23 research outputs found
First record of Rhabdoceras suessi (Ammonoidea, Late Triassic) from the Transylvanian Triassic Series of the Eastern Carpathians (Romania) and a review of its biochronology, paleobiogeography and paleoecology
Abstract
The occurrence of the heteromorphic ammonoid Rhabdoceras suessi Hauer, 1860, is recorded for the first time in the Upper Triassic limestone of the Timon-Ciungi olistolith in the Rarău Syncline, Eastern Carpathians. A single specimen of Rhabdoceras suessi co-occurs with Monotis (Monotis) salinaria that constrains its occurrence here to the Upper Norian (Sevatian 1). It is the only known heteromorphic ammonoid in the Upper Triassic of the Romanian Carpathians. Rhabdoceras suessi is a cosmopolitan species widely recorded in low and mid-paleolatitude faunas. It ranges from the Late Norian to the Rhaetian and is suitable for high-resolution worldwide correlations only when it co-occurs with shorter-ranging choristoceratids, monotid bivalves, or the hydrozoan Heterastridium. Formerly considered as the index fossil for the Upper Norian (Sevatian) Suessi Zone, by the latest 1970s this species lost its key biochronologic status among Late Triassic ammonoids, and it generated a controversy in the 1980s concerning the status of the Rhaetian stage. New stratigraphic data from North America and Europe in the subsequent decades resulted in a revised ammonoid biostratigraphy for the uppermost Triassic, the Rhaetian being reinstalled as the topmost stage in the current standard timescale of the Triassic. The geographic distribution of Rhabdoceras is compiled from published worldwide records, and its paleobiogeography and paleoecology are discussed
Pattern in Escalations in Insurgent and Terrorist Activity
The Red Queen's notion "It takes all the running you can do, to keep in the
same place" has been applied within evolutionary biology, politics and
economics. We find that a generalized version in which an adaptive Red Queen
(e.g. insurgency) sporadically edges ahead of a Blue King (e.g. military),
explains the progress curves for fatal insurgent attacks against the coalition
military within individual provinces in Afghanistan and Iraq. Remarkably
regular mathematical relations emerge which suggest a prediction formula for
the timing of the n'th future fatal day, and provide a common framework for
understanding how insurgents fight in different regions. Our findings are
consistent with a Darwinian selection hypothesis which favors a weak species
which can adapt rapidly, and establish an unexpected conceptual connection to
the physics of correlated walks.Comment: Added acknowledgements and author affiliatio
Sensitivity to Interaural Time Differences with Combined Cochlear Implant and Acoustic Stimulation
The interaural time difference (ITD) is an important cue to localize sound sources. Sensitivity to ITD was measured in eight users of a cochlear implant (CI) in the one ear and a hearing aid (HA) in the other severely impaired ear. The stimulus consisted of an electric pulse train of 100 pps and an acoustic filtered click train. Just-noticeable differences (JNDs) in ITD were measured using a lateralization paradigm. Four subjects exhibited median JNDs in ITD of 156, 341, 254, and 91 μs; the other subjects could not lateralize the stimuli consistently. Only the subjects who could lateralize had average acoustic hearing thresholds at 1,000 and 2,000 Hz better than 100-dB SPL. The electric signal had to be delayed by 1.5 ms to achieve synchronous stimulation at the auditory nerves
Cross-modulation interference with lateralization of mixed-modulated waveforms
Purpose: This study investigated the ability to use spatial information in mixedmodulated
(MM) sounds containing concurrent frequency-modulated (FM) and
amplitude-modulated (AM) sounds by exploring patterns of interference when
different modulation types originated from different loci as may occur in a
multisource acoustic field.
Method: Interaural delay thresholds were measured from 5 normal-hearing adults
for an AM sound in the presence of interfering FM and vice versa as a function of
interferer modulation rate. In addition, the effects of near versus remote interferer
rates, and fixed versus randomized interferer interaural delay, were investigated.
Results: AM interfered with lateralization of FM at all modulation rates. However,
the FM interfered with AM lateralization only when the FM rate was higher than the
AM rate. This rate asymmetry was surprising given the prevalence of low-frequency
dominance in lateralization, but was predicted by a cross-correlation model of
binaural interaction. Effects were similar for fixed and randomized interferer
interaural delays.
Conclusions: The results suggest that in multisource environments, sources containing
different modulation types significantly interfere with localization in complex ways
that reveal interactions between modulation type and rate. These findings contribute
to the understanding of auditory object formation and localization.This work was supported by Grant NSC 98-2410-H-008-
081-MY3 from the National Science Council, Taiwan; Grant
BCS0477984 from the National Science Foundation; and
Grant R01DC009659 from the National Institutes of Health