Simultaneous Arrival Research Articles

Preparative automated amino acid analysis: A new instrument permitting the exclusive collection of peaks

A new instrument, the Pulse Delay Unit (PDU-1), is described and its use in conjunction with a Beckman Model 120C Amino Acid Analyzer, a Beckman 125 Digital Integrator, and a modified Gilson Model MF Mini-Escargot Fraction Collector, is outlined. When amino acid analysis is performed using a split-stream method, the PDU-1 permits a portion of the analyzer column effluent to be collected during the estimation of ninhydrin-positive peaks. A simple method to ensure the simultaneous arrival of the split portions of each eluted peak at the colorimeter and the collector is also described. The use of the PDU-1 in nonsplit-stream preparative chromatography is discussed briefly.

Evidence for summation and voltage dependency in rabbit atrioventricular nodal fibers.

This study demonstrated summation in the rabbit AV node and suggested that the action potential rise time (dV/dt) of nodal cells was voltage dependent. Summation was produced in two ways. (1) The atrium and the floor of the coronary sinus were divided to establish two noncontiguous, anatomically separate atrial inputs to the AV node. Conduction to the His bundle occurred when both sides of the atrium were stimulated simultaneously at premature cycle lengths which produced local responses in the N region when either side was stimulated individually. (2) With the atrium intact, the atrium and the His bundle were stimulated together at intervals which allowed the simultaneous arrival of the advancing wave fronts at the impaled N cell. This collision resulted in an N action potential which occurred slightly earlier and had an increased dV/dt and amplitude, suggesting that the nodal cells tested, as well as other cardiac cells, were voltage dependent. Further evidence was provided by the influence of the N region on nodal action potential contours according to the direction of propagation. During orthograde conduction, cells close to N in the AN region had a larger dV/dt and cells in the NH region had a smaller dV/dt than these respective cells had during retrograde conduction. Since dV/dt is a major determinant of conduction velocity, during orthograde conduction rapid conduction within the AN region but relatively slow conduction where N cells supply excitatory current to NH cells occurred. In the retrograde direction, conduction from the His bundle to the midnodal region was prompt, but deceleration occurred where the N region feeds the upper nodal cells.

A model for reticular-like networks: Ladder nets, recruitment fuses, and sustained responses

This paper presents a theoretical model as a candidate for the internal organization of reticular-like networks based on a heuristic elaboration of the Scheibels' ‘poker chip’ model, and a working out of the dynamical properties of the model. We suppose that the electrical behavior of networks within the reticular formation may be approximated by that of our so-called ‘ladder nets’. The basic dynamic repertoire of ladder nets consists of recruitment fuses and sustained responses. That is, ladder net cells tend to fire in groups, and individual ladder net cells tend to fire bursts of spikes. Ladder nets are selectively sensitive to the speed of conduction of input fibers. In particular they respond preferentially to fibers which conduct at the same speed as do the fibers of the net. For slowly conducting nets this dependence can be very sensitive. Ladder nets are also particularly sensitive to appropriately patterned inputs when they are presented at rates greater than V N/2L, where V N the conduction speed in the net and L is the length of the axons. This follows from the so-called post-fuse facilitory waves which are a series of PSPs which reverberate back on a given cell immediately following its participation in a recruitment fuse. We suppose further that the overall organization of the reticular formation might be understandable in terms of a partitioning into a set of quasi-independent ladder-like subnets. Each subnet would signal a unique internal state of affairs according to its unique distribution of output fibers, and could thereby activate a particular mode of response. The activation of a particular mode of response would show up as the simultaneous arrival of single (recruitment fuse) or repeated (sustained response) spikes at all the output terminals of the activated ladder net. We would like very much to see anatomical measurements on the distribution of intercollateral lengths, and cross-correlation statistics from simultaneously recorded reticular cells to see if behavior similar to our recruitment fuses and sustained responses can be found in real reticular networks.

Adaptability and Site Tenacity in an Individual Starling

be excluded that the adult calls were also involved in attracting adults to the area; however, their nearly simultaneous arrivals seem to preclude this. These responses to the distress calls of the young show that the vocalizations alone are sufficient to elicit distraction displays from adult Killdeers. Previous studies (e.g., Deane, Auk 61:243, 1944) have emphasized injury-feigning with reference to intruders near the nest or the young, but the role of the young in eliciting distraction display has not been previously reported. I thank B. G. Murray, Jr., and R. W. Storer for criticizing earlier drafts of the manuscript.

Visual sensations produced by single fast particles.

IT has long been known that the sensation of light (phosphene) can be produced by the effect of ionizing X-radiation on the retina1–3. The threshold dose for a phosphene falls with dark adaptation but always corresponds to the simultaneous arrival of many X-ray photons. Little attention has, however, been paid to the question of whether single fast particles can produce phosphenes, with the exception of the pioneering attempts by D'Arcy and Porter4 to detect single relativistic cosmic-ray muons.

The earthquake P phases which penetrate the earth's core

abstract Travel times of all earthquake phases which enter the core as P and emerge as P are explained in terms of a core model containing two velocity discontinuities. Amplitudes of PKIKP and PKP change little with changes in distance from the source except in the rangeΔ = 142° to Δ = 152°. In this range large amplitubes are observed which result from the simultaneous arrival of two phases as well as large amplitudes which represent the PKP1 - PKP2 caustic. Amplitudes in the caustic allow detection of events perhaps smaller than magnitude 4. In all distance ranges PKIKP and PKP are useful in magnitude determination, but added care must be taken if they are used in the distance range where amplitudes are large. Magnitudes determined from PKIKP and PKP are very consistent as are focal depths. The PKJKP phase is small if present at all.

Association of CN in an Expansion Wave

The expansion wave generated by the simultaneous arrival of the ``contact'' surface and the reflected rarefaction wave was used for a direct kinetic study of a condensation process, the association of CN radicals generated by shocking C2N2/Ar mixtures to about 2000°K in the reflected-shock region. During the quenching-expansion phase the concentration of CN radicals decreases due to the concurrent chemical association and the lowering in total density. The CN concentration was followed spectrophotometrically at 3883 Å. The results were reduced in three ways: (A) unidirectional association to C2N2 in the presence of a third body, (B) relaxation to the local equilibrium via a three-body process, and (C) bimolecular reaction with C2N2 and CmNm polymers (formed during the heating process) to produce higher polymers. The data show that at the onset of quenching, the removal of CN was sluggish. This is attributed to failure to attain equilibrium in the preparation of the sample. After ≈200 μsec the data were best fitted by the third mechanism. This conclusion is in agreement with results obtained by another method and is supported by a reaction scheme which accounts for the formation and decay of CN in the presence of CmNm species. For a 2% initial concentration of C2N2, an average polymer number of ≈10 was indicated.

A Queue with Simultaneous Arrivals and Erlang Service Distribution

In this paper the method of generating functions is applied to a queue where the moments of arrival follow a Poisson distribution, but where at each of these moments several persons may arrive simultaneously. Assuming an Erlang distribution for the service times and first-come first-served discipline for the arriving groups, explicit formulas are obtained for the limiting values of the mean number of persons in the queue and in the system, and the mean time that a group of persons who arrive together must wait before one of them is served.

Radio wave emissions in the v.l.f-band observed near the auroral zone—II the physical properties of the emissions

The direction of arrival of the v.l.f.-emission in the 8 kc/s bands has been studied using two crossed loops with their planes lying in EW and NS directions, and by switching the loops alternately to the same amplifier channel. The v.l.f.-noise level was higher in the EW than in the NS direction, and this higher EW noise level was maintained during day and night for a year and also independently at two observing places lying 35 km apart. The v.l.f.-bursts came in on both frames with amplitudes of the same order of magnitude. It is concluded that Tromso is lying within an area of arrival of the v.l.f.-emissions, and that the energy is coming in from all directions. This point of view is confirmed by the polarization studies. The v.l.f.-emissions were picked up on two crossed frames, each of which was connected to identical amplifiers and displayed on the pairs of X, Y-plates on an oscillograph. Ordinary broad and irregular v.l.f.-bursts showed an irregular oscillograph pattern with changing amplitudes and irregularly appearing reversals of the sense of rotation. The oscillograph patterns are to be explained by the simultaneous arrival of several v.l.f.-noise trains which are uncorrelated. In some few cases when a sudden and single, sharp burst appeared the oscillograph pattern was different, the pattern was almost circular and the sense of rotation was always in the same direction. In this case it is assumed that the emission came down vertically along the field lines, circularly polarized, and only in the extraordinary mode. Examples of amplitude distribution are demonstrated in which a strong v.l.f.-emission is being built up by a series of sudden, discrete trains of bursts which gradually merge together into a continuous emission. The frequency-analysis of a number of bursts in the range 5–13 kc/s is demonstrated. It seems to be a general rule that at the start of a burst the higher frequency amplitudes on 12−10 kc/s are stronger, while at the end of a burst the lower frequency 6−5 kc/s is the strongest. A possible explanation of this effect is the gradual building-up of an absorption in the E-layer during a disturbance, which in the beginning will influence the higher frequencies more strongly than the lower. The mechanism of generation of the continuous band-emission, Cerenkov- and gyroradiations, are discussed, and it is concluded that the observations do not give any decisive proof for either of the two hypotheses. It is pointed out that the diurnal curve of occurrence of the v.l.f.-emissions at Tromso (the appearance being limited to the interval 1800–2400 hours M.E.T.) is difficult to explain and some more extended series of observations are needed at various places along the auroral zone.

On the Resolution of Small Time Intervals and the Effect of Conduction Delays on the Judgement of Simultaneity

In the course of experiments on the cerebral evoked potential, recorded by a summation technique through the scalp, it was possible to measure directly the latency of the potential due to afferent conduction time. In two subjects the response following electrical stimulation of the toes was found to occur approximately 20 millisec. later than that following stimulation of the fingers. Using similar stimuli to finger and toe, parallel experiments have been carried out to determine whether there is any corresponding error in the judgement of when two stimuli are simultaneous. The same subjects were presented with pairs of stimuli at a series of intervals up to 100 millisec. and made judgements as to whether they occurred at the same time, or if not, which was first. A control situation, in which the stimuli were given to the two index fingers, was compared with the experimental situation, in which stimuli were presented to finger and toe on opposite sides. The results showed a significant difference in the mean interval at which the two stimuli were judged simultaneous when the conduction pathways were of unequal length, and this difference was in the direction expected should the judgement of simultaneity depend on the simultaneous arrival of the afferent volleys centrally. However, in only one subject was this difference of the order of 20 millisec, as might be expected were the relevant event the onset of the cortical evoked potential. Further, in the other subject the point of apparent simultaneity in the control situation, in which stimuli were given to the right and left index fingers, does not correspond with the point of true simultaneity, as would be expected with conduction pathways of equal length. It is concluded, therefore, that while the temporal relationship of two stimuli is judged on the time of their central arrival rather than on the time of their occurrence at the periphery, judgements may be affected by factors other than conduction delays.

The role of hyperons in extensive air showers and in other high-energy phenomena

Experimental results obtained at the Geneva proton synchrotron support the hypothesis that in high energy nuclear collisions the particle which carries away most of the energy is often a hyperon. In proton collisions at 25 GeV this occurs in about 20% of the cases. The fraction of hyperons appears to increase further with increasing proton energy and probably reaches a value close to 50% for energies above ∼ 1000 GeV. It is shown that in the atmosphere most pions, μ-mesons, and γ-rays in the energy interval from a few times 1011 eV to about 1014 eV are due to hyperon decay rather than to direct pion production and that a large fraction of the primary energy appearing in the electron-photon component is transmitted through this process. The presence of hyperons in the nuclear cascade in the core of air showers gives rise to a large number of characteristic phenomena, both in the atmosphere and underground, some of which may be related to phenomena recently reported in the literature. Since hyperon decays result in a large excess of negative over positive mesons, charged eterminations on μ-mesons underground may give information on the relative yield of nucleons, nuclear isobars, and of strangeness one and strangeness two hyperons at high energies. It is further shown that the simultaneous arrival of two or more μ-mesons at great depth below ground signals the arrival and interaction of a complex primary nucleus at the top of the atmosphere.

Theory of Coincidence in Coulter Particle Counters

Theoretical relations are developed for the effect of coincidence (simultaneous arrival of two or more particles in the sensing zone) on the observed particle count in a Coulter counter, a device for counting particles in liquid suspensions. Two limiting cases are treated: (a) two or more particles are seen as a particle whose volume is the total particle volume present, (b) two or more particles are seen as the largest particle present. The theory was tested experimentally with a ``monodisperse'' polystyrene latex. It is shown that absolute particle volumes may be obtained from the ratio of solids content to number of counts under certain conditions. Case (b) coincidence predominates. The apparent breadth of the particle-size distribution curves in the ``monodisperse'' latex was greater than expected.

Interferometry of the intensity fluctuations in light. II. An experimental test of the theory for partially coherent light

A theoretical analysis is given of the correlation to be expected between the fluctuations in the outputs of two photoelectric detectors when these detectors are illuminated with partially coherent light. It is shown how this correlation depends upon the parameters of the equipment and upon the geometry of the experiment. The correlation may be detected either by linear multiplication of the fluctuations in the two outputs or by a coincidence counter which counts the simultaneous arrival of photons at the detectors. The theory is given for both these techniques and it is shown that they are closely equivalent. A laboratory test is described in which two photomultipliers were illuminated with partially coherent light and the correlation between the fluctuations in their outputs measured as a function of the degree of coherence. The results of this experiment are compared with the theory and it is shown that they agree within the limits of accuracy of the test; it is concluded that if there is any systematic error in the theory it is unlikely to exceed a few parts per cent.

Wöhler's 'Synthetic' Urea and the Rejection of Vitalism: A Chemical Legend

THAT Wohler synthetized urea in 1828 and there by rang the death-knell of vitalism in organic chemistry seems to be as firmly established a legend as that Galileo let fall at one and the same time from the leaning tower at Pisa two unequal weights, the thud of the simultaneous arrival of which upon the ground rang out the old Aristotelianism and rang in the new mechanics. But, as in the earlier, so in the later case, the facts are otherwise: there was no synthesis of urea, and chemists continued to assert the existence of vital force and to describe its role in the formation of organic substances. Wohler's experiments have, however, acquired an altogether inexplicable and widespread significance, both- in text-books and in popular scientific works, especially among those whose statements show that they cannot possibly have referred to his own account of them.

Deep‐focus earthquakes and their implications

No one any longer doubts that earthquakes occur at depths of several hundred kilometers. There is not the same unanimity in regard to the absolute depth of focus of these earthquakes, the relative merits of methods for measuring the depth, the character, and distribution of plutonic earthquakes; and especially is there disagreement as to their causes and mechanism and as to their geological implications.Several methods have been suggested for the measurement of depth of focus. Most of these are relative methods. Turner based his estimate of the relative depth of focus on the degree of earliness in the arrival time of longitudinal waves at the antipodes in the case of deep shocks as compared with normal earthquakes. Stechschulte took as his criterion the interval between the arrival of the direct longitudinal wave and that of the Walker reflection at the distance at which this interval reached its maximum. Scrase used Knott's calculations to determine the depth of focus from the departure of the travel‐time curves for deep earthquakes from those of normal earthquakes. Wadati has suggested a number of methods: First, the spacing of the isochrones or lines of simultaneous arrival; second, the time‐Intercept of the graph of the interval between the arrival of the longitudinal and that of the transverse waves against the absolute arrival time of the longitudinal waves; third, he used tables of calculated travel‐times from deep foci based on those of shallow earthquakes, each set of tables corresponding to a given depth of focus. Miyamoto determined the depth of focus by comparing the travel‐times of longitudinal and transverse waves reflected from the core of the Earth with those for normal earthquakes. Serlage uses the interval between the arrival of the direct longitudinal wave and that of the Walker reflection for direct calculation of the depth.