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Seventeen sites were drilled from ca. 53 Ma old mafic dykes intruded in the Linzizong Formation of the Linzhou Basin for palaeomagnetic studies. From 10 sites a higher coercivity component demagnetized between 20 and 100 mT could be isolated. Detailed rockmagnetic analyses reveal Ti-rich titanomagnetite as the remanence carrier, which indicates that the rock is not much altered and the remanent magnetization is likely of primary origin. This is supported by a positive fold test. Tilt correction could be performed by the bedding of overlying fluvial lacustrine sediments and tilt angles of ignimbrite columns post-dating the dyke emplacement. Bedding corrected directions give an overall mean direction of D/I = 12.3°/27.2° (α 95= 10.6°, k= 21.7, N= 10) corresponding to a palaeolatitude of 14.4°± 5.8°N. Comparison with previous Cretaceous data mainly from the Takena Formation yields a stable position of the Lhasa terrane during Cretaceous and Early Eocene. The difference between expected palaeolatitudes determined from the APWP of Eurasia and observed ones reveals relative northward movement of the Lhasa terrane of ca. 1847 ± 763 km since early Eocene. This is attributed to indentation of India into Asia and implies a considerable amount of north–south crustal shortening. Together with the extent of ‘Greater India’, we can derive an age for the India–Asia collision between ca. 53–49 Ma with a 95 per cent confidence limit of ± 6 Ma. [ABSTRACT FROM AUTHOR]

A palaeomagnetic study was carried out on low-middle Triassic red beds at Jingtai area of Hexi Corridor. The characteristic higher temperature component (HTC) ( Ds = 304.1°, Is = 38.4°, ks = 33.2, a95= 5.2°, N = 24 sites) isolated by stepwise thermal demagnetization exhibits dual polarity, which passes the McFadden's fold test at the 99 per cent confidence level and reversal test with classification C. Compared with coeval palaeomagnetic results from the North China Block (NCB), this result suggests insignificant palaeolatitude differences ( Pλ) between the observed and that expected at Jingtai area ( Pλ=−0.9°± 4.9° in the early Triassic or Pλ= 4.9°± 4.1° in the middle Triassic). This implies that the Hexi Corridor was the extension of the NCB by the middle Triassic. However, in comparison with early- and middle-Triassic results from the NCB, an anticlockwise rotation of studied area relative to the NCB with Rd= 25.4°± 5.2° or Rd= 26.6°± 4.5° is detected. Our result also suggests that Jingtai area of the western part of NCB was not connected with the Tarim block by the early-middle Triassic. [ABSTRACT FROM AUTHOR]

We report new palaeomagnetic data for red beds from the Ediacaran Brachina and Wonoka formations in the Adelaide Geosyncline, South Australia, and discuss their place with previously determined poles in the Ediacaran apparent polar wander path for Australia. Both formations behave similarly on thermal demagnetization, displaying high-temperature components that decay to the origin at 680 °C, consistent with haematite being the only magnetic mineral present. Restoring the strata to the palaeohorizontal yielded positive fold tests for both units at 99 per cent confidence, indicating that acquisition of magnetization occurred before the early Palaeozoic Delamerian Orogeny. For the Brachina Formation ( N= 91 specimens) the mean direction after unfolding is declination D= 178.2°, inclination I=–22.6° (α95= 4.4°), indicating a palaeolatitude λ= 11.8 ± 2.5° and a pole position at latitude λp= 46.0°S, longitude ϕp= 315.4°E, with confidence semi-axes dp= 2.4° and dm= 4.6°. The mean direction for the Wonoka Formation after unfolding ( N= 70) is D= 255.9°, I=–23.7° (α95= 6.4°), indicating λ= 12.3 +3.8/–3.4° and a pole position at latitude λp= 5.2°S, longitude ϕp= 30.5°E ( dp= 3.6° and dm= 6.8°). The mean directions for these units and other Ediacaran units in the Adelaide Geosyncline are significantly different from each other, which excludes blanket remagnetization of the units before Delamerian folding and therefore gives strong preference to their magnetization dating from close to the time of deposition. The late Cryogenian–Ediacaran–Cambrian apparent polar wander path for South Australia spans 150 Myr from ∼635 to 490 Ma and places Australia in low palaeolatitudes throughout the interval studied. The poles differ significantly from each other, suggesting Australia underwent continual drift during that time. Whereas the directional difference between the late Cryogenian Elatina Formation and early Ediacaran Nuccaleena Formation is mainly in inclination, for most other contiguous stratigraphic units the differences are mainly in declination with minor inclination differences, indicating Australia was rotating about a nearby Euler pole in low palaeolatitudes. The large and perhaps rapid polar shifts at 615–590 and 575–565 Ma in the Laurentian apparent polar wander path are not evident in the Ediacaran apparent polar wander path for Australia. Because true polar wander should be recorded globally, in the absence of evidence for any major stratigraphic break in the South Australian succession we conclude that large true polar wander did not occur during the Ediacaran. [ABSTRACT FROM AUTHOR]

New palaeomagnetic data from the central and western sectors of the Trans-Mexican volcanic belt (TMVB) are presented and analysed for palaeosecular variation (PSV) and tectonic rotations. Fifty-one sites with geochronological control were collected from selected volcanic lava flows, which cover the temporal and spatial activity in the magmatic arc for the past ∼11 Ma. Rock magnetic experiments reveal that generally Ti-poor titanomagnetites, sometimes maghemitized, are the magnetic carriers of the characteristic remanent magnetizations. After analysis of detailed progressive demagnetization data, 47 mean-site directions are determined. In addition, data from previous regional palaeomagnetic study in the eastern TMVB sector (53 sites) are re-analysed. Palaeomagnetic data are grouped according to geographic distribution (three structural sectors) and according to age (late Miocene, Pliocene or Quaternary). To avoid discarding tectonic effects, the less stringent criterion (i.e. a fixed cut-off angle to the mean equal to 45°) was applied to identify transitional data, affecting four sites. Palaeomagnetic results, backed by positive reversal tests, indicate no palaeomagnetically detectable vertical-axis block rotations in the study areas. The nearly geocentric axial dipole (GAD) inclinations suggest no significant tilting effects and negligible quadrupolar contributions. Since the mean palaeomagnetic directions for the study areas do not differ from reference directions from the North American polar wander path, two data sets for 11–5 and 5–0 Ma are tested for geomagnetic purposes. Virtual geomagnetic poles (VGPs) were selected using both fixed −45°- and optimum, variable cut-off angles. This resulted in VGP dispersions that increase back on time and are consistent with those obtained from globally distributed observations at the site latitude for their respective age ranges and cut-off criteria. Palaeomagnetic data from late Miocene and Pliocene TMVB rocks can be considered in the databases for time averaged field (TAF) and palaeosecular variation from lavas (PSVL) analyses and geomagnetic field geometry characterization during the past ∼11 Ma. [ABSTRACT FROM AUTHOR]

Continuous thermal demagnetization, in which measurements of magnetization are made at high temperature T during heating, is considerably faster than the conventional palaeomagnetic method of stepwise demagnetization, in which measurements are made at room temperature T0 in a series of cooling-reheating cycles. In the case of single-domain (SD) grains, the two methods give equivalent results after the continuous measurements are converted to equivalent room-temperature values by correcting for the reversible decrease of spontaneous magnetization MS between T0 and T. To test for equivalence of the two methods in larger pseudo-SD and multidomain grains, three different samples containing magnetite of different grain sizes and origins were heated in zero magnetic field and measurements taken either continuously at T during heating or at T0 after a set of cooling steps from T. Two samples contained 100–125 μm (mean 110 μm) and 125–150 μm (mean 135 μm) sieve fractions from a crushed natural crystal of magnetite, while the third sample is a natural diabase core sample containing coarse magnetite in the dark minerals and groundmass and fine magnetite in the plagioclase. Two different vibrating-sample magnetometers were used for continuous demagnetization and a mini-furnace and SQUID magnetometer were used for stepwise measurements. Both total thermoremanent magnetization (TRM) and partial TRMs with non-overlapping blocking temperatures ( TC, TI) and ( TI, T0) were demagnetized. The Thellier laws of partial TRMs are approximately although not exactly obeyed. In MS( T)-corrected continuous data, there is little overlap of unblocking temperatures: pTRM ( TC, TI) demagnetizes almost entirely above TI and pTRM ( TI, T0) almost entirely below TI, demonstrating reciprocity and independence. The stepwise measurements decrease more rapidly in intensity with increasing T than the corrected continuous results, some of which increase slightly with heating up to T≈ TI. Some additional decay of magnetization must occur during cooling from T, where the continuous measurement is made, to T0, where the stepwise result is measured. There are no high-temperature measurements of subsidiary cooling-heating cycles to confirm this deduction, but continuously recorded heating-cooling cycles below room temperature in inverse thermal demagnetization (or low-temperature demagnetization) show both reversible and irreversible features, depending on the remanence tested. The most important conclusion of this study is that MS( T)-corrected continuous demagnetization results do not exactly reproduce measured stepwise demagnetization results except for very fine grains, of SD size or close to it. Continuous thermal demagnetization cannot be used in general as a time-saving alternative to stepwise demagnetization if exact equivalence is required. [ABSTRACT FROM AUTHOR]

The Swift satellite early X-ray data show a very steep decay in most of the gamma-ray bursts light curves. This decay is either produced by the rapidly declining continuation of the central engine activity or by some leftover radiation starting right after the central engine shuts off. The latter scenario consists of the emission from an ‘ember’ that cools via adiabatic expansion and, if the jet angle is larger than the inverse of the source Lorentz factor, the large angle emission. In this work, we calculate the temporal and spectral properties of the emission from such a cooling ember, providing a new treatment for the microphysics of the adiabatic expansion. We use the adiabatic invariance of is the component of the electrons' momentum normal to the magnetic field, B) to calculate the electrons' Lorentz factor during the adiabatic expansion; the electron momentum becomes more and more aligned with the local magnetic field as the expansion develops. We compare the theoretical expectations of the adiabatic expansion (and the large angle emission) with the current observations of the early X-ray data and find that only ∼20 per cent of our sample of 107 bursts are potentially consistent with this model. This leads us to believe that, for most bursts, the central engine does not turn off completely during the steep decay of the X-ray light curve; therefore, this phase is produced by the continued rapidly declining activity of the central engine. [ABSTRACT FROM AUTHOR]

The Ap star HD 3980 appears to be a promising roAp candidate based on its fundamental parameters, leading us to search for rapid pulsations with the VLT UV-Visual Echelle Spectrograph (UVES). A precise Hipparcos parallax and estimated temperature of 8100 K place HD 3980 in the middle of the theoretical instability strip for rapidly oscillating Ap stars, about halfway through its main-sequence evolution stage. The star has a strong, variable magnetic field, as is typical of the cool magnetic Ap stars. Dipole model parameters were determined from VLT observations using Focal Reducer and low Dispersion Spectrograph (FORS)1. From Doppler shift measurements for individual spectral lines of rare-earth elements and the Hα line core, we find no pulsations above 20–30 m s−1. This result is corroborated by the inspection of lines of several other chemical elements, as well as with cross-correlation for long spectral regions with the average spectrum as a template. Abundances of chemical elements were determined and show larger than solar abundances of rare-earth elements. Further, ionization disequilibria for the first two ionized states of Nd and Pr are detected. We also find that the star has a strong overabundance of manganese, which is typical for much hotter HgMn and other Bp stars. Line profile variability with the rotation period was detected for the majority of chemical species. [ABSTRACT FROM AUTHOR]

Detailed palaeomagnetic integrated with rock magnetic studies have been carried out on a loess-palaeosol sequence in Baoji, Shaanxi province, southern Chinese Loess Plateau. For most samples stepwise thermal demagnetization revealed two well-defined magnetization components. A low-temperature component (LTC), which was isolated between 100 and 200 °C, is consistent with the present geomagnetic field direction. A high-temperature component (HTC), which was isolated between 250 and 620–680 °C, shows normal, reversed or transitional polarities. Our new magnetostatigraphy revealed two distinct geomagnetic excursions recorded in loess unit of L5 and palaeosol unit of S7, respectively, and the Matuyama-Brunhes (M-B) polarity boundary in loess unit of L8. Rock magnetic experiments demonstrated that the specimens from the excursion zones have the same magnetic properties as those from the Brunhes normal or Matuyama reversed polarity zones. Measurements of anisotropy of magnetic susceptibility (AMS) showed that the sediments have primary sedimentary fabrics. Based on the palaeoclimatological and magnetostratigraphic age models, the middle Brunhes excursion in loess L5 is dated at 413–433 ka, and the early Brunhes excursion is estimated to occur 23–33 ka after the M-B reversal. Comparing with previously reported geomagnetic excursions in the Brunhes chron, the middle Brunhes excursion (L5) is likely global. For the early Brunhes excursion (S7), we need further studies to examine its global occurrence. [ABSTRACT FROM AUTHOR]

We studied the evolution of anisotropy of magnetic susceptibility (AMS) during stepwise alternating fields (AF) demagnetization on various kinds of rock samples (loess and palaeosols, diorite, granite, gneiss) with very different degree of magnetic anisotropy. The variation of the magnetic fabric appears to be related to both the magnetic fabric before AF demagnetization and to the direction of AF application. The anisotropy change is mainly controlled by the initial magnetic fabric. The more anisotropic is the initial magnetic fabric, the less is the effect of the direction of field application. This can be clearly shown by determination of the difference of the susceptibility ellipsoids after and before AF application. Even for rocks with weak magnetic anisotropy, the effect of the initial AMS is significant. The difference ellipsoids allow in particular cases to point out that the initial magnetic fabric is composite. [ABSTRACT FROM AUTHOR]

The knowledge of the temperature radial distribution in the Earth's core is important to understand the heat balance and conditions in the Earth's interior. Molecular dynamics (MD) simulations were applied to study the properties of liquid iron under the pressure-temperature conditions of the Earth's outer core. It is shown that the model used for the MD simulations can reproduce recent experimentally determined structure factor calculations to the highest pressure of 58 GPa. Applying this model for higher pressures, the calculated densities and diffusion parameters agree well with the results of first-principles. The MD calculations indicate that a reasonable estimate of the adiabatic temperature profile in the Earth's outer core could be evaluated. [ABSTRACT FROM AUTHOR]

This paper presents the mathematical analysis of a single stage absorption cycle using heat rejected from thermoelectric modules to drive the cycle. The absorption cycle uses LiBr/H2 O solution as the working pair with thermoelectric modules sandwiched between the generator and absorber. The results of the analysis show that thermoelectric modules would provide the heat required to drive the absorption cycle and the overall coefficient of performance (COP) of the integrated system could be higher than unity. [ABSTRACT FROM AUTHOR]

We have developed a system to irradiate samples and record radioluminescence (RL), optically stimulated luminescence (OSL), and thermoluminescence (TL) at temperatures ranging from -150°C to 200°C. The system consists of a cryostat, an irradiation/stimulation unit fitted with an X-ray tube (40 kV Moxtek) and a quartz window for optical stimulation, and a detection unit that utilises a photomultiplier tube and an interchangeable filter pack. Experiments have been conducted with quartz and albite (a feldspar). TL and OSL experiments show that several optically sensitive trapping states are stable below -50°C. In addition, an increase in OSL is seen as the OSL stimulation temperature is lowered below -50°C, and an increase in RL is apparent as the temperature is lowered during irradiation. This indicates that not only are optically sensitive low temperature traps present but that luminescence becomes more efficient at low temperatures. [ABSTRACT FROM AUTHOR]

The measured values of the glitch healing parameter, Q, of the Vela pulsar are found to be inconsistent with the starquake mechanism for glitch generation in various neutron star (NS) models, based upon the parametrized equations of state (EOSs) of dense nuclear matter. Such models correspond to an unrealistic mass range ≤0.5 M⊙ for the pulsar, if the observational constraints of the fractional moment of inertia of the core component which is called the glitch healing parameter, Q, according to the starquake model, are imposed on these models. However, we show that these observational constraints yield a realistic mass range for NS models, corresponding to a core given by the stiffest equation of state, d P/d E= 1 (in geometrized units), and the envelope is characterized by the well-known EOS of an adiabatic polytrope , if the continuity of the adiabatic speed of sound , together with the pressure ( P), the energy density ( E) and the two metric parameters (ν and λ), is assured at the core–envelope boundary of the models and this boundary is worked out on the basis of the ‘compatibility criterion’ for hydrostatic equilibrium. The models yield a stable sequence of NS masses in the range 1.758 ≤ M≤ 2.2 M⊙, corresponding to the glitch healing parameter range 0 ≤ Q≤ 0.197, for a choice of the ‘transition density’ at the core–envelope boundary. The maximum stable value of 2.2 M⊙ in this sequence, in fact, corresponds to the lowest possible upper bound on NS masses calculated in the literature, on the basis of modern EOSs for NS matter. The models yield the surface redshift and mass M≃ 2.153 M⊙ for the ‘central’ weighted mean value, Q= 0.12 ± 0.07, of the glitch healing parameter of the Vela pulsar. This value of mass can increase slightly up to M≃ 2.196 M⊙, whereas the surface redshift can increase up to the value [which represents an ultracompact object ], if the observational constraint of the upper weighted mean value of Q≃ 0.19 is imposed on these models. However, for the lower weighted mean value of Q≃ 0.05, the mass and surface redshift can decrease to the values of zR≃ 0.6066 and M≃ 2.052 M⊙ respectively. These results set the lower bound on the energy of gravitationally redshifted radiation in the rather narrow range of 0.291–0.302 MeV. The observation of the lower bound on the energy of a γ-ray pulse at about 0.30 MeV from the Vela pulsar in 1984 is in excellent agreement with this result, provided that this energy can be interpreted as the energy of gravitationally redshifted electron–positron annihilation radiation from the surface of the star. [ABSTRACT FROM AUTHOR]

We present new palaeomagnetic results from Late Cretaceous red beds of the Paomagang Formation collected at 42 sites in the Yichang area (30.7°N, 111.7°E), middle–northern part of the South China Block. A high unblocking temperature component around 680°C was isolated from 26 sites by stepwise thermal demagnetization. Fold tests are positive at the 95 per cent confidence limit for 14 and 11 sites of the Paomagang and Wangdian areas, respectively. Normal and reversed polarity sequence found in the Wangdian area passed a reversal test at the 95 per cent confidence limit. The tilt-corrected mean direction for Yichang area is , corresponding to a palaeopole at 71.5°N, 280.0°E with . Comparison with the expected inclination from the 80 Ma Eurasian APWP pole indicates a inclination flattening of . Middle Cretaceous to Cenozoic NW–SE extension tectonics within the SCB contributes only 2.0° to the inclination flattening. While the massive samples of the Paomagang Formation show a moderate degree of anisotropy and steeper inclination , the laminated samples, which form more than 75 per cent of the studied samples, show a higher degree of anisotropy and shallower inclination value . A good correlation between remanence inclination and facies types indicates that depositional processes produced the observed shallow inclination in the Yichang area. [ABSTRACT FROM AUTHOR]

We investigate the linear stability of a shocked accretion flow on to a black hole in the adiabatic limit. Our linear analyses and numerical calculations show that, despite the post-shock deceleration, the shock is generally unstable to non-axisymmetric perturbations. The simulation results of Molteni, Tóth & Kuznetsov can be well explained by our linear eigenmodes. The mechanism of this instability is confirmed to be based on the cycle of acoustic waves between the corotation radius and the shock. We obtain an analytical formula to calculate the oscillation period from the physical parameters of the flow. We argue that the quasi-periodic oscillation should be a common phenomenon in accretion flows with angular momentum. [ABSTRACT FROM AUTHOR]

It may be difficult to isolate stable palaeomagnetic vectors of different ages if they lie in grain assemblages with overlapping ranges of coercivity or of unblocking temperature. This is because some moments associated with either vector may demagnetize at the same stage of experimental demagnetization. The sharp transition between vector components may be obscured and stable components may appear less linear on the demagnetization plot. Thermal and alternating field (AF) demagnetization techniques remove vector components on a quantitative basis, according to a discrete limiting unblocking temperature or coercivity. Low-temperature demagnetization (LTD) differs in that it removes vector components discretely, wherever there are mobile domain walls. Experiments tested the ability of LTD to improve the effectiveness of AF demagnetization on isothermal and anhysteretic remanent magnetizations (IRM, ARM) in diabase. Multicomponent NRMs were simulated IRMs or ARMs in different, non-overlapping coercivity ranges, along three orthogonal axes or along two non-orthogonal directions. The known directions of the experimentally applied vector components were always more successfully verified by AF demagnetization if LTD was first applied. For the same specimens, LTD reduced the same artificial remanences by ∼50 per cent for the coercivity range 0–15 mT, by ∼25 per cent for the range 15–30 mT, and negligibly for higher-coercivity fractions. LTD demagnetizes polydomain magnetite as domain walls rearrange on passing through a low-temperature transition, near 120 K. [ABSTRACT FROM AUTHOR]

Progress in development of thermodynamically based models of silicate equilibria with explicit entropy budgets has motivated a reexamination of the conclusion of McKenzie (Journal of Petrology 25, 713–765, 1984) that isentropic upwelling suffices as a model of mantle melting. An entropy budget equation for fractional melting with melt migration in an upwelling two-phase continuum is presented. The energetically self-consistent melt production model predicted by MELTS is used to evaluate numerically the magnitudes of differences between fractional melting (with melt migration) and equilibrium melting (without relative movement) that can be bounded in one dimension: chemical advection by out-of-equilibrium melt; thermal disequilibrium between migrating liquid and residue; frictional dissipation of gravitational potential; dissipation as a result of solid compaction. Like the familiar isobaric case in which fractional melting is significantly less productive than equilibrium melting, chemical isolation of the escaping melts from the residue reduces the oceanic crustal thickness by ∼1 km. Allowing escaping melts to move on their own adiabats and ascend at higher temperature than the residue further suppresses melting but yields only ∼100 m less crustal thickness. Extra crustal thickness as a result of gravitational dissipation is ∼100 m, much smaller than the effect of chemical isolation. Viscous dissipation as a result of compaction is negligible. [ABSTRACT FROM PUBLISHER]

Examines the isolation of archeomagnetic signals by combined low temperature and alternating field demagnetization in Linconshire, England. Compatibility of remanences with contemporary geomagnetic field orientations; Consolidation of material to prevent thermal demagnetization; Anisotropy of low-field magnetic susceptibility.

Examines the mechanisms of low-temperature demagnetization of remanence in multidomain magnetite. Behavior of saturation isothermal remanence; Occurrence of kinematic domain state reorganization; Assessment on the thermal cycling of rocks bearing multidomain magnetite.

Presents the paleointensity results for historic lavas from Mt Etna in Italy. Use of microwave demagnetization in the experiment; Effectivity of the technique; Factors affecting the estimates of the historic field.