The sedimentary record of late Matuyama magnetic excursions, between the end of the Olduvai Subchron and the Matuyama‐Brunhes boundary, has relied on North Atlantic Ocean Drilling Program (ODP) Sites ...983/984, and individual recordings at ODP Site 1021 from the California Margin, and Core MD972143 from the west Philippine Sea. North Atlantic IODP Sites U1305, U1306, U1307 (Eirik Drift, off SE Greenland), and Site U1308 (central Atlantic) provide new records from u‐channel samples and discrete (8 cm3) cubic samples, collected from multiple holes drilled at each site. The results confirm the existence of the Intra‐Jaramillo, Punaruu, Bjorn, Gardar, and Gilsa excursions and possibly the Kamikatsura excursion. These excursions are not recorded at all sampled sites, although they do correspond to excursions recorded at ODP Sites 983/984 and to relative paleointensity minima recorded at all studied sites. For some records, including that of the Bjorn excursion (1251 ka), antipodal magnetization directions yield virtual geomagnetic poles that reach high northern latitudes, implying that the excursion involved reversal of the main axial dipole field. On the other hand, excursions are often partially and inadequately recorded, attributable to a combination of the brevity of geomagnetic excursions, bioturbation, and filtering of the magnetization signal by the detrital remanent magnetization acquisition process, nonuniform sedimentation rates at millennial/centennial scales, and possibly unrecognized drilling/sampling disturbance.
Key Points
Newly documented magnetic excursions in the late Matuyama Chron
Magnetic excursions involve the main axial dipole, are likely to have been manifested globally, and are important stratigraphic markers
The inventory of magnetic excursions is important, not only for stratigraphy but for understanding the workings of the geodynamo
The two-parameter Poisson-Dirichlet distribution, denoted PD(α, θ), is a probability distribution on the set of decreasing positive sequences with sum 1. The usual Poisson-Dirichlet distribution with ...a single parameter θ, introduced by Kingman, is PD(0, θ). Known properties of PD(0, θ), including the Markov chain description due to Vershik, Shmidt and Ignatov, are generalized to the two-parameter case. The size-biased random permutation of PD(α, θ) is a simple residual allocation model proposed by Engen in the context of species diversity, and rediscovered by Perman and the authors in the study of excursions of Brownian motion and Bessel processes. For$0 < \alpha < 1$, PD(α, 0) is the asymptotic distribution of ranked lengths of excursions of a Markov chain away from a state whose recurrence time distribution is in the domain of attraction of a stable law of index α. Formulae in this case trace back to work of Darling, Lamperti and Wendel in the 1950s and 1960s. The distribution of ranked lengths of excursions of a one-dimensional Brownian motion is PD1/2, 0), and the corresponding distribution for a Brownian bridge is PD(1/2, 1/2). The PD(α, 0) and PD(α, α) distributions admit a similar interpretation in terms of the ranked lengths of excursions of a semistable Markov process whose zero set is the range of a stable subordinator of index α.
This paper provides an alternative approach to Duffie and Lando Econometrica 69 (2001) 633-664 for obtaining a reduced form credit risk model from a structural model. Duffie and Lando obtain a ...reduced form model by constructing an economy where the market sees the manager's information set plus noise. The noise makes default a surprise to the market. In contrast, we obtain a reduced form model by constructing an economy where the market sees a reduction of the manager's information set. The reduced information makes default a surprise to the market. We provide an explicit formula for the default intensity based on an Azéma martingale, and we use excursion theory of Brownian motions to price risky debt.
Background:
Differences in the location and incidence of lower extremity injuries have been reported between high and low arched individuals. These differences might be related to functional ...differences between the two foot types. In particular, the characteristics of the medial longitudinal arch may influence foot function. The purpose of this study was to investigate forefoot and rearfoot kinematics as well as tibial shock in participants with both high and low arches.
Materials and Methods:
Fifteen high arched and 15 low arched males were recruited. Tibial acceleration as well as forefoot, rearfoot and shank kinematic data were collected as participants ran at 3.5 m/s wearing gait sandals. Variables of interest included peak tibial acceleration in addition to rearfoot eversion excursion, forefoot eversion excursion, forefoot eversion velocity, forefoot abduction excursion and forefoot abduction velocity. MANOVA and effect sizes were used to investigate kinematic differences between groups.
Results:
Multivariate analysis revealed that foot type had an effect on the kinematic variables of interest (p = 0.04). Forefoot abduction excursion (High arched = 4.7 ± 1.3 degrees, Low arched 3.8 ± 1.0 degrees) and forefoot abduction velocity (High arched = 96.0 ± 24.8 degrees/s, Low arched = 69.3 ± 13.3 degrees/s) were greater in the high arched group. Tibial shock (p = 0.24) and other kinematic variables were similar between groups.
Conclusion:
Clear evidence of forefoot and rearfoot motion as a shock attenuation mechanism was not found. Differences in the foot kinematics during early stance were highlighted by a smaller forefoot abduction excursion and reduced forefoot abduction velocity in low arched compared to high arched individuals. It is suggested that low arched feet may have a reduced available range of motion through which the forefoot can pass before reaching the end range of motion point.
Clinical Relevance:
Foot kinematics during early stance warrant further investigation to establish a specific link to injury risk.
We obtained two years (1999–2001) of continuous, high resolution temperature and pressure data at two near-shore shallow water sites in McMurdo Sound, Ross Sea. Contrary to the long-held assumption ...of constant freezing conditions in the Sound, these records revealed dynamic temperature fluctuations and substantial warming during January to March reaching peak water temperatures of about −0.5°C. They also revealed that excursions above −1.1°C, the equilibrium melting point of ice in Antarctic notothenioid fish, totalled 8–21 days during the summer. Microscopic ice crystals are known to enter these fish but ice growth is arrested by antifreeze proteins. Prior to this study there were no known mechanisms of eliminating accumulated endogenous ice. The warm temperature excursions provide for the first time a possible physical mechanism, passive melting, for ice removal. The continuous records also showed a correlation between tidal pressures and cold temperature episodes, which suggests the influx of cold currents from under the Ross Ice Shelf may provide a mechanism for ice crystal nucleation as the source of the ice in McMurdo Sound fish. The accumulation of anchor ice on one logger caused it to float up which was recorded as a decrease in pressure. This is the first evidence for the time of onset of anchor ice formation in McMurdo Sound.
The purpose of this study was to determine the average facial proportions and mandibular movement capacity of 316 first-year dental students who carefully recorded them on each other.
This early ...exacting clinical experience was closely supervised by the authors in Columbus, Ohio during 1969-70. Five vertical and six horizontal distances were measured on each subject's face. An ala-tragus line and an occlusal line were drawn on the left side of the face to determine if these two lines were parallel. Measurements of mandibular movements involved maximum normal and hinge opening at the incisors and maximum amounts of right, left lateral and protrusive excursions of the mandible.
The ala width and distance between the tips of upper right and left canine cusps averaged (35.2 mm and 34.8 mm) but with very large individual variations. The distance between ala to occlusal plane lines was 29.9 mm at the tragus and 31.3 mm near the ala. The angle between orbitale and ala-tragus averaged 13.6 degrees.
The upper lip length was the most variable and the distance between the pupils was the most stable of the eleven facial measurements. The ala-tragus line and the occlusal plane lines were for all practical purposes parallel. Maximum jaw opening averaged 51.2 mm which was 3.0 times larger than maximal hinge opening of 17.2 mm. The maximum right plus left side jaw excursions (9.2 and 9.4 mm) totaled 18.6 mm, 2.3 times more than the 8.0 mm mean maximum forward protrusion.
We report high-resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of the Wilkes Land Basin (WLB), East Antarctica, in the frame of the ...Italian/Australian Wilkes Land Glacial History (WEGA) project. The studied cores, with a length of ca. 4
m each, were collected from the gentle and steep sides of sedimentary ridges present in the lower part of the continental rise, and consist of very fine-grained sediments. Paleomagnetic measurements were carried out on u-channel samples. Apart from a low-coercivity magnetic overprint, removed after the first steps of alternating field demagnetization, each core is characterized by a well defined characteristic remanent magnetization. Paleomagnetic inclinations fluctuate around the expected value (of ca. −77°) for such high latitude sites and always indicate normal magnetic polarity. Short period oscillations to anomalously shallow paleomagnetic inclinations (up to −20°) were identified at different levels of the sampled sequences; positive (reverse) inclination values were however not observed. Specific rock magnetic measurements indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences. For each core we reconstructed curves of relative paleointensity (RPI, as computed by NRM
20
mT
/
κ and NRM
20
mT
/ARM
20
mT
) variation of the geomagnetic field. An original age model was established by tuning the individual RPI curves with the available global and regional reference RPI stacks.
Paleomagnetic results, supported by other limited bio- and chronostratigraphic constraints, establish that all the cores are Late Pleistocene in age: two provide an expanded record of the last ca. 30
ka (PC18 and PC19), three span the last ca. 100, 200 and 300
ka (respectively, PC25, PC27 and PC26), and one reaches back to ca. 780
ka (PC20), approaching the Brunhes–Matuyama transition. Thus, the WEGA paleomagnetic record provides the first experimental data documenting the dynamics and amplitude of the geomagnetic field variations at high southern latitudes during the Brunhes Chron. The individual normalized RPI records were merged in a WEGA RPI stacking curve spanning the last 300
kyr. The comparison of the WEGA RPI individual and stacked curves with the global references RPI stacks shows that geomagnetic paleointensity variations, with periods longer than a few to tens kyr depending on the sedimentation rate, can be safely recognized in this sector of the peri-Antarctic margins. Furthermore, the stacking of the individual ChRM inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations may be correlated to the main known geomagnetic excursions of the Brunhes Chron, supporting the validity of the age models.
The reconstructed average sediment accumulation rates for the individual cores range from 0.6 to 19
cm/ka and are compatible with their position within the WLB, with the lowest rates found close to the ridge of the sedimentary drifts. Moreover, the high-resolution age models obtained in this study provide original constraints to assess chronology, rates and amplitudes of the climatic and environmental processes affecting this key area of the peri-Antarctic margins during the Late Pleistocene.
A duplicate high‐resolution magnetic record was obtained from two parallel loess sections separated by about 300 m near Baoji city, southern Chinese Loess Plateau. This reveals at least eight ...short‐lived reversed polarity episodes in the uppermost part of the Olduvai normal polarity subchronozone. Rock magnetic experiments and anisotropy of low‐field magnetic susceptibility confirm that the multiple occurrence of short‐lived reversals is not due to rock‐magnetic and/or sedimentary causes. Assuming a constant accumulation rate within the Olduvai subchron, the short episode zone was estimated to span about 24–30 ka and 24–31 ka for the two sections, respectively. The duration of each short episode ranges from about 0.3 ka to 2.1 ka. The present results together with previous worldwide observations show that the occurrence of numerous short reversals is peculiar to the latest Olduvai subchron. The geodynamo may have been in an anomalous state at that time.
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