Shunt Paths Research Articles

Zn ( PO 3 ) 2 Glass as a Doping Source for GaP ( Zn , O )

As an alternative to elemental Zn and powder, glass has been utilized as a convenient simultaneous source of Zn and O to dope . The synthesis of powder, from and is described together with some of its advantageous properties (low melting point, compactness, small surface area for adsorption). powder, was employed in the preparation of liquid‐phase epitaxial layers (on vapor grown substrates) and of solution‐grown (SG) platelets, for which red electroluminescence and photoluminescence efficiency maximization curves were determined, respectively. The results are comparable to those obtained previously by using Zn and . Analysis of the photoluminescence measurements, absorption spectra, and below‐gap excitation spectra on SG platelets indicates that the incorporation chemistry of Zn and O from powder, is in accord with previous findings using Zn and . Since the nonradiative shunt path component of the minority carrier lifetime in SG platelets is hole concentration dependent for growth solutions containing powder, as well as for those containing Zn and , it seems unlikely that the “killer center” associated with the shunt path is related to the background impurities introduced by these dopants.

Characteristics of aldosterone stimulated transport in isolated skin of the toad, Bufo bufo (L.)

Aldosterone not only stimulates active sodium transport through isolated toad skin but also initiates slough formation. This, in turn, affects both the active sodium transport and the passive transport of ions through the skin in a very nearly reversible manner. This overall response to aldosterone is studied by means of the short-circuit technique in combination with tracers. The analysis is based on the equivalent circuit analogue developed by Ussing, which allows the determination of the following parameters: the rate of active transport, the resistance to active transport, the electromotive force (EMF) of the active transport system, and the resistance as well as the sodium/chloride selectivity of the shunt path. The time course of the aldosterone response is tentatively divided into three more or less overlapping periods: (1) Initial stimulatory period: registered shortly after addition of aldosterone and characterized by an increased active sodium transport, a decreased resistance to active transport, and a decreased EMF of the active tránsport system. 1. (2) Refractory period: developing as slough formation takes place and starting about three hours after addition of aldosterone. During this period, the hormonal stimulation of the active transport disappears together with an increase in the resistance to active transport and an increase in the EMF of the active transport system. In addition, the shunt resistance decreases and its selectivity is lost. 2. (3) Final stimulatory period: starting about the time slough formation is concluded, i.e. 5–7 h after addition of aldosterone. Stimulation of the active sodium transport reappears, while the resistance to active transport and the EMF of the active transport system decrease. Also, the selectivity of the shunt path reappears. The results support the idea that aldosterone stimulates the entry of sodium into the cellular compartment from the outer solution, and are compatible with the view that slough formation and shedding of the cornified layer are accompanied by a shift of the functional stratification of the epithelium, i.e. the functionally outward-facing membrane moves to an underlying cell layer, and the same holds for the functioning tight junctions confined to the outermost part of the skin.

Luminescence and doping characteristics of liquid encapsulation Czochralski grown GaP(Zn, O)

A study of the luminescence and doping characteristics of liquid encapsulation Czochralski (LEC) grown GaP(Zn, O) is presented. Sections from the seed, middle and tail regions of 8 crystals grown from melts containing varying amounts of gallium oxide and zinc were examined with respect to red photoluminescence quantum efficiency, minority carrier lifetime, hole concentration and concentration of paired and unpaired oxygen. The measured minority carrier lifetimes in these crystals were found to be 2–3 orders of magnitude shorter than in crystals grown from solution with comparable zinc and oxygen incorporation. This result indicates that a strong shunt path for electron recombination exists in the LEC crystals, which in turn accounts for their lower red photoluminescence efficiency when compared with the efficiency of solution grown crystals.

Time Decay and Temperature Dependence of Radiative Recombination in (Zn, O)-Doped GaP

To understand the kinetics of the radiative emission in (Zn, O)-doped GaP, primarily at room temperature, we have measured luminescence lifetimes using pulsed photoexcitation from argon and He–Ne lasers. Measurements of time decay and temperature dependences of the radiative emission have enabled us to identify the emission in the near infrared as resulting from transitions involving a bound electron at an oxygen site to a free hole in the valence band. Measurements of the temperature dependence of the decay times and the luminescence intensities of the exciton (red) and bound-electron to free-hole (infrared) emissions also substantiate the conclusions that nonradiative recombination paths exist out of the Zn–O complex and provide evidence for the existence of a nonradiative ``shunt path'' out of the conduction band. The bound electron to free-hole recombination out of oxygen is believed to be primarily radiative. For an annealed sample, the decay times of the exciton and bound-to-free transitions are measured to be 170 nsec and 11.2 μsec at 300°K. From the relative variation of the excitonic and bound electron to free-hole intensities and their decay times in annealed and quenched samples it is reaffirmed that on annealing the quantum efficiency of the exciton emission increases and, furthermore, concluded that on annealing the quantum efficiency of bound-electron to free-hole emission also increases. A study of these effects increases our understanding of the process of annealing. Finally a weak correlation between the external quantum efficiency of excitonic (red) emission and its decay times is established for optimally doped, solution-grown GaP.

The morphological aspects of shunt-path in the epithelium of the frog skin ( R.temporaria)

The morphological aspects of the “shunt-paths” in the epithelium of the frog skin have been investigated. When the skin potential (PD) across the skin is artificially clamped at 170 mV (inside positive) by the application of an external source of EMF, the active sodium transport is virtually stopped and an outgoing current (reversed current) passes through the skin. This current is carried exclusively by passive ion fluxes and thus may be assumed to follow the “shunt paths”. Skins fixed under such conditions show a number of characteristic changes in the morphology of the epithelium. The changes are primarily seen in the cell layer just below the cornified layer (first reacting cell layer, 1st RCL). Two distinctly different reactions are observed: (1) pronounced shrinkage of the majority of cells; (2) appearance of individual cells showing pronounced swelling. In experiment with sulphate as the anion, the number of swollen cells is clearly correlated to the strength of the reversed current. Thus in these skins the current may pass mainly through the swollen cells. With chloride as the anion a correlation between current strength and the number of swollen cells is not apparent.

Effect of prolonged saline-exposure on sodium transport across frog skin.

1. Differences in Na transport between skins from Rana temporaria and R. esculenta maintained for up to several weeks in water or 0.7% saline (0.7 g NaCl in 100 ml. H(2)O), with and without daily injections of 4% saline (4 g NaCl in 100 ml. H(2)O), were measured, in vitro.2. In saline-treated skins, the following changes were found:(a) An increased Na content.(b) A consistent decrease in short-circuit current (I(sc)).(c) An increased d.c. resistance, R, the consistency of which varied with the anion content of the Ringer solution.(d) A highly significant fall in Na influx, accounting for the reduced I(sc); a small reduction in Na efflux was not significant, statistically.(e) The Pitressin-induced increment in I(sc) was usually considerably lower compared with that in water-exposed skins; considered relative to the pre-Pitressin values, however, there were no clear differences.(f) By calculation from the changes in resistance (R) caused by replacement of outer Na(2)SO(4) Ringer by K(2)SO(4) Ringer solution,I. E(0), the electromotive force of the active sodium transport system, was moderately, but significantly, reduced,II. R(shunt), the shunt path resistance, was moderately, but significantly, increased, andIII. R(ser), the series path resistance, was considerably, and highly significantly, increased.(g) K influx from outer K(2)SO(4) Ringer solution was reduced.3. Differences between skins from water-exposed and saline-treated frogs persisted, in vitro, despite the occurrence of anionic-dependent acute changes after mounting in Ringer solution.4. There were seasonal changes in I(sc), and in the effects of saline treatment.5. The findings are discussed in terms of decreased permeability of outer barriers to ion-diffusion, and reduced activity of a Na pump.

A distributed parameters model for solar cells

The distributive circuit element model consists of a chain of T elements. The elemental model is made up of series and shunt paths. The sheet resistance of the diffused layer constitutes the series path. The shunt paths are three-fold, consisting of the diode together with a series resistance, a conductance and a light generated current source. For a given cell, the parameters used in the model can be obtained by measuring the potential profiles for reverse-biased, forward-biased and short-circuited illuminated conditions and feeding the data obtained from the measurements in the solution of the differential equations for the model. The model has been successfully employed to compute optimum gridding for the cell.

A comparison of the electrical resistances of the surface cell membrane and cellular wall in the proximal tubule of the newt kidney.

1. The electrical properties of the proximal tubular cells were studied in the newt kidney by using microelectrode techniques.2. The surface membrane of the tubular cells behaved like a simple resistor when a minute current was applied intracellularly. The changes in the transmembrane potential was linearly proportional to the strength of applied current and there was neither the rectification nor the self-generative response within. a wide range of current strength.3. The potential change caused by the intracellular application of current spread over considerable distances along the longitudinal axis of the tubule. The tubular wall, thus, behaved like a core conductor.4. Application of the simple core conductor theory to the model of the tubular wall gave the values of 400μ for the space constant, 3.1×105Ωfor the effective resistance, 836Ωcm2 for the specific resistance of the surface membrane and 625Ωcm for the specific resistance of the core (cytoplasm including intercellular membranes).5. A comparison of the surface membrane resistance to the transtubular resistance suggests that there are significant extracellular shunt paths for electrolytes within the tubular wall. The leaky nature of the proximal segment was ascribed to the presence of such shunt paths.

``Shunt Path'' Photoconduction in Lead Sulfide Films

``Shunt Path'' Photoconduction in Lead Sulfide Films

Transmission Losses and Economy Loading by the Use of Admittance Constants

In order to operate a power system at optimum economy, the production costs and transmission losses must be coordinated. A straightforward derivation of the co-ordination conditions is given. A widely adopted method of finding transmission penalty factors used so-called "B-constants." These constants are not easily modified to consider changes in the transmission system or deviation from "base-case" system conditions. By starting with the equilibrium equation of a power system written in terms of admittance constants, a concise expression for the total losses of a power transmission system which does not neglect shunt paths to neutral or the effect of off-nominal turns ratios is developed. Following this same approach, an easily modified, approximate expression for the penalty factor is formed. Any errors incurred by using this approximate penalty factor are small when compared with the inaccuracy of the original data on production costs. Several test cases on hypothetical systems are given. The generation schedules for economic dispatch, using approximate penalty factors, compare quite favorably in actual hourly costs with the costs of schedules obtained by exact penalty factors.

Diode-shunting in magnetic amplifiers

IN THE self-saturating type of magnetic amplifier it is desirable to bias the saturable reactor to a particular point on its hysteresis loop. Higher gain and better linearity of the transfer function can be achieved in this manner. Shunt paths around the diodes of the magnetic amplifier afford a convenient means of biasing the saturable reactors.