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We present the analysis of Rossi X-ray Timing Explorer (RXTE) observations of the turn-on phase of a 35 day cycle of the X-ray binary Her X-1. During the early phases of the turn-on, the energy spectrum is composed of X-rays scattered into the line of sight plus heavily absorbed X-rays. The energy spectra in the 3–17 keV range can be described by a partial covering model, where one of the components is influenced by photoelectric absorption and Thomson scattering in cold material plus an iron emission line at 6.5 keV. In this paper we show the evolution of spectral parameters as well as the evolution of the pulse profile during the turn-on. We describe this evolution using Monte Carlo simulations which self-consistently describe the evolution of the X-ray pulse profile and of the energy spectrum.

We present pulse phase resolved spectra of the hypergiant high mass X-ray binary GX 301-2. We observed the source in 2001 October with RXTEcontinuously for a total on-source time of almost 200 ks. We model the continuum with both, a heavily absorbed partial covering model and a reflection model. In either case we find that the well known cyclotron resonant scattering feature (CRSF) at ~35 keV is – although present at all pulse phases – strongly variable over the pulse: the line position varies by 25% from 30 keV in the fall of the secondary pulse to 38 keV in the fall of the main pulse where it is deepest. The line variability implies that we are seeing regions of magnetic field strength varying between $3.4\times 10^{12}$G and $4.2\times 10^{12}$G.

We present the long term evolution of the timing properties of the black hole candidate Cygnus X–1in the 0.002–128 Hz frequency range as monitored from 1998 to 2001 with the Rossi X-ray Timing Explorer (RXTE). For most of this period the source was in its hard state. The power spectral density (PSD) is well modeled as the sum of four Lorentzians, which describe distinct broad noise components. Before 1998 July, Cyg X–1 was in a “quiet” hard state characterized primarily by the first three of these broad Lorentzians being dominant. Around 1998 May, this behavior changed: the total fractional rms amplitude decreased, the peak frequencies of the Lorentzians increased, the average time lag slightly increased, and the X-ray spectrum softened. The change in the timing parameters is mainly due to a strong decrease in the amplitude of the third Lorentzian. Since this event, an unusually large number of X-ray flares have been observed, which we classify as “failed state transitions”. During these failed state transitions, the X-ray power spectrum changes to that of the intermediate state. Modeling this PSD with the four Lorentzians, we find that the first Lorentzian component is suppressed relative to the second and third Lorentzian during the state transitions. We also confirm our previous conclusion that the frequency-dependent time lags increase significantly in the 3.2–10 Hz band during these transitions. We confirm the interpretation of the flares as failed state transitions with observations from the 2001 January and 2001 October soft states. Both the behavior of the PSD and the X-ray lag suggest that some or all of the Lorentzian components are associated with the accretion disk corona responsible for the hard state spectrum. We discuss the physical interpretation of our results.

We present pulse phase-resolved X-ray spectra of the high mass X-ray binary Vela X-1 using the Rossi X-ray Timing Explorer. We observed Vela X-1 in 1998 and 2000 with a total observation time of ~90 ksec. We find an absorption feature at $23.3^{+1.3}_{-0.6}~ke\kern -0.09em V$in the main pulse, that we interpret as the fundamental cyclotron resonant scattering feature (CRSF). The feature is deepest in the rise of the main pulse where it has a width of $7.6^{+4.4}_{-2.2}~ke\kern -0.09em V$and an optical depth of $0.33^{+0.06}_{-0.13}$. This CRSF is also clearly detected in the secondary pulse, but it is far less significant or undetected during the pulse minima. We conclude that the well known CRSF at $50.9^{+0.6}_{-0.7}~ke\kern -0.09em V$, which is clearly visible even in phase-averaged spectra, is the first harmonic and notthe fundamental. Thus we infer a magnetic field strength of $B=2.6\times 10^{12}$G.

We report on the analysis from ~110 ks of X-ray observations of Centaurus A carried out with the Proportional Counter Array (PCA) and the High Energy X-ray Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE) during three monitoring campaigns over the last 4 years (10 ks in 1996, 74 ks in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well described by a heavily absorbed power law with photon index 1.8 and a narrow iron line due to fluorescence of cold matter. The measured column depth decreased by about $30\%$between 1996 and 2000, while the detected 2-10 keV continuum flux remained constant between 1996 and 1998, but increased by $60 \%$in 2000. Since in all three observations the iron line flux did not vary, a corresponding decrease in equivalent width was noted. No appreciable evidence for a reflection continuum in the spectrum was detected. We present the interpretation of the iron line strength through Monte Carlo computations of various geometries. No significant temporal variability was found in Cen A at time scales from days to tens of minutes.

Die Wirkung der Kombinationen von Chloramphenicol mit β-Lactam-Antibiotika, wie Penicillin, Ampicillin, Cefotiam und Cefotaxim, auf je 20 Stämme vonHaemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidiswurde untersucht. Unter Verwendung der Checkerboard-Titration wurde kein Antagonismus beobachtet. Die Wechselwirkung war in den meisten Fällen indifferent. Dabei wurde die Bewertung gemäß dem FIC-Index diskutiert: Erst Werte über 2,0 wurden als Ausdruck eines Antagonismus angesehen. Die minimalen bakteriziden Konzentrationen von Chloramphenicol waren mit der minimalen Hemmkonzentration (MHK) identisch — die Substanz wirkt also bei den geprüften Spezies bakterizid. Weitere Untersuchungen über die Absterbekinetik haben gezeigt, daß Chloramphenicol in niedrigeren Konzentrationen eine Verzögerung der Bakterizidie des Kombinationspartners in den ersten Stunden bewirken kann. In höheren Konzentrationen (mehr als zweifache MHK) ist die Kinetik der Abtötung etwa mit der der Einzelsubstanzen identisch. Es ist unwahrscheinlich, daß die geringfügige Verzögerung der Abtötung eine klinische Bedeutung hat. Die Wirkung der Kombination ist annähernd so gut wie die des Chloramphenicol allein. The effect was studied of combinations of chloramphenicol with β-lactam antibiotics, such as penicillin, ampicillin, cefotiam and cefotaxime, on 20 strains each ofHaemophilus influenzae, Streptococcus pneumoniaeandNeisseria meningitidis. No antagonism was observed using the checkerboard titration method. In most cases no interaction could be established. An evaluation by the fractional inhibitory concentration index was discussed: only values above 2 were interpreted as antagonism. The minimal bactericidal concentrations of chloramphenicol were identical with the minimal inhibitory concentrations (MIC) — i. e. the antibiotic acted bactericidally on the species tested. Further investigations on the killing kinetics have shown that chloramphenicol in low concentrations can cause a delay in the bactericidal action of the antibiotic with which it is combined in the first few hours. At higher concentrations (more than double the MIC) the killing kinetics approximate those of the individual antibiotics. It is improbable that the minor delays in killing are of clinical significance. The combination is almost as effective as chloramphenicol.

Zusammenfassung Drei Modellansätze zur hydrodynamischen Beschreibung von Verkehrsströmen werden an einem Beispiel beschrieben. Es wird gezeigt, daß der üblicherweise angenommene Zusammenhang zwischen Stromdichte und Stromgeschwindigkeit im allgemeinen zu mehrdeutigen Lösungen führt. Ein umfassender Ansatz liefert eindeutige Lösungen, wenn man Unstetigkeiten im Dichteverlauf zuläßt. Stetige, eindeutige Lösungen erhält man schließlich, wenn die Geschwindigkeit nicht nur in Abhängigkeit von der Dichte, sondern auch vom Dichtegradienten angesetzt wird.

Zusammenfassung In der vorliegenden Untersuchung wird der Dupuitsche Ansatz für inhomogene Grundwasserleiter aus einem verallgemeinerten Filtergesetz abgeleitet und die zugehörige Differentialgleichung für instationäre Grundwasserspiegellagen unter Berücksichtigung allfälliger Oberflächenimmissionen aufgestellt. Zum Abschluß werden am Beispiel einer Klasse von rotationssymmetrischen Grundwasserströmungen einige Fragen behandelt, die von grundsätzlicher Bedeutung erscheinen.

The High Energy X-Ray Timing Experiment (HEXTE) is one of three scientific instruments aboard the RossiX-RayTimingExplorer(RXTE), which was launched on 1995 December 30. RXTEperforms timing and spectral studies of bright X-ray sources to determine the physical parameters of these systems. The HEXTE consists of two independent clusters of detectors, each cluster containing four NaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1° FWHM field of view. The field of view of each cluster is switched on and off source to provide near real-time background measurements. The net open area of the eight detectors is 1600 cm2, and each detector covers the energy range 15-250 keV with an average energy resolution of 15.4% at 60 keV. The in-flight performance of the HEXTE is described, the light curve and spectrum of the Crab Nebula/pulsar is given, and the 15-240 keV spectrum of the weak source, active galaxy MCG +8-11-11 is presented to demonstrate the weak source spectral capabilities of HEXTE.

Zusammenfassung Ein isotroper viskoelastischer Modellkörper wird in der Weise konstruiert, daß man Teilspannungen mit Hilfe eines Potenzspektrums superponiert. Diese Teilspannungen sind dabei entsprechend einer vonZaremba,Fromm undDeWitt verallgemeinerten Maxwell-Gleichung mit der Deformation verknüpft. Ein solcher Körper verhält sich in stationären Scherströmungen wie eineOstwald-De Waele-Flüssigkeit. In Dehnströmungen zeigt er dagegen weder ein flüssigkeits-noch ein festkörperartiges, sondern ein intermediäres Verhalten: Im Spannversuch (d. h. beim Anwenden einer konstanten Dehngeschwindigkeit) wachsen die Spannungen unbegrenzt, beim Relaxationsversuch (d. h. beim Anhalten dieses Dehnvorgangs) klingen sie vollständig ab.

The UCSD, WU, UCR and Nova collaboration has made significant progress on the necessary techniques for coded mask imaging of gamma-ray bursts: position sensitive CZT detectors with good energy resolution, ASIC readout, coded mask imaging, and background properties at balloon altitudes. Results on coded mask imaging techniques appropriate for wide field imaging and localization of gamma-ray bursts are presented, including a shadowgram and deconvolved image taken with a prototype detector/ASIC and MURA mask.