Mean Inclination Research Articles

Moving Magnetic Features as Prolongation of Penumbral Filaments

A sequence of 633 high spatial resolution magnetograms and continuum images from SOHO MDI of NOAA AR 0330 is used to study moving magnetic feature (MMF) activity in the moat surrounding a mature leader sunspot. The time-averaged frame shows that the moat region is covered by a magnetic field that exhibits the same polarity distribution as that observed in the penumbra. The moat field displays the true polarity of the spot in the sector where the penumbra displays it. Similarly, on the side where the penumbra shows a polarity opposite the true one (due to projection effects after the so-called apparent neutral line), the moat field also displays a polarity opposite the true one. This is only compatible with a moat field that is horizontal almost everywhere, as in the outer penumbra. Indeed, this horizontal moat field is seen to be physically connected with the penumbra. This connection is made evident when analyzing the individual structures detected in the averaged images, which we call moat filaments. The filaments stretch out for 12'' in the moat and can be traced back into the penumbra. The observed polarity distribution along them is only compatible with mean inclinations in the range of 80°-90°. Inside the spot, these filaments are linked to the more horizontal magnetic field component that is thought to carry a large part of the Evershed flow. Several bipolar MMFs are seen to originate inside the penumbra and cross the sunspot outer boundary to enter the moat region, following the paths outlined by the moat filaments. These results are discussed in the frame of our current theoretical understanding of the Evershed flow and MMF activity.

Results from 2002 Leonid meteor storm TV observations in Kyiv

Results are presented from double-station TV observations of the 2002 Leonids meteor storm as seen from Kyiv (Ukraine). The observations were carried out from two observational stations 54 km apart. The total observation time was five hours: from 23:30 till 4:30 UT on 18/19 November, 2002. The total number of two-station meteors was 38, 28 of which allowed for precise processing. The trajectories of the meteors in Earth’s atmosphere, their radiant coordinates, heliocentric orbital elements, etc., were calculated. The highest beginning height observed was 151.53 ± 2.79 km, and distributions of beginning and end heights are presented. Leonids registered during the onset of the storm between 3:00 and 4:00 UT had geocentric radiants (J2000.0) concentrated into a compact group with mean RA = 154°.43 ± 0°.55 and Decl. = 21°.91 ± 0°.58. The corresponding mean inclination and argument of perihelion of the orbit are i = 162°.62 ± 0°.61 and ω = 175°.13 ± 1°.37, respectively. The initial masses of meteoroids were calculated from photometry, from which a mass distribution index s = 1.43 ± 0.02 was derived. We determined that the number of meteors brighter than 4 m (1.54 × 10 −4 g) that crossed a horizontal circular area of radius 100 km at an altitude of 100 km, for an assumed radiant in zenith, changed during the observations from 350/h to 1400/h. The corresponding spatial density of Leonid stream particles was 4.3 × 10 −8–1.7 × 10 −7 km −3.

Palaeomagnetism of Ordovician and Silurian rocks from the Chu-Yili and Kendyktas mountains, south Kazakhstan

Despite significant progress during the last decade, the overwhelming majority of the details of the crustal evolution of Kazakhstan remain enigmatic. The central question of whether Kazakhstan amalgamated during the Ordovician and has acted as a coherent microplate since or whether Kazakhstan is the result of continuous accretion of terranes and arcs along a major subduction system throughout the Palaeozoic is still unanswered. Defining structural units and reconstructing their interaction relative to each other and with respect to Siberia and Baltica will improve our understanding of continent formation in Central Asia. Addressing this problem, a detailed palaeomagnetic study of the Palaeozoic formations in the Chu-Yili and Kendyktas mountains, south Kazakhstan was undertaken. Detailed stepwise thermal demagnetization experiments reveal the presence of a post-folding component of magnetization with intermediate to high unblocking temperatures (component A) in almost all samples. The in situ mean directions identified in 31 sites range in declination between 150° and 260° and show intermediate and upward pointing inclinations; based on the mean inclination a late Palaeozoic to early Mesozoic age is assumed for this secondary component of magnetization. After removal of component A a second component of magnetization (component B) was identified in red coloured argillites of early Arenigian age (Kendyktas Mountains) as well as in sediments of Early Silurian and Late Silurian to Early Devonian age (Chu-Yili Mountains). Component B passes the fold test (Enkin 2003) on the 95 per cent confidence level and yields a bedding-corrected site mean direction of D = 9.2°, I =−16.9° (five sites, k = 26.9, α95 = 15.0°) for the Lower Ordovician unit and D = 346.9°, I =+23.8° (eight sites, k = 20.8, α95 = 12.4°) for the Silurian and Lower Devonian units. Based on the age of angular unconformities, the timing of regional deformation in the Agalatas area can be constrained to be Late Ordovician in age and Middle Devonian in the Chu-Yili area. Based on the mean inclination, a southerly palaeolatitude of 8.6°–8.7°/+ 7.6° can be derived for the study area during the Early to Late Ordovician and a northerly palaeolatitude of 12.4°+ 7.7°/− 6.6° for the Silurian to Early Devonian. The observed mean declinations for the post-folding component A are significantly different from the expected reference directions for the Permian based on either the apparent polar wander path for Baltica or Siberia and suggest counter-clockwise rotations of Kazakhstan with respect to both during Devonian to Permian time.

Anterior tooth morphology and its effect on torque

This study was undertaken to determine the variation in crown-root angle (CRA) of the upper incisors and canines as well as the variation in their labial contour. In addition, the influence of the variability of the labial contour and of different bracket heights on torque was evaluated. Proximal radiographs were taken of 160 extracted maxillary teeth (81 incisors and 79 canines). They were digitized and analysed with Jasc Paint Shop Pro 7TM and Mathcad 2001 Professional. The incisal edge, the centre of the cemento-enamel junction (CEJ), and the root apex were digitized to define the crown and root long axis. For all teeth the CRA was measured. At several heights of the labial surface a tangent was determined, enabling measurement of the inclination of the labial surface. The CRA had great variability, ranging from 167 to 195 degrees for the canines (mean value 183 degrees) and from 171 to 195 degrees for the incisors (average 184 degrees). The mean inclinations of the labial surfaces for the incisors varied greatly. Between 4 and 4.5 mm from the incisal edge the standard deviations (SD) were the smallest and between 2 and 4.5 mm from the incisal edge the labial surface angle differed by approximately 10 degrees. For the canines the mean inclinations of the buccal surface also varied. This angle differed by around 10 degrees between 2 and 4.5 mm from the incisal edge, but the SD were much larger than for the incisors. It can be concluded that placement of a bracket on a tooth at varying heights, still within a clinically acceptable range, results in important differences in the amount of root torque.

Long-Term Evolution of the KOMPSAT-1 Orbit

A long-term orbital evolution of the Korea Multi-Purpose Satellite-1 is monitored and analyzed in this paper. Four years of orbital evolution is divided into four phases in terms of the operational status of the satellite. Orbit determination results, which are obtained from the satellite’s GPS navigation data, are used to convert the osculating orbit into the mean orbit. Variation of the mean altitude by orbit maneuvers and safe-hold mode operations is also analyzed. Decay of the mean altitude by natural atmospheric drag is correlated with the solar flux variation. Variation of the mean inclination is analyzed in terms of the shift of the local time of the ascending node crossing. The evolution from a near frozen orbit is monitored and analyzed in a phase plot of the mean argument of perigee and mean eccentricity.

Correction of inclination shallowing and its tectonic implications: The Cretaceous Perforada Formation, Baja California

A paleomagnetic and magnetic fabric study of the Aptian to Albian Perforada Formation, the oldest sedimentary unit of the Cretaceous Valle Group, was conducted to determine whether the Perforada inclination had been shallowed by burial compaction and to correct the inclination for any shallowing. The Perforada Formation is located on the Vizcaino terrane of the Vizcaino Peninsula of west central Baja California. An accurate paleolatitude will indicate whether the Vizcaino terrane is far-travelled. Eighty-eight specimens from 43 independently oriented hand samples and cores were collected from 11 sites. A small (10 m) fold was sampled in order to constrain the age of the magnetization with a fold test. Thermal and alternating field demagnetization was able to isolate characteristic magnetizations for most samples. Maximum unblocking temperatures near 580 °C indicate that magnetite is the magnetic carrier. The characteristic magnetization passes the fold test at the 99% confidence level. Anisotropy of anhysteretic remanence (AAR) and anisotropy of magnetic susceptibility (AMS) measurements show that five sites had well-developed bedding-parallel foliations, while four sites had poorly developed AAR fabrics but foliated AMS fabrics. The remaining two sites had poorly developed foliations for both AMS and AAR. The mean inclination ( I=35.6°) of the five sites with well-developed AAR foliations is 13.7° shallower than the mean inclination ( I=49.3°) of the two sites with poorly developed AAR and AMS fabrics. When the inclinations of the sites with well-developed AAR foliations are corrected using an individual particle anisotropy of 1.5, determined from magnetic extract/epoxy samples dried in 30–50 mT DC magnetic fields, the corrected mean inclination ( I=50.1°) is indistinguishable from the mean inclination of the sites with poorly developed AAR fabrics. A corrected formation mean direction for the Perforada Formation ( D=311.8°, I=47.0°, α 95=9.3°) indicates a 33.5°±11.1° counterclockwise rotation and 5.6°±7.7° of post-Cretaceous northward motion, after 3° of Neogene fault motion has been removed. These results indicate that the Vizcaino terrane has moved little with respect to the Peninsular Ranges terrane and cratonic North America since the Cretaceous.

Upregulation of functionally active vascular endothelial growth factor by human cytomegalovirus

Human cytomegalovirus (HCMV) infection is known to modulate host gene expression and has been linked to the pathogenesis of vasculopathies; however, relevant pathomechanisms are still unclear. It was shown that HCMV infection leads to upregulation of vascular endothelial growth factor (VEGF) expression in human foreskin fibroblasts and coronary artery smooth muscle cells (SMC). Activation of VEGF transcription by HCMV infection was confirmed by transient-expression experiments, which revealed that a short promoter fragment, pLuc135 (-85 to +50), is sufficient for activation. Site-directed mutagenesis of Sp1-recognition sites within this fragment abolished the upregulation of transcription. Functional VEGF protein is released into the culture supernatant of infected SMC. Incubation of endothelial cells with supernatants from HCMV-infected SMC cultures induced upregulation of VEGF receptor-2 expression on endothelial cells, as well as a significant upregulation of DNA synthesis, implicating cell proliferation. The mean incline of DNA synthesis at 48 and 72 h post-infection was 148 and 197 %, respectively. Addition of neutralizing antibodies against VEGF completely abolished this effect. Supernatants from SMC cultures incubated with UV-inactivated virus induced a comparable effect. This virus-induced paracrine effect may represent a molecular mechanism for HCMV-induced pathogenesis, such as inflammatory vasculopathies, by inducing a proatherogenic phenotype in SMC.

The frontal pelvic plane provides a valid reference system for implantation of the acetabular cup: Spatial orientation of the pelvis in different positions

Background The frontal pelvic plane has traditionally served as the reference plane for implantation of the acetabular cup during total hip arthroplasty, with referencing performed with the patient supine on the operating table. During daily activities in an upright position, the frontal pelvic plane changes from a horizontal to a vertical orientation. If this change in orientation is accompanied by a substantial change in pelvic inclination angle, it would mean that the use of the frontal pelvic plane as a reference plane for implantation of the acetabular cup would not be valid for proper alignment of the cup. To evaluate this possibility, we measured the change of inclination of the pelvis from the supine to the standing position.Subjects and methods We evaluated 120 patients, first positioned in a standing position and then supine on a table. Three pelvic landmarks were digitized percutaneously, and the spatial coordinates were calculated with regard to pelvic orientation in the horizontal and the vertical plane.Results We found a mean inclination of 6.7° in the standing position and 5.6° in the supine position. Patients who were more than 60 years of age who did not have coxarthrosis had a greater inclination angle (8.7°) while standing. Pelvic orientation was stable with regard to the supine and standing positions. These results were independent of sex, level of arthrosis, or status after implantation of a total hip replacement.Interpretation The frontal pelvic plane is a valid reference plane for implantation of the acetabular cup. ▪

Accuracy of acetabular component positioning with a fluoroscopically referenced CAOS system

Objective: This study evaluated the accuracy, repeatability, and reproducibility of a fluoroscopic referenced system used for guiding acetabular component positioning.Methods: Calibration of the Medtronic StealthStation Treon Plus system was performed using a Weber gage block to assess linearity. Metrologic validation of repeatability and reproducibility was done using a cadaveric pelvis with an uncemented cup placed in the target position of 45° inclination and 17.5° anteversion. A baseline assessment was done with a National Institute of Standards and Technology (NIST) traceable coordinate measuring machine (CMM).Results: Weber gage block analysis revealed a mean bias of 0.69 mm. For the cadaveric pelvis, the anterior pelvic plane was determined using the bilateral anterior superior iliac spines with the symphysis pubis as the inferior landmark. The mean CMM measurement was inclination of 46.023° (SD = 1.075; range: 43.318–46.844°) and anteversion of 15.787° (SD = 0.411; range: 15.068–16.384°). One surgeon performed a repeatability assessment (n = 8), finding mean inclination of 42.8° (SD = 1.5; range: 39.5–44.5°) and anteversion of 17.5° (SD = 3.0; range: 14.5–22.5°). Three surgeons performed a reproducibility assessment (n = 24), finding mean overall inclination of 48.5° (SD = 0.9; range: 46–50°) and anteversion of 17.8° (SD = 2.5; range: 13.5–23.5°). All measurements were within a predefined acceptability range of ± 5°.Discussion: The accuracy and reproducibility of the fluoroscopic referencing method was found to be suitable for determination of cup position in the surgical setting. Anteversion measurements were more variable for the fluoroscopic method and this may be related to the difficulty for the surgeon in predictably picking the anatomical points from the fluoroscopic image.

Parametric evaluation of 3D dispersion of rockfall trajectories

Abstract. The capability of evaluating and managing rockfall related risks is largely based on numerical modelling. Nevertheless, the reliability and accuracy of rockfall models is greatly affected by the strong uncertainty and spatial variability which characterise all the relevant parameters. In particular, 3D effects related to the variability of slope geometry and micro-topography play a major role in controlling the dynamics of falling blocks. The most important 3D effect is the "lateral dispersion" of rockfall trajectories, largely affecting the way we model rockfall dynamics, design countermeasures and assess rockfall hazard. Nevertheless, the dependence of lateral dispersion on different controlling factors has been hardly ever systematically evaluated. In this paper, the influence of different controlling factors on the dispersion of rockfall trajectories has been systematically evaluated by performing 3D parametric modelling. Numerical simulations have been performed through a new software code able to use both a lumped mass and an hybrid (kinematic-dynamic) approach. Parametric modelling has been performed at different spatial resolutions using sets of biplanar simplified slopes characterised by different mean inclination and roughness. Model results outlined a complex dependence of lateral dispersion phenomena on slope mean gradient (macro-topography), slope roughness (micro-topography) and the spatial resolution of the model (model-dependent topography). Furthermore, the sensitivity of model results in terms of kinematic variables of motion (i.e. velocity and height to the ground) to the factors controlling lateral dispersion has been evaluated, resulting in practical constraints on countermeasure design and hazard assessment.

Paleomagnetic and paleosecular variation study of the Mt. Cameroon volcanics (0.0–0.25 Ma), Cameroon, West Africa

Mt. Cameroon (4075 m) is a large volcanic horst and is presently the only active volcano on the Cameroon Volcanic Line (eight eruptions during the last century). This location belongs to the famous Bangui magnetic anomaly and is thus of particular interest for the investigation of the persistence and the evolution of the anomaly with time. We have conducted a paleomagnetic study of 94 samples drilled from 13 lavas flow on Mount Cameroon (0.0–0.25 Ma). Low-field susceptibility versus temperature ( k– T) and SIRM experiments indicated that magnetite (575 °C) was the dominant magnetic carrier and that several sites were characterized by low-temperature mineral phases (e.g. 100–200 °C and 300–400 °C), reflecting the presence of titanomagnetite with low Titanium content. At least eight samples from each site were demagnetized using both thermal treatment and alternating fields (a.f.). One contemporaneous site provided inconsistent and scattered directions and was rejected. Successful mean paleomagnetic directions were obtained for 12 sites but two sites exhibited inclinations which were significantly away from the inclination of the geocentric axial dipole (GAD) and VGP latitudes lower than 60°. Their age indicates that they were likely recorded during a period of reduced dipole intensity and they were thus discarded. The time-averaged direction derived from this final selection has a mean declination of 354.2° and a mean inclination of 5.1°, which is 3° lower than the GAD inclination. The corresponding VGP position is slightly far sided but contains the north geographic pole. The angular standard deviation (13.7°) of the VGPs is also not significantly different from the predictions of model G at this latitude. Thus we found no evidence for a long-term anomaly in this area but additional sites are needed to provide more conclusive indications.

The accuracy of free-hand cup positioning--a CT based measurement of cup placement in 105 total hip arthroplasties.

We studied 105 patients who received a total hip arthroplasty between June 1985 and August 2001 using freehand positioning of the acetabular cup. Using pelvic CT scan and the hip-plan module of SurgiGATE-System (Medivision, Oberdorf, Switzerland), we measured the angles of inclination and anteversion of the cup. Mean inclination angle was 45.8 degrees +/-10.1 degrees (range: 23.0-71.5 degrees ) and mean anteversion angle was 27.3 degrees +/-15.0 degrees (range: -23.5 degrees to 59.0 degrees ). We compared the results to the "safe" position as defined by Lewinnek et al. and found that only 27/105 cups were implanted within the limits of the safe position. We conclude that a safe position as defined by Lewinnek et al. [13] was only achieved in a minority of the cups that were implanted freehand.

A compaction correction for the paleomagnetism of the Nanaimo Group sedimentary rocks: Implications for the Baja British Columbia hypothesis

A paleomagnetic and magnetic anisotropy study of the Late Cretaceous Northumberland formation on Hornby Island, British Columbia, was conducted to determine if burial compaction could have caused its anomalously shallow inclinations. The shallow Nanaimo Group inclinations have been used to support the Baja British Columbia (Baja BC) model of continental dynamics in which superterranes were transported thousands of kilometers northward along the active North American continental margin in the Cretaceous. A mean of the site means from the Northumberland formation is D = 5.8°, I = 50.9°, α95 = 7.9° (N = 8). Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence (AAR) were measured to identify and correct for any inclination shallowing caused by depositional/compactional processes. Both concretion and fine‐grained rock samples had typical depositional/compactional AMS and AAR fabrics with bedding perpendicular minimum principal axes. A revised correction equation was used to account for the effects of either triaxial magnetic fabrics or small angular deviations of principal axes from the bedding plane. The average inclination was increased by 9.6° after the compaction correction (D = 6.1°, I = 60.5°, α95 = 7.1°, N = 8), and the mean inclination of concretion and fine‐grained rock sites was significantly steeper than Ward et al.'s [1997] result (I = 42.5°) placing Hornby Island and the Insular superterrane at a paleolatitude of 41°N in the Late Cretaceous. This paleolatitude indicates that Baja BC did translate northward since the Late Cretaceous by about 1600 km but not by the 3500 km previously indicated.

Semi-Analytic Formulas of Velocity Stirring Rates in Particle Disks

We have obtained viscous stirring and dynamical friction rates of planetesimals based on three-body orbital integrations, taking into account the Rayleigh distribution of eccentricities and inclinations. We have found that the evolution of root mean square eccentricities and inclinations calculated by using these rates agrees with N-body simulations quite well.

Oblique magnetic fabric in siderite-bearing pelitic rocks of the Upper Carboniferous Culm Basin, SW England: an indicator for palaeo-fluid migration?

Abstract A zone of siderite dominated magnetic fabrics is recognized within clastic argillaceous rocks of the southern part of the Upper Carboniferous Culm foreland basin of SW England. This zone was identified by measuring the anisotropy of magnetic susceptibility (AMS) before and after heat treatment of samples. A detailed investigation of a recumbent fold structure within this zone (at the well-known Crackington Haven locality) reveals the pre-folding nature of siderite formation. The restored κ max axes of AMS-ellipsoids plot on a segment of a small circle, with a mean inclination of c. 45° to the pole of the sedimentary bedding planes. This oblique magnetic fabric geometry is considered to reflect substrate-controlled siderite growth within a migrating fluid medium, which crystallized during diagenesis and the early stages of Variscan compression. The regional distribution of siderite growth, in combination with the directional information from the AMS, is discussed as an indicator for the palaeo-flow direction of diagenetic fluids within a foreland basin setting.

Effects of Temperature and Slope on the Sprint Speed and Stamina of the Eastern Fence Lizard, Sceloporus undulatus

Although effects of temperature on sprint performances of lizards are well documented, influences of slope are much less well known, and few studies have examined comparable effects on stamina. We monitored locomotor performance of Eastern Fence Lizards, Sceloporus undulatus, at temperatures from 15–40°C and slopes from 0–45° using two types of nonmotorized tracks. Body size did not significantly affect performance, but both sprint performance and stamina were significantly affected by temperature and slope. The optimal temperature for performance is approximately 30°C. As slope increased, both sprint speed and stamina progressively decreased. Mean incline speeds were significantly greater than mean decline speeds at all slopes other than 0°. There was a direct relationship between sprinting ability and stamina; lizards that ran faster tended to run for longer periods of time and distances. Neither sprint speed nor stamina data support the hypothesis that running velocity of lizards is limited by mechanical power output.

The Late Cretaceous palaeolatitude of the Neotethyan spreading axis in the eastern Mediterranean region

A compilation of available palaeomagnetic data from the Troodos (Cyprus) and Baër–Bassit (Syria) ophiolitic terranes of the eastern Mediterranean Tethyan orogenic belt is presented. The ophiolites represent fragments of oceanic lithosphere generated at a Neotethyan spreading axis in the Late Cretaceous, although debate continues over the tectonic setting of this spreading axis and its position within the eastern Mediterranean palaeogeography. Two types of model reconstructions have been proposed: Type 1—the ophiolites formed in a southerly Neotethyan basin by spreading above an oceanic subduction zone. The Baër–Bassit ophiolite was then emplaced a relatively short distance (tens of kilometers) southwards on to the Arabian continental margin, leaving the Troodos ophiolite isolated in an intra-oceanic setting to the west; and Type 2—the ophiolites formed in a northerly Neotethyan basin by spreading at a ‘normal’ oceanic ridge, with subsequent large-scale thrusting (hundreds of kilometers) to the south of emplaced ophiolites over microcontinental fragments to reach their present positions. Palaeomagnetic determination of the palaeolatitude of the Neotethyan spreading axis is, therefore, of considerable interest.Previous palaeomagnetic analyses have demonstrated the presence of significant, and in some cases extreme, relative tectonic rotations of a variety of origins in both ophiolites. To allow palaeomagnetic data from these rotated units to be combined, an inclination-only formulation of the palaeomagnetic tilt test is employed. This provides unequivocal evidence that both ophiolites retain pre-deformational remanent magnetizations, which are interpreted as original ocean-floor magnetizations acquired close to the time of crustal formation in the Late Cretaceous. The mean inclinations of 37.0±2.6° for the Troodos terrane and 41.1±3.4° for the Baër–Bassit terrane indicate respective palaeolatitudes for the spreading axes of 20.6°N±1.8° and 23.6°N±2.5°, consistent with a Late Cretaceous position between the Arabian and Eurasian margins. These data, together with a well-defined palaeolatitude of 25.5°N±4.5° for the eastern Pontides previously reported in the literature, provide constraints which must be incorporated in any successful tectonic reconstruction of the eastern Mediterranean Tethys. The implications of these constraints for Type 1 and 2 models are discussed using a series of plate tectonic cross-sections constructed along a line extending northwards from the Arabian continental margin. In the absence of palaeomagnetic data from Late Cretaceous rocks of the eastern Taurides, however, it is presently impossible to use these palaeolatitudinal constraints to resolve the root zone debate on a purely palaeomagnetic basis. Solutions which satisfy the constraints may be found for both types of model reconstruction. Additional, published field-based geological considerations, however, strongly support models in which the Troodos and Baër–Bassit (and other southerly) ophiolites were generated in a southern Neotethyan basin, rather than those involving generation in a northerly basin and subsequent large-scale thrust displacement to the south.

Significance of the deviations of the crack front into the plane perpendicular to the crack propagation direction – II. Crack-front vibration

In this part II, the influence of thermal vibration on the shape of a crack front and on the conditions for crack motion are investigated. We have considered a static crack model in mode I loading in a linear isotropic elastic medium whose front vibrates in the form of a standing wave with displacement ξ perpendicular to both the average crack plane and the crack propagation direction; ξis assumed to be sum of standing sine waves and the crack to be represented by a continuous distribution of vibrating edge dislocations. The displacement and stress fields due to an infinitely long edge dislocation, oscillating in the form of a standing wave, are first given. Then it is shown that, in free vibration conditions, ξ would satisfy the d'Alembert wave equation with a constant phase velocity corresponding to the velocity of a travelling sine wave along an edge dislocation. It is also shown that the sites for the initiation of crack motion are located on the average crack plane at the nodes of the vibrating crack front. The crack opening force G per unit length of the crack front, at the sites of crack propagation initiation, is found to be different from that of the rigid planar crack, when averaged over time, but the magnitude of the difference is relatively small. G decreases with increasing temperature T and is found to be proportional to T2 at very low temperature and to T at higher temperatures. The relation for G leads to view the vibrating crack front as being non straight on average over time. In tungsten, a nearly isotropic material, the theory yields a mean crack front inclination angle of about 1° at absolute zero, 3.2° at room temperature and 10.6° at the melting point.

Combined Paleomagnetic and Petromagnetic Study of the Upper Cretaceous Volcanic Sequence in Western Mexico: Implications for Tectonics and Magnetostratigraphy of the Jalisco Block

Results of detailed paleomagnetic studies of the Upper Cretaceous Autlan volcanic sequence from the Sierra Cacoma area (Jalisco block, western Mexico) are reported. The 67.4 ± 1.2 Ma whole-rock K-Ar date for these lavas and the magnetic polarity stratigraphy indicate that flows were emplaced after the Cretaceous Normal Superchron and just prior to the Cretaceous-Tertiary boundary. Fifteen sites (~150 oriented samples) were collected along two vertical profiles. Rock-magnetic experiments permit identification of magnetic carriers and assessment of the paleomagnetic stability. Continuous susceptibility measurements versus temperature in most cases yield reasonably reversible curves with Curie points close to magnetite. Judging from the ratios of hysteresis parameters, all samples fall in the pseudo-single domain grain-size region, probably indicating a mixture of multi-domain and a significant amount of single-domain grains. Reliable paleomagnetic directions were obtained for 14 sites, corresponding to 2 normal and 12 reverse polarity sites. Lowermost flows in the sequence yield reverse polarity magnetization, and probably formed during Chron 31r of the reference geomagnetic polarity time scale. The remaining flows, including those belonging to radiometrically dated sites, correspond to Chron 30n. These tentative magnetic correlations suggest that the entire volcanic sequence was emplaced during a time span of about 2 Ma. The mean paleo-direction obtained from 14 sites is Inc = 44.2°, Dec = 320.6°, k = 45, a95 = 6.0°. The mean inclination is in reasonably good agreement with the expected value for 65 and 70 Ma, as derived from reference poles for the North American craton. Declination is significantly different from expected (D = 345.8° for 65 Ma and D = 346.2° for 70 Ma), which suggests a counterclockwise tectonic rotation of about 25° for this region within the Jalisco block.

Gear, inertial work and road slopes as determinants of biomechanics in cycling.

In cycling the gear determines the distance travelled and the mean applied force at each leg thrust. According to Padilla et al. (J Appl Physiol 89:1522-1527, 2000), an elite cyclist was able to cycle for an hour at 14.6 m.s(-1 developing 510 W at a pedal frequency of 101 rpm. Thus, the opposing force was 34 N (=500/14.6), whereas the mean force, developed by the leg muscles, was 144.1 N. It can be calculated that in the same subject cycling on a 20% slope at the same pedal frequency, the velocity would be reduced by about 5 times, i.e. to 2.9 m.s(-1) because of a fivefold increase of the opposing force. In reality, the increase of mean force developed by leg muscles is even larger, because of the fall of the cadence to 60 rpm. In general, during mountain ascents cyclists develop high forces at low cadences that are likely to be more economical; in contrast, on flat ground, they increase the pedalling rates because their aerodynamic posture does not allow high force production. The intermittent pattern of muscular force application generates speed changes that become more evident at great inclines and low cadences. It can be shown that inertial work is appreciable in cycling, increasing with the incline of the road and decreasing with the cadence. However, inertial work does not seem to affect efficiency. Differences in physiologic potential make differences in performance more evident in time trials where the mean incline of the road is not negligible. Cyclists with low body size have an advantageous force versus mass ratio in high mountain ascents.