Surface chirality effects induced by magnetic fields

Symmetry breaking in magnetohydrodynamic vortices induces surface chirality on electrodeposit films.

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Transient behaviour of magnetic micro-bead chains rotating in a fluid by external fields

Magnetic micro-beads can facilitate many functions in lab-on-a-chip systems, such as bio-chemical labeling, selective transport, magnetic sensing and mixing. In order to investigate potential applications of magnetic micro-beads for mixing in micro fluidic systems, we developed a pin-jointed mechanism model that allows analysing the behaviour of rotating superparamagnetic bead chains. Our numerical model revealed the response of the chains on a rotating magnetic field over time. We could demonstrate that the governing parameters are the Mason number and number of beads in the chain. The results are in agreement with the simplified analytical model, assuming a straight chain, but also allow prediction of the transient chain shape. The modelled chains develop an anti-symmetric S-shape that is stable, if the Mason number for a given chain length does not surpass a critical value. Above that value, rupture occurs in the vicinity of the chain centre. However, variations in bead susceptibility can shift the location of rupture. Moreover, we performed experiments with superparamagnetic micro-beads in a small fluid volume exposed to a uniform rotating magnetic field. Our simulation could successfully predict the observed transient chain form and the time for chain rupture. The developed model can be used to design optimised bead based mixers in micro fluidic systems.     

Effects of magnetic fields on HCFC-141b refrigerant gas hydrate formation

Gas hydrates are crystalline compounds formed (usually above 0℃) by water reacting with some gases or volatile liquids (hydrate former). Guest molecules, such as gas or volatile liquid molecules, are enclosed firmly inside the host cavities and act with water molecules in weak van der Waals force. Gas hydrate usually includes natural gas hydrate, refrigerant gas hydrate and CO2 gas hydrate. Refrigerant hydrates can be formed above 0℃, and their crystallization is similar to the ordinary ice…     

Aqueous nanostructures in water induced by electromagnetic fields emitted by EDS

This article reports the experimental results of a conductometric study on the time evolution, over a 541-day period, of 450 samples of Extremely Diluted Solutions (EDS) of fullerene and carbon nanotube and 450 samples of twice-distilled water, stored in alternate rows of EDS and water spaced 0.5 cm apart. The purpose was to establish whether these two aqueous systems are able to transmit, via electromagnetic fields, their variations in the supramolecular structure of the solvent water which has not undergone any previous perturbation. The chemical-physical method employed was conductometry, which proved to be the simplest and most efficient means for quickly and accurately monitoring the structural variations. In addition, since it has been demonstrated that there is a clear linear correlation between specific conductivity and heat of mixing with alkaline solutions, the conductometric result can also be extended to the calorimetric result. These findings, though doubtless unexpected and intriguing, are highly significant. The alterations over time of the pure water samples follow those of the EDS surprisingly closely.     

Transient electroosmotic flow induced by DC or AC electric fields in a curved microtube

This study investigates transient electroosmotic flow in a rectangular curved microtube in which the fluid is driven by the application of an external DC or AC electric field. The resultant flow-field evolutions within the microtube are simulated using the backwards-Euler time-stepping numerical method to clarify the relationship between the changes in the axial-flow velocity and the intensity of the applied electric field. When the electric field is initially applied or varies, the fluid within the double layer responds virtually immediately, and the axial velocity within the double layer tends to follow the varying intensity of the applied electric field. The greatest net charge density exists at the corners of the microtube as a result of the overlapping electrical double layers of the two walls. It results in local maximum or minimum axial velocities in the corners during increasing or decreasing applied electric field intensity in either the positive or negative direction. As the fluid within the double layer starts to move, the bulk fluid is gradually dragged into motion through the diffusion of momentum from the double layer. A finite time is required for the full momentum of the double layer to diffuse to the bulk fluid; hence, a certain phase shift between the applied electric field and the flow response is inevitable. The patterns of the axial velocity contours during the transient evolution are investigated in this study. It is found that these patterns are determined by the efficiency of momentum diffusion from the double layer to the central region of the microtube.     

Structure of oxygen clathrate hydrate by neutron powder diffraction

Oxygen hydrate was prepared by reacting oxygen with deuteriated ice at high pressure. Its structure was examined with powder neutron diffraction. It was found to crystallize in the cubic space group witha=17.070(1) Å. The formation of the type II structure rather than type I can be attributed to the larger Langmuir constant of sorption for the oxygen molecules in the 12-hedral cages. The encaged oxygen molecules are orientationally disordered. A comparison of the oxygen thermal parameters in both cages suggests the existence of local potential minima in the 16-hedral cages.Published as NRCC 25940     

Advances in detection of magnetic fields induced by electrochemical reactions—a review

The paper summarizes achievements in applications of superconducting quantum interference device (SQUID) magnetometry in electrochemical activity sensing, especially in that related to remote corrosion detection. The studies deal with application of the SQUIDs operating in liquid helium or nitrogen with a spatial resolution of magnetic field detection of the order of a millimeter or greater. This made it possible to observe macroscopic magnetic fields, which originated from the large-scale surface currents (ionic and electronic), which resulted from electrochemical potential gradients on electrochemical interfaces. The gradients owed to variations in temperature, alloy composition, sample geometry, electrolyte flow characteristics (velocity, direction, and turbulence), etc. The measurements demonstrated the capability of SQUIDs to remotely sense corrosion across the integrated media consisting of gaseous and solid dielectrics, metal, and electrolyte. The results have shown the potential of magnetometry for practical corrosion detection in the restricted locations such as in ground or concrete. Despite significant efforts, the field is considered to be at an early stage from both fundamental and practical points of view. Contribution to special issue “Magnetic field effects in Electrochemistry”.     

Influences of different types of magnetic fields on HCFC-141b gas hydrate formation processes

Gas hydrates are crystalline compounds formedwhen gas molecules or volatile liquid molecules comein contact with water molecules through weak van derWaals force at favourable pressure and temperature.Refrigerant gas hydrates can be effectively formed atappropriate temperature (5—12℃) with a high reac-tion heat (320—380 kJ/kg). Because of their particularthermodynamic properties, refrigerant gas hydrate,especially low pressure refrigerant gas hydrate, hasbeen considered as one of the most pr…     

Control of photo-electron-transfer induced radical production by micellar cages,heavy-atom substituents and magnetic fields

Intramiceller radical pair formation and recombination kinetics in the electron transfer quenching of the thiomine triplet by aniline and various monohalogenated anilines have been studied by micro-second and nanosecond laser flash spectroscopy in reversed micellar solution of CDBA in benzene. Clear kinetic evidence of the micellar cage effect is provided by a comparative spectro-kinetical study in homogeneous aqueous and reversed micellar solution. In zero magnetic field the radical pairs which originate wrth a triplet spin alignment recombine in the waterpools of the micelles with a rate constant of about 3 × 10⁶s^-1 which is not sensitive to the hyperftue or spin-orbit coupling parameters of the aniline-type radical. Long lived radicals are formed by radical escape from the micelles occurring with a rate constant in the-order of 2 × 10⁶s^-1 and being insensitive to an external magnetic field. Intramicellar radical pair recombination is slowed down by an external magnetic field. A maximum effect (measured at 1 T) of a factor of 3 is observed for non-halogenated anilines. Halogen substituation attenuates this magnetic-field effect depending on the strength of spin-orbit coupling exhibited by the halogen substituent. The magnetic-field effect is interpreted in terms of the radical pair mechanism with special emphasis on the role of spin relaxation. Suppression of the magnetic-field effect by halogen substituents is attributed to the spin-rotational relaxation mechanism which is independent of a magnetic field. A heavy-atom suhstituent effect is also borne out in the primary yield of radical pairs which is decreased in the same way as in homogeneous solution. This is atttributed to the role of a triplet exciplex formed as a precursor of the radical pair, where heavy atom substitueuts cause very efficient rediationless decay to the ground state. A magnetic-field effect typical for the triplet mechanism in the exciplex has been detectable with 4-iodoaniline as quencher.     

Formation of lanthanide ion networks by orientation of the mesophases of their complexes in magnetic fields

A complex of a Tm(III) perfluoroalkylsulsphate with salicylaldimine Schiff's base was synthesized and its liquid crystallinity characterized by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. An additional phase transition was detected. 2D or 3D anisotropically-organized media were obtained by cooling of the lanthanide complex from different phases in an applied magnetic field. A huge positive magnetic anisotropy was observed for the resulting material.     

Formation of lanthanide ion networks by orientation of the mesophases of their complexes in magnetic fields

A complex of a Tm(III) perfluoroalkylsulsphate with salicylaldimine Schiff's base was synthesized and its liquid crystallinity characterized by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. An additional phase transition was detected. 2D or 3D anisotropically-organized media were obtained by cooling of the lanthanide complex from different phases in an applied magnetic field. A huge positive magnetic anisotropy was observed for the resulting material.     

Canonical orbital contributions to the magnetic fields induced by global and local diatropic and paratropic ring currents

The induced magnetic field (IMF) of naphthalene, biphenyl, biphenylene, benzocyclobutadiene, and pentalene is dissected to contributions from the total π system, canonical π‐molecular orbitals (CMO), and HOMO→π* excitations, to evaluate and interpret relative global and local diatropicity and paratropicity. Maps of the IMF of the total π system reveal its relative strength and topology that corresponds to global and local diatropic and paratropic ring currents. The total π magnetic response is determined by this of canonical HOMOs and particularly by paratropic contributions of rotational excitations from HOMOs to unoccupied π * orbitals. Low energy excitations and similar nodal structure of HOMO and π * induce strong paratropic fields that dominate on antiaromatic rings. High energy excitations and different nodal structures lead to weak paratropic contributions of canonical HOMOs, which are overwhelmed by diatropic response of lower energy canonical orbitals in aromatic rings. CMO‐IMF analysis is found in agreement with ring current analysis. © 2017 Wiley Periodicals, Inc.     

Transient magnetic fields in silicon ions traversing thin foils of Fe and Gd at high velocity

Spin precessions of the²⁸Si first 2⁺ state, caused by transient magnetic fields in thin Fe and Gd foils, were measured at a mean ion velocity of 7.5v ₀ (v ₀=c/137). Transient fields of 1.8 (3) kT and 1.1 (2) kT have been deduced for Fe and Gd, respectively. The observed field strengths are discussed in terms of the electron mean polarization in the SiK shell.     

Intelligent polymer gels controlled by magnetic fields

 In this paper we summarise the effects induced by electric and magnetic fields on the mobility and shape of polymer gels containing a complex fluid as a swelling agent. Magnetic-field-sensitive gel beads and monolith gels have been prepared by introducing magnetic particles of colloidal size into chemically cross-linked poly(N-isopropylacrylamide) and poly(vinyl alcohol) hydrogels. The influence of uniform and nonuniform fields has been studied. In uniform magnetic fields the gel beads form straight chainlike structures, whereas in nonhomogeneous fields the beads aggregates due to the magnetophoretic force directed to the highest field intensity. The ability of magnetic-field-sensitive gels to undergo quick, controllable changes in shape can be used to mimic muscular contraction. Received: 26 July 1999/Accepted: 27 August 1999     

On the mitochondrial aspect of reactive oxygen species action in external magnetic fields

Some retinoids or porphyrins can form radical pairs, alter transfer of electrons, and increase synthesis of reactive oxygen species in the mitochondrial respiratory chain. This leads to cell damage and apoptosis. We propose that co-application of an external static magnetic field of several to several hundreds miliTesla (mT) can enhance those effects by further alteration of electron flow in the mitochondrial respiratory chain, facilitation of forbidden transitions from the triplet to the singlet state of retinoid or porphyrin radicals, and modification of radical pair amount. Since electron flow in the mitochondrial respiratory chain seems to possess fractal dynamics, the magnetic field can initiate self- organization of the flow into more regular patterns, and create optimal conditions for damage of cancer cells without any detriment for the normal counterparts. External low magnetic field should improve effectiveness and selectivity of retinoid chemoprevention or porphyrin photodynamic therapy.     

Quantitative theory of chemically induced dynamic nuclear polarisation in high magnetic fields

Further development of the diffusional model of the radical pair is suggested. A function is proposed for the exponential distribution of the diffusional trajectories of the radicals in a radical pair. By this function, the differences in the populations of nuclear spin levels in the molecules are calculated for the S, T and U precursor pairs. The equations which express the relationship between the theoretically calculated population differences and the experimentally determined enhancement coefficients are derived.     

Search for memory effects in methane hydrate: structure of water before hydrate formation and after hydrate decomposition

Neutron diffraction with HD isotope substitution has been used to study the formation and decomposition of the methane clathrate hydrate. Using this atomistic technique coupled with simultaneous gas consumption measurements, we have successfully tracked the formation of the sI methane hydrate from a water/gas mixture and then the subsequent decomposition of the hydrate from initiation to completion. These studies demonstrate that the application of neutron diffraction with simultaneous gas consumption measurements provides a powerful method for studying the clathrate hydrate crystal growth and decomposition. We have also used neutron diffraction to examine the water structure before the hydrate growth and after the hydrate decomposition. From the neutron-scattering curves and the empirical potential structure refinement analysis of the data, we find that there is no significant difference between the structure of water before the hydrate formation and the structure of water after the hydrate decomposition. Nor is there any significant change to the methane hydration shell. These results are discussed in the context of widely held views on the existence of memory effects after the hydrate decomposition.     

Quantum simulations of toroidal electric ring currents and magnetic fields in linear molecules induced by circularly polarized laser pulses

Circularly polarized laser pulses may excite state selective unidirectional toroidal electric ring currents around the axis of oriented linear molecules. These in turn induce state selective magnetic fields. Quantum simulations for AlCl show that these effects are about one or even more than three orders of magnitudes larger than those which may be prepared in oriented planar molecules such as Mg-porphyrin, by means of either circularly polarized laser pulses, or by traditional magnetic fields, respectively.     

Evidence for electron orbital dependence of ion-beam induced attenuations of transient magnetic fields

From measurements of transient magnetic fields (TF) on⁵⁶Fe(2 ₁ ⁺ ) ions in Gd host there is evidence that beam induced attenuations of TF not only depend on the energy loss of the beam ions in the ferromagnet but also on the electron ns-orbitals of the probe ion contributing to the field. This has been demonstrated for 2s- and 3s-electron states of⁵⁶Fe ions which are preferentially populated by setting the ion velocity to their respective orbital Bohr velocities.     

Fe-N-C catalysts for oxygen electroreduction under external magnetic fields:Reduction of magnetic O2 to nonmagnetic H2O

An extensive analysis of iron-nitrogen-carbon(Fe-N-C)electrocatalysts synthesis and activity is presented concerning synthesis conditions such as initial Fe content,pyrolysis temperature and atmosphere(inert N₂,reducing NH₃,oxidizing Cl₂ and their sequential combinations)and the influence of an external magnetic field on their performance in oxygen reduction reaction(ORR).Thermosetting porous polymers doped with FeCl₃ were utilized as the Fe-N-C catalysts precursors.The pyrolysis temperature was varied within a 700-900℃range.The temperature and atmosphere of pyrolysis strongly affect the porosity and compositi on of the resultant Fe-N-C catalysts,while the in itial amount of Fe precursor shows much weaker impact.Pyrolysis under NH₃ yields materials similar to those pyrolyzed under an inert atmosphere(N₂).In contrast,pyrolysis under Cl₂ yields carbon of peculiar character with highly disordered structure and extensive microporosity.The application of a static external magnetic field strongly enhances the ORR process(herein studied in an alkaline environment)and the enhancement correlates with the Fe content in the Fe-N-C catalysts.The Fe-N-C materials containing ferromagnetic iron phase embedded in N-doped microporous carbon constitute attractive catalysts for magnetic field-aided anion exchange membrane fuel cell technology.