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Adhesive and viscous effects of several lubricants at the slider/disk interfaceJohnson, Janice K. 05 1900 (has links)
No description available.
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Magnetic couplings and superparamagnetic properties of spinel ferrite nanoparticlesVestal, Christy Riann 03 1900 (has links)
No description available.
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Macroscopic quantum phenomenon in molecular magnetsHu, Jianming, 胡建明 January 2003 (has links)
published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy
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A study of magnetic spectrograph measurements of muons at sea-level柳啓瑞, Lau, Kai-shui. January 1973 (has links)
published_or_final_version / Physics / Doctoral / Doctor of Philosophy
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Magnetic skeletons and 3D magnetic reconnectionHaynes, Andrew L. January 2008 (has links)
The upper atmosphere of the sun, the solar corona, is approximately 1,000,000K hotter than the surface of the Sun, a property which cannot be explained by the normal processes of heat conduction and radiation. It is now commonly believed that the magnetic fields which fill the solar atmosphere, and propagate down into the interior of the Sun, are important for transferring and transforming energy from the strong plasma flows inside the Sun into the corona as heat. I have investigated an elementary flux interaction which forms a fundamental building block of the coronal heating process. This interaction involves two opposite polarity sources on the Sun's surface in the presence of an overlying magnetic field. To fully understand how this interaction transfers heat into the solar corona, the magnetic skeleton is required, which shows possible sites of heating that are due to magnetic reconnection. A magnetic field is best described by its magnetic skeleton. The most important parts of the magnetic skeleton to find are the null points, from which separatrix surfaces extend that divide magnetic flux of different topology. Part of this thesis proposes a new method of finding null points, for which the accuracy is shown and then compared with another commonly used method (which gave false results). Using these techniques for finding the magnetic skeleton in the magnetic interaction above, the evolution of the skeleton was found to head through seven distinct states, some of which were far more complicated than expected. This included a high number of separators (the intersection of two separatrix surfaces), which are a known location of magnetic reconnection. This separator reconnection was shown to be the main heating mechanism in this interaction, from which the total amount and rates of reconnection in the experiment was calculated. This led to the discovery of recursive reconnection, a process where magnetic flux is reconnected before reconnecting back to its original state, to allow for the process to repeat again. This recursive reconnection was shown to allow far more reconnection than would have been previously expected, all of which releases heat into the neighbouring areas of the atmosphere. Finally, the interaction was modelled with sources of different magnetic radii but of equal flux. This showed that when the antisymmetric nature of the previous interactions was removed, there was little change in the reconnection rates, but when the strength of the overlying magnetic field was increased, the reconnection rates were found to increase. This increase in the overlying magnetic field strength also produced a new magnetic feature called a bald-edge, which was found to replace some of the null points. These bald-edges were found to be associated with surfaces similar to separatrix surfaces that divide flux of different topology but do not extend from a null point. Also features similar to separators extend from these bald-edges.
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An experimental study of collective motion of magnetospirillum magneticum strain AMB-1 / 趨磁螺菌AMB-1的集體運動觀測 / CUHK electronic theses & dissertations collection / experimental study of collective motion of magnetospirillum magneticum strain AMB-1 / Qu ci luo jun AMB-1 de ji ti yun dong guan ceJanuary 2013 (has links)
In this thesis, the collective motion of Magnetospirillum magneticum strain AMB-1 is studied. Bacteria have developed various types of mechanism in order to search for the optimum environment, which are called taxis. There are two types of taxis, aerotaxis and magnetotaxis, that are involved in AMB-1. It is commonly believed that the vertical component of the Earth magnetic field helps to align the bacteria and confine them in one dimension, whereas the oxygen gradient determines their swimming velocity. In this way, magnetotaxis is conceived as a passive response, while aerotaxis is active and they work independently. Previous works done by our group may suggest an alternative picture. In this thesis, two experiments were carried out to gain a better understanding of the taxis of AMB-1. In the first experiment, bacterial suspension of density around 10⁸ cells cm⁻³ was injected into a chamber of dimensions 5×5×0.025 mm³. The motion of the bacteria was captured by a video camera mounted in the microscope under darkfield condition. Tracking of the quasi-2D motions under different applied magnetic field generated by two pairs of Helmholtz coils was done. In this way, we could determine the effect of magnetic field on basic physical properties of the bacteria, such as the diffusive motion, the rate of change of the motion direction. In the second experiment, a one dimensional oxygen gradient was achieved inside a microfluidic chamber. An aerotactic band of highly concentrated bacteria was observed under darkfield condition when bacterial suspension of density around 10⁹ cells cm⁻³. It is found that the time for the formation of the band varies under different applied magnetic fields, which suggests that the magnetotaxis in AMB-1 may not be completely passive. / 這篇論文報告關於趨磁螺菌AMB-1在集體運動上的研究。為了在野外尋找最好的生存環境,細菌發展出不同的趨向性機制。AMB-1擁有趨磁性和趨氧性兩個機制。在普遍的認知裡,地球磁場的垂直分量會把牠們的運動局限為一維,氧氣濃度梯度則影響牠們游泳的速度。趨磁性一直被認為是被動反應,而趨氧是主動的,兩者獨立運作。我課題組最近的實驗結果提出了存在另一種機制的可能性。為更了解AMB-1的趨向性機制,我們進行了兩個實驗。 / 在首個實驗中,濃度約為每立方厘米10⁸個的細菌溶液被注入到5×5×0.025立方毫米的空間。我們用攝像機把顯微鏡暗場觀測下的細菌運動記錄下來,在兩對亥姆霍茲線圈產生的不同磁場下,追蹤細菌的準二維運動。這樣,我們可以測定細菌的基本物理性質在不同磁場下的影響,例如其擴散運動、運動方向的轉換頻率等等。在第二個實驗中,我們在一個微流控空間裡建立了一維的氧氣濃度梯度。當細菌懸液濃度達到每立方厘米10⁹個時,在暗場條件下可以一條由高濃度細菌組成的趨氧性帶。我們發現帶形成所需的時間隨不同的外加磁場而改變,顯示AMB-1的趨磁性可能不是一個完全被動的反應。 / Lau, Tsz Ki = 趨磁螺菌AMB-1的集體運動觀測 / 劉子麒. / Thesis M.Phil. Chinese University of Hong Kong 2013. / Includes bibliographical references (leaves 53-58). / Abstracts also in Chinese. / Title from PDF title page (viewed on 12, October, 2016). / Lau, Tsz Ki = Qu ci luo jun AMB-1 de ji ti yun dong guan ce / Liu Ziqi. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.
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Relation between bandstructure and magnetocrystalline anisotropy : iron and nickelWang, Haiyan 14 February 2000 (has links)
A large amount of research has been done in which the magnetocrystalline
anisotropy energy for fcc Ni and bcc Fe was calculated based on the electronic
structure of these elements. Unfortunately; the results of these studies don't agree
with each other and also differ from the experimental observation. In a previous
thesis the effects of numerical errors in the Brillouin zone integrations were investigated.
The results of that work explain why different calculations give different
results, but do not explain the difference with experiment. The conclusion was
that the underlying bandstructure, which was calculated using standard approximations,
was not correct.
The bandstructure of these elements will be different when improved
prescriptions for the exchange-correlation energy are used. There is, however, no
clear indication along which lines this approximation should be improved. Here
we have taken a different approach to change the bandstructure. We suspected
that some important interactions between different atomic orbitals are either
ignored or miscounted. In this work, we examined the sensitivity of the energy on
the interaction between those orbitals and studied in detail the consequences of
changes in some interaction parameters which gave rise to a large energy change.
The main result of this work is a better understanding of the relation between
changes in the electronic structure in k-space and the resultant change in the
magnetocrystalline anisotropy energy. In addition, this work takes another step
in trying to find a better understanding how the magnetocrystalline anisotropy
energy relates to interactions between neighboring atoms. / Graduation date: 2000
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Critical scaling of thin-film YBaCuO and NdCeCuO resistivity-current isotherms : implications for vortex phase transitions and universalityRoberts, Jeanette Marie 13 April 1995 (has links)
Graduation date: 1995
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Orienting lignocellulosic fibers by means of a magnetic fieldZauscher, Stefan 09 November 1992 (has links)
Controlling the orientation and spatial distribution of
discontinuous fibers in composite materials enables product
properties to be tailored to anticipated use. Electric
fields are already (albeit rarely) used to affect alignment
in lignocellulosic (LC) fiber composites. The use of
magnetic fields has not, however, been suggested or
explored; this is apparently because LC fibers are
essentially non-magnetic. The approach may offer, however,
some considerable advantages, as long as ferromagnetism may
be imparted to the fibers.
In the present research several fiber modification
processes were considered and two, electroless nickel
plating and spray application of a coating containing nickel
in suspension, were investigated in more depth. The latter
was chosen to render highly engineered, elongated wood
particles responsive to magnetic fields. Individual treated
particles were suspended in viscous, newtonian silicone
fluids and their rotation under the influence of a
controlled magnetic field was video recorded.
The magnetic torque on the particle was, under the
above conditions, directly proportional to the fluid
viscosity, to the particle's angular velocity and to a
characteristic shape constant. The maximum of the specific
magnetic torque (magnetic torque divided by the shape
constant) was found to reflect the influence of field
strength and particle Ni-treatment on rotation. Results
were scaled to an arbitrarily chosen viscosity for
comparison.
The dependencies of the magnetic torque found in the
present research compare with those theoretically predicted
for ellipsoidal and cylindrical bodies. For field strengths
ranging from 0.07T to 0.15T (below magnetic saturation) the
magnetic torque increased almost linearly with increasing
field strength. Magnetic torque was also found to increase
nearly linearly with increasing bulk Ni-concentration (5g/kg
- 50g/kg).
Rotational motion was sometimes impeded at low field
strengths and this was attributed to a permanent magnetic
moment obtained by the particle. A coercive field strength
of 7600A/m supported this hypothesis. Judiciously switched
field polarity increased magnetic torque at small alignment
angles.
The present research indicates that orienting LC fibers
with magnetic fields is possible and promising. To study
dynamics of fiber motion in low viscosity fluids, such as
air, a different experimental method is necessary; however,
dependencies of the magnetic torque found in the present
study still hold true. / Graduation date: 1993
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Characterization of soft-tissue response to mechanical loading using nuclear magnetic resonance (NMR) and functional magnetic resonance imaging (fMRI) of neuronal activity during sustained cognitive-stimulus paradigmsWellen, Jeremy W. January 2003 (has links)
Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: diffusion; tendon; NMR; fMRI. Includes bibliographical references (p. 172-179).
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