A TEST OF THREE FITTING CRITERIA FOR MULTIRESPONSE NON-LINEAR MODELING

This work evaluates objective functions for multiresponse non-linear modeling using computersimulations.Tests are performed under a variety of signal-to-noise ratios and noise variance-covariancestructures.The standard error of prediction for the model parameters,computed from 50 trials,is usedfor performance comparisons.The full rank and rank-deficient problems are considered.For the fullrank problem one model was investigated,a first-order two-step consecutive reaction model,and twoobjective functions were considered,the total sum of squares and the determinant criterion.Nodistinction could be made between the two objective functions for this model.For the rank-deficient case two models were investigated,a first-order two-step consecutive reactionas in the full rank case,and a pH titration model described by the Henderson-Hasselbalch equation.Three objective functions were investigated for the rank-deficient case,the total sum of squares,aweighted total sum of squares and the determinant criterion.The total sum of squares was found toperform poorly under all conditions tested compared to the weighted total sum of squares and thedeterminant criterion.The determinant criterion was found to perform much better than the other twocriteria when the data have a combination of a low signal-to-noise ratio and high variance-covariancenoise structure.     

Natural and anthropogenic influences on the geochemistry of Quaternary lake sediments from Holzmaar, Germany

 The accumulation of heavy metals and trace elements has been investigated in a well laminated sequence of Holocene and late Pleistocene lake sediments composed of diatomaceous gyttja, tuff and silt and clay sediments. Varve chronology of the annually deposited gyttja yielded a continuous high-resolution time sequence and allowed the absolute age dating of the sediment. Fluxes of elements remained largely uniform from the late Pleistocene into the Holocene (12 867–2 364 VT years ago; VT: varve time, years before 1950). Higher trace element and heavy metal fluxes occur from 2 322 to 862 VT years ago and reached their maxima in the uppermost sediments (<845 VT years ago). These increasing element fluxes correlate with increasing inputs of clastic material. The changing accumulation rates are the result of elevated soil erosion in the lake catchment caused by human settlement, deforestation and agricultural activities. Thus disturbances of the natural geochemical cycles of the Holzmaar region have occurred since the beginning of the Iron Age and especially since the beginning of the Middle Ages. Received: 29 May 1996 · Accepted: 19 August 1996     

The Imataca Complex, NW Amazonian Craton,Venezuela： Crustal evolution and integration of geochronological and petrological coolinghistories

SHRIMP U/Pb-zircon data and Nd mean crustal residence ages indicate that the lmataca Complex developed from an Archean (≥3.2Ga) continental protolith which has undergone considerable isotopic disturbance plus and juvenile accretion during late-Archean (-2.8Ga) times. Transamazonian granulites experienced peak metamorphic conditions of 750-800℃, 6-8kbar with associated transpressive thrusting and tectonic imbrication. Geochronology on zircon, pyroxene and garnet constrains the timing of peak metamorphism at 1.98-2.05Ga. Diffusion modeling of Fe-Mg exchange between biotite inclusions and host garnet yields (near metamorphic peak) cooling rates of 50-100℃/Ma, with petrological cooling rates being generally consistent with cooling rates determined from geochronology. Combining the retrograde P-T path with cooling rates suggests that after the metamorphic peak, large portions of the lmataca Complex were exhumed from 30 to 17km at a rate of 7-2km/Ma.After this, exhumation rates progressively decreased as the rocks approached the surface. Rapid overall upliftlerosion had ceased when the rocks passed below 600-550℃ at 2.01-1.96 Ga ago. Observed variations in mineral cooling ages are interpreted as to reflect episodic differential tectonic exhumation within major fault systems. Inferred (maximum) ages of fault re-activation generally coincide with major continental accretion events in the Amazonian Craton and reflect long-term thermal evolution of the lmataca terrane, as conditioned by variable response to continued continental convergence during the Proterozoic.     

Balloon observations of fast intensity fluctuations and flare-like enhancements of X-ray emission from Cygnus X-1

The paper presents the results of the investigation on the short term X-ray emission characteristics of Cyg X-1 in the 20–150 keV range. The observations were made with balloon-borne oriented scintillation telescope and the flights were conducted from Hyderabad, India. The source was tracked over a duration of 1 hr that enabled detailed observations with time resolution of the order of 1 min. Fluctuations in the intensity of Cyg X-1 with time scales of the order of minutes have been detected besides short-term flare-like enhancements. The spectral characteristics of the flare emission features are discussed and their relationship to the phase of the binary is examined.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Post-storm mid-latitude green aurora and electron precipitation

Unusual auroral emission at mid-latitudes, showing nearly exclusively the green oxygen line (557.7 nm) and occurring during the early part of the recovery phase after strong magnetic storms is described. The emission has a life-time of up to several hours, consists of cloud-like patches and appears quite isolated at medium latitudes with no simultaneous aurorae at higher latitudes. The name “post-storm mid-latitude green aurora” is proposed for this emission. For the event observed during the night of 29–30 August 1978, additional ionospheric measurements from heights below the mid-latitude aurora ($\text{?}{}_{\min }$, A3-LF data) are available from nearby observations. Our investigation shows that the emission was observed just at the beginning of a post-storm effect (PSE) in ionospheric absorption. The optical and absorption data have been used to extract information on precipitating high-energy electrons, assumed to be the cause of both the optical emisson and the excessive absorption. During the night in question precipitating electrons with fluxes above the quiet-time level and energies upto at least 200 keV were found in a region extended in latitude (2.7 < L < 3.3) and probably even more extended in longitude. Latitudinally narrow bands, elongated along shells of constant L, with extremely high fluxes of 10–20keV electrons (according to our estimates at least 5. 10⁷ el cm^?2s^?1) were embedded within this region.     

Interplanetary magnetic field and geomagnetic Dst variations

The interplanetary magnetic field has been shown to influence the ring current field represented by Dst. Explorer 28 hourly magnetic field observations have been used with the hourly Dst values. The moderate geomagnetic storms of 60 and quiet-time fluctuations of 10–30 are correlated with the North to South change of the interplanetary field component perpendicular to the ecliptic. This change in the interplanetary field occurs one to three hours earlier than the corresponding change in the Dst field.     

Multidirectional scanning of active regions with a slit-jaw spectrograph and a solar chromatograph

At the Swedish Solar Observatory in Anacapri we have simultaneously used the following combination of instruments in our investigation of active regions:

1. A spectrograph with an image rotator placed in front of the slit.
2. A subtractive double dispersive spectrograph (solar Chromatograph).
3. A Hα+0.5 Å patrol instrument. Scans over the 3b flare of August 4th 1972 are used to illustrate the method. The illustrations clearly show downflowing matter connected with bright knots and filaments in the emitting area, possibly in accordance with Hyder's infall-impact mechanism.

     

Observation of solar particle fluxes over extended solar longitudes

Detailed particle observations from various Pioneer Spacecrafts located at different heliolongitudes during the complex solar flare events of March 30–April 10, 1969 have been utilised to investigate the energy dependence of azimuthal gradients of cosmic ray particles and its effect on the decay of the flare intensity. For an observer located to the east of the centroid of the population, the azimuthal corotation term and the convection term will be additive, resulting in a short decay time constant. An observer located to the west of the centroid of the population will experience a much longer decay time constant, the corotation term partially or completely compensating the loss of particles due to convection. At very low energies, the azimuthal corotation term may even be more than the convection term, thus resulting in a rise in intensity instead of decay during late in the event. Using the relationship showing the dependence of the spectral exponent of the cosmic ray flux late in a flare event on the azimuth from the centroid of the population given by McCracken et al., the energy dependence of the decay time constant and the cross-over energy at which the azimuthal gradient term equals the convection term are investigated. The experimental observations are shown to be generally consistent with the theoretical picture, confirming the importance of convection and the azimuthal gradient in determining the decay profile of flare events.On leave from Physical Research Laboratory, Ahmedabad, India.Now at CSIRO, G.P.O. Box 136, North Ryde, N.S.W., Australia.