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Dark-adapted observers reported whether the offset of a test flash (30′ to the right of fixation) occurred before or after the onset of a probe flash (2°30′ to the left of fixation) as the interstimulus interval was varied. Visual persistence (the interstimulus interval at the point of subjeptive equality for test flash offset/probe flash onset) was found to decrease with either increases in flash duration or flash luminance. These effects were shown to be independent of differential visual latencies to the onsets of flashes. For equal-energy flashes (variable luminance and duration), persistence was constant up to 100 msec, and thereafter declined linearly with log flash duration, a result attributable to changes in the shape of the function relating persistence to flash duration at lower luminances. The systematic increase for equal-energy stimuli in the duration of the total visual response with increase in flash duration suggests a basis for the recent finding that at threshold equally-detectable stimuli of different durations are discriminable.

The collision-induced dissociation (CID) mass spectra of the [MH]+ ions of a variety of C4 to C6 mono-, di-, and tri-alkyl amines have been determined at 8 keV collision energy and also as a function of collision energy over the range 5–100 eV (laboratory scale). The two major primary fragmentation pathways observed following either mode of activation are (i) production of an alkyl cation by expulsion of ammonia or an alkyl amine, and (ii) formation of a smaller protonated amine by loss of an olefin. In addition, alkane elimination from [MH]+, by a variety of pathways, is a common reaction for protonated dialkyl and trialkyl amines, especially in the 8 keV spectra. However, these alkane elimination reactions are of considerably less importance in the low energy CID spectra because they have high onset energies. The differences observed in the spectra produced by the two methods of activation are discussed in terms of the distributions of internal energies deposited in [MH]+ by the collision process. Keywords: protonated amines, collision-induced fragmentation, energy-resolved mass spectrometry.

This paper reports the low energy, low temperature mass spectra of the 27 alcohols and ethers containing up to five carbon atoms. The observed fragmentation pathways are discussed in energetic terms. Except in one instance, pentan-1-ol and 3-methylbutan-1-ol, the spectra are diagnostic of the structure of the compounds; even in this case, subtle differences can be used to determine structure. The advantage of the low energy, low temperature mass spectra in identifying low energy fragmentation routes is emphasized.

The species UO/sub 2/(DMA)/sup 2 +//sub 5/ is shown from /sup 1/H NMR studies to be the greatly predominant dioxouranium(VI) species existing in a series of dilute N,N-dimethylacetamide (DMA) solutions in CD/sub 2/Cl/sub 2/ diluent. Complete line shape analyses of exchange-modified /sup 1/H NMR DMA line shapes show the rate law for DMA exchange to be 5k/sub ex/(UO/sub 2/(DMA)/sup 2 +//sub 5/) over a 24.05-fold variation of (DMA). The mechanism of the DMA exchange is considered to be of the D type. A typical set of rate parameters are k/sub ex/(260 K) = 81 +- 2 s/sup -1/, ..delta..H/sup 2 +/ = 10.2 +- 0.2 kcal mol/sup -1/ and ..delta..S/sup 2 +/ = -10.4 +- 0.7 cal deg/sup -1/ mol/sup -1/ for a solution in which (UO/sub 2/(DMA)/sup 2 +//sub 5/), (DMA), and (CD/sub 2/Cl/sub 2/) are respectively 0.1518, 0.7108, and 14.15 M.

Organische Ionen zerfallen in den feldfreien Bereichen eines Massenspektrometers nach einer wohldefinierten Lebensdauer (t ≈ 10−5 s), die – verglichen mit der Zeitskala von Molekulschwingungen – sehr gros ist. Die im Ubergangszustand einer Dissoziation vorhandene Uberschusenergie („non fixed energy”) ist mit der von Reaktionen in Losung vergleichbar. Allgemein gilt, das nur die energetisch gunstigsten Zerfallswege miteinander konkurrieren konnen. Die Analyse von Ubergangssignalen der unimolekularen Zerfalle metastabiler Ionen liefert Informationen uber die bei der Reaktion freigesetzte kinetische Energie („kinetic energy release”), T; bei Experimenten in Losung sind diese auserst wertvollen Daten aufgrund von Stosen nicht zuganglich. Die Chemie von Ionen kann bequem studiert werden, wenn man die Ionen in einem Massenspektrometer erzeugt und die Zerfalle metastabiler Ionen analysiert.

The reactions of metastable [C5H10O]+ ˙ radical cations produced by ionization of 4-penten-1-ol are reported and discussed. These [C5H10O]+ ˙ species undergo mainly ethyl radical loss, with smaller contributions of methyl radical and water expulsion. 2H-Labelling studies reveal different specificities of hydrogen selection in these three fragmentations. The behaviour of these [C5H10O]+ ˙ ions is compared to those reported previously for isomeric radical cations containing linear alkenyl chains and a terminal hydroxyl group.

The slow unimolecular reactions of metastable CH3CHN+HR [R = C2H5, (CH3)2CH, and CH3CH2CH2] ions are reported and discussed in energetic and mechanistic terms. These immonium ions eliminate an alkene (R–H) derived by hydride abstraction from the incipient carbonium ion R+. This reaction is interpreted as occurring via an ion–dipole complex comprising the incipient carbonium ion co-ordinated to CH3CHNH, followed by rearrangement to another complex in which (R–H) and CH3CHNH are bound to a common proton. 2H-Labelling experiments show a different specificity in the hydrogenabstraction step for R = ethyl and R =n-propyl: transfer of a deuterium atom from the β-carbon predominates when R = CH2CD3, but CH3CHN+HCD2CH2CH3 expels a substantial proportion of C3H5D. The behaviour of the CH3CHN+HR ions is compared with that of their CH2N+HR homologues. An analysis is presented of the influence of the structure of R on the properties of the associated ion-dipole complexes.

The slow unimolecular reactions of six isomers of [C7H16]+˙ are reported and discussed. These results are interpreted in terms of dissociation via complexes of incipient carbonium ions and the appropriate associated radical. In some cases, rearrangement of the incipient carbonium ion precedes or accompanies decomposition; such isomerization generally favours alkyl radical loss, relative to elimination of the corresponding alkane.

Estimates of financial and economic net benefits to irrigation water supply are shown for a case study area in the northern Nile delta region of Egypt. Linear programming models of representative farms in the study area are formulated with particular attention to the possibilities of using less water per crop as well as shifting crops in response to hypothetical reductions in water supply. Net benefits are defined as gross revenues minus costs of production, including an imputed charge for family labor. Model solutions are based on both 1980 government prices with production controls (financial net benefits) and hypothetical 1980 international market prices with relaxed controls (economic net benefits). Five different water supply scenarios are analyzed: from the current, adequate level of supply, down to a 40% reduction from that level. Total, average, and marginal net benefit functions are reported. Implications of the differences between the financial and economic benefit functions for farmers are discussed.

The slow unimolecular dissociations of six members of the [CnH2n-3]+ (n = 3-8) series of unsaturated carbonium ions are explained in terms of a potential surface approach together with some concepts of mechanistic organic chemistry. The occurrence of some dissociations is shown to be precluded because either the reacting configurations or product combinations are inaccessible at energies appropriate to metastable transitions. The approach permits correct predictions to be made concerning the shapes of metastable peaks for dissociations which occur without σ-bond formation in the final step. In particular, the observation of a composite peak, thus indicating two channels for reaction, for C2H4 loss from [C7H11]+ is naturally accommodated.

The slow, unimolecular dissociations of four isomers of CH3CHO–C4H9 and two isomers of CH3CHO–C5H11 are compared. The results are interpreted in terms of a general mechanism involving an intermediate in which the incipient carbonium ion, C4H9+ or C5H11+, is co-ordinated to acetaldehyde. Rearrangement of this intermediate can take place, to form a complex in which acetaldehyde and a potential olefin, C4H8 or C5H10, are bound to a common proton. Dissociation can then occur, the nascent neutral species having the greater proton affinity retaining the proton. In some cases, rate-determining isomerisation of the incipient carbonium ion takes place. The mechanism explains the observed competition between CH3CHO and C4H8(or C5H10) elimination and also the relative magnitude of the kinetic energy released upon decomposition of isomeric ions.

An analysis is presented of ways in which the total duration of perception of transient visual stimuli may be determined by means of psychophysical judgments of the simultaneity (or relative precedence) of two sensory events. This analysis yields a new method for measuring the duration of perception that only requires judgments of the simultaneity of the offset of one visual target with the onset of another (“offset-onset” judgments), and is thus free of differential biases between onset-onset and offset-onset judgments of simultaneity which could be involved in previous measurements. When three or more perceived durations need to be determined, the new method is more efficient than earlier methods; it requires measurement of only one PSE in order to evaluate one response duration as compared to two PSEs per response duration for previous methods. We also describe ways of determining the presence of some kinds of biases and quantitatively evaluating the magnitude of bias in the new method, as well as bias in onset-onset or offset-offset judgments of simultaneity alone; such evaluations of differential bias were not possible for the earlier methods. An experimental example of a bias analysis is described. No significant biasing effects were detected in the measures of perceived duration that were extracted as either retinal location or background luminance was changed, although background luminance itself markedly influenced the values of perceived duration.

The behaviour of six members of a homologous series of oxonium ions, C3H7O+CR1R2 (R1, R2 = H or CH3) are discussed. For the two lowest members (R1 = R2 = H) isomerization of the propyl side-chain from n- to iso-structure is possible at energies lower than those required to promote decomposition of either ion. For higher members, rearrangement of the propyl side-chain from n- to iso-structure constitutes the rate-determining step in the dissociation of the ion in question. Extension of the analysis, including a consideration of plausible reactions which are found not to occur, permits estimates to be made for the heats of formation of the intermediates required for rearrangement of the propyl side-chain of C3H7O+CR1R2. It is suggested that these intermediates are stabilized by an ion—dipole interaction between the incipient propyl cation and the potential carbonyl compound, OCR1R2. The magnitude of this stabilization appears to lie in the range 15–25 kcal mol−1.

The unimolecular decompositions of two isomers of [C3H8N]+, and , are discussed in terms of the potential energy profile over which reaction may be considered to occur. The energy needed to promote slow (metastable) dissociations of either ion is found to be less than that required to cause isomerization to the other structure. This finding is supported by the observation of different decomposition pathways, different metastable peak shapes for C2H4 loss, the results of 2H labelling studies, and energy measurements on the two ions. The corresponding potential energy profile for decomposition of the oxygen analogues, and , is compared and contrasted with that proposed for the [C3H8N]+ isomers. This analysis indicates that for the oxygen analogues, the energy needed to decompose either ion is very similar to that required to cause isomerization to the other structure. Consequently, dissociation of either ion is finely balanced with rearrangement to the other and similar reactions are observed. Detailed mechanisms are proposed for loss of H2O and C2H4 from each ion and it is shown that these mechanisms are consistent with 2H and 13C labelling studies, the kinetic energy release associated with each decomposition channel, the relative competition between H2O and C2H4 loss and energy measurements.

The low voltage, low temperature mass spectra of a series of octane derivatives n-C8H17X with X=CH3, OH, OCH3, NH2, NHCH3, N(CH3)2, CO2H, CO2CH3, CO2C2H5, CHO and COCH3 are reported and discussed, using arguments involving thermochemistry where appropriate. The structures of these compounds can be uniquely assigned on the basis of such mass spectra.

When brightness-pulse duration relations are studied with a simultaneous brightness discrimination procedure, three classes of observers emerge (Bowen & Markell, 1980). These classes are defined by whether or not observers perceive temporal brightness enhancement (the Broca-Sulzer effect) under two asynchrony conditions for pulses to be compared: simultaneous onset and simultaneous offset. Type A observers perceive brightness enhancement for both asynchrony conditions; Type B observers perceive brightness enhancement for simultaneous offset of pulses but not for simultaneous onset; Type C observers do not generate the Broca-Sulzer effect under either asynchrony condition. Here we present supplementary measures on observers of all three types: (1) magnitude estimation of the brightness of single pulses of light of varying duration, (2) modulation sensitivity for sin~wave flicker, and (3) contrast sensitivity for moving sine-wave gratings. The magnitude estimation data differentiated the three types of observers, but flicker and motion sensitivity did not. The three classes of observers probably differ in the perceptual criteria they employ in judging the brightness of isolated pulses of light; they probably do not differ in their underlying neurophysiological responses.

Experiments were conducted to evaluate two extenders (egg-yolk Tris and egg-yolk lactose), varying concentrations of two cryopreservatives (glycerol and dimethyl sulfoxide), and rates for cooling to 5 degrees C, cooling from 5 to -100 degrees C, and warming for canine spermatozoa packaged in 0.5-ml French straws. At optimal concentrations of glycerol, egg-yolk Tris extender was superior to egg-yolk lactose in preserving spermatozoal motility. Addition of dimethyl sulfoxide, alone or in combination with glycerol in either extender, was not beneficial to spermatozoal survival after thawing. Canine spermatozoa withstood a range of cooling and equilibration times with no detrimental effect on spermatozoal motility prior to freezing. However, there were differences in spermatozoal motility immediately after thawing; these differences were variable, resulting in a cooling time by equilibration time interaction. Spermatozoal motility after thawing was best preserved by freezing in egg-yolk Tris extender containing 2-4% glycerol, using a moderate rate of cooling from 5 to -100 degrees C (-5 degrees C/min from 5 to -15 degrees C, then -20 degrees C/min from -15 to -100 degrees C). Three of 12 bitches inseminated intravaginally with semen frozen using this protocol became pregnant.

The slow unimolecular fragmentation reactions of 18 gaseous protonated aliphatic amines of general formula R1NH+R2R3(R1= Prn, Pri, Bun, Bui, Bus, or But; R2,R3= H,CH3) are reported and discussed. Two decomposition routes are observed for metastable ions R1NH+R2R3. The first involves elimination of a neutral amine, R2R3NH, and formation of a carbocation, R1+, via a mechanism involving an incipient cation bound to the developing amine by an ion–dipole attraction. Rearrangement of the cation, to give thermodynamically more stable isomers, is feasible in these ion–dipole complexes. Further reorganization of the complexes leads to a species in which an incipient olefin [R1– H] and an amine [R2R3NH] are co-ordinated to a common proton. Dissociation of these proton-bound complexes, with retention of the proton by the developing amine, results in olefin loss, which is the second reaction undergone by metastable ions R1NH+R2R3. The relative abundance of amine expulsion is greater for protonated amines containing a primary alkyl group, R1, than is the case for isomeric ions containing secondary or tertiary alkyl groups. Progressive methylation of the nitrogen atom decreases the relative abundance of amine loss from R1NH+R2R3, regardless of the nature of the principal alkyl group. These two trends are explained in terms of the energetics of the intermediates and products involved in the decomposition of the protonated amines.

Electron impact mass spectra obtained with 12.0 eV ionizing electrons at a source temperature of 350 K are reported for 32 saturated alkylamines. The abundances of molecular ions and primary daughter ions are discussed in energetic terms, and the effects of extending the alkyl chain or methylation of the nitrogen atom are considered. A contrast is found between the spectra of amines and those of the analogous alcohols and ethers.

Proton magnetic resonance studies show that UO 2 (DMF) 2+ 5 , pentakis(N,N-dimethylformamide)dioxouranium(VI) ion, is the greatly predominant dioxouranium(VI) species in mixed solutions of DMF and d 2 -methylene chloride. The virtual independence of the rate of intermolecular exchange of DMF of free DMF concentration over a 20.3 fold concentration range is interpreted in terms of a dissociative exchange mechanism. A typical set of kinetic data for this process is k ex (220K) = 199 ± 11 s −1 , ΔH ♯ = 31.9 ± 0.3 kJ mol −1 and ΔS ♯ = −53.4 ± 1.5 J K −1 mol −1 , where the observed exchange rate = 5 k ex [UO 2 (DMF) 2+ 5 ], and the concentrations of UO 2 (DMF) 2+ 5 , DMF and d 2 -methylenechloride are respectively 0.008648, 0.04323 and 15.05 mol dm −3 . The observed magnetic equivalence of the methyl groups in bound DMF over the experimental temperature range 170–300 K is shown to arise as a consequence of the cis and trans DMF methyl groups experiencing significantly different magnetic shielding modifications upon coordination to the dioxouranium(VI) ion probably in part as a consequence of the magnetic anisotropy of that ion.

Alternative approaches to allocating and recovering costs for water on Egyptian farms are proposed and evaluated in accordance with the societal objectives of allocative efficiency, equity of income distribution and cost recovery. A linear programming model of a study area in Egypt's northern Delta predicts farmers' response to the proposed cost-sharing instruments over a range of water supply conditions. Transactions costs for each charging instrument are estimated and incorporated into the allocative efficiency analysis. Flat land charges, supplemented by water quotas in the event of increasing water scarcity, best achieve societal objectives in the current and prospective Egyptian situation. Volumetric charging instruments were judged to be somewhat less desirable, due to higher tangible and intangible costs of implementation. The results highlight the importance of transactions costs, the degree of water scarcity and other governmental revenue raising policies in determining an appropriate charging mechanism.

The major slow unimolecular reactions undergone by C4H7+, C5H9+ and C6H+11 are discussed in terms of a potential surface approach and the organic chemist's concept of mechanism. It is shown that the observed decompositions which do not involve σ-bond formation in the dissociation step are precisely those expected from the model. Further use of the model correctly predicts the slow reactions of C7H+13 which have not previously been reported. The approach also permits useful limits to be set on the transition state energies for reactions involving σ-bond formation in the dissociation step (H2,CH4 loss). It is concluded that stepwise addition of ethylene to the allyl cation is preferred to a concerted 4-electron process which is symmetry forbidden.

The mass spectra are reported for 19 aurones (2-benzylidenecoumaran-3-ones) having a wide variety of functional groups and substitution patterns. The principal ions in these spectra are consistent with the operation of proximity effects demonstrated previously for 6-methoxyaurones.

During field studies in 1981 on the transmission of bluetongue viruses in ruminants in Florida, a virus was isolated from Culicoides insignis collected near water buffalo (Bubalus bubalis) recently imported from Trinidad. Electron microscopy showed that this isolate, for which the name Bivens Arm virus is proposed, has rhabdovirus morphology. Serologic comparisons were made with recognized rhabdoviruses from terrestrial vertebrates and hematophagous arthropods. Indirect fluorescent antibody, complement fixation and neutralization tests indicated antigenic reactivity between Bivens Arm virus and two rhabdoviruses found only in Australia, Tibrogargan and Coastal Plains viruses. The Australian isolates cause subclinical infections in cattle and water buffalo and are believed to be transmitted by Culicoides. Initially, it was thought that Bivens Arm virus may have been introduced to Florida with the water buffalo from Trinidad, but a serologic survey of cattle serum, collected before the importation of the buffalo revealed antibody to the virus in cattle on farms located in diverse areas of Florida.

We have previously identified categorical individual differences in the occurrence of temporal brightness enhancement (TBE) by using a simultaneous brightness discrimination paradigm (Bowen & Markell, 1980).TBE is a nonmonotonic relation between brightness and pulse duration, pulses of intermediate duration (75–125 msec) can appear brighter than longer or shorter pulses of the same luminance. Three classes of observers can be defined based on whether they perceive TBE under one of two conditions of temporal asynchrony between a short test pulse and a longer (500 msec) comparison pulse:simultaneous onset of the pulses orsimultaneous offset. Type A observers show TBE for both asynchrony conditions; Type B observers show the effect for simultaneous offset but not simultaneous onset; Type C observers do not show TBE for either asynchrony. In the present study, we show that Type A and Type C observers maintain a constant brightness-duration relation as the asynchrony between test and comparison pulses is varied from simultaneous onset to simultaneous offset. Type B observers show a gradual shift in the brightness-duration relation as asynchrony changes. In a separate experiment, we find that practice has little effect on Type A and Type B observers but that Type C observers may change in classification to Types A and B over as few as five experimental sessions. The hypothesis that individual differences are due to differential “weighting” of chromatic (sustained) and achromatic (transient) visual channels is discussed.

Ovulated rabbit oocytes were fertilized in vitro in chemically defined media supplemented with bovine serum albumin and either cultured up to the expanding blastocyst stage or transferred to recipients after varying periods of culture. Embryos transferred after up to 72 hours of in vitro culture were born as viable young. Oocytes from young virgin does were superior to oocytes from nonvirgin does for the purpose of in vitro fertilization (54% versus 26% fertilized, P less than 0.01). Capacitated sperm from artificially inseminated capacitators resulted in fertilization rates slightly lower than those from naturally mated does (46% versus 57% fertilized, P less than 0.025). Removal of cumulus and corona cells from oocytes with hyaluronidase and repeated aspiration through a fine pipette resulted in lowered fertilization rates (51% versus 73%, P less than 0.025). Linbro Disposo Tray wells were as good as glass tissue-culture dishes for the in vitro mixing of gametes and were more convenient to use. Modified Ham's F10 medium was used to culture the in vitro-fertilized embryos. However, when a modified Brackett's medium was used instead of modified Ham's F10 for the initial 4-hour period after mixing gametes, more oocytes were fertilized (52% versus 28%, P less than 0.01).

An input-output model was used to estimate the degree of tax pyramiding and exporting in the State of Hawaii. Tax exporting is an important political objective in export-based economies. The concern of tax pyramiding arises from Hawaii's multi-stage, multi-rate gross receipts tax. This paper briefly describes how the State Input-Output model was modified and used to analyze these two issues. Given specific assumptions on tax shifting by industry and by type of tax, reasonable estimates can be made of the amount of taxes paid by out-of-state consumers (tax exporting) and pattern of price increases across industries and commodities caused by taxes levied on businesses at all stages of production (tax pyramiding). Empirical results are presented for the simplest case analyzed, that of full forward shifting of all taxes.

The oxidation of glucose by E. coli has been studied by observations of an anode placed in the solution, its change of potential with time being noted. The oxidations of various possible intermediates has also been studied similarly. From the number of coulombs required to produce the large changes of potential characteristic of an end-point, it is deduced that the predominant oxidative path is via fructose, pyruvate and formate intermediates.

Coefficients of static friction of six metals (Fe, Ni, Cu, Pb, Sn, and Zn) have been measured at temperatures ranging from liquid helium up to room conditions (and in two cases above this). Shear strengths and hardnesses of these metals were measured over the same range of temperatures. It was found that in spite of the generally large variation of both of these latter quantities with temperature, their ratio is in most cases dependent, to only a slight extent, on temperature, following rather closely the change of the static‐friction coefficient with temperature. This fact tends to substantiate the adhesion theory of friction proposed by F. P. Bowden.

The oxygen-platinum electrode in alkaline solutions behaves like an oxygen-peroxide couple at relatively low peroxide concentrations. The required Nernst dependence of the potential upon on the peroxide and oxygen concentration is closely approximated by the empirical results, ie ∂E/∂ log [H2O2]′ and ∂E/∂ log [O2] are −30 and +30 mV respectively. In addition the empirical standard potential is within +10 and +24 mV of the theoretical value of 0·752 V(he). A mixed-potential region roughly independent of peroxide concentration occurs in higher concentrations of peroxide. This region exhibits a dependence on the oxygen concentration in qualitative agreement with theoretical predictions.

(1956). BOATS OF THE INDUS CIVILIZATION. The Mariner's Mirror: Vol. 42, No. 4, pp. 279-290.

The near‐reversible nature of the oxygen–peroxide couple on platinum is demonstrated by substantial exchange currents. The transition between current by reduction of oxygen to peroxide and the reduction of peroxide to hydroxide ion is shown. Diagnostic criteria for determining the mechanism have been measured. The cathodic behavior of oxygen–peroxide systems in 1M potassium hydroxide is determined by the reduction of oxygen to peroxide when the concentration of peroxide is relatively low, and by the reduction of peroxide to water when its concentration is relatively large. At low peroxide concentrations Tafel slopes of approximately −2.3(2RT / 3F) are observed. With increasing oxygen activity these Tafel curves are translated towards increased currents in direct proportion to the pressure. In contrast, peroxide concentration changes do not influence the Tafel slopes in low concentration ranges. At high concentrations of peroxide, peroxide reduction becomes the predominant source of the observed current. The diffusion‐limited currents are translated toward higher currents in direct proportion to the concentration of peroxide. A mechanistic interpretation of the reduction of oxygen to peroxide indicates that a fast one‐electron step in quasiequilibrium precedes a slow one‐electron rate‐determining step. This latter may be a slow proton transfer to a superoxide species or a slow desorption of peroxide. The computed and observed diagnostic derivatives are in good agreement. The specific rate constant based on the proposed mechanisms show good constancy with change over two orders of magnitude in oxygen and peroxide concentration.