction leading to Ohm's law type formulations are also examined: a simplified multi-layer model, in which xylem (root axial) resistance is neglected, and a bulk approach, in which soil-root interaction is represented by only one layer. Numerical simulations performed in different standard conditions show that these simpler representations do not provide accurate estimates of the transpiration rate, when compared to the values obtained by the complete algorithm.

Enhancement of ADP-induced Platelet Aggregation by Adrenaline in Vivo and Its Prevention

1973 ◽  
Vol 29 (02) ◽  
pp. 490-498 ◽  
Author(s):  
Hiroh Yamazaki ◽  
Itsuro Kobayashi ◽  
Tadahiro Sano ◽  
Takio Shimamoto
Keyword(s):  
Platelet Count ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
The Other ◽  
Endothelial Surface ◽  
Important Interaction ◽  
Blood Coagulability ◽  
The Difference

SummaryThe authors previously reported a transient decrease in adhesive platelet count and an enhancement of blood coagulability after administration of a small amount of adrenaline (0.1-1 µg per Kg, i. v.) in man and rabbit. In such circumstances, the sensitivity of platelets to aggregation induced by ADP was studied by an optical density method. Five minutes after i. v. injection of 1 µg per Kg of adrenaline in 10 rabbits, intensity of platelet aggregation increased to 115.1 ± 4.9% (mean ± S. E.) by 10∼5 molar, 121.8 ± 7.8% by 3 × 10-6 molar and 129.4 ± 12.8% of the value before the injection by 10”6 molar ADP. The difference was statistically significant (P<0.01-0.05). The above change was not observed in each group of rabbits injected with saline, 1 µg per Kg of 1-noradrenaline or 0.1 and 10 µg per Kg of adrenaline. Also, it was prevented by oral administration of 10 mg per Kg of phenoxybenzamine or propranolol or aspirin or pyridinolcarbamate 3 hours before the challenge. On the other hand, the enhancement of ADP-induced platelet aggregation was not observed in vitro, when 10-5 or 3 × 10-6 molar and 129.4 ± 12.8% of the value before 10∼6 molar ADP was added to citrated platelet rich plasma (CPRP) of rabbit after incubation at 37°C for 30 second with 0.01, 0.1, 1, 10 or 100 µg per ml of adrenaline or noradrenaline. These results suggest an important interaction between endothelial surface and platelets in connection with the enhancement of ADP-induced platelet aggregation by adrenaline in vivo.

Energy Approximation

2017 ◽  
Author(s):  
Philip Isett
Keyword(s):  
Main Lemma ◽  
The Other ◽  
Coarse Scale ◽  
Continuous Solutions ◽  
Material Derivative ◽  
Energy Variation ◽  
Energy Approximation ◽  
The Difference ◽  
Derivatives Of

This chapter presents the equations and calculations for energy approximation. It establishes the estimates (261) and (262) of the Main Lemma (10.1) for continuous solutions; these estimates state that we are able to accurately prescribe the energy that the correction adds to the solution, as well as bound the difference between the time derivatives of these two quantities. The chapter also introduces the proposition for prescribing energy, followed by the relevant computations. Each integral contributing to the other term can be estimated. Another proposition for estimating control over the rate of energy variation is given. Finally, the coarse scale material derivative is considered.

Pengaruh Unsur Budaya Lokal dalam Ungkapan Berbahasa Perancis

Metahumaniora ◽  
2017 ◽  
Vol 7 (3) ◽  
pp. 378
Author(s):  
Vincentia Tri Handayani
Keyword(s):  
Mental Representation ◽  
Cultural Context ◽  
Oral Tradition ◽  
Minimal Element ◽  
The Other ◽  
Local Culture ◽  
Community Groups ◽  
Cultural Community ◽  
The Difference ◽  
Complex Words

AbstrakFolklor yang menghasilkan tradisi lisan merupakan perwujudan budaya yang lahirdari pengalaman kelompok masyarakat. Salah satu bentuk tradisi lisan adalah ungkapan yangmengandung unsur budaya lokal dalam konstruksinya yang tidak dimiliki budaya lainnya.Ungkapan idiomatis memberikan warna pada bahasa melalui penggambaran mental. Dalambahasa Perancis, ungkapan dapat berupa locution dan expression. Perbedaan motif acuansuatu ungkapan dapat terlihat dari pengaruh budaya masyarakat pengguna bahasa. Sebuahleksem tidak selalu didefinisikan melalui unsur minimal, tidak juga melalui kata-kata,baik kata dasar atau kata kompleks, namun dapat melalui kata-kata beku yang maknanyatetap. Hubungan analogis dari makna tambahan yang ada pada suatu leksem muncul dariidentifikasi semem yang sama. Semem tersebut mengarah pada term yang diasosiasikan danyang diperkaya melalui konteks (dalam ungkapan berhubungan dengan konteks budaya).Kata kunci: folklor, ungkapan, struktur, makna idiomatis, kebudayaanAbstractFolklore which produces the oral tradition is a cultural manifestation born out theexperience of community groups. One form of the oral tradition is a phrase that containsthe elements of local culture in its construction that is not owned the other culture. Theidiomatic phrase gives the color to the language through the mental representation. InFrench, the expression can consist of locution and expression. The difference motivesreference of an expression can be seen from the influence of the cultural community thelanguage users. A lexeme is not always defined through a minimal element, nor throughwords, either basic or complex words, but can be through the frost words whose meaningsare fixed. The analogical connection of the additional meanings is on a lexeme arises fromthe identification of the same meaning. The meaning ‘semem’ leads to the associated termsand which are enriched through the context (in idiom related to the cultural context).Keywords : folklore, idioms, structure, idiom meaning, cultureI PENDAHULUAN

Problems of species and the features of geographical distribution in colonial volvocine algae (Chlorophyta)

2020 ◽  
Vol 54 (2) ◽  
pp. 299-311
Author(s):  
A. G. Desnitskiy
Keyword(s):  
New Species ◽  
Geographical Distribution ◽  
World Literature ◽  
The Other ◽  
Disjunct Distribution ◽  
Published Data ◽  
Species Problem ◽  
Comprehensive Review ◽  
Volvocine Algae ◽  
Cryptic Taxa

More than ten new species of colonial volvocine algae were described in world literature during recent years. In present review, the published data on taxonomy, geographical distribution and the species problem in this group of algae, mainly from the genera Gonium, Pandorina, Eudorina, and Volvox, are critically discussed. There are both cosmopolitan volvocalean species and species with local or disjunct distribution. On the other hand, the description of new cryptic taxa in some genera of the colonial family Volvocaceae, such as Pandorina and Volvox, complicates the preparation of a comprehensive review on their geography.

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