Magnetic fields

Top PDF Magnetic fields:

Childhood Leukemia Not Linked with ELF Magnetic Fields

Childhood Leukemia Not Linked with ELF Magnetic Fields

In this situation, based on just epidemiological evidence at power frequency the IARC classified magnetic fields in the entire range of extremely low frequencies as “possibly carcinogenic” class 2B [1], and in regu- lations authorities included disclaimers that exposure limits would not address “the long-term effects” including possible carcinogenic effects by arguing that “currently” there would be no conclusive scientific evidence estab- lishing a causal relationship [2] [4]. However, it has been added that if such evidence emerged, appropriate actions would be taken thus suggesting that this was a plausible expectation [4].
Show more

11 Read more

Modelling neutron star magnetic fields

Modelling neutron star magnetic fields

While the impact of the Hall effect on the crustal magnetic field is becoming clearer, further steps are needed to achieve a global understanding of magnetic field structure and evolution in neutron stars. The physics of the inner part of the crust and the core need to be assessed, especially with respect to ambipolar diffusion and superconduc- tivity. Moreover, the crust itself may not be static but evolves slowly in response to the changes of the magnetic field and its rota- tion frequency; could these changes affect the evolution of the field itself? Finally, the magnetosphere comprises a complicated electric circuit with twisted magnetic fields, electric currents and charged regions; an important question here is how exactly the magnetosphere is coupled to the neutron star and how it reacts to internal magnetic field evolution. Answering these questions will open new paths and brings us closer to understanding these wonderful objects. ●
Show more

6 Read more

PLANET B magnetic fields investigation

PLANET B magnetic fields investigation

A special effort has been made to reduce the total mass of the MGF system. This is one of the most challenging items in the design phase of each subsystem to realize the PLANET- B mission. In the MGF instrument, HIC technology has been introduced to the analog electronics component. Gate arrays and surface-mount-type devices are adopted for digital components. The subsystem weight becomes about 1/3 in comparison with a similar type of magnetometer previously manufactured. To reduce the total mass even more, a great challenge was introduced, that is, the subsystem power unit and the telemetry/command I/F control unit are shared with UVS (ultraviolet spectrometer), PET (electron temperature probe), and MST (extensible mast) instruments. The elec- tronic boards for these subsystems are installed in one unit (MPM-E). A common CPU controls both telemetry and command interface. It also gathers raw data from MGF, PET, and UVS and edits them to send through the telemetry. During the ground test of the spacecraft, significant efforts have been made to reduce spacecraft-generated magnetic fields through the cooperation of many people, including members of the PWA team and other scientific and engi- neering teams. Special care has been taken in the design of each subsystem, such as the wiring inside the spacecraft and the layout of the solar cell arrays. Care was taken during the design phase to minimize the use of sources of stray fields such as permanent magnets and electromagnets. When an unavoidable stray field was found in the ground test, a magnet was used to cancel it. Currently, we can confirm that the bias field from the spacecraft would be smaller than 1 nT at the location of the magnetometer sensor. The final reso- lution will be obtained from the ground test which begin in October 1997.
Show more

6 Read more

Neutron stars velocities and magnetic fields

Neutron stars velocities and magnetic fields

Abstract. We study a model that explain neutron stars velocities due to the anisotropic emission of neutrinos. Strong magnetic fields present in neutron stars are the source of the anisotropy in the system. To compute the velocity of the neutron star we model its core as composed by strange quark matter and analice the properties of a magnetized quark gas at finite temperature and density. Specifically we have obtained the electron polarization and the specific heat of magnetized fermions as a functions of the temperature, chemical potential and magnetic field which allow us to study the velocity of the neutron star as a function of these parameters.
Show more

7 Read more

Magnetic fields and polarization in AGN jets

Magnetic fields and polarization in AGN jets

Abstract. In the literature there is now a wealth of images of AGN in both linear and circular polarization at milliarcsecond resolution of many sources at multiple epochs and wavelengths. This review is a broad overview of our current state of knowledge of the polarization properties of AGN jets, and of what we can infer about the structure of their magnetic fields and the distribution of Faraday rotating material, and also what is premature to infer. We suggest that while many of the observations of transverse rotation measure gradients may be correct, they have in general been observed with neither enough resolution nor sensitivity to be incontrovertible. Fortunately, this could be remedied using the new broad-band receivers on the VLBA. We also argue that while a transverse rotation measure gradient is a strong indicator of a toroidal component of magnetic field, it does not necessarily imply a helical magnetic field. In jets where the dominant field component appears to be parallel to the jet, it more likely consists of sheared loops or compressed random fields that are not vector ordered. Finally, we draw attention to the power of imaging in all four Stokes parameters at multiple frequencies to constrain the three-dimensional magnetic field structure and the particle content of jets and measure fundamental physical properties.
Show more

12 Read more

Magnetic fields on young, solar-type stars

Magnetic fields on young, solar-type stars

This thesis describes an investigation aimed at using spectropolarimetric observations of the magnetic fields of young solar-type stars to improve the understanding of the early development of solar and stellar dynamos and activity cycles. The emergence of stellar dynamos is important in understanding the evolution of young stars (and activity effects on any attendant emerging planetary systems). Stars were selected on the basis of their rapid rotation and activity. HD 106506, HD 76298, HD 35256, HD 29613 and EK Draconis formed the primary targets. Spectropolarimetric data were obtained with the Anglo-Australian Telescope, the Canada-France-Hawaii Telescope and the T´elescope Bernard Lyot with supporting broadband photometric data from the Mount Kent Observatory. Reduction and analysis of the data were performed to produce magnetic field detections, spot occupancy and magnetic field maps, differential rotation values, chromospheric flux estimates, starspot light curves and other measurements. Several results were obtained, as follows: (1) A distributed dynamo fundamentally different to the modern Sun’s interface-layer dynamo appears widespread in young solar- type stars, with all targets displaying significant surface azimuthal fields consistent with the dynamo operating throughout the convection zone. (2) All stars showed significant enhancement in chromospheric activity that appears to be primarily a function of rapid stellar rotation (3) Multi-epoch observations of the young solar analogue EK Draconis demonstrated a rapidly evolving magnetic field that could not be explained due to differential rotation alone, and hints at the presence of temporal variability due to the rapid evolution from a strongly toroidal magnetic field (∼80%) to a more balanced poloidal-toroidal configuration in three months of observations. (4) The differential rotation of HD 29615, with a rotational shear δΩ = 0.58 +0.14 −0.12 rad d −1 is one of the
Show more

352 Read more

Uniform magnetic fields in density functional theory

Uniform magnetic fields in density functional theory

The outline of this paper is as follows. In Sec. II, we review paramagnetic CDFT and adapt some of the technical mathematical details to allow for uniform magnetic fields. We continue in Sec. III by detailing the formulation of LDFT. Both constrained-search and convex formulations are given. Some HK-like results, which turn out to be stronger than the CDFT analogues, are also explored along with issues such as expectation-valuedness and N- representability. In Sec. IV we discuss Kohn–Sham theory, with focus on invariance with respect to gauge degrees of freedom and additive separability of the exchange–correlation functional. Next, in Sec. V, we briefly comment on the possibility of using gauge-invariant, physical quantities instead of the paramagnetic current density or canonical momenta. We also comment on a recent hybrid formulation due to Pan and Sahni featuring both the canonical, gauge-dependent magnetic moment and the physical current density [39]. Finally, in Sec. VI, we give some concluding remarks.
Show more

27 Read more

The energy budget of stellar magnetic fields

The energy budget of stellar magnetic fields

The toroidal component of stellar magnetic fields contains the free energy that, once liberated, is responsible for energetic events. Flares, coronal mass ejections and space weather in general have a large influence on the stellar environment, and can affect any plan- ets orbiting the star (Zarka 2007; Grießmeier, Zarka & Spreeuw 2007; Llama et al. 2011; Vidotto et al. 2012, 2013, 2015; See et al. 2014, 2015; Cohen et al. 2015). Presently, the toroidal compo- nent of stellar magnetic fields has only been studied in single, or small samples, of stars. Petit et al. (2008) studied a sample of four solar-like stars and noted that the stellar rotation period plays an important role in determining the fraction of magnetic energy in the toroidal component of the stellar field. However, the rotation period cannot be the sole parameter that determines the toroidal en- ergy fraction since stars with similar rotation periods show different toroidal energy fractions. Additionally, observations of individual stars, over multiple epochs, show that the toroidal energy frac- tion can change significantly on the time-scale of years (Donati & Collier Cameron 1997; Donati et al. 1999, 2003b; Petit et al. 2009; Fares et al. 2010, 2013; Morgenthaler et al. 2012; Jeffers et al. 2014; Boro Saikia et al. 2015). This indicates that the dynamo is dy- namic in nature and cannot be characterized by single time averaged parameters.
Show more

10 Read more

Magnetic fields of Herbig Ae/Be stars

Magnetic fields of Herbig Ae/Be stars

As mentioned above, all previously studied Herbig Ae/Be stars exhibit a single-wave variation in the longitudinal magnetic field during the stellar rotation cycle. These observations are usually consid- ered as evidence for a dominant dipolar contribution to the magnetic field topology. Magnetospheric accretion theories traditionally consider simple ∼kG dipolar magnetic fields that truncate the disk and force in-falling gas to flow along the field lines. The assumption of the dominance of dipole fields is usually made for simplicity or due to the lack of available information about the true large-scale mag- netic field topology of these stars. Indeed, the recent work of Adams & Gregory (2012 [30]) shows that high order field components may even play a dominant role in the physics of the gas inflow, as the accretion columns approach the star.
Show more

6 Read more

LABORATORY V MAGNETIC FIELDS AND FORCES

LABORATORY V MAGNETIC FIELDS AND FORCES

To open the EMField application, just click on the EMField icon on your desktop. Click anywhere for instructions. To study magnetic fields of current carrying wires, you will want to choose the 2D Line Currents option in the Sources menu. At the bottom of the window, there will be a list of various line currents of different magnitudes. Choose one by clicking and dragging it into the screen. Under the Field and Potential menu, you should choose the Field Vector option. This option for magnetic fields behaves exactly like that for electric fields. Hence, it is useful to review the EMField instructions from labs 1 and 2. Once you have a clear picture of what the direction of the field is, print it out using the Print command under File. You might also find it useful to play around with different sizes of current to note any changes.
Show more

24 Read more

The Genesis of Magnetic Fields in White Dwarfs

The Genesis of Magnetic Fields in White Dwarfs

Liebert et al. (2005, 2015) asked, “Where are the magnetic white dwarfs with detached, non-degenerate companions?” This question is awaiting an answer and thus the pro- genitors of the MCVs still need to be identified. As already noted, the proposal by Tout et al. (2008), that the existence of high magnetic fields in all WDs, isolated and in binaries, is related to their duplicity prior to CEE is gaining momentum. Observational support for the binary origin of magnetic fields in MCVs is also strengthening. Zoro- tovic et al. (2010) listed about 60 post CE binaries (PCEBs) from the SDSS and other surveys consisting of a WD with an M-dwarf companion. The periods of these PCEBs range from about 0.08 to 20 d and the WD e ff ective temperatures in the range 7 500 to 60 000 K. According to current binary evolution theory, one third of these systems should lose angular momentum from their orbits by magnetic braking and gravitational radiation and are expected to come into contact within a Hubble time. However none of these 60 binaries contains a MWD, even if observations indicate that 20 to 25 per cent of all CVs harbour one. Furthermore, magnitude limited samples of WD have shown an incidence of magnetism of about 2 to 3 per cent and thus some pre-MCVs should be present among the objects listed by Zorotovic et al. (2010). This finding indicates that magnetic white dwarf primaries are only present in those binaries that are already interacting or are close to interaction. The magnetic systems originally known as Low-Accretion Polars (LARPS, Schwope et al., 2002) have been proposed to be the progenitors of the polars (Schwope et al., 2009). The first LARPS were dis- covered in the Hamburg / ESO Quasar Survey (HQS, Wisotzki et al., 1991) and then by the SDSS by virtue of their unusual colours arising from the presence of strong cyclotron harmonic features in the optical band together with a red excess owing to the presence of a low-mass red companion star. The MWDs in LARPS are generally quite cool (T e ff < ∼ 10 000 K) and have low-mass MS companions which underfill their
Show more

167 Read more

Effects of Magnetic Fields on the Electrodeposition Process of Cobalt

Effects of Magnetic Fields on the Electrodeposition Process of Cobalt

Magnetic fields parallel to electric fields were applied in the experiment to prepare cobalt thin films from the electrolyte without chemical additives. Influences of various magnetic intensities on the electrochemistry process, deposition mass and surface morphology were studied. According to the experiment, steady state current and deposition mass decreased gradually with the increase of magnetic intensities. The result of electrochemical impedance showed that transfer resistance increased with the magnetic intensity ranged from 0 to 1 T. During the electrodeposition process, cobalt near cathode is lower than other places in the solution. A gradient in the concentration of paramagnetic cobalt ions leads to a gradient in the magnetic susceptibility which would induce to a magnetic driving force when the magnetic field was applied. This magnetic driving force would push the cobalt ions away from cathode to hinder cobalt deposition resulting in decrease of steady state current and transfer resistance. The cobalt films are composed of typical nodular structures. However, hill-like structures could be observed with the increase of magnetic intensity. Cobalt grains tend to grow perpendicularly to the substrate with the condition of higher magnetic intensity due to the ferromagnetic property of cobalt atoms.
Show more

8 Read more

On Nucleation Temperature of Pure Aluminum in Magnetic Fields

On Nucleation Temperature of Pure Aluminum in Magnetic Fields

energy, during phase transformations whose kinetic or thermodynamic behaviors might be regulated, and further their final structures and properties could be altered. Hence, it is necessary to extend to investigate phase transformations of non-magnetic substances in order to deeply understand the essence of changes in magnetic fields. Solidification of metals and alloys is one of the most common phase transformations in which nucleation plays a crucial role. Unfortunately, the research on the subject in a magnetic field is in much lack except that the solidification temperature of pure bismuth with diamagnetism was observed to increase in a magnetic field [10, 11].
Show more

8 Read more

The energy budget of stellar magnetic fields

The energy budget of stellar magnetic fields

The toroidal component of stellar magnetic fields contains the free energy that, once liberated, is responsible for energetic events. Flares, coronal mass ejections and space weather in general have a large influence on the stellar environment, and can affect any plan- ets orbiting the star (Zarka 2007; Grießmeier, Zarka & Spreeuw 2007; Llama et al. 2011; Vidotto et al. 2012, 2013, 2015; See et al. 2014, 2015; Cohen et al. 2015). Presently, the toroidal compo- nent of stellar magnetic fields has only been studied in single, or small samples, of stars. Petit et al. (2008) studied a sample of four solar-like stars and noted that the stellar rotation period plays an important role in determining the fraction of magnetic energy in the toroidal component of the stellar field. However, the rotation period cannot be the sole parameter that determines the toroidal en- ergy fraction since stars with similar rotation periods show different toroidal energy fractions. Additionally, observations of individual stars, over multiple epochs, show that the toroidal energy frac- tion can change significantly on the time-scale of years (Donati & Collier Cameron 1997; Donati et al. 1999, 2003b; Petit et al. 2009; Fares et al. 2010, 2013; Morgenthaler et al. 2012; Jeffers et al. 2014; Boro Saikia et al. 2015). This indicates that the dynamo is dy- namic in nature and cannot be characterized by single time averaged parameters.
Show more

10 Read more

Galactic magnetic fields as a consequence of inflation

Galactic magnetic fields as a consequence of inflation

or battery (Subramanian 1996, Colgate et al. 2000) effects require large- scale separation of charges i.e. substantial ionization, which is hard to realize as late as galaxy formation. Thus, the origin of the seed field is most likely primordial. Since it breaks isotropy the generation of large- scale magnetic fields has to occur out of thermal equilibrium. Therefore, before decoupling, magnetogenesis is possible either at phase transitions or during inflation (for a review see Grasso & Rubinstein 2000).

8 Read more

The Effect of Anomalous Magnetic Fields on Malignant Diseases

The Effect of Anomalous Magnetic Fields on Malignant Diseases

Introduction: Natural earth’s magnetic field (EMF) is promoter of mother cell division into two daughter cells. Cancer is a cell that divides unlimited and destroys the body. Aim: Measurements presented in this paper show that malignant diseases are formed in anomalous magnetic fields (AMF) in patient’s beds. Removal of patients from AMF explains the etiological uncertainties in the medical literature. Methods: Measuring of AMF in patients’ beds was performed by proton mag- netometer. Measuring points are on square net, 10 × 10 cm. The results are shown with contour lines on drawings. The health status of residence in the Earth’s natural magnetic field (EMF) was monitored. The etiologic data from the literature are explained. Results: Research lasted 25 years. AMF were measured in 1500 patients’ beds. There was a correlation between AMF and location of the diseased organ. AMF surfaces were shown in beds where the diseased organ is, on the contrary, there were natural values of EMF in the rest of the bed surface. Furthermore, the results found that three cases of breast cancer with metastases survived after surgical interventions and sub- sequent removal into natural EMF in contrast to 26 cases with the same diagnosis and surgical in- terventions who died after short period and staying in AMF. Another example was brain malig- nancy, which was decreased by living in natural EMF for one year. Conclusion: Based on the results of measurement of AMF, the medical condition of the patient when staying in a natural EMF, and explanation of uncertainties etiologies, the main conclusion was: AMF is the main cause of the ma- lignant diseases.
Show more

12 Read more

Rayleigh-Taylor Instabilities with Sheared Magnetic Fields

Rayleigh-Taylor Instabilities with Sheared Magnetic Fields

The magnetic Rayleigh–Taylor (MRT) instability is impor- tant in many astrophysical systems. Some examples are buoy- ant magnetized bubbles identified in clusters of galaxies (see Robinson et al. (2004) and Jones & De Young (2005) for studies in two-dimensional (2D), and O’Neill et al. (2009) for three-dimensional (3D) configurations). MRT instabilities also manifest themselves in shells of young supernova remnants, this has been investigated by Jun et al. (1995) in 2D and 3D Cartesian configurations and by Jun & Norman (1996) in 3D using spherical coordinates. Bucciantini et al. (2004) have nu- merically investigated the development of the MRT instability at the interface between an expanding pulsar wind nebula and its surrounding supernova remnant. Stone & Gardiner (2007) stud- ied the behavior of MRT instability in three dimensions with special focus on the structure and dynamics of the nonlinear evolution of the system. They analyzed various configurations including the situation in which magnetic fields change direc- tion at the interface between the two fluids. Stone & Gardiner (2007) used the MRT instability to explain the structure of the optical filaments observed in the Crab nebula.
Show more

12 Read more

Evaluation of Magnetic Parameters and Kinetics of the Magnetic Nanoparticles in High Magnetic Fields

Evaluation of Magnetic Parameters and Kinetics of the Magnetic Nanoparticles in High Magnetic Fields

The force/weight acting on the particle in the various models were also estimated. A 100nm magnetic nanoparticle was placed in the magnetic field and using finite element analysis the electromagnetic behaviour of the particle was studied in Quickfield software, and the results were computed 2- dimensionally, for evaluation, single coils were used. The coil strength was increased by increasing the number of turns in the coils. When the force acting on the particles were evaluated, the displacement and acceleration kinetics of the particles were studied in saline and to model the tissues the drag forces were increased up to 1000 times to simulate the motion in tissues with higher values. In the initial part of the study nickel (Ni) rings were placed at various locations from the electromagnets and maximum electric current (A/C or D/C) was passed in these Ni rings. This is to study the electromagnetic distortions and eddy currents which tend to form by the Ni rings when placed near high magnetic fields. The details of the model and the elaborate results are available in the Quickfield webstite. The supplement website gives elaborate details of the calculations including force, the force/ weight values and motion dynamics of the nanoparticles.
Show more

46 Read more

The emergence of weakly twisted magnetic fields in the Sun

The emergence of weakly twisted magnetic fields in the Sun

The interaction of the magnetic lobes leads to the emission of flows that are driven either by reconnection (hot jets) or by the gradient of the plasma pressure (cool and dense outflows) at the interface between the magnetic lobes. In both cases, the associated plasma emission is confined within the EFR, forming a system of hot and cool loops that arch over the emerging field. Therefore, this mechanism should be considered as a possible driver for the formation of coronal loops of different temperatures that have repeatedly been observed to coexist in ARs and arch-filament systems (e.g., Isobe et al. 2005). The cool outflows, which are emitted before the reconnection jets, might account for Hα surges in EFRs (e.g., Canfield et al. 1996; Liu & Kurokawa 2004; Jiang et al. 2007). Similar flows have also been found to form in 2D and 3D numerical experiments of emerging fields with an undulating configuration (e.g., Isobe et al. 2007; Archontis & Hood 2009). They form at the valleys between interacting magnetic fields due to a pressure gradient force. A similar mechanism has been used to explain the emission of cool outflows associated with the emergence of new magnetic flux at the outskirts of an AR (e.g., Harra et al. 2012). The cool emission originates from the area where the interacting magnetic fields experience more compression than reconnection. On the other hand, the hot reconnection jets that are produced in the present simulations could be observed as X-ray jets (e.g., Shibata et al. 1992). In previous studies, similar jets were produced as a result of reconnection between emerging and preexisting magnetic fields (e.g., Archontis et al. 2010; Archontis & Hood 2013).
Show more

15 Read more

Pion decay in magnetic fields

Pion decay in magnetic fields

Background magnetic fields are known to impact significantly on the physics of strongly interacting matter – affecting the hadron spectrum, creating an anisotropy in the ground state and influencing the phase structure of QCD. For reviews on this subject and the most recent results on the phase diagram see, e.g., Refs. [1–3]. Notable examples for systems in nature that exhibit strong magnetic fields include off-central heavy-ion collisions, the inner core of magnetized neutron stars and, possibly, the early stage of the evolution of our universe. The magnetic fields in these situations may range up to B ≈ 10 14−15 T, so that the interaction between quarks and B becomes as strong as the coupling
Show more

8 Read more

Show all 9763 documents...