Field Magnetic Susceptibility Research Articles

Thermodynamic equilibrium of [formula omitted] Ising model on square lattice

We constructed a theoretical magnetic phase diagram in an external magnetic field T(P+), making it possible to determine the conditions for the existence of ferromagnets, antiferromagnets, and spin glass phases. The high-performance CUDA software package was used to the complete enumeration of all configurations of finite number spins in the ±J Ising model. We performed the rigorous numerical calculation of the partition function of N=8×8 systems of interacting spins with open boundary conditions. We used Monte Carlo methods like the Metropolis algorithm to calculate the critical temperatures for N=40×40 spins. The results of the Monte Carlo experiments are consistent with rigorous calculation data. The transition from the spin glass to the induced ferromagnetic state in an external field occurs without any critical change in the heat capacity. We used the ±J Ising model to calculate the instability line (AT—line) for the heat capacity of spin glass in the H−T diagram in an external magnetic field and the behavior of magnetic susceptibility in an external magnetic field. A rigorous calculation of the partition function allowed us to calculate all possible states and their thermodynamic probability. The calculation of the partition function meant that the model’s physics was obtained in an equilibrium state. The instability line was calculated for spin glass in the equilibrium state.

Structural, morphological, and magnetic properties of carbon-modified nanocrystalline Pr5Co19 alloys

Nanocrystalline rare-earth (R) and transition metal (T) alloys are known for their outstanding magnetic properties, which are driven by the combination of (R) and (T) magnetic moments. Adding carbon (C) has been proven to alter these magnetic properties. In the present work, we use X-ray diffraction, transmission electron microscopy, and atom probe tomography to investigate and characterize the impact of carbon addition on the crystalline structure, morphology, and chemical distribution of Pr5Co19 and its carbides Pr5Co19Cx. The nanocrystalline Pr5Co19 compound was synthesized by high-energy ball milling and the addition of carbon was performed by a solid-solid reaction between Pr5Co19 and C10H14. TEM study revealed that after carbonation the microstructure is refined, and the mean grain size decreases from 126 nm in Pr5Co19 to 65 nm with a carbon of content 1.5. Three-dimensional APT was performed to characterize the chemical composition of Pr-Co binary systems. The analyzed Pr5Co19C1.5 sample reveals an irregular nano-lamella structure decorated by carbon atoms, the distance between the lamellas varying from 8 to 20 nm. An under-stoichiometry of Co was found in the C-rich lamellas. Fundamental magnetic properties such as saturation magnetization Ms, exchange field Hex and magnetic susceptibility χ of the Pr5Co19 and its carbides were calculated using the random magnetic anisotropy (RMA) method.

A simple physical model for simulation and design magneto-plethysmograph in application non-invasive hemoglobin measurement

The magneto-plethysmograph method is a combination of magnetic field and sensors used to detect changes in blood flow pulsation. However, to detect the magnetic properties of blood related to hemoglobin concentration, physical modeling and simulation are required. This approach involves designing simulations using magnetic field equations and magnetic susceptibility, where a permanent magnet is placed on the surface of blood vessels, and sensors based on giant magnetoresistance are placed at a distance r. The design originates from a simple approach involving the magnetization and detection of Fe atoms in hemoglobin. Parameters involved include the magnetic susceptibility of oxyhemoglobin and deoxyhemoglobin, with an external magnetic field exceeding 1 Tesla. From the physical modeling and simulation, graphs are obtained depicting the influence of hemoglobin concentration on the number of Fe atoms and its magnetization. This enables the design of non-invasive hemoglobin measurement sensor devices. The uniqueness of this simple physical model and simulation lies in its ability to produce specially designed device models for measuring hemoglobin concentration. This differs from other research focusing on blood flow pulse measurements; the results of this study provide new insights into the benefits of simple physics equations that can be developed for medical diagnostic research and device development.

A Two-Dimensional Transient Computational Multi-Physics Model for Analyzing Magnetic and Non-Magnetic Particle (Red Blood Cells and E. Coli Bacteria) Dynamics in a Traveling Wave Ferro-Magnetic Microfluidic Device for Potential Cell Separation and Sorting

Abstract This paper presents the theory and development, validation, and results of a transient computational multiphysics model for analyzing the magnetic field, particle dynamics, and capture efficiency of magnetic and nonmagnetic (e.g., Red Blood Cells and E. Coli bacteria) microparticles in a traveling wave ferromagnetic microfluidic device. This computational model demonstrates proof-of-concept of a method for greatly enhancing magnetic bioseparation in ferromicrofluidic systems using an array of copper conductive elements arranged in quadrature to create a periodic potential energy landscape. In contrast to previous works, our approach theoretically uses a microfluidic device with an electronic chip platform consisting of integrated copper electrodes that carry currents to generate programable magnetic field gradients locally. Alternating currents are applied to the electrodes in quadrature (using a 90 deg phase change from the neighboring electrode) to create a periodic magnetic field pattern that travels along the length of the microchannel. Our previous work evaluated magnetic and nonmagnetic particles in a static magnetic field within the same channel geometry. This work is a phase 2 study that expands on the previous work and analyzes the dynamics of magnetic and nonmagnetic entities characterized by material magnetic susceptibility in a transient magnetic field. This is an improvement over our previous work. The model, which is described in more detail in the methods section, combines a Eulerian-Lagrangian and two-way particle-fluid coupling CFD analysis with closed-form magnetic field analysis that is used to predict magnetic separation considering dominant magnetic and hydrodynamic forces similar to our previous works in magnetic drug targeting. The model was also validated with an experimental low frequency stationary flow study on separating nonmagnetic latex fluorescent particles in a water based ferrofluid. The results from the experimental study and the developed model demonstrate that the proposed device may potentially be used as an effective platform for microparticle and cellular manipulation and sorting. The developed multiphysics model could potentially be used as a design optimization tool for traveling wave ferromicrofluidic devices.

Mineral magnetic properties of urban forest soils tailored to soil quality indicator

Ecosystem surveys reveal the benefits to society, provided by the natural environment, which in turn is chiefly regulated by the geodiversity. Thus, physico-chemical processes regulating the solid rock/sediment response to environmental changes comprise an important part in the assessment of natural ecosystems. Environmental magnetism provides a wide set of field and laboratory data able to discover natural and anthropogenic processes affecting different environmental compartments. Despite this, geosciences and environmental magnetism in particular, are under-represented in ecosystem assessment tools due to the lack of unified and clearly articulated application template. In this study, we propose a new mineral magnetic indicator of soil’s quality, based on detailed appraisal of field- and laboratory mineral magnetic characteristics of a collection of 453 urban topsoil samples. Field magnetic susceptibility (Kfield) and laboratory measurements of magnetic parameters revealed that soil magnetism reflects sensitively soils affected by vehicle traffic and park’s alleys foot load from semi-natural soil. Geochemical analyses of the content of Potentially Toxic Elements (PTEs) on a sub-set of samples was used for magnetic data validation. Correlation analysis showed strong positive link between magnetic parameters and the main PTEs, the strongest being obtained between magnetic susceptibility and the complex pollution load index (PLI). Factor analysis suggested that three factors account for the 74% of data variability. They were assigned to: 1) traffic emissions, 2) pedogenic contribution and 3) lithogenic input plus anthropogenic organic waste additions. Novel mineral magnetic Indicator (MAG) was defined, combining information on composition, concentration and grain size of ferrimagnetic iron oxides, using scored contributions from five magnetic parameters and grain size sensitive ratios. Evaluation of the spatial MAG map showed its suitability as a complex indicator of soils’ contamination with PTEs. Kfield reflected sensitively overall anthropogenic load not necessarily related to PTEs contamination but also to foot trampling and application of fertilizers.

Multi-devices field magnetic susceptibility: ‘3D’ spatialization of metallic contamination in soils and reverse correlation in carbonated context (Jebel Ressas, Tunisia)

Soil contamination linked to abandoned lead–zinc mining wastes represents a serious environmental hazard of worldwide concern, raising the need for cost-effective tools to spatialize the contaminated area and assess the risks. In worldwide industrial environments, positive correlation between magnetic susceptibility and heavy metal soil contamination is often reported and used for fast preliminary site assessments. In this study, we report monitoring of an olive grove, situated below one of the abandoned tailings dump of the former Jebel Ressas Pb–Zn mining site (Tunisia), with three different commercial susceptibilimeters (Terraplus KT10, Bartington MS2D and Geonics EM38 induction device). Integration depths of above-mentioned susceptibilimeters vary from 3 to 150 cm. Similar broad-scale magnetic susceptibility maps for the three devices emphasize the effect of topography and runoff transfer as the main mechanisms for tailings material dispersion. Very low susceptibilities (~ 10 × 10–5 SI) characterize the contaminants magnetic signal, while uncontaminated soils susceptibilities are one order of magnitude higher (100–150 × 10–5 SI). This unique case of reverse correlation between magnetic susceptibilities and contamination (Pb, Zn, Cd) trace efficiently the degree of contamination and is substantiated by further mineralogical and magnetic properties analyses showing the predominance of iron amorphous oxyhydroxides in the dump, while (titano)maghemite is the main natural magnetic carriers in the uncontaminated soils in this specific carbonated context. The Geonics EM 38, with a proper calibration procedure, reveals a performant tool increasing the depth of investigation and when combined with shallower susceptibilimeter, opens perspectives for qualitative 3D spatialization of metallic contamination.

Theoretical Methods for coding a strand of DNA bases and nucleotides with C2Fe+, A DFT study

DNA strands are essential in a cell for growth, metabolism regulation and carrying genetic information bases to new generations, in every creatures . The function of DNA bases is a 0 and 1 system. In this theoretical research , we try to make two other 0 and 1 systems for DNA bases .In both methods, C2Fe+ is attached to DNA bases and nucleotides like a flag to make derivatives. In the first method NMR susceptibility and Magnetization of pristine DNA bases, nucleotides and their C2Fe varieties are determined theoretically by using Gauss view and Gaussian programs. With effect of a magnetic field (H) and NMR susceptibility of these compounds, their calculate magnetizations , certain signals can be created as a mark of DNA bases and their compounds. These resulted not only can be considered as a method to make a new (0) and (1) system. In the second method, by using Gauss view and Gaussian programs the theoretically UV-Visible spectrum of pristine DNA bases, nucleotides and their C2Fe varieties are determined which the spectrum absorption of the pristine compounds are in different range with the absorption range of C2Fe varieties. With a little change in spectrophotometer construction another 0 and 1 coding system can be created, again.

Quark condensate and magnetic moment in a strong magnetic field

This paper studies the quark condensate, magnetic moment, magnetic polarization, and magnetic susceptibility in a strong external magnetic field by employing the Dyson–Schwinger equations (DSE). The results show these physical quantities as functions of the magnetic field. We note that the quark’s spin polarizations are approximately proportional to the magnetic field magnitude. For comparison, we investigate the magnetic moments and susceptibility of the nucleon in the constituent quark model framework and demonstrate that both these quantities increase as the magnetic field rises.

Rock Magnetism and Magnetic Fabric Study of the Icelandite and Rhyodacite Long Volcanic Sequence at Mauna Kuwale, Wai’anae Volcano, Oahu, Hawaii, USA

In order to understand further the emplacement (i.e., volcanic growth) of 22 Icelandite and 3 Rhyodacite cooling units in one of the long volcanic sequences known as Mauna Kuwale of the Wai’anae volcano (ca. 3.3 Ma), Oahu Hawaii we have conducted appropriate rock magnetic experiments described below as well as anisotropy of magnetic susceptibility (AMS) studies of such 25 units. We have undertaken rock magnetic investigations such as continuous and partial thermo-magnetic cycles of low field magnetic susceptibility versus temperature dependence, (k-T) curves experiments. We classified the k-T heating-cooling dependence of susceptibility in three groups A, B and C. Type A: yielded two components of titano-magnetite with a predominat Ti rich phase and occasionally a relevant magnetite component phase. Type B: samples are characterized by Ti poor magnetites. Magnetite dominates as the main magnetic carrier. Type C: k-T curves show one single phase of titanomagnetite, and Ti poor magnetite. The coercivity or remanence, determined by back field magnetization is always <60 mT, which suggest the predominance of magnetic components of low coercivity, like magnetite. Usually, two coercivity components are identified in the specimens. In addition we also conducted magnetic granulometry analyses on 27 specimens to determine the domain state of the flows. The ratio of hysteresis parameters (Mr/Mrs versus Hcr/Hc) show that overall samples fall in the Pseudo-Single Domain (PSD) region with high values of Mr/Mrs and very low values of Hcr/Hc. Only two samples from cooling units 17 and specially 22 show a Single Domain (SD) magnetic behavior and a sample from one unit approaches the SD-MD mixture region. We measured the magnetic susceptibility of all cooling units and we found out that in all analyzed units the magnetic susceptibility is low 13.7 ± 8.8 (10−3 SI). Magnetic anisotropy/magnetic fabric is used as a tool in rock fabric analyses to investigate the preferred orientation of magnetic minerals in rocks. Magnetic anisotropy is low on all (measured) flows from the Icelandite cooling units from 1 to 17 (mean P’ = 1.010), but becomes noticeably distinct and high in rhyodacite cooling units 23, 24 and 25 (mean P’ = 1.074). Four units show a magnetic fabric with k3 axes vertical to sub-vertical which may be denoted as normal for the horizontal to sub horizontal units. Two Icelandite cooling units display oblate shapes and two other cooling units triaxial shapes. K1 axes are horizontal but point in different directions, i.e., NE and NW. Remaining cooling units show different magnetic fabric. Units 17, 23, 24 and 25, despite important variations in anisotropy (low for units 25 and high for units 23 and 24) and shape of ellipsoid (oblate in cooling unit 23, prolate in 24 and triaxial in 25) the k3 axes show the same orientation, SW to SSW dipping around 45° and a very steady magnetic lineation azimuth NW nearly horizontal to sub horizontal. The magnetic mineralogy and magnetic fabric indicate that both the Icelandite and Rhyodacite cooling units the magmatic evolution during the shield stage of the entire Wai’anae volcano and that such growth was not affected by tectonic deformation.

Development of biocompatible Ni-ferrite nanoparticles with PEG-coated for magnetic hyperthermia

In this study, NiFe2O4 nanoparticles were prepared as a thermophilic agent for magnetic thermotherapy. To improve biocompatibility, the particles were coated with polyethylene glycol, which is hydrophilic and nontoxic; X-ray diffraction measurements confirmed that the particle size could be controlled to 3, 6, 9, and 17 nm. Fourier-transform infrared spectroscopy confirmed PEG modification to the particles. Biocompatibility with cells were improved by coating with PEG of high molecular weight. The heat-generating effect of the particles was investigated by measuring the magnetic susceptibility and temperature rise in an AC magnetic field. Furthermore, a device using a zero-voltage switching circuit was developed to generate heat. Finally, in vitro experiments using human breast cancer cells were successfully performed to confirm the onset of the hyperthermia effect.

Analysis of Magnetic Field Distribution and Magnetic Susceptibility of the Lithosphere in East Dabie Region, China: Relationship to Crustal Structures

Analysis of Magnetic Field Distribution and Magnetic Susceptibility of the Lithosphere in East Dabie Region, China: Relationship to Crustal Structures

Magnetic susceptibility, mineral chemistry, and geothermobarometry of granitoids from Lohit Plutonic Complex, Arunachal Trans‐Himalaya, Northeast India: Implications on emplacement and crystallization conditions of oxidized calc alkaline magmatic arc system

AbstractThe Lohit Plutonic Complex (LPC) of Arunachal Trans‐Himalaya represents the northeast extension of Trans‐Himalayan magmatic arc system located in the north of Indus Tsangpo Suture Zone (ITSZ). Field relation, magnetic susceptibility (MS), and phase petrology on the granitoids of LPC was conducted in order to assess the granite series (magnetite, oxidized vs. ilmenite, reduced types), and physico‐chemical conditions of the LPC granitoid magmas. The studied granitoids are well‐exposed in the Dibang and Lohit valleys, and their MS values indicate a bi‐modal patterns corresponding to ilmenite (reduced) series (71%) and magnetite (oxidized) series (29%) granites. The variation of MS in the LPC granitoids is related to the alteration of ferromagnetic minerals, and later tectonic and deformational processes that acted upon them. The amphiboles from the LPC granitoids are calcic (CaB >1.5, Si = 6.30–7.06 apfu) and exhibit tschermak substitutions typical to their evolution in a calc alkaline, metaluminous (I‐type) felsic magmas. Al‐in‐hornblende rims estimate the emplacement of quartz diorite and granodiorite magmas at shallow (~5 km) and mid (~16 km) crustal depths. Geothermometric results point to a regime of magmatic crystallization (940–837°C for quartz diorite; 882–829°C for granodiorite) sufficiently above the solidus of respective melts. Biotites from LPC granitoids are primary to re‐equilibrated, and transitional between magnesio‐ and ferri‐biotites. Quartz diorite and granodiorite biotites evolved under oxidizing magmas (log ƒO2−14 to log ƒO2−13) in a temperature range of ~750–950°C, typical to their formation in a calc alkaline magma of subduction zone environment. However, the biotites from leucogranite appear to have evolved under a mildly reducing magma environment, most likely attained in a collisional setting. The obtained results suggest that the oxidized nature of calc alkaline, subduction‐related magmatic arc rocks of the LPC is largely modified and reduced by post‐magmatic, and later tectonothermal and deformational events that operated during Himalayan and Trans‐Himalayan orogenesis.

Santonian-Campanian Boundary Interval in the Kyunetsa Section, Western Srednogorie Zone, Bulgaria

The Kyunetsa section, 2.5 km west of Kosharevo, exposes mainly pelagic Upper Cretaceous marly limestones and marls of the Srednogorie Zone, part of the intermediate Balkanides in Bulgaria. The Melove Formation of Coniacian to early Campanian age involves a prominent Santonian-Campanian boundary interval of grey and reddish sediments, including CORBs (Cretaceous Oceanic Red Beds). The base of the Campanian can be discerned in bed 7c by the first rare (single) occurrence of the nannofossil Broinsonia (Aspidolithus) parca parca. A positive carbon isotope peak below, and a field magnetic susceptibility peak above may enhance correlation to other Tethyan sites such as the proposed GSSP at Bottaccione (Italy), the Postalm section (Austria) and the Mudurnu-Göynük Basin (Turkey).

Pinning potential in highly performant CaKFe4As4 superconductor from DC magnetic relaxation and AC multi-frequency susceptibility studies

We have investigated the pinning potential of high-quality single crystals of superconducting material CaKFe4As4 having high critical current density and very high upper critical field using both magnetization relaxation measurements and frequency-dependent AC susceptibility. Preliminary studies of the superconducting transition and of the isothermal magnetization loops confirmed the high quality of the samples, while temperature dependence of the AC susceptibility in high magnetic fields show absolutely no dependence on the cooling conditions, hence, no magnetic history. From magnetization relaxation measurements were extracted the values of the normalized pinning potential U*, which reveals a clear crossover between elastic creep and plastic creep. The extremely high values of U*, up to 1200 K around the temperature of 20 K lead to a nearly zero value of the probability of thermally-activated flux jumps at temperatures of interest for high-field applications. The values of the creep exponents in the two creep regimes resulted from the analysis of the magnetization relaxation data are in complete agreement with theoretical models. Pinning potentials were also estimated, near the critical temperature, from AC susceptibility measurements, their values being close to those resulted (at the same temperature and DC field) from the magnetization relaxation data.

On the structural, refractive index and energy bandgap based optical properties of Lithium ferrite nanoparticles dispersed in silica matrix

Lithium ferrite nanoparticles dispersed in silica matrix [Li0.5Fe2.5O4]1–x[SiO2]x (x = 0, 50–90%) have been synthesized using ultrasonic assisted sol–gel method. Agglomeration due to higher surface energy and interparticle interactions is reduced due to dispersion in silica; which modifies the nanoparticle surface and revamp properties of the system. X–ray diffractometer (XRD) measurement reveals simple cubic spinel structure without any impurities. Dynamic magnetic field susceptibility studies show that reversible nature of magnetic domain walls dominates over the irreversible nature. Energy band gap (Eg) determined from UV–Visible (UV–Vis) spectroscopy shows an escalation (1.47 eV to 1.59 eV) for change in silica from 0% to 90%. An empirical formula for refractive index as μ = A(silica content)2+B(silica content)+C has been derived using theoretical fit. With increase in silica content, the refractive index, optical dielectric constant, dielectric susceptibility and oxygen packing density show decrements from 3.82 to 1.77, 8.1204 to 7.6825, 0.6465 to 0.6117 and 70.3157 to 60.974, respectively. The reflectivity, absorption coefficient, molar refractive index, molar electronic polarizability, reflection loss, polaron radius and optical basicity also show reduction. This is attributed to change in density and interparticle interaction due to change in silica content. Dielectric polarizability, transmission coefficient and metallization criterion show increment from 14.85 Å3 to 39.29 Å3, 0.5968 to 0.6086 and 0.2698 to 0.2808; respectively. Observed effects have been ascribed to higher strain, reduction in reflection loss and more non-metallic nature of the samples. Swift changes in parameters indicate their fine tuning through optimum magnitude of silica.

Mitigation of the Magnetic Field Susceptibility of Transition-Edge Sensors Using a Superconducting Groundplane

Transition edge sensor (TES) microcalorimeters and bolometers are used for a variety of applications. The sensors are based on the steep temperature-dependent resistance of the normal-to-superconducting transition, and are thus intrinsically sensitive to magnetic fields. Conventionally the detectors are shielded from stray magnetic fields using external magnetic shields. However, in particular for applications with strict limits on the available space and mass of an instrument, external magnetic shields might not be enough to obtain the required shielding factors or field homogeneity. Additionally, these shields are only effective for magnetic fields generated external to the TES array, and are ineffective to mitigate the impact of internally generated magnetic fields. Here we present an alternative shielding method based on a superconducting groundplane deposited directly on the backside of the silicon nitride membrane on which the TESs are located. We demonstrate that this local shielding for external magnetic fields has a shielding factor of at the least ~ 75, and is also effective at reducing internal self-induced magnetic fields, as demonstrated by measurements and simulation of the eddy current losses in our AC biased detectors. Measurements of 5.9 keV X-ray photons show that our shielded detectors have a high resilience to external magnetic fields, showing no degradation of the energy resolution or shifts of the energy scale calibration for fields of several microTesla, values higher than expected in typical real-world applications.

The magnetic susceptibility of Pleistocene paleosols as a martian paleoenvironment analog

This work aims to introduce and test various semiquantitative field methods and environmental magnetic measurements to help prepare future planetary missions on Mars. For analog observations, paleosols of loess successions in various stages of soil development were investigated and were used as models to infer environmental change during environmental change on early Mars. Methods commonly used in terrestrial soils and sediment environments, such as soil development indices and low field and frequency-dependent magnetic susceptibility, are introduced and evaluated as potential proxies to constrain paleoenvironmental conditions and climate change on Mars billions of years ago. These methods include the following: 1) low field magnetic susceptibility, which may aid in the identification of weathered horizons (e.g., palaeosols) and provide insight into the degree of weathering intensity; 2) frequency-dependent magnetic susceptibility can constrain nanoscale magnetic contributions, including some with possible biogenic/bacterial origin, but its applicability to indicate the degree of pedogenesis is limited; and 3) the vertical distribution of low field magnetic susceptibility, i.e., the pattern of magnetic susceptibility curves, seems to work well in the indication of the balance between the sedimentary and pedogenic environment. Analysis of magnetic susceptibility curves may contribute to the identification of Martian paleosols, the characterization of the transition period between the soil-forming and subsequent sedimentary periods (Noachian-Hesperian and Hesperian-Amazonian transitions) and the identification of climate cycles; thus, these may be used as a frame of reference for evaluating paleoclimatic changes on Mars to e.g., the Noachian warm Mars and”Snowball Mars” periods.The results also suggest that the time dependence of the magnetic enhancement of paleosols seems to be nonlinear compared to the length of the pedogenic period itself, and magnetic susceptibility may work as a relative chronometric parameter, which can help to constrain the duration of pedogenic alteration and soil formation on Mars.

NMR Susceptibility and Magnetization of DNA Bases, Nucleotides and Their Derivatives with C2Fe+, A DFT Study

DNA strands and their bases are in the cells in every creature. They essential for growth, metabolism regulation and carrying genetic information bases to new generations. The bases of DNA are working with 0 and 1 system. In this theoretical research, first, by using Gaussian program, NMR susceptibility of DNA bases and their C2Fe+ attached varieties are determined. In the next step, with effect of magnetic field (H) and NMR susceptibility of these compounds, their resulted Magnetization (M) is calculated. These resulted magnetizations not only can be considered as a method to make a new (0) and (1) system for DNA bases but also can be used as creating certain signals to mark of DNA bases and their compounds which are attached to C2Fe+.

A detailed magnetic record of Pleistocene climate and distal ash dispersal during the last 800 kyrs - The Suhia Kladenetz quarry loess-paleosol sequence near Pleven (Bulgaria)

Loess-paleosol sequences (LPS) from the Lower Danube area are valuable terrestrial archives of environmental change in SE Europe during the Pleistocene. A twenty-seven meters thick sequence has been sampled in Central North Bulgaria near the city of Pleven within the Suhia Kladenetz (SK) quarry. The sedimentary sequence consists of seven loess units and six interbedded paleosol complexes covering the last 800 kyrs. The continuous 2 cm resolution sampling depth interval enabled the recovery of several cryptotephras in addition to a ~ 20 cm thick tephra deposit observed in the field within the L2 loess unit. All cryptotephras are clearly identified in laboratory analyses by their strong magnetic signal, particularly well expressed by concentration – dependent anhysteretic susceptibility (χARM), isothermal remanence (IRM), low field magnetic susceptibility (χlf) and in some cases by frequency dependent magnetic susceptibility (Δχ), coercivity of remanence (BCR), and hard isothermal remanence (HIRM2.0–0.3T). Complementary optical and scanning electron microscope analyses of single grains from the tephra deposit and cryptotephra intervals reveal the presence of volcanogenic grains with smooth glassy surfaces and vesicular internal structure; fluidal grains with bulbous surfaces and dense irregular grains. Grain size sensitive magnetic ratios χARM/χlf, ARM/IRM100mT, IRM2T/χlf are not always discriminative, suggesting that (crypto)tephras do not have a single uniform source. Preliminary correlative age models are used to estimate ages for the (crypto)tephras and propose likely associated volcanic eruptions. Finally, strong pedogenic magnetic enhancement of the younger paleosols (S4, S3, S2 and partly S1) contrasts with the smeared and low magnetic signal of the older paleosols (S6 and S5). Moreover, an enhanced content of low-coercivity hematite observed from the upper part of the S5 paleosol upwards to the present and a sharp increase in the concentration of maghemite at the expense of magnetite observed for the S3, S2 and S1 paleosols provides strong evidence for a significant paleoenvironmental change. The timing of this change, based on the SK LPS age models, is compatible with the mid-Brunhes climate transition.

Topological susceptibility and fourth cumulant in a uniform magnetic field

We study the topological susceptibility and fourth cumulant of the QCD vacuum in a background magnetic field (H) using three-flavor chiral perturbation theory (χPT) for arbitrary quark masses and n-flavor χPT with degenerate quark masses. We find that the enhancement by the magnetic field of the topological susceptibility relative to the H=0 vacuum value is larger in the three-flavor χPT compared to two-flavor χPT. Additionally, in comparing the fourth cumulant, we find that its suppression is comparable for magnetic fields, eH≲0.8mπ2, and weaker for larger magnetic fields in three-flavor χPT with its enhancement beginning at a significantly lower critical magnetic field compared to two-flavor χPT. We also find that the enhancement of the topological susceptibility in n-flavor χPT with degenerate quarks is significantly larger and the suppression of the topological cumulant significantly greater at weak fields with the critical magnetic field pushed out to larger magnetic fields compared to both two and three-flavor χPT.