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SUMMARY Changes in the geomagnetic field over geologic timescales can be used to study the evolution and processes of its sources in Earth's deep interior. As a stark contrast to the geomagnetic field behaviour of the recent past, the field in the late Neoproterozoic is defined by ambiguous polar wander paths, ultralow field strengths and a period of extreme reversal hyperactivity. Palaeointensity data from this time are still scarce and conclusions made from these data suffer from large uncertainties brought by a low sampling density. In this study, we present new palaeomagnetic and palaeointensity data from quarry outcrops and five deep drill cores, covering the longest and most complete profiles through the Ediacaran units in the Volyn Basalt Province (NW Ukraine) to date. Palaeodirectional analysis of thermal and alternating field demagnetization experiments reveals at least six reversals in the profile as well as four palaeopoles that agree with previously published poles. Whole-rock palaeointensity estimates are derived from a multimethod approach that utilizes thermal and microwave Thellier experiments performed using Coe and IZZI protocols as well as Wilson and double-heating Shaw experiments. These produce instantaneous site-mean palaeointensity estimates in the range of 2.1 ± 0.4 to 11.1 ± 3.5 µT and virtual dipole moments in the range of 0.31 ± 0.06 × 1022 to 1.67 ± 0.53 × 1022 A m2. Small-scale variations of palaeointensities throughout the profile not only show extremely weak field strengths around polarity changes but could also suggest that the field strength never fully recovered between reversals. These new results increase the density of intensity data coverage for Baltica in the Late Ediacaran and, in combination with previously published Ediacaran dipole moments, support an extremely weak field that seems to increase in strength towards the Ediacaran–Cambrian transition.

SUMMARY Changes in palaeosecular variation, dipole moment and polarity reversal frequency are salient features of the Earth’s magnetic field over the geological past, yet how these changes are linked by the geodynamo remains controversial. To further understand this issue, we provide new absolute (API) and relative (RPI) palaeointensities from the ∼1-km-thick basaltic sequence of Waja (North Ethiopia) emplaced around 31 Ma, yielding an instantaneous virtual dipole moment of 57 ± 9 ZAm2 (1σ, N = 18) and a relative variability in intensity εF = 0.39 ± 0.07 (1σ, N = 19). Our analysis of the API database with strict selection criteria (inclusion of Thellier-style determinations with pTRM checks only, at least five determinations per cooling unit, and within-unit relative standard error lower than 10 per cent) fails to identify any robust correlation between changes in dipole moment and reversal frequency over the past 155 Myr. More convincingly, the available RPI results are consistent with an increase of the palaeosecular-variation proxy εF with reversal rate, as predicted by numerical dynamo simulations. We also find that the API-based estimate εF = 0.40 ± 0.03 (1σ, N = 104), computed from the filtered version of the World Palaeointensity Database for the 0.77–31 Ma interval, is consistent with the scaling rule, suggesting that the API record has been sufficiently sampled over the past 31 Ma. We thus speculate that the absence of negative correlation between changes in dipole moment and reversal frequency in the API database over the past 155 Myr may be the result of insufficient sampling prior to 31 Ma rather than the signature of an intrinsic geomagnetic feature.

—The experiments have been carried out on the acquisition of thermochemical remanent magnetization (TCRM) in basalt samples containing titanomagnetite (TM) with the Curie temperature Тс ~200°C by their rapid heating to maximum temperatures Т* from 450 to 530°C followed by slow cooling in the laboratory magnetic field Blab. At different stages of the preliminary thermal treatment of the initial samples, a set of magnetomineralogical studies including electron microscopy, X-ray diffraction and thermomagnetic analyzes, and measurements of magnetic hysteresis parameters were performed. It is shown that as early as the very beginning of the cooling process, all samples demonstrate explosive growth of TCRM corresponding to the stage of rapid single-phase oxidation of the initial titanomagnetite fraction of basalt, and that TCRM is acquired by the increase of Тс and volume of single-phase oxidized parts of TM grains as well as by the growth of the volume of Ti-depleted (relative to the initial TM) cells of microstructure of the subsequent oxidative exsolution. The Arai–Nagata diagrams for the samples carrying TCRM have a form of a broken line consisting of two linear segments. The low-temperature interval T < Т* corresponds to a mixture of thermochemical and thermoremanent (TRM) magnetizations and gives a slightly overestimated Blab because of the effect of a low cooling rate during the acquisition of TCRM and TRM. The high-temperature interval corresponds to pure TCRM and the Blab strength determined from this interval is underestimated by 20–27%. It is recommended to reject samples whose Araii–Nagata diagram has two or more linear segments against the background single-component NRM.

The magnetic properties of chernozem soils, dark and light gray forest soils, and sod-podzolic soils present in the Republic of Tatarstan have been researched and described using the petromagnetism method, coercive spectrometry, and X-ray phase analysis with the purpose of improving the soil monitoring system in relation to fallow and virgin soils. In the course of soil genesis, iron compounds undergo transformations and the magnetic parameters of the soil profile change in comparison with the parent rocks. It can be said that the magnetic profile reflects the pedogenesis processes. A statistically significant relationship between the humus content on the one hand and the susceptibility and intensity of remanent saturation magnetization (Jrs) on the other hand has been identified. A technique making it possible to separate the contributions of lithogenic and pedogenic magnetic minerals to the saturation remanence (Jrs) intensity has been developed on the basis of coercive spectrometry. In the studied soils, the pedogenic component primarily consists of the organogenic extracellular constituent of the magnetite–maghemite association, which is the best candidate to proxy in assessments of the humus concentration in soils at various depths with magnetic methods.

This paper presents the results of a study of soil cover in the Mari Chodra national park in the southeastern part of the Republic of Mari El. Magnetic properties of soddy-medium-podzolic sandy loam soils and soddy-podzolic loam soils are studied. Samples are taken along the shoreline of the karst Yalchik Lake and up the slope from the lake. Based on the results of magnetic susceptibility measurements, it is shown that the studied soil profiles are characterized by both the accumulative and eluvial–illuvial distribution of mineral components, depending on the conditions of soil formation and recreational activity of the given territory. It is shown that the increase in magnetic susceptibility in the organogenic horizons of soddy-medium-podzolic and soddy-podzolic soils is due to the contribution of a ferrimagnetic component. Differential thermomagnetic analysis and decomposition of coercive spectra into components revealed that the main carriers of the magnetization of the soils are fine-grained magnetite and hematite that have a pedogenic origin.

—The experiments on the determination of paleointensity Banc of the Earth’s magnetic field by Thellier method on basalts of the Berd (Jurassic) and Paravakar (Cretaceous) collections sampled in the northeastern Armenia in 2006 revealed an anomalous behavior of the Arai–Nagata diagrams. The anomaly manifests itself by a sharp drop in the intensity of natural remanent magnetization (NRM) under heating of samples to about 400°C, which is accompanied by a very weak acquisition of partial thermoremanent magnetizations (pTRMs) in this temperature interval. The further increase in temperature leads to the opposite phenomenon—an unexpectedly sharp rise in pTRMs intensity with almost no decrease in NRM, which creates the L-shape of the Arai–Nagata diagram. A similar phenomenon of a steep decline during thermal demagnetization was also established for remanent saturation magnetization Mrs(T). We carried out a number of magnetomineralogical experiments from which we conclude that, consistent with the hypothesis suggested by (Kosterov and Prevot, 1998), the sharp drop in Mrs(T) and NRM(T) curves is caused by the transitions of the domain state from a metastable configuration to a more stable one. These transitions are initiated by the processes of single- and heterophase oxidations of primary titanomagnetites under the laboratory heating of samples to moderate temperatures.

—Variations in the magnetic and geochemical properties of the sediments of Lake Bolshoe Yarovoe (Altai Territory) were studied. The data were derived from five core columns (up to 4.5 m long) covering a time interval of more than 8000 years. In addition, coercive spectra were obtained for 792 samples taken every 2 cm. Coercive spectra were then used to identify soft magnetic (10–15 mT) and hard magnetic (35–50 mT) components. The soft magnetic component is detrital, and the hard magnetic component is biogenic, which is confirmed by microscopic studies. Moreover, the samples contain micrometeorite particles. Variations in geochemical properties allow reconstruction of the environmental history of the lake. Sediments in the lower part of the section vary both in the content of ferrimagnetic components and in geochemical properties, which indicates a sharp environmental change between ~6100 and ~7600 years ago. Quasiperiodic alternation of warm (dry) and cool (humid) periods is observed higher in the section, between ~4100 and ~6100 years ago. The variations in the magnetic components are consistent with the environmental changes and can be used for the historical reconstruction.

Oxidation decomposition of titanomagnetite grains to the magnetite–ilmenite lattice during the formation of igneous rock can lead to thermochemical remanent magnetization (TCRM). Computer simulation of TCRM in the system of single-domain interacting particles and numerical simulation of the Thellier experiments to determine the paleointensity have been carried out. Contrary to the concerns, the Thellier technique factually applied to the TCRM-bearing samples yields a result that is very close to the true value of the external magnetic field applied to the sample during formation of the TCRM. Together with the recently published laboratory experimental data, these calculations are indicative of a good perspective for obtaining reliable paleomagnetic data on TCRM-bearing samples and can expand the class of rocks suitable for determination of the paleointensity.

Monte Carlo numerical simulation of the formation of chemical remanent magnetization (CRM) by the mechanism of the growth of volumes from superparamagnetic (SPM) to single-domain (SD) in the ensembles of magnetostatically interacting particles, thermoremanent magnetization (TRM), and experiments on determining paleointensity by the Thellier–Coe and Wilson–Burakov methods are carried out. The obtained results agree with the Smirnov–Tarduno hypothesis (Smirnov and Tarduno, 2005) that the similarity of the spectra of blocking temperatures Tb of CRM and TRM can be due to the narrowness of the interval of the blocking temperatures Tb of CRM and TRM, with the reservation that the similarity can be observed on part of the total interval of the Tb spectrum provided that this interval accommodates a significant fraction of the total CRM intensity. The analytical examination of the case of non-interacting particles (sparse concentration of grains) shows that in this case, the (quasi-)linearity of the Arai–Nagata diagrams is due to the presence of a plateau on the curves of the derivative dCRM/dpTRM (pTRM is partial thermoremanent magnetization) which emerges in a narrow spectrum of blocking temperatures. The results of the numerical experiments suggest that at a particle concentration of above 0.2% magnetostatic interaction leads to the practically full linearity of the Arai–Nagata diagram over a significant interval of the total spectrum of blocking temperatures for CRM. At the same time, on the remaining temperature interval, both the Arai–Nagata diagrams and the CRM(TRM) curves are substantially concave, indicating the lack of similarity between the spectra of blocking temperatures for CRM and TRM. The analysis of the empirical data revealed their resemblance, up to a certain point, to the results of simulation but at the same time clearly demonstrated the noticeable distinction between them, associated with the significant differences in the conditions of the numerical and laboratory experiments.

The consistency of the empirical data on the paleointensity and paleoinclinations contained in the BOROKPINT paleointensity world database with the Geocentric Axial Dipole (GAD) hypothesis and the Giant Gaussian Process (GGP) model describing the geomagnetic field variations in the Brunhes epoch is tested. The calculation procedure is based on the representation of the geomagnetic field potential by the sum of the spherical functions of a spatial coordinate with random coefficients, which enables the computer simulation of the data that correspond to the given statistical characteristics of the coefficients. The estimation shows that according to the Kolmogorov–Smirnov and Anderson–Darling tests, the GAD hypothesis in its canonical form should be rejected. The extension of GAD to GGD with nonzero time-average quadrupole and octupole terms brings the paleointensity and paleoinclination data into agreement with the GGP model realizations; however, these models turn out to be mutually exclusive because their parameters are inconsistent with each other. Testing the paleoinclination data against GDP model demonstrates the necessity of introducing a small correction to the purely dipole component of the geomagnetic field. At the same time, the analysis of the paleointensity data shows that these data with a very high probability agree with the GGP models with a high quadrupole contribution making up 1/3 of the dipole coefficient, which is strongly at odds with the parameters of the model corresponding to the paleoinclination data. This inconsistency is most probably caused by the artifacts due to the incorrect determinations of paleointensity; however, this interpretation leaves unsolved the question about the causes of such a strong latitudinal dependence of the intensity of the Virtual Axial Dipole Moment (VADM) what follows from the empirical data.

The analysis of the statistical characteristics of the geomagnetic field generated in the numerical geodynamo models has shown that the distribution of the spherical harmonic coefficients in some cases is not Gaussian but, instead, has much in common with the Laplace distribution. The shape of the corresponding histograms depends on the time scale, which allows interpreting the obtained data in terms of a mixture of Gaussian distributions. The similar effects associated with the intermittence were observed in the experiments in a turbulent fluid flow. Hence, the behavior of secular variations in the magnetic field of the Earth should perhaps be described in terms of a mixture of several Gaussian stationary processes corresponding to switching between the different regimes of geodynamo generation.

The results of the Thellier–Coe experiments on paleointensity determination on the samples which contain chemical remanent magnetization (CRM) created by thermal annealing of titanomagnetites are reported. The results of the experiments are compared with the theoretical notions. For this purpose, Monte Carlo simulation of the process of CRM acquisition in the system of single-domain interacting particles was carried out; the paleointensity determination method based on the Thellier–Coe procedure was modeled; and the degree of paleointensity underestimation was quantitatively estimated based on the experimental data and on the numerical results. Both the experimental investigations and computer modeling suggest the following main conclusion: all the Arai–Nagata diagrams for CRM in the high-temperature area (in some cases up to the Curie temperature T c) contain a relatively long quasi-linear interval on which it is possible to estimate the slope coefficient k and, therefore, the paleointensity. Hence, if chemical magnetization (or remagnetization) took place in the course of the magnetomineralogical transformations of titanomagnetite- bearing igneous rocks during long-lasting cooling or during repeated heatings, it can lead to incorrect results in determining the intensity of the geomagnetic field in the geological past.

An extensive city heat network contains many segments, and each segment operates with different efficiency of heat energy transfer. This work proposes an original technical approach; it involves the evaluation of the energy efficiency function of the heat network segment and interpreting of two hyperbolic functions in the form of the transcendental equation. In point of fact, the problem of the efficiency change of the heat network depending on the ambient temperature was studied. Criteria dependences used for evaluation of the set segment efficiency of the heat network and finding of the parameters for the most optimal control of the heat supply process of the remote users were inferred with the help of the functional analysis methods. Generally, the efficiency function of the heat network segment is interpreted by the multidimensional surface, which allows illustrating it graphically. It was shown that the solution of the inverse problem is possible as well. Required consumption of the heating agent and its temperature may be found by the set segment efficient and ambient temperature; requirements to heat insulation and pipe diameters may be formulated as well. Calculation results were received in a strict analytical form, which allows investigating the found functional dependences for availability of the extremums (maximums) under the set external parameters. A conclusion was made that it is expedient to apply this calculation procedure in two practically important cases: for the already made (built) network, when the change of the heat agent consumption and temperatures in the pipe is only possible, and for the projecting (under construction) network, when introduction of changes into the material parameters of the network is possible. This procedure allows clarifying diameter and length of the pipes, types of insulation, etc. Length of the pipes may be considered as the independent parameter for calculations; optimization of this parameter is made in accordance with other, economical, criteria for the specific project.

The mechanics of twisted threads with rectilinear core, which serves to describe the failure of both individual components as well as the thread as a whole, is analyzed. The article proposes a hypothesis according to which obstruction of weak sites of the core thread by a contact load from the direction of the winding thread with loading of the composite (core-spun) thread may serve to account for the observed extremal variation in strength.

The reliability of the Thellier method for determining the paleointensity of a geomagnetic field is explored on recent igneous rocks of Kamchatka. The main magnetic mineral in the studied rocks is titanomagnetite with different degree of oxidation. It is obtained that the reliability of the results can be assessed based on the deviations of the check points of the partial thermoremanent magnetization (pTRM) during the Thellier experiment. Besides, for different rocks, it is found that the stability of titanomagnetites to heating during the experiments can be insufficient for validating the reliability of the results of paleointensity determination; however, at the same time, the reliability may depend on the initial (oxidation) state of the magnetic minerals of the studied rocks.

Acquisition curves of isothermal remanent magnetization for 1057 samples of core KDP-01 from Lake Hovsgul (Mongolia) are decomposed into three endmembers using non-negative matrix factorization. The obtained mixing coefficients also decompose hysteresis loops, back-field, and strong-field thermomagnetic curves into their related endmember components. This proves that the endmembers represent different mineralogical fractions of the Lake Hovsgul sedimentary environment. The method used for unmixing offers a new possibility to apply rock magnetism in paleoecological and paleoclimatic studies. For Lake Hovsgul it indicates that a low-coercivity component with a co-varying paramagnetic phase represents a coarse-grained magnetite fraction from terrigenous influx probably via fluvial transport. A second component with coercivities close to 50∼mT is identified as a magnetite fraction related to magnetosomes of magnetotactic bacteria. The third component has coercivities near 85∼mT and is identified as greigite of biotic or abiotic origin common in suboxic/anoxic sediments. Significant positive correlations between variations of intensity of all three mineralogical components along the core are found. A rapid drop in all endmember concentrations by more than one order of magnitude at about 20∼m depth testifies to a major change of the environmental or geological conditions of Lake Hovsgul. It possibly is related to the onset of MIS∼10 marking the termination of arid climate conditions. Short intervals of high productivity are characterized by an abundance of magnetite magnetosomes and may highlight glacial-interglacial transition intervals. For the rest of the core greigite magnetization substantially exceeds that of magnetite, indicating a predominantly anoxic environment. This article is protected by copyright. All rights reserved.

The quadrature formula is obtained for the distribution function (DF) of the intensity of the geomagnetic field B and the corresponding virtual axial dipole moment VADM in the model of the Giant Gaussian Process (GGP). The predictions of this model are compared, up to a high degree of detail, with the empirical data for the Brunhes Epoch, which are contained in the global databases (GDB) for paleointensity. With a fixed latitude φ, the DFs f B (B, φ) and f VADM(VADM, φ) are close to Gaussian within the first approximation. At the same time, the global DF f B (B) has a high coefficient of asymmetry a = 0.35 since the mean of this function is latitude-dependent. In contrast, the global DF f VADM(VADM) has far lower asymmetry a = 0.16, since its mean barely varies with latitude. The comparison between the distribution histograms of VADM according to the PINT GDB data for the Brunhes Epoch and the results calculated by the BGP model shows that the empirical data and the calculations by the GGP model noticeably differ in the interval of the small VADM. Specifically, the histogram based on PINT GDB data shows a significant predominance of these data compared to the model predictions. At the same time, the same data fairly well agree with the GGP model in directions. This contradiction is probably accounted for by the underestimation of the paleointensity values in the experiments by the Thellier method if the rock carries chemical magnetization instead of thermal remanent magnetization. An alternative explanation suggests a short drop in the geomagnetic dynamo power associated with a simultaneous decrease in both the mean value of the axial dipole and in the variances of all the other terms of the spherical expansion of the geomagnetic field (i.e., quadrupole, octupole, and other components).

The results of numerical modeling of the geomagnetic secular variation by the method of the Giant Gaussian Process (GGP) are presented and compared with the information derived from the presentday databases for paleointensity. The variances of the positions of the virtual geomagnetic pole (VGP) calculated from the synthetic and experimental data (Brunhes epoch, effusive rocks) are nearly similar, which supports the validity of the theoretical model. The average value of the virtual axial geomagnetic dipole (VADM) calculated from the PINT world database on paleointensity and the Sint-2000 model is lower than VADM calculated by the GGP model; at the same time, the estimates based on the archaeomagnetic data give the VADM value slightly above the model prediction. The largest difference is observed in the variances of VADM, which is for all the three databases noticeably higher than the value calculated from the GGP model. Most probably, this is due to the contribution of the neglected measurement errors of VADM.

A detailed analysis of the data on the intensity of the geomagnetic dipole and frequency of its reversals presented in the world’s paleointensity databases provided the arguments in favor of the hypothesis of the negative correlation between the average virtual dipole moment (VDM) and the frequency of the reversals on the interval from 5 Ma to 100 Ma ago. However, the statistical confidence level of this hypothesis is only 60–70%, which is far below 95%, the standard required confidence level of a hypothesis to be considered statistically reliable. At a high level of confidence (above 99%), the presence of a positive correlation between the mean value and variance of VDM for a number of intervals of stable polarity in the Cenozoic and Mesozoic is confirmed. This finding means that the distribution of VDM on these time intervals is certainly non-Gaussian and is rather described by the gamma- or lognormal law. At the same time, in contrast to the earlier intervals, the histogram of VDM for the Brunhes epoch is closer to the normal distribution. Compared our conclusions with the published results on the numerical modeling of the geodynamo, we found that they are consistent in terms of a probable negative correlation between the average VDM and reversal frequency, as well as the lack of correlation between the average VDM and the length of the interval of stable polarity.

This article presents a theory of the contact interaction of two filaments that are twisted together. A formula is obtained for the contact load, which is expressed through the tension of one filament (one component). Another formula is obtained for the strength of the twisted filament, and a weak local strength maximum is found. The conditions under which the outer filament and the axis of the twisted filament are parallel were determined analytically: 1) the twisting of the initial filament K 1 and the secondary twisting K must be done in opposite directions (the twist K 1 has a minus sign in Eq. (13)); 2) the secondary twist K must be exactly half as great as the twist for the initial filament K 1.

The effects of mutations in bacteriophage T4 genes uvsX and 49 on the double-strand break (DSB)-promoted recombination were studied in crosses, in which DSBs were induced site-specifically within the rIIB gene by SegC endonuclease in the DNA of only one of the parents. Frequency of rII+ recombinants was measured in two-factor crosses of the type i×ets1 and in three-factor crosses of the type i×ets1 a6, where ets1 is an insertion in the rIIB gene carrying the cleavage site for SegC; i's are rIIB or rIIA point mutations located at various distances (12-2040 bp) from the ets1 site, and a6 is rIIA point mutation located at 2040 bp from ets1. The frequency/distance relationships were obtained in crosses of the wild-type phage and of the amber mutant S17 (gene uvsX) and the double mutant S17 E727 (genes uvsX and 49). These data provide information about the frequency and distance distribution of the single-exchange (splices) and double-exchange (patches) events. The extended variant of the splice/patch coupling (SPC) model of recombination, which includes transition to the replication resolution (RR) alternative is substantiated and used for interpretation of the frequency/distance relationships. We conclude that the uvsX mutant executes recombination-dependent replication but does it by a qualitatively different way. In the absence of UvsX function, the DSB repair runs largely through the RR subpathway because of inability of the mutant to form a Holliday junction. In the two-factor crosses, the double uvsX 49- is recombinationally more proficient than the single uvsX mutant (partial suppression of the uvsX deficiency), while the patch-related double exchanges are virtually eliminated in this background.

SUMMARY A combined palaeodirectional and palaeointensity study of a representative collection of plutonic rocks from the Antarctic Peninsula batholith from the western part of the Antarctic Peninsula, near the Ukrainian Antarctic base 'Academik Vernadsky' were carried out. Petrographically, the collection includes gabbros, diorites and quartz diorites, tonalities, granodiorites and granites. The ages of igneous complex emplacement vary from 50 to 117 Ma with most of the rocks belonging to the Cretaceous Normal Superchron. The characteristic remanent magnetizations were isolated by stepwise thermal demagnetization over the temperature interval 440–590°C and their intensities amount to 95 per cent of the NRM. The geographic positions of palaeopoles do not contradict the ‘key poles’ of the Antarctic Peninsula between 90 and 60 Ma. A significant part of the collection was subjected to Coe-modified Thellier palaeointensity experiments with the pTRM checks, which yielded seven reliable palaeointensity determinations for seven different locations. The obtained VDMs are relatively low for all sites, being on average about half of the present day VDM. The analysis of available palaeointensity data for the Cretaceous, Miocene and Middle Jurassic indicates the existence of strong correlations between the mean VDM and VDM scatter versus the rate of reversals. However, due to the shortage of data, the correlations are not significant at the 5 per cent significance level.

A combined palaeodirectional and palaeointensity studies of a representative collection of plutonic rocks from the western part of Antarctic Peninsula, near the Ukrainian Antarctic base “Academik Vernadsky” were carried out. Chemically, the collection includes gabbros, diorites and quartz diorites, tonalities, granodiorites and granites. The ages of igneous complex vary from 50 to 117 Ma, most of rocks belong to the Cretaceous Normal Superchron. The characteristic remanent magnetization was isolated by stepwise thermal demagnetization in temperature interval 440-590°C and its intensity amounts to 95% of NRM. The geographic positions of palaeopoles do not contradict to the ‘key poles’ of the Antarctic Peninsula for Late Cretaceous and Paleocene. A significant part of collection was subjected to Coe-modified Thellier protocol with the pTRM check procedure and seven reliable palaeointensity determinations are obtained for seven different locations. VDMs obtained are relatively low for all sites, being in average about a half of the present day VDM. The analysis of available palaeointensity data for the Cretaceous, Miocene and Middle Jurassic indicates an inverse correlation between both the mean value and dispersion of VDMs versus the rate of reversals calculated for these periods.

A theory of biaxial stretching of fabric taking account of the extensibility of the warp and weft threads and the structural changes occurring in the fabric during deformation is presented. The problem of calculating the loads arising in a fabric undergoing stretching is solved for a fabric with prescribed structure and density over the warp and weft and with prescribed linear density and deformation characteristics of the threads. The fabric strength is calculated as a limiting state.

A representative collection of Cretaceous rocks of Mongolia is used for the study of the magnetic properties of the rocks and for determination of the paleodirections and paleointensities Hanc of the geomagnetic field. The characteristic NRM component in the samples is recognized in the temperature interval from 200 to 620–660°C. The values of Hanc are determined by the Thellier-Coe method with observance of all present-day requirements regarding the reliability of such kind of results. Comparison of data in the literature on paleointensity in the Cretaceous superchron and in the Miocene supports the hypothesis of the inverse correlation between the average intensity of the paleofield and the frequency of geomagnetic reversals. The increase in the average intensities is accompanied by an appreciable increase in the variance of the virtual dipole moment (VDM). We suggest that the visible increase in the average VDM value in the superchron is due to the greater variability of VDM in this period compared to the Miocene.

The double-strand break (DSB) repair via homologous recombination is generally construed as a high-fidelity process. However, some molecular genetic observations show that the recombination and the recombinational DSB repair may be mutagenic and even highly mutagenic. Here we developed an effective and precise method for studying the fidelity of DSB repair in vivo by combining DSBs produced site-specifically by the SegC endonuclease with the famous advantages of the recombination analysis of bacteriophage T4 rII mutants. The method is based on the comparison of the rate of reversion of rII mutation in the presence and in the absence of a DSB repair event initiated in the proximity of the mutation. We observed that DSB repair may moderately (up to 6-fold) increase the apparent reversion frequency, the effect of being dependent on the mutation structure. We also studied the effect of the T4 recombinase deficiency (amber mutation in the uvsX gene) on the fidelity of DSB repair. We observed that DSBs are still repaired via homologous recombination in the uvsX mutants, and the apparent fidelity of this repair is higher than that seen in the wild-type background. The mutator effect of the DSB repair may look unexpected given that most of the normal DNA synthesis in bacteriophage T4 is performed via a recombination-dependent replication (RDR) pathway, which is thought to be indistinguishable from DSB repair. There are three possible explanations for the observed mutagenicity of DSB repair: (1) the origin-dependent (early) DNA replication may be more accurate than the RDR; (2) the step of replication initiation may be more mutagenic than the process of elongation; and (3) the apparent mutagenicity may just reflect some non-randomness in the pool of replicating DNA, i.e., preferential replication of the sequences already involved in replication. We discuss the DSB repair pathway in the absence of UvsX recombinase.

We present the results of analyzing a representative collection of the middle Miocene 12.4–10.0 Ma basalts that compose the volcanic cover of the Shufan and Sovgavan plateaus, namely the Nikolo-L’vovsk (NL) and Sovetskaya Gavan (SG) volcanic fields. Preliminary data are obtained about the relicts of some volcanic edifices within the West and East Sikhote-Alin volcanic belts, namely the Shishlovskii, Malyshevo, and Truzhenik objects. It is established that the volcanic rocks from these localities are characterized by similar petrologic and magnetic properties. Thermal cleaning of the samples is carried out, and the coordinates of the paleomagnetic pole are determined as Λ = 190.2°E, Φ = 71.3°N for basalts of the Nokolo-L’vovsk area and Λ = 180.4°E, Φ = 71.9°N for rocks from the Sovgavan locality. These values are consistent with the data for coeval volcanics from other regions of Eurasia. Reliable determinations of the paleointensity H pal for a representative collection of samples were obtained using the Thellier method. The corresponding values of the virtual dipole moment (VDM) are almost half its present-day value. The analysis of the Miocene VDM values available from the world database revealed a low average field 5.06 × 1022 Am2 characterized by high variance σ = 2.13 × 1022 Am2 at that time. The similarity of VDM values for the Miocene characterized by frequent inversions and for the Cretaceous Superchron supports the hypothesis of the lack of a correlation between the VDM values and the frequency of geomagnetic inversions.

The influence of collisions between the clusters of a precipitating material on its magnetization at the precipitation stage in an aqueous medium is analyzed. In laboratory experiments, when the sedimentation rate exceeds the value of this rate under natural conditions by several orders of magnitude, collisions are an important factor which sharply decreases the value of magnetization. Only the case of precipitation in distilled water, when the probability of aggregation of particles with their collision approach is small, can be an exception to this rule. Under natural conditions, the concentration of the precipitating solid phase plays the decisive role. For the conditions of deep-water lakes and coastal sea basins with the relatively high sedimentation rate its concentration is sufficient for intensification of the flocculation process, beginning from a certain depth. However, the quantity of material precipitating on the surface for areas distant from continents is too small and in these regions the role of collisions is of negligible importance. The magnetization of the precipitating suspension under conditions of intense flocculation has a linear dependence on the field and is defined by at least seven parameters, which characterize both magnetic and nonmagnetic particles. Such a multiparametric dependence of the magnetization value on the precipitation conditions is responsible for the practical impossibility of estimating the magnitude of the ancient geomagnetic field by the method of reprecipitation in view of the impossibility of adequately reproducing in the laboratory the precipitation conditions in the natural basins.

Coagulation of particles into aggregates during their deposition in a reservoir is numerically simulated with regard for Brownian motion, Van der Waals forces, gravitation, Stokes friction, and magnetostatic interaction, and the effect of this process on the depositional magnetization (DRM) is estimated. Clusters obtained due to random aggregation of smaller clusters have a loose and branching structure. The average fractal dimension of the clusters is d = 1.83 ± 0.23. In the process of coagulation, magnetic particles do not form chains or clusters, as was supposed in a number of preceding works, but become rather uniformly distributed among nonmagnetic particles, which provides an additional argument in favor of the fact that chains of magnetite particles in marine sediments are of biogenic origin rather than a result of mutual attraction of magnetic particles due to magnetostatic interaction. The deposition process is shown to obey a kind of the principle of scale invariance: the number of clusters and their average number of particles do not change if the basin depth H and the surface concentration of initial material c 0 simultaneously change (provided that temperature and the initial particle size r are constant) in such a way that Hc 0 = const. Coagulation is the most important factor forming the bottom layer structure and the magnetization of the suspension at a relatively high concentration c 0 Typical of redeposition conditions, lakes, and shelf seas. Coagulation virtually does not influence oceanic sediments because of the smallness of c 0.

A large volume of data on the paleointensity Han obtained by A.S. Bol’shakov and G.M. Solodovnikov is ignored in modern reconstructions because the authors did not indicate whether they used the check-point procedure for the detection of chemical alterations in rocks associated with determination of Han. The paper presents new values of Han determined by the Thellier-Coe method with the use of the checkpoint procedure from samples of the Armenian collection of Cretaceous rocks used in published studies of Bol’shakov and Solodovnikov. The new results are close to the published ones and point to a small value of the geomagnetic field in the Cretaceous, thereby corroborating Bol’shakov-Solodovnikov’s hypothesis on a low paleofield in the Mesozoic. Our study of samples of the collection studied confirms the reliability of Bol’shakov-Solodovnikov’s determinations of Han.

A method for in vivo studying the fidelity of DNA double-strand break (DSB) repair in bacteriophage T4 has been developed. The frequency of reversion of rII mutations to the wild phenotype was measured in i segC+ × i ets1 segCΔ crosses, where ets1 is an insertion in the initial part of the rIB gene carrying a sequence recognized by SegC endonuclease; i designates a rIIB or rIIA mutation located at some distance from ets1, and segCΔ is a deletion in the segC gene. In such cross, a DSB occurs in the site of ets1. Their repair involves genetic recombination and DNA replication in the neighborhood of ets1. In parallel, the frequency of reversion of the same i mutant in the absence of DSBs is measured in i × i self-crosses. Reversions of different types (base substitutions, deletions, insertions) can be studied with the use of structurally different i mutations located at varying distances from ets1. The reversion frequencies were determined for three rIIB mutations and one rIIA mutation. The results obtained suggest that DSB repair in bacteriophage T4 is a process of high fidelity with the rate of errors that does not essentially exceed that in the case of usual phage multiplication.

Щербаков Василий Петрович, старший преподаватель кафедры систем управления, Южно- Уральский государственный университет, г. Челябинск; vs_develop@mail.ru. Андреева Анастасия Андреевна, магистрант кафедры систем управления, Южно-Уральский государственный университет, г. Челябинск; anafrens@bk.ru. V.P. Shcherbakov, vs_develop@mail.ru, A.A. Andreeva, anafrens@bk.ru South Ural State University, Chelyabinsk, Russian Federation This article describes the results of using elliptic and loxodromic methods for identification of nonlinear systems with applying of the distributed computing and Acsocad software. Presents the existing methods for identification of objects and systems in the time domain, and also describes standard methods and identification algorithms by using Acsocad. The research of nonlinear objects with two and three unknown parameters are done. For their identification the methods of global minimum search by ellipse and spiral for two-dimensional case and with using ellipsoid and loxodromic curves for three-dimensional case are developed. This article describes the results of researches, which contain the parameters estimation error, standard deviation, the number of performed operations, and also the map of the global minimum search. Рассматриваются результаты использования эллиптических и локсодромических методов для идентификации нелинейных систем с применением распределенных вычислений и программного комплекса Acsocad. Представлены существующие способы идентификации объектов и систем во временной области, а также описаны стандартные методы и алгоритмы идентификации с применением Acsocad. Проведено исследование нелинейных объектов, которые имеют два и три неизвестных параметра. Для их идентификации разработаны методы поиска глобального минимума при помощи эллипсов и спирали для двумерного случая, а также эллипсоидом и локсодромой для трехмерного случая. В статье представлены результаты исследований, которые состоят из значения погрешности оценки параметров, среднеквадратичного отклонения, количества выполненных операций, а также карты поиска глобального минимума.

A representative collection of Upper Cretaceous rocks of Georgia (530 samples from 24 sites) is used for the study of magnetic properties of the rocks and the determination of the paleodirection and paleointensity (H an) of the geomagnetic field. Titanomagnetites with Curie points of 200–350°C are shown to be carriers of natural remanent magnetization (NRM) preserving primary paleomagnetic information during heatings to 300–350°C. The characteristic NRM component of the samples is identified in the interval 120–350°C. The Thellier and Thellier-Coe methods are used for the determination of H an meeting modern requirements on the reliability of such results. New paleointensity determinations are obtained and virtual dipole magnetic moment (VDM) values are calculated for four sites whose stratigraphic age is the Upper Cretaceous (Cenomanian-Campanian). It is shown that, in the interval 99.6–70.6 Ma, the VDM value was two or more times smaller than the present value, which agrees with the majority of H an data available for this time period. According to our results, the H an value did not change at the boundary of the Cretaceous normal superchron.

An exact differential equation for the equilibrium of an elastic fibre loaded on the free end with a concentrated force and over the entire length of the elastic line of the distributed power load caused by the weight of the fibre was obtained in conditions of large movements. A method was developed for determining the flexural rigidity of the fibre which consists of bending the fibres and numerically solving the equation from the geometric nonlinear theory of bending of elastic fibres.

Analytical expressions for the contact load and tensions of the components that ensure the equilibrium structure of textile-metal fibres in the spinning conditions are reported. Differential equations for contour movement of a rotating fibre were obtained and solved; using the experimental data, the fibre tension in the balloon was calculated.

The role of 3′–5′ exonucleases in double-strand break (DSB)-promoted recombination was studied in crosses of bacteriophage T4, in which DSBs were induced site specifically within the rIIB gene by SegC endonuclease in the DNA of only one of the parents. Frequency of rII+ recombinants was measured in two-factor crosses of the type i × ets1, where ets1 designates an insertion in the rIIB gene carrying the cleavage site for SegC and i's are rIIB or rIIA point mutations located at various distances (12–2040 bp) from the ets1 site. The frequency/distance relationship was obtained in crosses of the wild-type phage and dexA1 (deficiency in deoxyribonuclease A), D219A (deficiency in the proofreading exonuclease of DNA polymerase), and tsL42 (antimutator allele of DNA polymerase) mutants. In all the mutants, recombinant frequency in crosses with the i-markers located at 12 and 33 bp from ets1 was significantly enhanced, implying better preservation of 3′-terminal sequences at the ends of the broken DNA. The effects of dexA1 and D219A were additive, suggesting an independent action of the corresponding nucleases in the DSB repair pathway. The recombination enhancement in the dexA1 mutant was limited to short distances (

The global database on the paleointensity, containing determinations of the virtual dipole moment (VDM) for a stable (normal) regime of the geomagnetic field in a time interval of up to 3.5 Ga, is supplemented by new VDM determinations and analyzed. The field generation process started no later than 3–3.5 Ga (earlier data are absent) at the stage of the Earth’s core formation. Since that time, the dipole value has differed from its present value by no more than an order of magnitude, and the deviations that have already been detected tend toward smaller values. The distribution of VDM values in the time interval 0–400 Ma is bimodal, which apparently reflects the presence of two different generation levels of the geomagnetic field distinguished by a relatively large value (close to the present field value) and a relatively small value (approximately half as large as the present value). The total duration of decreased VDM values appreciably exceeds that of increased VDM values (179.1 and 28.6 Myr, respectively). On the whole, data on the paleointensity do not contradict the hypothesis about the dipole nature of the field over the last 400 Myr; however, the number of determinations at high paleolatitudes is too small to draw decisive conclusions on the validity (or invalidity) of the dipole field approximation based solely on paleointensity data.

The territory of Karelia (Baltic Shield) is virtually not represented in the global paleomagnetic database for the Lower Riphean time interval (1650—1350 Ma). As regards the paleointensity Han, the huge interval 1–2 Ga in length is represented in the global paleointensity database by only eight determinations concentrated in the interval 1–1.35 Ga. The paper presents results of paleomagnetic studies of volcanic and subvolcanic rocks composing the Early Riphean Salmi Formation, which outcrops in the valley of the lower Tulemaioki River in the northern coast area of Lake Ladoga. Results of the study indicate that, in the Early Riphean time, the East European craton was located in the tropical region of the Southern Hemisphere between 15° S and 40° S. The inferred value of Han is close to the lower boundary of the interval (1.36–11.56) × 1022 A m2, encompassing previously published intensity values of the paleofield 1–1.35 Ga; this supports the hypothesis on the existence of long intervals of a lower field in the period in question [Maquoin et al., 2003].

Summary We report an experimental and theoretical study of non-linear Arai–Nagata diagrams for samples containing pseudo-single-domain (PSD) and multidomain (MD) magnetite. Our aim is to reveal the physical reasons for the deviation of these plots from ideal straight lines. Contrary to expectations, the concavity of the Arai–Nagata diagrams is not related to the two most noticeable violations of the Thellier laws documented for non-single-domain particles: the tail of partial thermoremanence and the dependence of the magnitude of pTRM on the thermal history of the sample. Indeed, the contributions from these two factors mutually cancel each other. Phenomenologically, the non-linear Arai–Nagata plots occur because samples during low-temperature stages of the Thellier procedure lose too much remanence and recover too little of it. The excessive loss of the previously imparted total TRM is due at least partly to some partial demagnetization of high-temperature TRM components and to progressive stabilization of domain structure during the repetitive heatings to moderate temperatures that form the basis of the Thellier procedure. For natural MD samples a linear fit to the low-temperature data points on the Arai–Nagata plots leads to a palaeointensity overestimated by as much as 60 per cent. The samples containing hydrothermally grown or crushed and sieved MD magnetite provide low-temperature apparent palaeointensities two to three times larger than the correct value. For small PSD samples the overestimate is less than 10–20 per cent and, in general, PSD samples can be used for the palaeointensity determinations.

Recombinational analysis Genetic recombination Gene 39 Gene 61 Topoisomerase II Primase a b s t r a c t The effects of primase and topoisomerase II deficiency on the double-strand break (DSB) repair and genetic recombination in bacteriophage T4 were studied in vivo using focused recombination. Site-specific DSBs were induced by SegC endonuclease in the rIIB gene of one of the parents. The frequency/distance relationship was determined in crosses of the wild-type phage, topoisomerase II mutant amN116 (gene 39), and primase mutant E219 (gene 61). Ordinary two-factor (i × j) and three-factor (i k × j) crosses between point rII mutations were also performed. These data provide information about the frequency and distance distribution of the single-exchange (splice) and double-exchange (patch) events. In two-factor crosses ets1 × i, the topoisomerase and primase mutants had similar recombinant frequencies in crosses at ets1–i distances longer than 1000 bp, comprising about 80% of the corresponding wild-type values. They, however, differ remarkably in crosses at shorter distances. In the primase mutant, the recombinant frequencies are similar to those in the wild-type crosses at distances less than 100 bp, being a bit diminished at longer distances. In two-factor crosses ets1 × i of the topoisomerase mutant, the recombinant frequencies were reduced ten-fold at the shortest distances. In three-factor crosses a6 ets1 × i, where we measure patch-related recombination, the primase mutant was quite proficient across the entire range of distances. The topoisomerase mutant crosses demonstrated virtually complete absence of rII+ recombinants at distances up to 33 bp, with the frequencies increasing steadily at longer distances. The data were interpreted as follows. The primase mutant is fully recombinationproficient. An obvious difference from the wild-type state is some shortage of EndoVII function leading to prolonged existence of HJs and thus stretched out ds-branch migration. This is also true for the topoisomerase mutant. However, the latter is deficient in the ss-branch migration step of the DSB repair pathway and partially deficient in HJ initiation. In apparent contradiction to their effects on the DSB-induced sitespecific recombination, the topoisomerase and primase mutants demonstrated about 3–8-fold increase in the recombinant frequencies in the ordinary crosses, with the recombination running exclusively via patches. This implies that most of the spontaneous recombination events are not initiated by dsDNA ends in these mutants.

[1] The sequence of durations of the geomagnetic polarity intervals is often described in terms of a nonhomogenous Poisson process with time-dependent reversal rate, reflecting the nonstationarity of the underlying geodynamo process. This view has recently been challenged, and here we show that the first-passage time statistics of random walks taking place on a flat potential relief yields a much more consistent interpretation of the distribution of geomagnetic polarity intervals. A possible physical explanation suggests that the stability of a polarity chron of the Earth's magnetic field is controlled by a sum of statistically independent, randomly behaving, dynamo processes in the outer core. The random-walk hypothesis naturally includes the observed occurrences of very long superchrons, and it provides a new, considerably longer statistical estimate for the total duration of the present Brunhes chron predicting that the probability for a geomagnetic field reversal within the next 30 Ka is ≈5% and the probability that we live in a chron longer than 2 Ma is about 30%.

In previous papers we described an extra recombination mechanism in T4 phage, which contributed to general recombination only when particular mutations were used as geneticmarkers (high recombination or HR markers), whereas it was practically inactive towards other rIIB mutations (low recombination or LR markers). This marker-dependent recombination pathway was identified as a repair of mismatches in recombination heteroduplexes. We suggested that the first step in this pathway, recognition and incision of the mismatch, is performed by endonuclease VII (endo VII) encoded by the T4 gene 49. In the present paper, we tested this hypothesis in vivo. We used an experimental model system that combines site-specific double-strand breaks with the famous advantages of the recombination analysis of bacteriophage T4 rII mutants. We compared recombination of homoallelic HR and LR markers in the S17 and S17 E727 background (amber mutations in the uvsX and in the uvsX and 49 genes, respectively). In S17-crosses, the HR and LR markers retain their respective high-recombination and low-recombination behavior. In S17 E727-crosses, however, the HR and LR markers show no difference in the recombination frequency and both behave as LR markers. We conclude that endo VII is the enzyme that recognizes mismatches in recombinational heteroduplexes and performs their incision. This role for endo VII was suggested previously from biochemical studies, but this is its first in vivo demonstration.

[1] Coagulation of particles into aggregates during their settling in an aqueous solution is numerically simulated with regard to Brownian motion, Van der Waals and Stokes's forces, gravitation, and magnetostatic interactions. Clusters obtained have a fractal structure with the average fractal dimension d = 1.83. Magnetic grains do not group until their concentration exceeds at least a few percent. The deposition process obeys a scaling principle: the sizes of clusters arriving at the bottom of a basin do not change if the product of the basin depth H and the concentration of initial material c0 is constant. Attempts at numerical simulations of laboratory redeposition experiments are made. Good agreement between numerical simulations and experimental results by van Vreumingen (1993) demonstrates that the modeling algorithm is based on reasonable physical assumptions. The magnetization of a flocculating suspension is defined by at least seven parameters, which characterize magnetic and nonmagnetic particles, as well as the aqueous medium. This multiparametric dependence hinders estimations of paleofield intensity by the redeposition method because it is practically impossible to reproduce natural conditions in the laboratory. Flocculation influences the magnetization intensity of the settling suspension at concentrations c0 typical for redeposition experiments or natural sedimentation in lakes and shallow seas. Flocculation is of minor importance for deep oceanic regions because of their extremely low sedimentation rate. However, factors like small-scale turbulence and biotic processes are not taken into account by the model and may require modification of these conclusions. Also, a simple model of pDRM acquisition based on elastic and plastic properties of sediment slurry is proposed.