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RADIATIVE TORQUES ALIGNMENT IN THE PRESENCE OF PINWHEEL TORQUES
2009-01-01
We study the alignment of grains subject to both radiative torques and pinwheel torques while accounting for thermal flipping of grains. By pinwheel torques we refer to all systematic torques that are fixed in grain body axes, including the radiative torques arising from scattering and absorption of isotropic radiation. We discuss new types of pinwheel torques, which are systematic torques arising from infrared emission and torques arising from the interaction of grains with ions and electrons in hot plasma. We show that both types of torques are long-lived, i.e., may exist longer than gaseous damping time. We compare these torques with the torques introduced by E. Purcell, namely, torques due to H2 formation, the variation of accommodation coefficient for gaseous collisions and photoelectric emission. Furthermore, we revise the Lazarian and Draine model for ...
Torques on Spheroidal Silicate Grains Exposed to Anisotropic Interstellar Radiation Fields
2007-09-27
Radiative torques, due to the absorption and scattering of starlight, are thought to play a major role in the alignment of grains with the interstellar magnetic field. The absorption of radiation also gives rise to recoil torques, associated with the photoelectric effect and photodesorption. The recoil torques are much more difficult to model and compute than the direct radiative torque. Here, we consider the relatively simple case of a spheroidal grain. Given our best estimates for the photoelectric yield and other relevant grain physical properties, we find that the recoil torques contribute at the 10% level or less compared with the direct radiative torque. We recommend that the recoil torques not be included in models of radiation-driven grain alignment at this time. However, additional experimental characterization of the surface properties and photoelectric yield for sub-micron grains is needed to better quantify the magnitude of these torques.
Radiative Torques Alignment In The Presence Of Pinwheel Torques
We study the alignment of grains subject to both radiative torques and pinwheel torques while accounting for thermal flipping of grains. Lazarian \\& Draine model of thermal grain flipping. We perform calculations for grain flipping time, taking into account stochastic torques associated with pinwheel torques, e.g. the stochastic torques arising from H$_2$ formation. We take into account the Barnett relaxation and nuclear relaxation. We also consider both paramagnetic and superparamagnetic grains. We show that sufficiently small grains flip fast and because of this get thermally trapped, i.e. rotate thermally in spite of the presence of pinwheel torques. We show that for sufficiently large grains the pinwheel torques can increase the degree of grain alignment achievable with the radiative torques. The effect arises from increasing the magnitude of the angular momentum of grains aligned by radiative torques. We predict that for ordinary paramagnetic grains the degree of grain alignment may correlate with the pinwheel torque efficiency.
Radiative Torques on Interstellar Grains; 2, Grain Alignment
Radiative torques on irregular dust grains, in addition to producing superthermal rotation, play a direct dynamical role in the alignment of interstellar dust with the local magnetic field. The equations governing the orientation of spinning, precessing grains are derived; H_2 formation torques and paramagnetic dissipation are included in the dynamics. Stationary solutions (constant alignment angle and spin rate) are found; these solutions may be stable ("attractors") or unstable ("repellors"). The equations of motion are numerically integrated for three exemplary irregular grain geometries, exposed to anisotropic radiation with the spectrum of interstellar starlight. The resulting "trajectory maps" are classified as "noncyclic", "semicyclic", or "cyclic", with examples of each given. We find that radiative torques result in rapid grain alignment, even in the absence of paramagnetic dissipation. It appears that radiative torques due to starlight can account for the observed alignment of interstellar grains with the Galactic magnetic field.
Radiative torques alignment in the presence of pinwheel torques
2008-01-03
We study the alignment of grains by radiative torques and pinwheel torques taking into account internal relaxations and thermal flipping. We identify with radiative torques the torques arising from anisotropic radiation, while all torques that are fixed in grain body axes, including the radiative torques arising from extinction of isotropic radiative field, we identify with pinwheel torques. We discuss new type of pinwheel torques, namely, regular torques arising from grain emission, as well as, pinwheel torques arising from the interaction of grains electrons in hot plasma. We show that both types of torques are long-lived, i.e. may exist longer than the grain damping time. We also show that the torques, first introduced by E. Purcell, arising from photoelectric emission of electrons, can also be long-lived. The other two types of Purcell's torques, namely, those arising from H$_2$ formation and variations of the grain accommodation coefficient, we identify with short-lived torques, although their actual life-time is rather uncertain. For long-lived pinwheel torques, we observe that new attractor points appear. Grains at these points rotate fast mostly due to pinwheel torques and are perfectly aligned with their long axes perpendicular to magnetic field. For short-lived pinwheel torques, we find a new effect of the suppression of grain flipping by strong radiative field. The mechanisms of alignment we discuss here do not invol ve paramagnetic relaxation. The only effect of magnetic field on grains that we consider is Larmor precession. We discuss implications of the alignment for interstellar medium and circumstellar regions.
Radiative Torques Alignment in the Presence of Pinwheel Torques
We study the alignment of grains subject to both radiative torques and pinwheel torques while accounting for thermal flipping of grains. By pinwheel torques we refer to all systematic torques that are fixed in grain body axes, including the radiative torques arising from scattering and absorption of isotropic radiation. We discuss new types of pinwheel torques, which are systematic torques arising from infrared emission and torques arising from the interaction of grains with ions and electrons in hot plasma. We show that both types of torques are long-lived, i.e., may exist longer than gaseous damping time. We compare these torques with the torques introduced by E. Purcell, namely, torques due to H2 formation, the variation of accommodation coefficient for gaseous collisions and photoelectric emission. Furthermore, we revise the Lazarian and Draine model for grain thermal flipping. We calculate mean flipping timescale induced by Barnett and nuclear relaxation for both paramagnetic and superparamagnetic grains, in the presence of stochastic torques associated with pinwheel torques, e.g., the stochastic torques arising from H2 formation, and gas bombardment. We show that the combined effect of internal relaxation and stochastic torques can result in fast flipping for sufficiently small grains and, because of this, they get thermally trapped, i.e., rotate thermally in spite of the presence of pinwheel torques. For sufficiently large grains, we show that the pinwheel torques can increase the degree of grain alignment achievable with the radiative torques by increasing the magnitude of the angular momentum of low attractor points and/or by driving grains to new high attractor points.
RADIATIVE TORQUES ALIGNMENT IN THE PRESENCE OF PINWHEEL TORQUES
We study the alignment of grains subject to both radiative torques and pinwheel torques while accounting for thermal flipping of grains. By pinwheel torques we refer to all systematic torques that are fixed in grain body axes, including the radiative torques arising from scattering and absorption of isotropic radiation. We discuss new types of pinwheel torques, which are systematic torques arising from infrared emission and torques arising from the interaction of grains with ions and electrons in hot plasma. We show that both types of torques are long-lived, i.e., may exist longer than gaseous damping time. We compare these torques with the torques introduced by E. Purcell, namely, torques due to H{sub 2} formation, the variation of accommodation coefficient for gaseous collisions and photoelectric emission. Furthermore, we revise the Lazarian and Draine model for grain thermal flipping. We calculate mean flipping timescale induced by Barnett and nuclear relaxation for both paramagnetic and superparamagnetic grains, in the presence of stochastic torques associated with pinwheel torques, e.g., the stochastic torques arising from H{sub 2} formation, and gas bombardment. We show that the combined effect of internal relaxation and stochastic torques can result in fast flipping for sufficiently small grains and, because of this, they get thermally trapped, i.e., rotate thermally in spite of the presence of pinwheel torques. For sufficiently large grains, we show that the pinwheel torques can increase the degree of grain alignment achievable with the radiative torques by increasing the magnitude of the angular momentum of low attractor points and/or by driving grains to new high attractor points.
2008-01-03
We consider grains with superparamagnetic inclusions and report two new condensed matter effects that can enhance the internal relaxation of the energy of a wobbling grain, namely, superparamagnetic Barnett relaxation, as well as, an increase of frequencies for which nuclear relaxation becomes important. This findings extends the range of grain sizes for which grains are thermally trapped, i.e. rotate thermally, in spite of the presence of uncompensated pinwheel torques. In addition, we show that the alignment of dust grains by radiative torques gets modified for superparamagnetic grains, with grains obtaining perfect alignment with respect to magnetic fields as soon as the grain gaseous randomization time gets larger than that of paramagnetic relaxation. The same conclusion is valid for the mechanical alignment of helical grains. If observations confirm that the degrees of alignment are higher than radiative torques can produce alone, this may be a proof of the presence of superparamagentic inclusions.
2009-01-01
Earlier studies of grain alignment dealt mostly with interstellar grains that have strong internal relaxation of energy which aligns the grain axis of maximum moment of inertia (the axis of major inertia) with respect to the grain's angular momentum. In this paper, we study the alignment by radiative torques for large irregular grains, e.g., grains in accretion disks, for which internal relaxation is subdominant. We use both numerical calculations and the analytical model of a helical grain introduced by us earlier. We demonstrate that grains in such a regime exhibit more complex dynamics. In particular, if initially the grain axis of major inertia makes a small angle with angular momentum, then radiative torques can align the grain axis of major inertia with angular momentum, and both the axis of major inertia and angular momentum are aligned with the magnetic field when ...
Radiative torques on interstellar grains; 1, superthermal spinup
1996-05-09
Irregular dust grains are subject to radiative torques when irradiated by interstellar starlight. It is shown how these radiative torques may be calculated using the discrete dipole approximation. Calculations are carried out for one irregular grain geometry, and three different grain sizes. It is shown that radiative torques can play an important dynamical role in spinup of interstellar dust grains, resulting in rotation rates which may exceed even those expected from H_2 formation on the grain surface. Because the radiative torque on an interstellar grain is determined by the overall grain geometry rather than merely the state of the grain surface, the resulting superthermal rotation is expected to be long-lived. By itself, long-lived superthermal rotation would permit grain alignment by normal paramagnetic dissipation on the "Davis-Greenstein" timescale. However, radiative torques arising from anisotropy of the starlight background can act directly to alter the grain alignment on much shorter timescales, and are therefore central to the process of interstellar grain alignment. Radiative torques depend strongly on the grain size, measured by a_eff, the radius of a sphere of equal volume. In diffuse clouds, radiative torques dominate the torques due to H2 formation for a_eff=0.2micron grains, but are relatively unimportant for a_eff0.1 micron grains in diffuse clouds are aligned, while there is little alignment of a_eff < 0.05 micron grains. We show that radiative torques are ineffective at producing superthermal rotation within quiescent dark clouds, but can be very effective in star-forming regions such as the M17 molecular cloud.
Radiative torques: analytical model and basic properties
2007-01-01
ABSTRACT We attempt to get a physical insight into grain alignment processes by studying basic properties of radiative torques (RATs). For this purpose we consider a simple toy model of a helical grain that reproduces well the basic features of RATs. The model grain consists of a spheroidal body with a mirror attached at an angle to it. Being very simple, the model allows analytical description of RATs that act upon it. We show a good correspondence of RATs obtained for this model and those of irregular grains calculated byddscat. Our analysis of the role of different torque components for grain alignment reveals that one of the three RAT components does not affect the alignment, but induces only for grain precession. The other two components provide a generic alignment with grain long axe...
Radiative torque alignment: essential physical processes
2008-01-01
ABSTRACT We study the physical processes that affect the alignment of grains subject to radiative torques (RATs). To describe the action of RATs, we use the analytical model (AMO) of RATs introduced in our previous paper. We focus our discussion on the alignment by anisotropic radiation flux with respect to the magnetic field, which defines the axis of grain Larmor precession. Such an alignment does not invoke paramagnetic dissipation (i.e. the Davis-Greenstein mechanism), but, nevertheless, grains tend to be aligned with long axes perpendicular to the magnetic field. When we account for thermal fluctuations within grains, we show that for grains that are characterized by a triaxial ellipsoid of inertia, the zero-J attractor point obtained in our earlier study develops into a low-J attract...
What Grain Alignment can Tell about Circumstellar Disks and Comets
Grain alignment theory suggests that grains should be aligned in circumstellar regions and the observational data available supports this conclusion. We discuss the alignment of grains via (1) magnetic relaxation, (2) mechanical processes, and (3) radiative torques. We show that ferromagnetic relaxation is likely to be more important than superparamagnetic relaxation if the dust in circumstellar regions is similar to species recently captured in Earth atmosphere. Outflows and stellar winds provide grain streaming along magnetic field lines and therefore mechanical alignment competes with the ferromagnetic and radiative alignments. We estimate measures of grain alignment in circumstellar regions, comets and interplanetary space and conclude that in many circumstellar regions and in the interplanetary space radiative torques may constitue the major alignment mechanism which aligns grain longer axes perpendicular to the direction of magnetic field. Observations in submillimeter and microwave ranges are suggested as a means of disentangling effects of multiple scattering from those related to aligned grains.
Grain Alignment and CMB Polarization Studies
2008-11-07
Polarized microwave emission from dust is an important foreground that may contaminate polarized CMB studies unless carefully accounted for. Modeling of polarization from dust requires a quantitative understanding of grain alignment. I review the current status of grain alignment theory outlining recent advances in quantitative description of the alignment. In particular, I show that the grain-alignment theory is a predictive one, and its results nicely match observations. Those indicate that the most important process of alignment is related to radiative torques acting on irregular grains. The recently developed analytical model of radiative torque alignment has proven to be a very efficient tool for predicting the degree of grain alignment. We expect the alignment theory to further mature before CMBPol flight, which would ensure a better accounting for the dust-related polarization. At the same time, CMBPol should provide the additional testing of grain alignment, clarifying the reliability of polarimetry for tracing of magnetic field.
Radiative torques: analytical model and basic properties
We attempt to get a physical insight into grain alignment processes by studying basic properties of radiative torques (RATs). For this purpose we consider a simple toy model of a helical grain that reproduces well the basic features of RATs. The model grain consists of a spheroidal body with a mirror attached at an angle to it. Being very simple, the model allows analytical description of RATs that act upon it. We show a good correspondence of RATs obtained for this model and those of irregular grains calculated by DDSCAT. Our analysis of the role of different torque components for grain alignment reveals that one of the three RAT components does not affect the alignment, but induces only for grain precession. The other two components provide a generic alignment with grain long axes perpendicular to the radiation direction, if the radiation dominates the grain precession, and perpendicular to magnetic field, otherwise. The latter coincides with the famous predictions of the Davis-Greenstein process, but our model does not invoke paramagnetic relaxation. In fact, we identify a narrow range of angles between the radiation beam and the magnetic field, for which the alignment is opposite to the Davis-Greenstein predictions. This range is likely to vanish, however, in the presence of thermal wobbling of grains. In addition, we find that a substantial part of grains subjected to RATs gets aligned with low angular momentum, which testifies that most of the grains in diffuse interstellar medium do not rotate fast, that is, rotate with thermal or even subthermal velocities. This tendency of RATs to decrease grain angular velocity as a result of the RAT alignment decreases the degree of polarization, by decreasing the degree of internal alignment, that is, the alignment of angular momentum with the grain axes. For the radiation-dominated environments, we find that the alignment can take place on the time-scale much shorter than the time of gaseous damping of grain rotation. This effect makes grains a more reliable tracer of magnetic fields. In addition, we study a self-similar scaling of RATs as a function of ?/aeff. We show that the self-similarity is useful for studying grain alignment by a broad spectrum of radiation, that is, interstellar radiation field.
2008-12-31
Earlier studies of grain alignment dealt mostly with interstellar grains that have strong internal relaxation of energy which aligns grain axis of maximum moment of inertia with respect to grain's angular momentum. In this paper, we study the alignment by radiative torques for large irregular grains, e.g., grains in accretion disks, for which internal relaxation is subdominant. We use both numerical calculations and the analytical model of a helical grain introduced by us earlier. We demonstrate that grains in such a regime exhibit more complex dynamics. In particular, if initially the grain axis of maximum moment of inertia makes a small angle with angular momentum, then radiative torques can align the grain axis of maximum moment of inertia with angular momentum, and both axis of maximum moment of inertia and angular momentum are aligned with the magnetic field when attractors with high angular momentum (high-J attractors) are available. For the alignment without high-J attractors, beside the earlier studied attractors with low angular momentum (low-J attractors), there appears new low-J attractors. The former and later cases correspond to the alignment with long axes perpendicular and parallel to the angular momentum, respectively. In addition, we study the alignment of grains in the presence of strong internal relaxation, but induced not by a radiation beam as in earlier studies, instead, induced by a complex radiation fiel d, that can be decomposed into dipole and quadrupole components. We find that in this situation, the parameter space $q^{max}$, for the existence of high-$J$ attractors is more extended, which entails higher degrees of polarization expected. Our obtained results are useful for modeling polarization arising from aligned grains in molecular clouds and accretion disks.
Alignment of Dust by Radiative Torque: Recent Developments
2009-01-05
Alignment of dust by radiative torques (RATs) has proven to be the most promising mechanism to explain alignment in various astrophysical environments, from comet atmospheres to accretion disks, molecular clouds, and diffuse interstellar gas. We discuss some of the major advances, which include, first of all, formulating of the analytical model of RATs. This model was shown to reproduce well the torques acting on actual irregular dust grains and allowed studies of the parameter space for which the alignment happens with long axes perpendicular and parallel to the magnetic field. Such a study resulted in an important conclusion that, without any paramagnetic relaxation, the RAT alignment always happens for interstellar grains with long axes perpendicular to the magnetic field. We show that the gaseous bombardment in some cases increases the degree of alignment by knocking out grains from the positions of imperfect alignment when the grains rotate slowly to more stable positions of perfect alignment where grains rotate fast. In terms of pinwheel torques, important revisions have been made in the Lazarian and Draine model of grain flipping and thermal trapping. Those, however, do not change the major conclusion that very small grains (i.e. grain size smaller than ~0.03 micron) should be marginally aligned. Recent work made the RAT alignment a predictive theory which is ready for quantitative modeling of astrophysical polarization. We predict that the microwave emission from the Zodiacal dust presents an important contaminant, which should be included into foreground polarization templates.
We consider grains with superparamagnetic inclusions and report two new condensed matter effects that enhance the internal relaxation of the energy of a wobbling grain, namely, superparamagnetic Barnett relaxation, and an extension of the range where nuclear relaxation is important to higher frequencies. In addition, we report a new effect related to grain rotation: in situations where grains otherwise rotate subthermally subject to radiative torques, they get into a state of fast rotation in the presence of superparamagnetic inclusions. This effect enhances alignment, as fast rotating grains, unlike slowly rotating ones, exhibit the perfect alignment of grain axes with respect to the ambient astrophysical, e.g., interstellar, magnetic fields. Thus measurements of the polarization degree provide a possibility of testing whether grains have superparamagnetic inclusions.
Radiative torque alignment: Essential Physical Processes
2007-07-26
We study physical processes that affect the alignment of grains subject to radiative torques (RATs). To describe the action of the RATs we use the analytical model (AMO) of RATs introduced in Paper I, namely, in Lazarian & Hoang (2007). We focus our discussion on the RAT alignment by anisotropic radiation flux in respect to magnetic field. Such an alignment does not invoke paramagnetic, i.e. Davis-Greenstein, dissipation, but, nevertheless, grains tend to align with long axes perpendicular to magnetic field. We use phase space trajectory maps to describe the alignment. When we account for thermal fluctuations within grain material, we show that for grains, which are characterized by a triaxial ellipsoid of inertia, the zero-J attractor point obtained in our earlier study develops into a low-J attractor point. Value at the latter point is the order of thermal angular momentum corresponding to the grain temperature. We show that the alignment of grains with long axes parallel to magnetic field (``wrong alignment'') reported in Paper I, for situations when the direction of radiative flux was nearly perpendicular to magnetic field, disappears in the present of thermal fluctuations. Thus all grains get aligned with their long axes perpendicular to magnetic field. We show effects that stochastic gaseous bombardment drives grains from low-J to high-J attractor points in the cases when the high-J attractor points are present, thus gase ous bombardment can increase the degree of grain alignment in respect to magnetic field. We consider the effects of torques, induced by H_2 formation and show that those change the value of angular momentum at high-J attractor point, but marginally affect low-J attractor points.
Quantitative Theory of Grain Alignment: Probing Grain Environment and Grain Composition
2009-03-09
While the problem of grain alignment was posed more than 60 years ago the quantitative model of grain alignment that can account for the observed polarization arising from aligned grains has been formulated only recently. The quantitative predictions of the radiative torque mechanism, which is currently accepted as the dominant mechanism of grain alignment, open avenues to tracing magnetic fields in various astrophysical environments, including diffuse and dense interstellar gas, molecular clouds, circumstellar environments, accretion disks, comet tails, Zodiacal dust etc. At the same time, measurements of the absolute value of polarization and its variations can, in addition, provide unique information about the dust composition and dust environment. In the review I describe the analytical model describing well radiative torques acting on irregular grains and discuss how the alignment induced by radiative torques varies in the presence of superparamagnetic inclusions and pinwheel torques, e.g. arising from the molecular hydrogen formation over grain surface. I also describe observations that can establish whether grains are superparamagnetic and whether recoils from molecular hydrogen formations are powerful enough to give rise to substantial uncompensated torques. Answering to these questions should allow for reliable modeling of astrophysical polarization with numerous important applications, from accounting for dust contrib ution in Cosmic Microwave Background polarization studies to obtaining magnetic field strength using Chandrasekhar-Fermi technique.
Quantitative Theory of Grain Alignment: Probing Grain Environment and Grain Composition
While the problem of grain alignment was posed more than 60 years ago the quantitative model of grain alignment that can account for the observed polarization arising from aligned grains has been formulated only recently. The quantitative predictions of the radiative torque mechanism, which is currently accepted as the dominant mechanism of grain alignment, open avenues to tracing magnetic fields in various astrophysical environments, including diffuse and dense interstellar gas, molecular clouds, circumstellar environments, accretion disks, comet tails, Zodiacal dust etc. At the same time, measurements of the absolute value of polarization and its variations can, in addition, provide unique information about the dust composition and dust environment. In the review I describe the analytical model describing well radiative torques acting on irregular grains and discuss how the alignment induced by radiative torques varies in the presence of superparamagnetic inclusions and pinwheel torques, e.g. arising from the H2 formation over grain surface. I also describe observations that can establish whether grains are superparamagnetic and whether recoils from H2 formations are powerful enough to give rise to substantial uncompensated torques. Answering to these questions should allow for reliable modeling of astrophysical polarization with numerous important applications, from accounting for dust contribution in Cosmic Microwave Background polarization studies to obtaining magnetic field strength using Chandrasekhar-Fermi technique.
On the Disalignment of Interstellar Grains
2006-03-11
Several mechanisms have been proposed to explain the alignment of grains with the interstellar magnetic field, including paramagnetic dissipation, radiative torques, and supersonic gas-grain streaming. These must compete with disaligning processes, including randomly directed torques arising from collisions with gas atoms. I describe a novel disalignment mechanism for grains that have a time-varying electric dipole moment and that drift across the magnetic field. Depending on the drift speed, this mechanism may yield a much shorter disalignment timescale than that associated with random gas atom impacts. For suprathermally rotating grains, the new disaligning process may be more potent for carbonaceous dust than for silicate dust. This could result in efficient alignment for silicate grains but poor alignment for carbonaceous grains.
On the Disalignment of Interstellar Grains
Several mechanisms have been proposed to explain the alignment of grains with the interstellar magnetic field, including paramagnetic dissipation, radiative torques, and supersonic gas-grain streaming. These must compete with disaligning processes, including randomly directed torques arising from collisions with gas atoms. I describe a novel disalignment mechanism for grains that have a time-varying electric dipole moment and that drift across the magnetic field. Depending on the drift speed, this mechanism may yield a much shorter disalignment timescale than that associated with random gas atom impacts. For suprathermally rotating grains, the new disaligning process may be more potent for carbonaceous dust than for silicate dust. This could result in efficient alignment for silicate grains but poor alignment for carbonaceous grains.
Disorientation of Suprathermally Rotating Grains and Grain Alignment Problem
We discuss the dynamics of dust grains subjected to uncompensated torques arising from H_2 formation. In particular, we discuss grain dynamics when a grain spins down and goes through a ``crossover''. As first pointed out by Spitzer & McGlynn (1979), the grain angular momentum before and after a crossover event are correlated, and the degree of this correlation affects the alignment of dust grains by paramagnetic dissipation. We calculate the correlation including the important effects of thermal fluctuations within the grain material. These fluctuations limit the degree to which the grain angular momentum J is coupled with the grain principal axis a_1 of maximal inertia. We show that this imperfect coupling of a_1 with J plays a critical role during crossovers and can substantially increase the efficiency of paramagnetic alignment for grains larger than 10^{-5} cm. As a result, we show that for reasonable choices of parameters, the observed alignment of $a\\gtrsim 10^{-5}$ cm grains could be produced by paramagnetic dissipation in suprathermally rotating grains, if radiative torques due to starlight were not present. We also show that the efficiency of mechanical alignment in the limit of long alignment times is not altered by the thermal fluctuations in the grain material.
The axisymmetric pulsar magnetosphere
1985-01-01
A tentative model is discussed for the steady spin-down of an aligned rapidly rotating magnetic neutron star within the framework of classical physics. The electron currents which exert the braking torque on the star flow from the polar caps out to and beyond the light-cylinder, picking up energy from the electric force and angular momentum from the magnetic torque. At high enough energies the electrons emit incoherent gamma radiation. The associated loss of angular momentum enables the currents to cross magnetic field lines and so ultimately to return to the star at lower latitudes. (author)
On the Efficiency of Grain Alignment in Dark Clouds
A quantitative analysis of grain alignment in the filamentary dark cloud L1755 in Ophiuchus is presented. We show that the observed decrease of the polarization-to-extinction ratio for the inner parts of this quiescent dark cloud can be explained as a result of the decrease of the efficiency of grain alignment. We make quantitative estimates of grain alignment efficiency for six mechanisms involving grains with either thermal or suprathermal rotation, interacting with either magnetic field or gaseous flow. We also make semiquantitative estimates of grain alignment by radiative torques. We show that in conditions typical of dark cloud interiors, all known major mechanisms of grain alignment fail. All the studied mechanisms predict polarization at least an order of magnitude below the currently detectable levels of ~1%. On the contrary, in the dark cloud environments where Av < 1, the grain alignment can be much more efficient. There the alignment of suprathermally rotating grains with superparamagnetic inclusions, and possibly also radiative torques, account for observed polarization. These results apply to L1755, which we model in detail, and probably also to B216 and other similar dark clouds. Our study suggests an explanation for the difference in results obtained through polarimetry of background starlight and polarized thermal emission from the dust itself. We conjecture that the emission polarimetry selectively reveals aligned grains in the environment far from thermodynamic equilibrium, as opposed to starlight polarization studies that probe the alignment of grains all the way along the line of sight, including the interiors of dark quiescent clouds, where no alignment is possible.
Radiative Torques: Analytical Model And Basic Properties
We attempt to get a physical insight into grain alignment processes by studying basic properties of radiative torques (RATs). For this purpose we consider a simple toy model of a helical grain that reproduces well the basic features of RATs. The model grain consists of a reflecting spheroidal body with a reflecting mirror attached at an angle to it. Being very simple, the model allows analytical description of RATs that act upon it. We show a good correspondence of RATs obtained for this model and those of irregular grains calculated by DDSCAT. Our analysis of the role of different torque components for grain alignment reveals that one of the three RAT components does not affect the alignment, but induces only for grain precession. The other two components provide a generic alignment with grain long axes perpendicular to the light radiation, if the radiation dominates the grain precession, and perpendicular to magnetic field, otherwise. The latter coincides with the famous predictions of the Davis-Greenstein process, but our model does not invoke paramagnetic relaxation. In addition, we find that a substantial part of grains subjected to RATs gets aligned with low angular momentum, which testifies, that most of the grains in diffuse interstellar medium do not rotate fast, i.e. rotate with thermal or even sub-thermal velocities. For the radiation-dominated environments, we find that the alignment can take place on the time scale much shorter than the time of gaseous damping of grain rotation.
Radiative torque alignment: essential physical processes
We study the physical processes that affect the alignment of grains subject to radiative torques (RATs). To describe the action of RATs, we use the analytical model (AMO) of RATs introduced in our previous paper. We focus our discussion on the alignment by anisotropic radiation flux with respect to the magnetic field, which defines the axis of grain Larmor precession. Such an alignment does not invoke paramagnetic dissipation (i.e. the Davis-Greenstein mechanism), but, nevertheless, grains tend to be aligned with long axes perpendicular to the magnetic field. When we account for thermal fluctuations within grains, we show that for grains that are characterized by a triaxial ellipsoid of inertia, the zero-J attractor point obtained in our earlier study develops into a low-J attractor point. The value of angular momentum at the low-J attractor point is of the order of the thermal angular momentum corresponding to the grain temperature. We show that, for situations when the direction of radiative flux is nearly perpendicular to a magnetic field, the alignment of grains with long axes parallel to the magnetic field (i.e. `wrong alignment') reported in our previous paper, disappears in the presence of thermal fluctuations. Thus, all grains are aligned with their long axes perpendicular to the magnetic field. We study the effects of stochastic gaseous bombardment and show that gaseous bombardment can drive grains from low-J to high-J attractor points in cases when high-J attractor points are present. As the alignment of grain axes with respect to angular momentum is higher for higher values of J, counter-intuitively, gaseous bombardment can increase the degree of grain alignment with respect to the magnetic field. We also study the effects of torques induced by H2 formation and show that they can change the value of angular momentum at high-J attractor points, but marginally affect the value of angular momentum at low-J attractor points. We compare the AMO results with those obtained using the direct numerical calculations of RATs acting upon irregular grains and we validate the use of the AMO for realistic situations of RAT alignment.
Electric Dipole Moments And Disalignment Of Interstellar Dust Grains
The observed polarization of starlight is due to the alignment of interstellar dust grains with the Galactic magnetic field. The degree to which the grains are aligned is dependent on both alignment and disalignment mechanisms. For decades, disalignment was presumed to be principally due to collisions with gas atoms, with each collision imparting a random angular impulse to the grain. Recently, a new candidate disalignment mechanism for a grain with a changing electric dipole moment, drifting across a magnetic field, was proposed. Here we investigate this mechanism, modeling the effects of individual charging events on the dipole magnitude and orientation. We simulate these effects for amorphous silicate grains ? 0.1 m in size and of different levels of electrical conductivity, and present quantitative disalignment time estimates for each grain type. Our results indicate disalignment timescales that are shorter than those for radiative torque alignment, except for grains with superparamagnetic inclusions.
Radiative Alignment Of Dust Grains And Atoms: Tracing Magnetic Fields
Magnetic field plays crucial roles in many astrophysical processes (e.g., star formation, heat conduction and cosmic rays transport). One reliable way to study the topology of the magnetic field is based on polarized radiation of absorption and emission by aligned dust and atoms. We show that dust grains can be efficiently aligned by radiative torques (RATs) resulted from anisotropic radiation. Using an analytical model (AMO) for RATs, we show that grains tend to align with longer axes perpendicular to magnetic field, which corresponds to the Davis-Greenstein mechanism, but our model does not involve paramagnetic relaxation. We calculate the polarization arising from dust grains aligned with respect to a magnetic field, as a function of visual extinction for Taurus cloud, and obtain a good agreement with observation data. The alignment of atoms provides a new technique to study magnetic fields. This technique is based on the ability of atoms with fine and hyperfine structure to be aligned in their ground or metastable state by anisotropic radiation. The alignment induces polarization of both scattered and absorbed radiation. As the aligned atoms precess in magnetic field, the field modifies the observed polarization. For instance, absorption lines get polarized with the polarization direction that reveals the direction of magnetic field. We show that the atomic alignment can provide unique information about the 3D magnetic field topology that is not available with any other technique. The expected degree of polarization may exceed 30\\% for a favorable geometry of observations and therefore be easily detectable.
Electric dipole moments and disalignment of interstellar dust grains
2009-01-01
ABSTRACT The degree to which interstellar grains align with respect to the interstellar magnetic field depends on disaligning as well as aligning mechanisms. For decades, it was assumed that disalignment was due primarily to the random angular impulses a grain receives when colliding with gas-phase atoms. Recently, a new disalignment mechanism has been considered, which may be very potent for a grain that has a time-varying electric dipole moment and drifts across the magnetic field. We provide quantitative estimates of the disalignment times for silicate grains with size Formula Not Shown . These appear to be shorter than the time-scale for alignment by radiative torques, unless the grains contain superparamagnetic inclusions.
Electric dipole moments and disalignment of interstellar dust grains
2009-05-14
The degree to which interstellar grains align with respect to the interstellar magnetic field depends on disaligning as well as aligning mechanisms. For decades, it was assumed that disalignment was due primarily to the random angular impulses a grain receives when colliding with gas-phase atoms. Recently, a new disalignment mechanism has been considered, which may be very potent for a grain that has a time-varying electric dipole moment and drifts across the magnetic field. We provide quantitative estimates of the disalignment times for silicate grains with size > approximately 0.1 micron. These appear to be shorter than the time-scale for alignment by radiative torques, unless the grains contain superparamagnetic inclusions.
Electric dipole moments and disalignment of interstellar dust grains
The degree to which interstellar grains align with respect to the interstellar magnetic field depends on disaligning as well as aligning mechanisms. For decades, it was assumed that disalignment was due primarily to the random angular impulses a grain receives when colliding with gas-phase atoms. Recently, a new disalignment mechanism has been considered, which may be very potent for a grain that has a time-varying electric dipole moment and drifts across the magnetic field. We provide quantitative estimates of the disalignment times for silicate grains with size >~0.1?m. These appear to be shorter than the time-scale for alignment by radiative torques, unless the grains contain superparamagnetic inclusions.
Orientation of optically trapped nonspherical birefringent particles
2006-02-23
While the alignment and rotation of microparticles in optical traps have received increased attention recently, one of the earliest examples has been almost totally neglected the alignment of particles relative to the beam axis, as opposed to about the beam axis. However, since the alignment torques determine how particles align in a trap, they are directly relevant to practical applications. Lysozyme crystals are an ideal model system to study factors determining the orientation of nonspherical birefringent particles in a trap. Both their size and their aspect ratio can be controlled by the growth parameters, and their regular shape makes computational modeling feasible. We show that both external shape and internal birefringence anisotropy contribute to the alignment torque. Three-dimensionally trapped elongated objects either align with their long axis parallel or perpendicular to the beam axis depending on their size. The shape-dependent torque can exceed the torque due to birefringence, and can align negative uniaxial particles with their optic axis parallel to the electric field, allowing an application of optical torque about the beam axis.
Orientation of Optically Trapped Nonspherical Birefringent Particles
2006-01-01
While the alignment and rotation of microparticles in optical traps have received increased attention recently, one of the earliest examples has been almost totally neglected the alignment of particles relative to the beam axis, as opposed to about the beam axis. However, since the alignment torques determine how particles align in a trap, they are directly relevant to practical applications. Lysozyme crystals are an ideal model system to study factors determining the orientation of nonspherical birefringent particles in a trap. Both their size and their aspect ratio can be controlled by the growth parameters, and their regular shape makes computational modeling feasible. We show that both external shape and internal birefringence anisotropy contribute to the alignment torque. Three-dimensionally trapped elongated objects either align with their long axis parallel or perpendicular to the beam axis depending on their size. The shape-dependent torque can exceed the torque due to birefringence, and can align negative uniaxial particles with their optic axis parallel to the electric field, allowing an application of optical torque about the beam axis. Publisher: American Physical Society through the American Institute of Physics Contributor: Gary S. Grest Coverage: 2006-02-01T00:00:00Z
Grain Alignment in OMC1 as Deduced from Observed Large Circular Polarization
2009-03-16
The properties of polarization in scattered light by aligned ellipsoidal grains are investigated with the Fredholm integral equation method (FIM) and the T-matrix method (Tmat), and the results are applied to the observed circular polarization in OMC1. We assume that the grains are composed of silicates and ellipsoidal (oblate, prolate, or tri-axial ellipsoid) in shape with a typical axial ratio of 2:1. The angular dependence of circular polarization p_c on directions of incident and scattered light is investigated with spherical harmonics and associated Legendre polynomials. The degree of circular polarization p_c also depends on the Rayleigh reduction factor R which is a measure of imperfect alignment. We find that p_c is approximately proportional to R for grains with |m|x_{eq} 0.5. Such a strong alignment cannot be explained by the Davis-Greenstein mechanism; we prefer instead an alternative mechanism driven by radiative torques. If the grains are mixed with silicates and ice, the degree of circular polarization p_c decreases in the 3 micron ice f eature, while that of linear polarization increases. This wavelength dependence is different from that predicted in a process of dichroic extinction.
Improving the sensitivity of a torsion pendulum by using an optical spring method
2009-01-01
We present a scheme aiming at improving the sensitivity of a torsion pendulum by means of radiation-pressure-induced optical spring. Two partial-reflective mirrors are installed on the opposite sides of a torsion pendulum, and one high-reflective mirror is mounted at the end of the torsion beam so that two identical Fabry-Perot cavities can be formed and aligned in series. Due to the antisymmetric radiation pressures acting on the opposite sides of the torsion beam, a negative restoring coefficient can be generated within a certain dynamic range, such that both the resultant torsional rigidity and the resonant frequency of the torsion pendulum are reduced, and the minimum detectable response torque in high-frequency region can be reduced accordingly
Casimir torque between corrugated metallic plates
2008-04-25
We consider two parallel corrugated plates and show that a Casimir torque arises when the corrugation directions are not aligned. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We compare our results with the proximity force approximation, which overestimates the torque by a factor 2 when taking the conditions that optimize the effect. We argue that the Casimir torque could be measured for separation distances as large as 1 {mu}m.
Casimir torque between corrugated metallic plates
2008-01-01
We consider two parallel corrugated plates and show that a Casimir torque arises when the corrugation directions are not aligned. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We compare our results with the proximity force approximation, which overestimates the torque by a factor 2 when taking the conditions that optimize the effect. We argue that the Casimir torque could be measured for separation distances as large as 1 mum
Casimir torque between corrugated metallic plates
2007-10-31
We consider two parallel corrugated plates and show that a Casimir torque arises when the corrugation directions are not aligned. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We compare our results with the proximity force approximation, which overestimates the torque by a factor 2 when taking the conditions that optimize the effect. We argue that the Casimir torque could be measured for separation distances as large as 1 $\\mu{\\rm m}.$
Rotational Electrophoresis of Striped Metallic Microrods
2005-11-28
Analytical models are developed for the translation and rotation of metallic rods in a uniform electric field. The limits of thin and thick electric double layers are considered. These models include the effect of stripes of different metals along the length of the particle. Modeling results are compared to experimental measurements for metallic rods. Experiments demonstrate the increased alignment of particles with increasing field strength and the increase in degree of alignment of thin versus thick electric double layers. The metal rods polarize in the applied field and align parallel to its direction due to torques on the polarized charge. The torque due to polarization has a second order dependence on the electric field strength. The particles are also shown to have an additional alignment torque component due to non-uniform densities along their length. The orientation distributions of dilute suspensions of particles are also shown to agree well with results predicted by a rotational convective-diffusion equation.
Radiation effects in polyolefins below the gel point as measured by torque rheometry
1981-01-01
Torque rheometry is used to obtain information about radiation effects on polymers (crosslinking, degradation) below the gel point. It is shown that rheometric melt viscosity measurements at different shear rates are related changes in the relaxation spectrum. In particular there is a significant radiation effect on low shear rate viscosities but a negligible effect on high shear rate viscosities. The fact that the shear rate in the torque rheometer oscillates about a mean value is utilized to relate torque amplitude measurements to entanglements at zero dose and to crosslink density at absorbed doses below or close to the gel point.
Drag-Gravity torques on galaxies in clusters: radial small-scale alignment effects
2008-10-13
We calculate the torque on galaxies in clusters due to gravity and to dynamical friction forces in order to study the possible origin of small-scale alignment effects as the result of interactions with their environment. The equation of motion for the position angle of a galaxy is derived by using a ple model. We find that weak radial alignment effects can be produced by this mechanism involving only the most massive galaxies. We also introduce a dependence on the cluster eccentricity to our equations in order to explore the alignment of galaxies with the cluster's major axis. We find that in the inner regions of high eccentricity clusters, alignments of massive galaxies with the cluster's major axis dominate over the radial ones. This mechanism could account for the observed alignment effects of the most massive galaxies with the major axis of their host cluster. Our results suggest that dynamical friction is a viable generator of alignment only for the most massive cluster galaxies. For the observed alignments of normal galaxies a primordial origin has to be explored.
2008-08-05
I review the theory of angular momentum acquisition of galaxies by tidal torquing, the resulting angular momentum distribution, the angular momentum correlation function and discuss the implications of angular momentum alignments on weak lensing measurements: Starting from linear models for tidal torquing I summarise perturbative approaches and the results from n-body simulations of cosmic structure formation. Then I continue to discuss the validity of decompositions of the tidal shear and inertia fields, the effects of angular momentum biasing, the applicability of parameterised angular momentum correlation models and the consequences of angular momentum correlations for shape alignments. I compile the result of observations of shape alignments in recent galaxy surveys as well as in n-body simulations. Finally, I review the contamination of weak lensing surveys by spin-induced shape alignments and methods for suppressing this contamination.
Environmental Qualification of an Actuator Torque Switch
2006-01-01
Environmental qualification testing was performed on a modified Limitorque torque switch for the torque switch safety functions in the Limitorque type SMB actuators located inside and outside containment in a nuclear power plant. The torque switch specimen was installed in a Limitorque SMB-1 electric actuator mounted on an 8'' Velan gate valve and operated with a customized programmable logic controller to allow normal torque switch behaviour to be observed. The present paper describes the qualification testing performed. The modified torque switch was aged to a 30-year service life at the normal service conditions for both inside and outside containment. Aging included radiation, thermal and cycle aging. A seismic test and then a combined Loss of Coolant Accident (LOCA) and Main Steam Line Break (MSLB) steam accident simulation were followed. After each stage of aging, ...
Portable means for testing automatic transmissions
1989-02-21
A portable machine is described for testing a rebuilt automatic transmission having a bell housing and a torque converter assembly prior to installation on the vehicle, the machine comprising: a saddle having a cross bar and a pair of brackets, one adjacent each end, each of the brackets having a foot portion adapted to seat against the forward end surface of the transmission's bell housing for receiving a fastener element for detachably securing it to the bell housing; a journal secured to the cross bar and a shaft rotatably mounted in the journal; the axis of the shaft being aligned with the axis of the torque converter; first means for separately adjusting the spacing between the brackets and second means for adjusting the position of the journal lengthwise of the bar, third means permitting the selection of different ones of the openings in the bell housing to effect alignment of the axes of the shaft and torque converter; the opposite end of the shaft being adapted to be secured to a portable source of variable speed rotary motion.
Zero secular torque on asteroids from impinging solar photons in the YORP effect: A simple proof
2010-01-01
YORP torques, where "YORP" stands for "Yarokovsky-O'Keefe-Radzievskii-Paddack," arise mainly from sunlight reflected off a Solar System object and the infrared radiation emitted by it. We show here, through the most elementary demonstration that we can devise, that secular torques from impinging solar photons are generally negligible and thus cause little secular evolution of an asteroid's obliquity or spin rate.
2010-04-19
The decay of non-topological electroweak strings formed during the electroweak phase transition in the early universe may leave an observable imprint in the universe today. Such strings can naturally seed primordial magnetic fields. Protogalaxies then tend to form with their axis of rotation parallel to the external magnetic field, and moreover, the external magnetic field produces torque which forces the galaxy axis to align with the magnetic field, even if the two axis were not aligned initially. This can explain an (observed, but as of yet unexplained) alignment of the quasars' polarization vectors. We demonstrate that the shape of a magnetic field left over from two looped electroweak strings can explain the non-trivial alignment of quasar polarization vectors and make predictions for future observations.
Aligned sintered compacts of RBa2Cu3O(7-x) (R = Dy, Er, Eu, Gd, Ho, Y)
1988-01-01
X-ray, microscopic, and magnetic measurements have been obtained in order to investigate sintered compacts of magnetically aligned single-crystal particles. It is found that magnetic fields and pressure can yield substantial alignment of RBa2Cu3O(7-x) grains, even at sintering densities. The c-axis is shown to preferentially align parallel to the field for R = Dy, Ho, and Y, but to be normal to the field for R = Er, Eu, and Gd. Although strongly anisotropic hysteresis curves are obtained, the bulk critical current density remains low. It is suggested that the final alignment may be determined by the morphology and final packing of the grains, and not by the magnetic torque alone. 11 references
Type I Migration in Radiatively Efficient Discs
2010-10-04
We study Type I migration of a planet in a radiatively efficient disk using global two dimensional hydrodynamic simulations. The large positive corotation torque is exerted on a planet by an adiabatic disk at early times when the disk has the steep negative entropy gradient. The gas on the horseshoe orbit of the planet is compressed adiabatically during the change of the orbit from the slow orbit to the fast orbit, increasing its density and exerting the positive torque on the planet. The planet would migrate outward in the adiabatic disk before saturation sets in. We further study the effect of energy dissipation by radiation on Type I migration of the planet. The corotation torque decreases when the energy dissipates effectively because the density of the gas on the horseshoe orbit does not increase by the compression compared with the gas of the adiabatic disk. The total torque is mainly determined by the negative Lindblad torque and becomes negative. The planet migrates inward toward the central star in the radiatively efficient disk. The migration velocity is dependent on the radiative efficiency and greatly reduced if the radiative cooling works inefficiently.
Torque magnetometry on the electron-doped high-temperature superconductor Pr0.88LaCe0.12CuO4-?
We have used cantilever and extraction magnetometry to measure magnetization in optimally doped n-type high-temperature superconductors Pr0.88LaCe0.12CuO4-? (Tc = 24K) for magnetic field aligned close to the c-axis, over the temperature range (4K to 300K). We observed a distinct irreversibility line below which the torque magnetization is irreversible. Also, we observed a complex torque behavior where the sign of normal state torque response with field (d?/dH) is the same as that of the superconducting counterpart. From dc magnetization experiments, we conclude that superconducting torque signal arises primarily from out-of-plane diamagnetism, whereas in-plane paramagnetism dominates for the normal state.
Measurement of orbital angular momentum in optical tweezers
2004-01-01
Several techniques have been proposed and used for the rotation or alignment of microparticles in optical tweezers. In every case the optical torque results from the exchange of angular momentum between the beam and the particle, and, in principle, can be measured by purely optical means. Measurement of this torque could be useful for quantitative measurements in biological systems and is required to measure properties such as viscosity of liquids in microlitre (or less) volumes. Although elongated particles will align with the plane of polarisation, the torque efficiency is low, typically about 0.05 hbar per photon. The use of a beam with an elongated focal spot can increase this torque by a factor of 10-20 times, due to the transfer of orbital angular momentum. We report measurements of the orbital component using an analysing (Laguerre-Gauss) hologram. As a proof of principle experiment, an elliptical beam scattered off a glass rod was simulated on a macroscopic scale. The torque was found to be as much as 0.8 hbar per photon. Microscopic elongated objects have been aligned and rotated in optical tweezers and we plan to make measurements of the torques involved. ©2004 COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. Publisher: SPIE - International Society for Optical Engineering Contributor: Kishan Dholakia; Gabriel C. Spalding Coverage: 2004-01-01T00:00:00Z
2010-01-01
A number of synchronous moons are thought to harbor water oceans beneath their outer ice shells. A subsurface ocean frictionally decouples the shell from the interior. This has led to proposals that a weak tidal or atmospheric torque might cause the shell to rotate differentially with respect to the synchronously rotating interior. Applications along these lines have been made to Europa and Titan. However, the shell is coupled to the ocean by an elastic torque. As a result of centrifugal and tidal forces, the ocean would assume an ellipsoidal shape with its long axis aligned toward the parent planet. Any displacement of the shell away from its equilibrium position would induce strains thereby increasing its elastic energy and giving rise to an elastic restoring torque. In the investigation...
Paramagnetic grain alignment associated with internal friction and the polarization efficiency
1986-01-01
Alignment mechanisms associated with paramagnetic relaxation are re-investigated for spheroidal dielectric grains. By taking into account the tight coupling of grain axis with angular momentum due to effective dissipation of rotational energy by internal friction, the degree of alignment by paramagnetic torque will be distinctly improved as compared with that by the classical Davis-Greenstein process. Incorporated with new results by Rogers and Martin on the polarizing effectiveness of spheroidal grains, the ''improved'' DG theory is used to calculate the polarization efficiency due to incompletely aligned grains. It is found that oblate grains with axial ratio of 1/2 or less and size of 0.1 mum can explain the observed polarization if the magnetic field strength is approx = 3 muG in the general interstellar medium where ...
Compensating for Torsion Windup in Steerable Needles
2008-10-19
Full Text Available.Long, flexible, bevel-tip needles curve during insertion into tissue, and rotations of the needle base reorient the tip to steer subsequent insertions. Friction between the tissue and the needle shaft, however, can cause a severe discrepancy between the needle base and tip angles. In this paper, I demonstrate an algorithm to properly align the entire length of the needle using torque measured at the base. My algorithm uses several intermediate base rotations to align the orientation of points along the shaft with the desired angle, with minimal remaining torque exerted by the base. I performed an experimental validation with four angle sensors attached to the needle throughout the tissue. My compensation algorithm decreased the lag throughout the needle by up to 88%.
Sporadically Torqued Accretion Disks Around Black Holes
2005-01-21
The assumption that black hole accretion disks possess an untorqued inner boundary, the so-called zero torque boundary condition, has been employed by models of black hole disks for many years. However, recent theoretical and observational work suggests that magnetic forces may appreciably torque the inner disk. This raises the question of the effect that a time-changing magnetic torque may have on the evolution of such a disk. In particular, we explore the suggestion that the ``Deep Minimum State'' of the Seyfert galaxy MCG--6-30-15 can be identified as a sporadic inner disk torquing event. This suggestion is motivated by detailed analyses of changes in the profile of the broad fluorescence iron line in XMM-Newton spectra. We find that the response of such a disk to a torquing event has two phases; an initial damming of the accretion flow together with a partial draining of the disk interior to the torque location, followed by a replenishment of the inner disk as the system achieves a new (torqued) steady-state. If the Deep Minimum State of MCG--6-30-15 is indeed due to a sporadic torquing event, we show that the fraction of the dissipated energy going into X-rays must be smaller in the torqued state. We propose one such scenario in which Compton cooling of the disk corona by ``returning radiation'' accompanying a central-torquing event suppresses the 0.5-10 keV X-ray flux coming from all but the innermost regions of the disk.
Magnetic Determination of Hc2 under Accurate Alignment in (TMTSF)2ClO4
Cantilever magnetometry has been used to measure the upper critical magnetic field Hc2 of the quasi one-dimensional molecular organic superconductor (TMTSF)2ClO4. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, Hc2 at low temperature is shown to reach 5T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large Hc2 in this system and provide support for spin triplet pairing in this unconventional superconductor.
Alignment and commissionig of the APS beamline front ends
Fifteen out of forty phase-one beamline front ends have been installed in the storage-ring tunnel at the 7-GeV Advanced Photon Source (APS). For the front-end installation, a four-step alignment process was designed and consists of (1) prealigning the front-end components with support tables in the preassembly area, (2) installing the components with tables in the storage-ring tunnel and aligning relative to the APS global telescope survey network, (3) confirming the alignment using a tooling laser alignment system, and (4) performing adjustments with the synchrotron-radiation beam during commissioning. The laser alignment system and the prealignment data- base have been of great importance for the expedient maintenance of front-end components. These tools are very important to a large synchrotron radiation facility such as the APS, since they make a quick alignment setup possible and minimize alignment time inside the tunnel. This paper will present the four-step alignment process, the laser alignment system, and discuss the alignment confirmation results. 6 refs., 5 figs.
Alignment and commissionig of the APS beamline front ends
1995-12-31
Fifteen out of forty phase-one beamline front ends have been installed in the storage-ring tunnel at the 7-GeV Advanced Photon Source (APS). For the front-end installation, a four-step alignment process was designed and consists of (1) prealigning the front-end components with support tables in the preassembly area, (2) installing the components with tables in the storage-ring tunnel and aligning relative to the APS global telescope survey network, (3) confirming the alignment using a tooling laser alignment system, and (4) performing adjustments with the synchrotron-radiation beam during commissioning. The laser alignment system and the prealignment data- base have been of great importance for the expedient maintenance of front-end components. These tools are very important to a large synchrotron radiation facility such as the APS, since they make a quick alignment setup possible and minimize alignment time inside the tunnel. This paper will present the four-step alignment process, the laser alignment system, and discuss the alignment confirmation results. 6 refs., 5 figs.
Vacuum Electromagnetic Counterparts of Binary Black-Hole Mergers
2009-12-14
As one step towards a systematic modeling of the electromagnetic (EM) emission from an inspiralling black hole binary we consider a simple scenario in which the binary moves in a uniform magnetic field anchored to a distant circumbinary disc. We study this system by solving the Einstein-Maxwell equations in which the EM fields are chosen with astrophysically consistent strengths. We consider binaries with spins aligned or anti-aligned with the orbital angular momentum and study the dependence of gravitational and EM signals with these spin configurations. Overall we find that the EM radiation in the lowest l=2, m=2 multipole accurately reflects the gravitational one, with identical phase evolutions and amplitudes that differ only by a scaling factor. We also compute the efficiency of the energy emission in EM waves and find that it is given by E^rad_EM/M ~ 10^-15 (M/10^8 M_Sun)^2 (B/10^4 G)^2, hence 13 orders of magnitude smaller than the gravitational energy for realistic magnetic fields. The corresponding luminosity is much smaller than the accretion luminosity if the system is accreting at near the Eddington rate. Most importantly, this EM emission is at frequencies of 10^-4 (10^8 M_Sun/M) Hz, well outside those accessible to astronomical radio observations. As a result, it is unlikely that the EM emission discussed here can be detected directly and simultaneously with the gravitational-wave one. However, indirect processes, driven by changes in the EM fields behavior could yield observable events. In particular if the accretion rate of the circumbinary disc is small and sufficiently stable over the timescale of the final inspiral, then the EM emission may be observable indirectly as it will alter the accretion rate through the magnetic torques exerted by the distorted magnetic field lines.
The SLS storage ring support and alignment systems
Storage rings of third generation synchrotron radiation facilities pose severe challenges for lowering the beam emittances and increasing the lifetimes, requiring thus increasing positioning and alignment precisions that must be preserved over long time spans. This work describes the SLS storage ring mechanical support, alignment and disturbances compensation systems that allow to meet these requirements. In particular, their design, the tests done on the respective prototypes and the applicability of the developed arrangement to beam-based alignment are addressed.
1989-01-05
When sunlight is struck on the 2-ton class communication satellite which is being planned for future satellite communication, the satellite will be affected by the torque due to solar radiation pressure. Since this torque has great influence on the antenna requiring a very accurate directivity, adequate consideration is needed in the stage of design. The intensity of the solar pressure torque and the causes of torque generation on a 2-ton class, three-axis stable communication setellite with two asymmetrical large antennas were studied using a computation program designed with consideration on the shut-off of sunlight with a structure. Also, the rolling-plane and yawing-plane components of the periodic torque generated because of complex structures installed on the satellite were determined. In addition, a method for determining the bias momentum needed to achieve the yaw-axis attitude accuracy required for multibeam satellite communication was studied using a pure bias momentum attitude control system. 14 refs., 7 figs., 2 tabs.
Method of making a parabolic-cylindrical concentrator and device for its implementation
1982-01-01
A method is proposed for making a parabolic-cylindrical concentrator by elastic deformation of the reflecting plate through application of forces and torque to its two opposite edges with subsequent fixing of the spatial arrangement of the plate. In order to improve concentration of radiation in the focal plane with manufacture of the fragmented concentrator, unequal torques are applied to the plate.
Analysis and design modification of an airborne mirror alignment system. Master's thesis
1978-03-01
This study deals with an electronic control system modification to solve a torque limitation problem in the Airborne Dynamic Alignment System aboard the Airborne Laser Lab. This control system is reduced in complexity and modeled in the frequency and state space domains. Closed loop system response over a desired frequency range is obtained from the frequency domain model. Stability data is calculated through eigenvalue analysis of the state space model. A low pass filter is introduced to decrease the demand on the torque saturated motor. The main result of this modification is that the filter does not appreciably alter the closed loop response. This is due to the fact that the cutoff frequency of the filter must be extremely high to keep the modified system stable. It is concluded that the complimentary filter does not solve the torque saturation problem. A recommendation is made that further analysis be concentrated in the time domain through modern state space techniques and the design approach to an optimal controller is presented.
Orientation of biological cells using plane-polarized Gaussian beam optical tweezers
2003-08-28
Optical tweezers are widely used for the manipulation of cells and their internal structures. However, the degree of manipulation possible is limited by poor control over the orientation of trapped cells. We show that it is possible to controllably align or rotate disc shaped cells - chloroplasts of Spinacia oleracea - in a plane polarised Gaussian beam trap, using optical torques resulting predominantly from circular polarisation induced in the transmitted beam by the non-spherical shape of the cells.
Starquake-induced Magnetic Field and Torque Evolution in Neutron Stars
The persistent increases in spin-down rate offsets seen to accompany glitches in the Crab and other pulsars suggest increases in the spin-down torque. We interpret these offsets as due to starquakes occurring as the star spins down and the rigid crust becomes less oblate. We study the evolution of strain in the crust, the initiation of starquakes, and possible consequences for magnetic field and torque evolution. Crust cracking occurs as equatorial material shears under the compressive forces arising from the star's decreasing circumference, and matter moves to higher latitudes along a fault inclined to the equator. A starquake is most likely to originate near one of the two points on the rotational equator farthest from the magnetic poles. The material breaks along a fault approximately aligned with the magnetic poles. We suggest that the observed offsets come about when a starquake perturbs the star's mass distribution, producing a misalignment of the angular momentum and spin axes. Subsequently, damped precession to a new rotational state increases the angle alpha between the rotation and magnetic axes. The resulting increase in external torque appears as a permanent increase in the spin-down rate. Repeated starquakes would continue to increase alpha, making the pulsar more of an orthogonal rotator.
Dynamics of the Sharp Edges of Broad Planetary Rings
2009-04-07
(Abridged) The following describes a model of a broad planetary ring whose sharp edge is confined by a satellite's m^th Lindblad resonance (LR). This model uses a streamline formalism to calculate the ring's internal forces, namely, ring gravity, pressure, viscosity, as well as a hypothetical drag force. The model calculates the streamlines' forced orbit elements and surface density throughout the perturbed ring. The model is then applied to the outer edge of Saturn's B ring, which is maintained by an m=2 inner LR with the satellite Mimas. Ring models are used to illustrate how a ring's perturbed state depends on the ring's physical properties: surface density, viscosity, dispersion velocity, and the hypothetical drag force. A comparison of models to the observed outer B ring suggests that the ring's surface density there is between 10 and 280 gm/cm^2. The ring's edge also indicates where the viscous torque counterbalances the perturbing satellite's gravitational torque on the ring. But an examination of seemingly conventional viscous B ring models shows that they all fail to balance these torques at the ring's edge. This is due ring self-gravity and the fact that a viscous ring tends to be nearly peri-aligned with the satellite, which reduces the satellite's torque on the ring and makes the ring's edge more difficult to maintain. Nonetheless, the following shows that a torque balance can still be achieved in a viscous B ring, but only in an extreme case where the ratio of the ring's bulk/shear viscosities satisfy ~10^4. However, if the dissipation of the ring's forced motions is instead dominated by a weak drag force, then the satellite can exert a much stronger torque that can counterbalance the ring's viscous torque.
Temperature dependences were measured between T=223 K and 341 K on magnetic alignment processes of micron-sized talc crystals dispersed in liquid medium. The field intensity required for achieving alignment decreased with temperature, because of an increase in paramagnetic anisotropy and a decrease in the thermal rotational energy. The diamagnetic anisotropies estimated at infinite temperature were -3.3 10-4 and -1.2 10-4 emu/mol for two different kinds of talc samples. The order of magnitude of diamagnetic anisotropy as well as the direction of the magnetically stable axis of a material can be estimated from the measurement, even if the material contains paramagnetic ions and is too small for torque measurements.
We use two simulations performed within the Constrained Local UniversE Simulation (CLUES) project to study both the shape and radial alignment of (the dark matter component of) subhaloes; one of the simulations is a dark matter only model while the other run includes all the relevant gas physics and star formation recipes. We find that the involvement of gas physics does not have a statistically significant effect on either property - at least not for the most massive subhaloes considered in this study. However, we observe in both simulations including and excluding gas dynamics a (pronounced) evolution of the dark matter shapes of subhaloes as well as of the radial alignment signal since infall time. Further, this evolution is different when positioned in the central and outer regions of the host halo today; while subhaloes tend to become more aspherical in the central 50 per cent of their host's virial radius, the radial alignment weakens in the central regime while strengthening in the outer parts. We confirm that this is due to tidal torquing and the fact that subhaloes at pericentre move too fast for the alignment signal to respond.
Disorientation of interstellar grains in suprathermal rotation
1979-01-01
As pointed out by Purcell, interstellar grains are subject to an unbalanced torque which produces spin-up to high angular speeds. Magnetic relaxation then aligns the grain rotation with B during the time t/sub r/. However, changes in the grain surface are likely to change these systematic torques, occasionally reversing them. The rotational velocity then decreases to a minimum at ''crossover'' and then increases again. The mean interval between crossovers is uncertain but may be much less than the value of t/sub r/ resulting from paramagnetic relaxation. If so, and if the grains are disoriented during crossover, paramagnetic relaxation then falls short by about an order of magnitude in accounting for the polarization of starlight.This paper computes the cumulative deflection angle, chi/sub T/, of the grain's angular momentum, J, during crossover, using both a simple ...
Apparatus for measuring rotational velocity of a shaft
1984-12-18
An apparatus is disclosed for mounting a rotational signal transducer on a rotary shaft where the transducer generates a signal proportional to the shaft's rotational velocity. The apparatus includes a gear mounted for rotation with the shaft. A support platform is rotatably secured to the shaft by a roller bearing. The roller bearing permits the shaft and platform to rotate relative to one another but prevents relative axial motion between the shaft and platform. A transducer is mounted on the platform and operably aligned over the gear and generates a signal as gear teeth pass the transducer. A torque rod pivotally fixed to both the platform and a stationary support restrains the platform from rotating with the shaft. The pivotal connections of the torque rod permit the platform to move axially with the shaft.
2009-12-08
We provide a set of general tools for studying the alignments of dark matter halos and galaxies with respect to the large scale structure. The statistics of the positioning of these objects is represented by a Probability Distribution Function (PDF) of their Euler angles. The PDF corresponding to halos located in the shells of the cosmic voids is inferred from previous results. This PDF is used to show how to recover the outcomes found for the alignments of the axes of these halos in simulations. We also explore the orientation of the angular momentum of the halos, both with respect to the halo axes and with respect to the large scale structure. We present an expression which describes well numerical results for the alignment of the angular momentum of the halo with respect to the halo axes for randomly chosen halos. We also propose a model that relates the orientation of the angular momentum with the halos axes accounting for the orientation of the halo axes with the large scale structure. This model is shown to recover accurately the observed PDF of the halo angular momentum with respect to the void radial direction. In addition, we give an expression for determining the degradation of the angular momentum intrinsic alignment when observational errors are accounted. This expression is also used to determine the departure of the observed value of the alignment from the initial expectation (as provided by the tidal torque theor y) due to the rotation of the angular momentum of the halo with respect to the initial torque. For voids, we find that the strength of the alignment is reduced to half the original value. We discuss how to adapt the void results to other cosmic large scale structures (i.e. filaments, walls, etc).
Solar sensing arrangement for use in a uniaxis solar collector tracking system
1985-05-07
A sensor for use in aligning a solar collector system wherein the sensor includes a radiation detector providing signals responsive to impinging radiation and means for focusing the radiation into an astigmatic image positioned on the detector when the system is misaligned.
Alignment and shields in the M2 primary proton beamline at J-PARC
In the J-PARC project, the 3-GeV 333-?A proton beam will be transported from the 3-GeV ring to the neutron source located in the Materials and Life Science Facility. In the M2 tunnel, where the muon target is situated, the radiation level is expected to reach up to 20 MGy/y. Therefore, beamline components will need to be installed and aligned remotely from the maintenance area, which is located 4 m above the floor level. We have adopted alignment plates with pivots to position each component precisely in the beamline. Then, by using the surrounding iron shields as guides, a beamline component can be smoothly inserted and precisely aligned onto its alignment plate. In this paper, the alignment strategy used in the M2 tunnel is described.
Patient alignment device for cobalt-60 radiation therapy
1987-11-01
A technique has been described for fabrication of a radiation therapy stent that can help to stabilize the head when adjustable alignment devices are used to position a patient during radiation therapy. The technique can save time for the radiotherapist, enhance accuracy in treatment, increase patient comfort, and save the dentist time in stent fabrication.
Spin induced galaxy alignments and their implications for weak lensing measurements
2000-09-04
Large scale correlations in the orientations of galaxies can result from alignments in their angular momentum vectors. These alignments arise from the tidal torques exerted on neighboring proto-galaxies by the smoothly varying shear field. We compute the predicted amplitude of such ellipticity correlations using the Zel'dovich approximation for a realistic distribution of galaxy shapes. Weak gravitational lensing can also induce ellipticity correlations since the images of neighboring galaxies will be distorted coherently. On comparing these two effects that induce shape correlations, we find that for current weak lensing surveys with a median redshift of z_m = 1, the intrinsic signal is of order 1 - 10 percent of the measured signal. However, for shallower surveys with z_m < 0.3, the intrinsic correlations dominate over the lensing signal. The distortions induced by lensing are curl-free, whereas those resulting from intrinsic alignments are not. This difference can be used to disentangle these two sources of ellipticity correlations.
Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
2006-01-09
We present 2D MHD simulations of the radiatively driven outflow from a rotating hot star with a dipole magnetic field aligned with the star's rotation axis. We focus primarily on a model with moderately rapid rotation (half the critical value), and also a large magnetic confinement parameter, $\\eta_{\\ast} \\equiv B_{\\ast}^2 R_{\\ast}^{2} / \\dot{M} V_{\\infty} = 600$. The magnetic field channels and torques the wind outflow into an equatorial, rigidly rotating disk extending from near the Kepler corotation radius outwards. Even with fine-tuning at lower magnetic confinement, none of the MHD models produce a stable Keplerian disk. Instead, material below the Kepler radius falls back on to the stellar surface, while the strong centrifugal force on material beyond the corotation escape radius stretches the magnetic loops outwards, leading to episodic breakout of mass when the field reconnects. The associated dissipation of magnetic energy heats material to temperatures of nearly $10^{8}$K, high enough to emit hard (several keV) X-rays. Such \\emph{centrifugal mass ejection} represents a novel mechanism for driving magnetic reconnection, and seems a very promising basis for modeling X-ray flares recently observed in rotating magnetic Bp stars like $\\sigma$ Ori E.
Alignment of the ATLAS Inner Detector Tracking System
Introduction The ATLAS Inner Detector (ID) consists of two silicon subsystems, the Pixel detector and the Semiconductor Tracker (SCT), complemented by the Transition Radiation Tracker (TRT) composed of drift tubes. After the assembly of the detector, the position of the individual modules is known with much worse accuracy than their intrinsic resolution. Therefore a track-based alignment procedure has to be applied. The baseline goal of the alignment is to determine the position and orientation of the modules with such precision that the track parameters' determination is not worsened by more than 20% with respect to that expected from the perfectly aligned detector. This is crucial for efficient track reconstruction and precise momentum measurement and vertex reconstruction.
Nematic elastomers with aligned carbon nanotubes: new electromechanical actuators
2003-09-09
We demonstrate, for the first time, the large electromechanical response in nematic liquid crystalline elastomers filled with a very low (~0.01%) concentration of carbon nanotubes, aligned along the nematic director at preparation. The nanotubes create a very large effective dielectric anisotropy of the composite. Their local field-induced torque is transmitted to the rubber-elastic network and is registered as the exerted uniaxial stress of order ~1kPa in response to a constant field of order ~1MV/m. We investigate the dependence of the effect on field strength, nanotube concentration and reproducibility under multiple field-on and -off cycles. The results indicate the potential of the nanotube-nematic elastomer composites as electrically driven actuators.
Magnetic determination of H(c2) under accurate alignment in (TMTSF)2ClO4.
Cantilever magnetometry has been used to measure the upper critical magnetic field H(c2) of the quasi-one-dimensional molecular organic superconductor (TMTSF)2ClO4. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, H(c2) at low temperature is shown to reach 5 T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large H(c2) in this system and provide support for spin triplet pairing in this unconventional superconductor.
Magnetic Determination of $H_{c2}$ under Accurate Alignment in (TMTSF)$_2$ClO$_4$
2004-01-29
Cantilever magnetometry has been used to measure the upper critical magnetic field $H_{c2}$ of the quasi-one dimensional molecular organic superconductor (TMTSF)$_2$ClO$_4$. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, $H_{c2}$ at low temperature is shown to reach 5T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large $H_{c2}$ in this system and provide support for spin triplet pairing in this unconventional superconductor
Thermal Flipping and Thermal Trapping$$bNew Elements in Dust Grain Dynamics
Since the classical work by Purcell (1979) it has been generally accepted that most interstellar grains rotate suprathermally. Suprathermally rotating grains would be nearly perfectly aligned with the magnetic field by paramagnetic dissipation if not for ``crossovers'', intervals of low angular velocity resulting from reversals of the torques responsible for suprathermal rotation; during crossovers grains are susceptible to disalignment by random impulses. Lazarian and Draine (1997) identified thermal fluctuations within grain material as an important component of crossover dynamics. For grains of size less than 0.1 micron, these fluctuations ensure good correlation of angular momentum before and after crossover resulting in good alignment, in accord with observations of starlight polarization. In the present paper we discuss two new processes which are important for the dynamics of grains with a<0.1 micron. The first -- ``thermal flipping'' -- offers a way for small grains to bypass the period of greatly reduced angular momentum which would otherwise take place during a crossover, thereby enhancing the alignment of small grains. The second effect -- ``thermal trapping'' -- arises when thermal flipping becomes rapid enough to prevent the systematic torques from driving the grain to suprathermal rotation. This effect acts to reduce the alignment of small grains. The observed variation of grain alignment with grain size would then result from a combination of the thermal flipping process -- which suppresses suprathermal rotation of small grains -- and due to molecular hydrogen formation and starlight -- which drive large grains to suprathermal rotation rates.
The effects of static and dynamic imbalance on a horizontal axis wind turbine
1997-08-01
In this note the differences between static and dynamic balancing of a wind turbine rotor are addressed. The paper begins with a definition of each type of balancing. It is demonstrated that even if a horizontal axis wind turbine rotor is in static balance, the rotor can still be dynamically imbalanced. Dynamic imbalance can result in a yaw and/or teeter producing torque. A turbine rotor is only in a state of dynamic balance when the principle axes of inertia are aligned with the angular velocity vector. This criteria is illustrated with a point mass model.
Monopole and Topological Electron Dynamics in Adiabatic Spintronic and Graphene Systems
2009-01-23
A unified theoretical treatment is presented to describe the physics of electron dynamics in semiconductor and graphene systems. Electron spin fast alignment with the Zeeman magnetic field (physical or effective) is treated as a form of adiabatic spin evolution which necessarily generates a monopole in magnetic space. One could transform this monopole into the physical and intuitive topological magnetic fields in the useful momentum (K) or real spaces (R). The physics of electron dynamics related to spin Hall, torque, oscillations and other technologically useful spinor effects can be inferred from the topological magnetic fields in spintronic, graphene and other SU(2) systems.
Hydromagnetic rotational braking of magnetic stars
1980-08-15
It is suggested that the magnetic Ap stars can be rotationally decelerated to long periods by the braking action of the associated magnetic field on time scales of order 10/sup 7/--10/sup 10/ years depending on whether the star's dipole field is aligned perpendicular or parallel to the rotation axis. Rotation includes a toroidal magnetic field in the plasma surrounding a star, and the accompanying magnetic stresses produce a net torque acting to despin the star. These results indicate that it is not necessary to postulate mass loss or mass accretion for this purely hydromagnetic braking effect.
Effect of carbon nanotubes on response time of ferroelectric liquid crystals
We present the results of the fast electro-optic response of multiwalled carbon nanotubes (MWCNTs)-doped deformed helix ferroelectric liquid crystal (DHFLC). The fastening of the response in MWCNTs-doped DHFLC has been attributed to the decrease in rotational viscosity and increase in anchoring energy. The decrease in the former is due to the experience of the torque both by MWCNTs and DHFLC and perturbation of order parameter of the DHFLC while the increase in the latter is due to the ?-? electrons stacking between the MWCNTs, DHFLC molecules, and alignment layers. The increase in conductance in doped cells has also been observed.
Nature and measurements of torque ripple of permanent-magnet adjustable-speed motors
Torque ripple of permanent-magnet motors can be classified into four types depending on the nature of their origin. The four types are pulsating torque, fluctuating torque, reluctance cogging torque, and inertia and mechanical system torque. Pulsating torques are inherently produced by the trapezoidal back-emf`s and trapezoidal currents used in certain permanent-magnet adjustable-speed motors. The torque ripples caused by pulsating torques may be reduced by purposely produced fluctuating counter torques. Air-gap torque measurements are conducted on a sample motor. Experimental results agree with theoretical expectations.
Nature and measurements of torque ripple of permanent-magnet adjustable-speed motors
1995-08-01
Torque ripple of permanent-magnet motors can be classified into four types depending on the nature of their origin. The four types are pulsating torque, fluctuating torque, reluctance cogging torque, and inertia and mechanical system torque. Pulsating torques are inherently produced by the trapezoidal back-emf`s and trapezoidal currents used in certain permanent-magnet adjustable-speed motors. The torque ripples caused by pulsating torques may be reduced by purposely produced fluctuating counter torques. Air-gap torque measurements are conducted on a sample motor. Experimental results agree with theoretical expectations.
The Large-Scale Orientations of Disk Galaxies
2010-02-11
We use a 380 h-1 pc resolution hydrodynamic AMR simulation of a cosmic filament to investigate the orientations of a sample of ~100 well-resolved galactic disks spanning two orders of magnitude in both stellar and halo mass. We find: (i) At z=0, there is an almost perfect alignment at a median angle of 18 deg, in the inner dark matter halo regions where the disks reside, between the spin vector of the gaseous and stellar galactic disks and that of their inner host haloes. The alignment between galaxy spin and spin of the entire host halo is however significantly weaker, ranging from a median of ~46 deg at z=1 to ~50 deg at z=0. (ii) The most massive galaxy disks have spins preferentially aligned so as to point along their host filaments. (iii) The spin of disks in lower-mass haloes shows, at redshifts above z~0.5 and in regions of low environmental density, a clear signature of alignment with the intermediate principal axis of the large-scale tidal field. This behavior is consistent with predictions of linear tidal torque theory. This alignment decreases with increasing environmental density, and vanishes in the highest density regions. Non-linear effects in the high density environments are plausibly responsible for establishing this density-alignment correlation. We expect that our numerical results provide important insights for both understanding intrinsic alignment in weak lensing from the astrophysical perspective and for mation and evolution processes of galactic disks in a cosmological context.
Crosslinking effects on flow of irradiated polyolefins
1979-10-01
Low-dose radiation crosslinking has a greater effect on viscosity at low shear rates than at high shear rates. Thus, form stability of the shaped plastic as it leaves the die can be improved without affecting processing conditions. Measurements with a torque rheometer demonstrate dependence of rheological behavior on absorbed radiation dosage.
2007-06-12
We report a direct observational evidence for the existence of the galaxy spin alignments with the local tidal shears. We calculate the real space tidal field from the density field reconstructed recently from the Two Mass Redshift Survey (2MRs) by Erdogdu et al. in 2006. Then, we select late-type face-on spiral galaxies from the Tully Galaxy Catalogue and calculate the orientations of their spin axes relative to the 2MRS tidal field. We find a clear signal of the intrinsic correlations between the galaxy spins and the local tidal shears. The null hypothesis of no alignment is rejected at 99.9% confidence level. We also find that the correlation strength increases as the morphological types of the spiral galaxies increase. The observational result is quantitatively consistent with analytic prediction based on the tidal torque theory. Our detection supports the idea that the galaxy spins are fossil records of the linear tidal field and thus can provide a new complimentary probe of the dark matter distribution.
2010-09-22
It has been widely thought that measuring the misalignment angle between the orbital plane of a transiting exoplanet and the spin of its host star was a good discriminator between different migration processes for hot-Jupiters. Specifically, well-aligned hot-Jupiter systems (as measured by the Rossiter-McLaughlin effect) were thought to have formed via migration through interaction with a viscous disc, while misaligned systems were thought to have undergone a more violent dynamical history. These conclusions were based on the assumption that the planet-forming disc was well-aligned with the host star. Recent work by Lai et al. has challenged this assumption, and proposes that the star-disc interaction in the pre-main sequence phase can exert a torque on the star and change its rotation axis angle. We have estimated the stellar rotation axis of a sample of stars which host spatially resolved debris disks. Comparison of our derived stellar rotation axis inclination angles with the geometrically measured debris-disk inclinations shows no evidence for a misalignment between the two.
Survey and alignment of Pohang light source
1996-01-01
Pohang Light Source (PLS) which is operated by Pohang Accelerator Laboratory (PAL) of Pohang University of Science and Technology (POSTECH) is the third generation synchrotron radiation source. The project was initiated in April 1988, and completed in December 1994. As a method to achieve the required positional accuracy of a few tenths of a millimeter for the PLS machines, we have introduced various precision surveying instruments and techniques. For linac alignment, we applied an optical tooling technique to a prealignment process, and developed a laser alignment system of a He-Ne laser and Fresnel zone plates for final alignment in the accelerator tunnel. We introduced a non-contact 3-dimensional measuring system with theodolites, conventional surveying technique with survey network for storage ring alignment, and a GEONET program for data analysis and database management. A smoothing analysis using a low-path filtering method was developed for estimating the electron beam orbit and offset error of the magnets in the storage ring. The positional errors of 0.15mm in rms value has been obtained in positioning the quadrupoles and sextupoles of the storage ring. In this presentation described are; linac alignment, storage ring alignment, the estimation of positional errors, smoothing analysis, survey network and so on. (author)
Alignment of the Atlas Inner Detector tracking system
The ATLAS experiment is equipped with a charged particle tracking system built on three subdetectors, which provide high precision measurements made from a fine detector granularity. The pixel and microstrip subdetectors, which use the silicon technology, are complemented with the transition radiation tracker. The alignment of the ATLAS Inner Detector tracking system requires the determination of its almost 36000 degrees of freedom. From the tracking point of view, the alignment parameters should be known with few microns accuracy. This permits to attain an optimal measurement of the parameters of the charged particles trajectories, thus enabling ATLAS to achieve its ambitious physics goals. The implementation of the alignment software, its framework and the data flow will be discussed, including the selection of an alignment and calibration stream at the ATLAS Event Filter stage. The results obtained on the recent computing challenges, where large scale simulation samples have been used in order to mimic the off-line ATLAS operation, will be presented. Special attention will be payed on the alignment results obtained from the real cosmic ray data taking. Using those samples one has derived the first ever alignment constants set for the commissioned ATLAS Inner Detector. These constants are ready to be used for the reconstruction of the first LHC collisions.
2008-10-28
We create a complete gravity torque map of the disk of the LINER/Seyfert 1.9 galaxy NGC4579. We quantify the efficiency of angular momentum transport and search for signatures of secular evolution in the fueling process from r~15kpc down to the inner r~50pc around the Active Galactic Nucleus (AGN). We use both the 1-0 and 2-1 line maps of CO obtained with the Plateau de Bure Interferometer (PdBI) as part of the NUclei of Galaxies-(NUGA)-project. We derive the stellar potential from a NIR (K band) wide field image of the galaxy. The K-band image, which reveals a stellar bar, together with a high resolution HI map of NGC4579 obtained with the Very Large Array (VLA), allow us to extend the gravity torque analysis to the outer disk. The bulk of the gas response traced by the CO PdBI maps follows the expected gas flow pattern induced by the bar potential in the presence of two Inner Lindblad Resonances (ILR). We also detect an oval distortion in the inner r~200pc of the K-band image. The oval is not aligned with the large-scale bar, a signature of dynamical decoupling. The morphology of the outer disk suggests that the neutral gas is currently piling up in a pseudo-ring formed by two winding spiral arms that are morphologically decoupled from the bar structure. In the outer disk, the decoupling of the spiral allows the gas to efficiently produce net gas inflow on intermediate scales. The corotation barrier seems to be overcome due t o secular evolution processes. The gas in the inner disk is efficiently funneled by gravity torques down to r~300pc. Closer to the AGN, the two m=2 modes (bar and oval) act in concert to produce net gas inflow down to r~50pc, providing a clear smoking gun evidence of fueling with associated short dynamical time-scales.
Dynamic alignment of beam on the crystal during data collection was studied. Development of silicon photo-diode detectors for the vacuum ultraviolet and soft X-ray spectral regions has led to the use of such devices as beam alignment tools for Protein Crystallography beamlines on the Synchrotron Radiation Source at Daresbury. Quadrant photo-diodes are used to provide signals proportional to the number of photons hitting each photo-diode, these are amplified, digitised and then summed to give the x-y position of the beam centre. (author)
YORP effect with anisotropic radiation
2010-09-09
The influence of optical scattering and thermal radiation models an the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is studied. Lambertian formulation is compared with Hapke scattering and emission laws and Lommel-Seeliger reflection. Although the form of reflectivity function strongly influences mean torques due to scattering or thermal radiation alone, their combined contribution to the rotation period YORP is not much different from the standard Lambertian values. For higher albedo values the differences between the Hapke and Lambert models become significant for the YORP in attitude.
Disorientation of interstellar grains in suprathermal rotation
1979-07-15
As pointed out by Purcell, interstellar grains are subject to an unbalanced torque which produces spin-up to high angular speeds; magnetic relaxation then aligns the grain rotation with B during the time t/sub r/. However, changes in the grain surface are likely to change these systematic torques, occasionally reversing them; the rotational velocity then decreases to a minimum at ''crossover'' and then increases again. The mean interval between crossovers is uncertain but may be much less than the value of t/sub r/ resulting from paramagnetic relaxation; if so, and if the grains are disoriented during crossover, paramagnetic relaxation then falls short by about an order of magnitude in accounting for the polarization of starlight.This paper computes the cumulative deflection angle, chi/sub T/, of the grain's angular momentum, J, during crossover, using both a simple theoretical model and detailed dynamical computer calculations. The results indicate that the disorientation is relatively complete in two to three crossovers. Hence paramagnetic relaxation theory can readily account for grain orientation only if ''long-lived spin up'' is assumed, with infrequent crossovers.
Elastic Wave Radiation from a Line Source of Finite Length
1998-11-04
Straightforward algebraic expressions describing the elastic wavefield produced by a line source of finite length are derived in circular cylindrical coordinates. The surrounding elastic medium is assumed to be both homogeneous and isotropic, anc[ the source stress distribution is considered axisymmetic. The time- and space-domain formulae are accurate at all distances and directions from the source; no fa-field or long-wavelength assumptions are adopted for the derivation. The mathematics yield a unified treatment of three different types of sources: an axial torque, an axial force, and a radial pressure. The torque source radiates only azirnuthally polarized shear waves, whereas force and pressure sources generate simultaneous compressional and shear radiation polarized in planes containing the line source. The formulae reduce to more familiar expressions in the two limiting cases where the length of the line source approaches zero and infinity. Far-field approximations to the exact equations indicate that waves radiated parallel to the line source axI.s are attenuated relative to those radiated normal to the axis. The attenuation is more severe for higher I?equencies and for lower wavespeeds. Hence, shear waves are affected more than compressional waves. This fi-equency- and directiondependent attenuation is characterized by an extremely simple mathematical formula, and is readily apparent in example synthetic seismograms.
Initial experience with megavoltage (MV) CT guidance for daily prostate alignments
Purpose: The on-board megavoltage (MV) computed tomography (CT) capabilities of a TomoTherapy Hi*ART unit were used to obtain daily MVCT images of prostate cancer patients. For patient alignment the daily MVCT image needs to be registered with the planning CT image to calculate couch shifts. Three manual techniques of registering the MVCT images with the planning kilovoltage (kV) CT images were evaluated. The techniques are based on visual alignment of (1) fiducial prostate markers (2) CT anatomy, and (3) kVCT contours. Methods and Materials: One hundred and twelve alignments from 3 patients were available for analysis. The radiation therapists visually registered the MVCT images with the planning kVCT images based on fiducial markers for actual patient alignment. Retrospectively, the therapists registered each image set using anatomy and contour-based techniques. In addition to the therapists, a physician retrospectively registered each image set based on each of the three techniques. For each MVCT to kVCT image pair a reference alignment was computed from the center-of-mass (COM) of the three fiducial markers. All registration results were compared with these reference alignments. The physician's image registrations were compared with the radiation therapists' registrations to assess the user variability of the different techniques. Results: The marker-based registration results agree best with the reference alignments, while the contour-based registrations show the least degree of agreement. Using anatomy and contour-based registrations, the radiation therapist's alignments differed by {>=} 3 mm from the reference alignments in 24%, 33%, and 3% and 55%, 48%, and 21% of all registrations in the anterior-posterior, superior-inferior, and lateral directions, respectively. The respective values for the marker-based alignments were 3%, 6%, and 3%. The physician's registrations showed the same general trend. The marker-based registrations showed the least amount of inter-user variability while the contour-based ones showed the most. Conclusion: The use of fiducial markers for MVCT image guidance is advantageous to reduce the inter-user variability of the image registration. If fiducial markers are not used, anatomy-based registrations outperform contour-based registrations in terms of (1) agreement with a reference alignment and (2) inter-user variability.
The Casimir effect in the nanoworld
2008-09-02
The Casimir effect is a force arising in the macroscopic world as a result of radiation pressure of vacuum fluctuations. It thus plays a key role in the emerging domain of nano-electro-mechanical systems (NEMS). This role is reviewed in the present paper, with discussions of the influence of the material properties of the mirrors, as well as the geometry dependence of the Casimir effect between corrugated mirrors. In particular, the lateral component of the Casimir force and restoring torque between metal plates with misaligned corrugations are evaluated.
Dynamics of a split torque helicopter transmission
A high reduction ratio split torque gear train has been proposed as an alternative to a planetary configuration for the final stage of a helicopter transmission. A split torque design allows a high ratio of ...
Fossil evidence for spin alignment of Sloan Digital Sky Survey galaxies in filaments
ABSTRACT We search for and find fossil evidence that the spin axes of galaxies in cosmic web filaments relative to their host filaments are not randomly distributed. This indicates the fact that the action of large-scale tidal torques affected the alignments of galaxies located in cosmic filaments. To this end, we constructed a catalogue of clean filaments containing edge-on galaxies. We started by applying the multiscale morphology filter technique to the galaxies in a redshift-distortion-corrected version of the Sloan Digital Sky Survey Data Release 5. From this sample, we extracted 426 filaments that contained edge-on galaxies (b/a < 0.2). These filaments were then visually classified relative to a variety of quality criteria. These selected filaments contained 69 edge-on galaxies. Statistical analysis using `feature measures' indicates that the distribution of orientations of these edge-on galaxies relative to their parent filament deviates significantly from what would be expected on the basis of a random distribution of orientations. Fewer than 1 per cent of orientation histograms generated from simulated random distributions show the same features as observed in the data histogram. The interpretation of this result may not be immediately apparent, but it is easy to identify a population of 14 objects whose spin axes are aligned perpendicular to the spine of the parent filament (cos? < 0.2). The candidate objects are found in relatively less dense filaments. This happens because galaxies in such locations suffer less interaction with surrounding galaxies and consequently better preserve their tidally induced orientations relative to the parent filament. These objects are also less intrinsically bright and smaller than their counterparts elsewhere in the filaments. The technique of searching for fossil evidence of alignment yields relatively few candidate objects, but it does not suffer from the dilution effects inherent in correlation analysis of large samples. The candidate objects could be the subjects of a programme of observations aimed at understanding in what way they might differ from their non-aligned counterparts.
1992-01-01
Tight mechanical tolerances must be held for each magnet being fabricated for the Accelerator Systems String Test (ASST) of the Superconducting Super Collider (SSC) Particle Accelerator. The beam tube, single phase pipes, liquid and gaseous helium return pipes, liquid nitrogen pipes, radiation shields, and vacuum vessel must be checked with a tightly toleranced alignment gage to assure that they are installed in their intended locations at the ends of each individual magnet. The proper alignment of these critical features within each magnet will permit a series of several magnets to be successfully connected for the ASST. This paper documents the design and use of the mechanical alignment gage, verifies its adequacy to perform the necessary measurements within tightly specified tolerances, and presents recommendations for a second generation of gages to be used with ...
Commissioning and Alignment of the ATLAS Inner Detector using Cosmic Data
The ATLAS experiment is one of the two general purpose detectors at the LHC at CERN. ATLAS is equipped with a charged particle tracking system built on three sub-detectors, which provide high precision measurements made from a high detector granularity. The pixel and microstrip sub-detectors, which use the silicon technology, are complemented with the transition radiation tracker. The ATLAS detector is operational since 2008 and more than ten million cosmic tracks crossing the Inner Detector have been collected in 2008 and 2009. These data are used for the commissioning of the experiment. The alignment of the Inner Detector tracking system was performed using the 2008 cosmic data. The tracking performance obtained using this alignment is approaching the one obtained using Monte Carlo simulated with perfectly aligned geometry. The effect of systematic misalignments on physics measurements is being studied.
Spin absorption, windmill, and magneto-optic effects in optical angular momentum transfer
Laser beams exert torque on microparticles through very different physical mechanisms. In this paper, optical angular momentum transferred by laser light to a trapped absorbing superparamagnetic microsphere has been studied, distinguishing between different contributions. We have found the main contribution to the torque arising from the transfer of the spin angular momentum carried by absorbed laser light. Detailed polarization status contribution of the laser light to the momentum transfer has been then analyzed. A general method to separate and quantify contributions to the optical angular momentum transferred has been developed. We have thus quantified contributions due to radiation pressure, through an effect similar to the wind on a windmill, and contributions arising from magneto-optic effects.
Spin absorption, windmill, and magneto-optic effects in optical angular momentum transfer
2004-01-01
Laser beams exert torque on microparticles through very different physical mechanisms. In this paper, optical angular momentum transferred by laser light to a trapped absorbing superparamagnetic microsphere has been studied, distinguishing between different contributions. We have found the main contribution to the torque arising from the transfer of the spin angular momentum carried by absorbed laser light. Detailed polarization status contribution of the laser light to the momentum transfer has been then analyzed. A general method to separate and quantify contributions to the optical angular momentum transferred has been developed. We have thus quantified contributions due to radiation pressure, through an effect similar to the wind on a windmill, and contributions arising from magneto-optic effects
Spin absorption, windmill, and magneto-optic effects in optical angular momentum transfer
Laser beams exert torque on microparticles through very different physical mechanisms. In this paper, optical angular momentum transferred by laser light to a trapped absorbing superparamagnetic microsphere has been studied, distinguishing between different contributions. We have found the main contribution to the torque arising from the transfer of the spin angular momentum carried by absorbed laser light. Detailed polarization status contribution of the laser light to the momentum transfer has been then analyzed. A general method to separate and quantify contributions to the optical angular momentum transferred has been developed. We have thus quantified contributions due to radiation pressure, through an effect similar to the wind on a windmill, and contributions arising from magneto-optic effects.
Evaluation of curing and physical properties of NR/SBR blends using radiation-grafting copolymer
2009-01-01
The curing characterizations of natural rubber (NR) and styrene butadiene rubber (SBR) lattices and their blends with and without NR-g-MA and SBR-g-MA were studied by using oscillating disc rheometer methods. The minimum value for torque decreases with increasing NR in the blends and with the incorporation ofNR-g-MA and SBR-g-MA. The value of maximum torque increases with increasing of SBR in the blend and with the presence of (NR-g-MA and SBR-g-MA) is decreased. The mechanical properties of the samples were studied. The tensile strengths increased steadily with an increase of NR content in the blend. Thermal characteristics of these latex blends were studied by thermogravimetric analysis. Thermal degradation of these individual lattices and their blends were investigated with special refe...
Texturing hard Nd-Fe-B powdered ribbons in high magnetic field
2009-01-01
A new route to texture NdFeB alloys in magnetic field was presented in a recent paper, constituting an attempt towards the preparation of anisotropic bonded magnets. NdFeB ribbons composed of Nd2Fe14B grains embedded in a Nd-Cu eutectic matrix, were annealed under an applied magnetic field up to 16T, at temperatures above the Nd-Cu melting temperature. A crystallographic texture was found to progressively develop at annealing temperatures, above 700 deg. C. In this paper, it is proposed that the grain orientation mechanism involves a competition between the aligning magnetic field torque acting on the magnetic grains and thermal disordering effects which becomes more and more significant as the temperature is increased. A simple model is developed to evaluate these effects. It is shown as well that a lowering of the alloy coercivity takes place ...
Outflows and accretion in a star--disc system with stellar magnetosphere and disc dynamo
The interaction between a protostellar magnetosphere and a surrounding dynamo-active disc is investigated using an axisymmetric mean-field model. In all models investigated, the magnetic field in the disc arranges itself such that it is anti-aligned with the central dipole so that no X-point forms. When the magnetospheric field is strong enough (stellar surface field strength around 2 kG or larger), accretion happens in a recursive fashion with periods of around 15 to 30 days, which is somewhat longer than the stellar rotation period of around 10 days. In the case of a stellar surface field strength of at least 1 kG, the star is being braked by the magnetic torque exerted on the disc. The stellar accretion rates are always reduced by the presence of a magnetosphere which tends to divert a larger fraction of the disc material into the wind.
Orientation of biological cells using plane-polarized gaussian beam optical tweezers
2003-01-01
Optical tweezers are widely used for the manipulation of cells and their internal structures. However, the degree of manipulation possible is limited by poor control over the orientation of the trapped cells. We show that it is possible to controllably align or rotate disc-shaped cells-chloroplasts of Spinacia oleracea-in a plane-polarized Gaussian beam trap, using optical torques resulting predominantly from circular polarization induced in the transmitted beam by the non-spherical shape of the cells. Publisher: Taylor & Francis Ltd Contributor: P. L. Knight; R. W. Boyd Coverage: 2003-01-01T00:00:00Z
Optical properties of liquid crystals
1977-01-01
Liquid crystals are strongly anisotropic liquids. Their textures are stabilized by a usually weak culvature elasticity. External fields act coherently through induced torques to align the liquid crystal textures. Low fields can have large optical effects. These properties explain the interest of liquid crystals for electrooptical applications. The optical properties of liquid crystals are those of positive uniaxial or biaxial solid crystals. An important parameter is the existence of a possible regular twist, spontaneous or not, on an optical wavelength scale or larger. This results in Bragg scattering of light, a very large associated rotatory power or possibly a wave-guide regime for polarized light. Light scattering is an important source of noise close to the transmitted beam, and it is difficult to filter because of the large associated correlation time. A highly ...
Hardware development for Gravity Probe-B
Gravity Probe-B (GP-B), also known as the Stanford Relativity Gyroscope Experiment, will test two fundamental predictions of Einstein's General Theory of Relativity by precise measurement of the precessions of nearly perfect gyroscopes in earth orbit. This endeavor embodies state-of-the-art technologies in many fields, including gyroscope fabrication and readout, cryogenics, superconductivity, magnetic shielding, precision optics and alignment methods, and satellite control systems. These technologies are necessary to enable measurement of the predicted precession rates to the milliarcsecond/year level, and to reduce to 'near zero' all non-General Relativistic torques on the gyroscopes. This paper provides a brief overview of the experiment followed by descriptions of several specific hardware items with highlights on progress to date and plans for future development and tests.
2005-06-01
The paper describes developments in gear technology by Hansen Transmissions, to meet demands of deep underground mining in South and Southern Africa, and for materials handling, cooling tower, water treatment and mixer industries. The company's invertible gearbox, I4, is accepted as the standard in the SA coal mining industry. It is now available in six sizes with torque ratings up to 100 kNm. A self-aligning, low speed, rigid flange coupling range for shift mounted gearbox applications has been designed. The M4 gear unit was launched in 2004, of monobloc design with easy maintenance, improved lubrication and sealing, and reduced noise levels. The company's gearboxes are used worldwide. 2 photos.
Engineering design and R and D of Impurity Influx Monitor (divertor) for ITER
2008-01-01
The harsh environment in the ITER device presents many diagnostic challenges. A proposed design engineered at the Japan Atomic Energy Agency (JAEA) is of an optical alignment system installed on mirrors behind double vacuum windows. Due to the harsh environment, a piezo-motor is used as an actuator and a sliding bearing is used as a pivot. The required torque of the actuator is estimated. Trial results indicate that the actuator as described fulfills requirements. A prototype of a key optical component, the micro-retro-reflector array, is produced through the electro-forming method. Measured reflectivity yields a sufficient signal for in situ calibration. A Cassegrain telescope prototype is designed and produced using simple spherical mirrors and achromatic lenses made of silica and CaF2. The measured focal length concurs with design objectives. ...
Drill section and method of hydraulically mining mineral formations
1983-11-15
An improved drill section and method of hydraulically mining mineral deposits which includes plural flow conduits extending through the drill section, having complimentary shaped tapered thread sections at opposite ends thereof, is disclosed. The tapered thread sections distribute and accommodate high tortional forces and ensure registered alignment of the flow conduits. Seals are provided at the interface between the multiple drill sections which simultaneously seal each of the flow conduits positioned within the interior of the drill sections. The outer casing of the drill section permits the introduction of high pressure fluid and includes a plurality of pressure-responsive plugs adapted to rupture at a predetermined pressure value thereby releasing fluid to lubricate the drill string and reduce the torque encountered during the mining operation.
A nonelectromagnetic motor comprising a base, a bent shaft which is rotatable relative to the base wherein the bent shaft comprises a straight portion aligned with a main axis and an offset portion that is offset with respect to the main axis; and a drive means for driving the offset portion of the bent shaft along a generally circular path in a plane perpendicular to the main axis to rotate the bent shaft. The bent shaft and drive means for driving the bent shaft can be selected from piezoelectric, magnetostrictive, rheological and shape memory alloys. The drive means of the nonelectromagnetic motor can additionally comprise a shell which shell surrounds and houses the bent shaft and precesses or gyrates which in turn causes the bent drive shaft to rotate. The nonelectromagnetic motor does not rely on friction for the application of torque upon a rotor. 11 figs.
A nonelectromagnetic motor comprising a base, a bent shaft which is rotable relative to the base wherein the bent shaft comprises a straight portion aligned with a main axis and an offset portion that is offset with respect to the main axis; and a drive means for driving the offset portion of the bent shaft along a generally circular path in a plane perpendicular to the main axis to rotate the bent shaft. The bent shaft and drive means for driving the bent shaft can be selected from piezoelectric, magnetostrictive, rheological and shape memory alloys. The drive means of the nonelectromagnetic motor can additionally comprise a shell which shell surrounds and houses the bent shaft and precesses or gyrates which in turn causes the bent drive shaft to rotate. The nonelectromagnetic motor does not rely on friction for the application of torque upon a rotor.
A nonelectromagnetic motor comprising a base, a bent shaft which is rotable relative to the base wherein the bent shaft comprises a straight portion aligned with a main axis and an offset portion that is offset with respect to the main axis; and a drive means for driving the offset portion of the bent shaft along a generally circular path in a plane perpendicular to the main axis to rotate the bent shaft. The bent shaft and drive means for driving the bent shaft can be selected from piezoelectric, magnetostrictive, rheological and shape memory alloys. The drive means of the nonelectromagnetic motor can additionally comprise a shell which shell surrounds and houses the bent shaft and precesses or gyrates which in turn causes the bent drive shaft to rotate. The nonelectromagnetic motor does not rely on friction for the application of torque upon a rotor.
Installation and Alignment of Neutron Guides for In-pile Plug Assembly and Primary Shutter
2008-12-15
The HANARO will be equipped with a neutron guide system, in order to transport cold neutrons from the neutron source to the neutron scattering instruments in the neutron guide hall near the reactor building. The neutron guide system of HANARO consists of the in-pile plug assembly with in-pile guides, the primary shutter with in-shutter guides, the neutron guides in the guide shielding room with dedicated secondary shutters, and the neutron guides connected to the instruments in the neutron guide hall. Neutron guides have rectangular shapes of glass which is specially coated inside by Ni and Ti. It is very important to align neutron guides accurately in order to minimize a loss of cold neutrons which are transferred to scattering instruments. The alignment is one of significant factors together with a reflectivity and a manufacturing accuracy, which decide the performance of neutron guides. So it is necessary to develop special alignment tools and techniques to align neutron guides successfully. There is some limit of accessibility and workability to use optical measurement while aligning neutron guides of the in-pile plug assembly and the primary shutter because of a high radiation level at the CN beam port. So we adopted a laser tracker as the measurement system to align neutron guides accurately in a radiation environment. The laser tracker enables to measure coordinates of neutron guides at far and offset positions of the beam port. This report describes a method of neutron guides alignment for the in-pile plug assembly and the primary shutter using a laser tracker. The result of the installation and the alignment of neutron guides is also presented.
Alignment of neutron guides for the in-pile plug assembly and the primary shutter
2009-05-15
KAERI has been developing a neutron guide system for cold neutron research facilities in HANARO since 2003. The neutron guide system plays an important role in transporting cold neutrons from the cold neutron source to the neutron scattering instruments in the neutron guide hall. A beam port assigned for the cold neutron (CN) has been used for an 8-m SANS without neutron guides until early 2008. The old instrument at the CN beam port was removed and a completely new system has been installed, which is composed of an in-pile plug assembly with in-plug guides, a primary shutter with in-shutter guides, removable shielding blocks, and a vacuum system. It is very important to align the neutron guides accurately in order to minimize a loss of cold neutrons which are transferred to scattering instruments. The alignment is one of significant factors together with a reflectivity and a manufacturing accuracy, which decide the performance of neutron guides. So it is necessary to develop special alignment tools and techniques to align the neutron guides successfully. There exist some limits of accessibility and workability to use conventional optical measurements while aligning the neutron guides for the in-pile plug assembly and the primary shutter because of a high radiation level at the CN beam port. So we adopted a laser tracker as a measurement system to align the neutron guides in a radiation environment. The accurate alignment of neutron guides was safely achieved by a laser tracker through measuring the coordinates of neutron guides at far and offset positions of the beam port. This paper presents the successful result of the installation and alignment of neutron guides for the in pile plug assembly and the primary shutter using a laser tracker.
Opto-mechanical devices for the Antares automatic beam alignment system
1981-01-01
Antares is a 24-beam CO/sub 2/ laser system for controlled fusion research, under construction at Los Alamos National Laboratory. Rapid automatic alignment of this system is required prior to each experimental shot. Unique opto-mechanical alignment devices, which have been developed specifically for this automatic alignment system, are discussed. A variable focus alignment telescope views point light sources. A beam expander/spatial filter processes both a visible Krypton Ion and a 10.6 ..mu..m CO/sub 2/ alignment laser. The periscope/carousel device provides the means by which the alignment telescope can sequentially view each of twelve optical trains in each power amplifier. The polyhedron alignment device projects a point-light source for both centering and pointing alignment at the polyhedron mirror. The rotating wedge alignment device provides a sequencing point-light source and also compensates for dispersion between visible and 10.6 ..mu..m radiation. The back reflector flip in remotely positions point-light sources at the back reflector mirrors. A light source box illuminates optic fibers with high intensity white light which is distributed to the various point-light sources in the system.
Battery hydrometer with analog output
1982-09-21
There is disclosed a battery hydrometer for providing an analog electrical signal having a magnitude related to the specific gravity of a battery electrolyte. The hydrometer includes a source of radiation for providing a detectable beam of radiation and a piston member arranged to be submerged within the electrolyte and to intercept and modulate the beam of radiation in response to the specific gravity of the electrolyte. The piston member is suspended within the electrolyte by a spring which exerts a compressive force upon the piston member against which the electrolyte must act. The hydrometer further includes a radiation detector aligned with the radiation source for providing an analog electrical signal having a magnitude responsive to the modulated beam of radiation.
21 CFR 892.5780 - Light beam patient position indicator.
...Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES...monitor alignment of the radiation beam with the patient's anatomy. (b) Classification. Class I (general...
21 CFR 892.5780 - Light beam patient position indicator.
...Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES...monitor alignment of the radiation beam with the patient's anatomy. (b) Classification. Class I (general...
2010-01-01
Some quality control procedures used for mammography, such as focal spot evaluation, requires previous alignment of the measurement equipment with the X-ray central beam. However, alignment procedures are, in general, the most difficult task and the one that needs more time to be performed. Moreover, the operator sometimes is exposed to radiation during this procedure. This work presents an automatic alignment system for mammographic equipment that allows locating the central ray of the radiation beam and, immediately, aligns with it by dislocating itself automatically along the field. The system consists on a bidirectional moving device, connected to a CCD sensor for digital radiographic image acquisition. A computational analysis of a radiographic image, acquired at any position on the field, is performed in order to determine its positioning under the X-ray beam. ...
(Reverse) Engineering Vacuum Alignment
In the presence of spontaneous symmetry breaking, the alignment of the vacuum with respect to the gauge group is often controlled by quadratically divergent operators in the low energy non-linear sigma model. In principle the magnitudes and signs of these operators can be changed by making different assumptions about the ultraviolet physics, but in practice all known ways of regulating these theories preserve the naive vacuum alignment. We show that by "integrating in" different sets of heavy spin-one fields, it is possible to UV extend certain non-linear sigma models into two distinct UV insensitive theories. These UV extensions have identical low energy degrees of freedom but different radiative potentials, making it possible to engineer two different vacuum alignments for the original non-linear sigma model. Our construction employs "non-square" theory spaces which generically violate the common lore that the preferred vacuum alignment preserves the maximal gauge symmetry. By UV extending the SO(9)/(SO(4) X SO(5)) little Higgs model, we find a radiative potential that deviates from the naive expectation but does not stabilize the correct vacuum for proper electroweak symmetry breaking.
Wind turbine driven, doubly-fed, induction generator for grid connected and stand-alone applications
1995-12-31
Simulation results of a variable speed doubly-fed induction generator (DFIG) driven by a wind turbine are presented for grid-connected and stand alone operation. Operation below and above synchronous speed is considered with a Scherbius scheme. The machine and the supply side converter control strategies use vector control techniques. The machine control uses a reference frame aligned along the stator flux vector position. A decoupled control of the electrical torque and the rotor excitation current is obtained. For stand alone operation the stator magnetizing current is regulated hence indirectly controlling the stator voltage. Constant stator frequency is obtained by imposing rotor currents at the correct slip frequency. Both in the grid-connected and the stand alone schemes optimum the operating point for the wind turbine is tracked. The supply side converter uses a reference aligned with the stator voltage vector position. (Author)
Tidal Torquing of Elliptical Galaxies in Cluster Environments
2010-09-23
Observational studies of galaxy isophotal shapes have shown that galaxy orientations are anisotropic: a galaxy's long axis tends to be oriented toward the center of its host. This radial alignment is seen across a wide range of scales, from galaxies in massive clusters to small Milky Way type satellite systems. Recently, this effect has also been detected in dark matter simulations of cosmological structure, but the degree of alignment of dark matter substructures in these studies is significantly stronger than seen in observations. In this paper we attempt to reconcile these two results by performing high-resolution numerical experiments on N-body multi-component models of triaxial galaxies orbiting in an external analytical potential. The large number of particles employed allows us to probe deep into the inner structure of the galaxy: we show that the discrepancy between observed galaxies and simulated dark matter halos is a natural consequence of induced radial shape twisting in the galaxy by the external potential. The degree of twisting depends strongly on the orbital phase and eccentricity of the satellite, and it can, under certain conditions, be significant at radii smaller than the dark matter scale radius. Such internal misalignments will have important consequences, both for the dynamical evolution of the galaxy itself, and for mass modeling of galaxies in clustered environments.
2010-06-10
We present a detailed analysis of a disc galaxy forming in a high-resolution fully cosmological simulation to investigate the nature of the outer regions of discs and their relevance for the disc formation process. Specifically, we focus on the phenomenon of misaligned disc components and find that the outer disc warp is a consequence of the misalignment between the inner disc and the surrounding hot gaseous halo. As the infalling cold gas sinks toward the centre of the galaxy, it is strongly torqued by the hot gas halo. By the time the fresh gas reaches the central disc-forming region its angular momentum is completely aligned with the spin of the hot gas halo. If the spin of the hot gas halo, in turn, is not aligned with that of the inner disc, a misaligned outer disc forms comprised of newly accreted material. The inner and outer components are misaligned with each other because they respond differently to infalling substructure and accretion. The warped disc feeds the main gas disc due to viscous angular momentum losses, but small amounts of star formation in the warp itself form a low-metallicity thick disc. We show that observations of resolved stellar populations in warped galaxies in the local universe could provide evidence for the presence of these processes and therefore indirectly reveal ongoing gas accretion and the existence of hot gas halos.
Hydrodynamics of isotropic and liquid crystalline active polymer solutions
2006-07-11
We describe the large-scale collective behavior of solutions of polar biofilaments and both stationary and mobile crosslinkers. Both mobile and stationary crosslinkers induce filament alignment promoting either polar or nematic order. In addition, mobile crosslinkers, such as clusters of motor proteins, exchange forces and torques among the filaments and render the homogeneous states unstable via filament bundling. We start from a Smoluchowski equation for rigid filaments in solutions, where pairwise crosslink-mediated interactions among the filaments yield translational and rotational currents. The large-scale properties of the system are described in terms of continuum equations for filament and motor densities, polarization and alignment tensor obtained by coarse-graining the Smoluchovski equation. The possible homogeneous and inhomogeneous states of the systems are obtained as stable solutions of the dynamical equations and are characterized in terms of experimentally accessible parameters. We make contact with work by other authors and show that our model allows for an estimate of the various parameters in the hydrodynamic equations in terms of physical properties of the crosslinkers.
2009-11-04
We investigate the effects of pseudoscalar-photon mixing on electromagnetic radiation in the presence of correlated extragalactic magnetic fields. We model the universe as a collection of magnetic domains and study the propagation of radiation through them. This leads to correlations between Stokes parameters over large scales and consistently explains the observed large-scale alignment of quasar polarizations at different redshifts within the framework of the Big Bang model. We also report that the linear polarization develops quadratically with the number of domains, for optical frequencies.
Trace element measurements using white synchrotron radiation
1986-11-10
Synchrotron radiation, when used for x-ray fluorescence (XRF) has several advantages over conventional x-ray sources. Our group at Brookhaven National Laboratory is developing the equipment and expertise to make XRF measurements with synchrotron radiation. The apparatus is briefly described, along with the alignment techniques. Some minimum detectable limits for trace elements in thin biological standards measured with white light irradiations are presented.
The GEM Detector projective alignment simulation system
1993-07-09
Precision position knowledge (< 25 microns RMS) of the GEM Detector muon system at the Superconducting Super Collider Laboratory (SSCL) is an important physics requirement necessary to minimize sagitta error in detecting and tracking high energy muons that are deflected by the magnetic field within the GEM Detector. To validate the concept of the sagitta correction function determined by projective alignment of the muon detectors (Cathode Strip Chambers or CSCs), the basis of the proposed GEM alignment scheme, a facility, called the ``Alignment Test Stand`` (ATS), is being constructed. This system simulates the environment that the CSCs and chamber alignment systems are expected to experience in the GEM Detector, albeit without the 0.8 T magnetic field and radiation environment. The ATS experimental program will allow systematic study and characterization of the projective alignment approach, as well as general mechanical engineering of muon chamber mounting concepts, positioning systems and study of the mechanical behavior of the proposed 6 layer CSCs. The ATS will consist of a stable local coordinate system in which mock-ups of muon chambers (i.e., non-working mechanical analogs, representing the three superlayers of a selected barrel and endcap alignment tower) are implemented, together with a sufficient number of alignment monitors to overdetermine the sagitta correction function, providing a self-consistency check. This paper describes the approach to be used for the alignment of the GEM muon system, the design of the ATS, and the experiments to be conducted using the ATS.
Intrafraction Geometric Uncertainties in Frameless Image-Guided Radiosurgery
Purpose: Frameless radiosurgery allows the possibility of intrafraction patient movement. Because radiosurgery delivers the entire radiation dose during one or a few fractions, intrafraction misalignment can result in significant underdosage of the treatment site. This article compares alignment errors and their effect on target coverage for treatments that rely only on initial (fixed) alignment vs. those that make intrafraction corrections (dynamic alignment). Methods and Materials: This study analyzed 577 records of intrafraction patient movement observed during frameless cranial and spinal radiosurgery. For each fraction, the average misalignment per fraction was calculated. Then each fraction was divided into n minifractions and margin formulae developed for hyperfractionated radiotherapy were used to estimate the planning margin that would be necessary to preserve target coverage for the observed intrafraction movement. Results: Dynamic alignment reduced the number of fractions with a mean misalignment greater than 2 mm from approximately 20% to nearly zero. For fixed alignment, the estimated margins for optimal target coverage were 3.6-4.5 mm for the various treatment sites. For dynamic alignment, the optimal margins were 1.2-1.6 mm. Conclusions: The estimated margins show the large influence of systematic intrafraction shifts and the capacity of dynamic alignment to correct for them. For dynamic alignment, the margin approximately equates with the traditional precision tolerances for radiosurgery, whereas for fixed alignment, the margin is three times greater. Although these margins may not be directly applicable to radiosurgery planning, they expose the effects of intrafraction motion on target coverage.
2009-01-01
Horizontally aligned single-walled carbon nanotubes (SWNTs) were directly grown across trenches produced on SiO2/Si substrate, forming suspended aligned SWNTs over the trenches, and were fabricated with simple methods for infrared (IR) detection application. The horizontally aligned SWNTs can grow across trenches as wide as 40 mum. The detector based on such SWNTs shows sharp and remarkable responses to the ON/OFF state changes of the IR lamp and IR radiation with different frequencies. The resistance of the SWNTs decreases about 22.86% under IR radiation with power less than 4 mW. The detector photoresponse to IR radiation of 120 Hz at room temperature could be easily observed. The response time constant is only about 500 mus, which is more than two orders of magnitude shorter than that of the reported devices based on SWNT films and ...
Heat-responsive alignment system and solar collection device
1980-11-25
A system which automatically aligns itself, and any attached hardware such as a solar energy collection device, in response to changes in the solar position is described. The alignment system comprises a directional sunlight-admission element which is adapted to be focused over a relatively wide azimuth angle in advance of the direction of change of the solar elevation relative to the location of the device on earth, an infrared radiation-absorbing member having a fixed position relative to the sunlight admission element and aligned to receive and absorb sunlight passing through said admission element over said azimuth angle and to generate heat in response thereto, and a heat-responsive adjustment means in heat-conductive association with said radiation-absorbing member and adapted to move both said sunlight -admission element and said radiation-absorbing member in response to periodic substantial changes in temperature conducted thereto. The adjustment means is also adapted to be connected to and to move a support system for an associated working element such as a solar energy collection system, a telescope, a camera or other device, so that the associated system is automatically and periodically adjusted in response to changes in the solar elevation and azimuth as occur during the year.
2006-12-07
We investigated the lamellar orientation in thin films of a diblock copolymer P(S-b-MMA), under competing effects of surface interactions and an electric field applied perpendicular to the substrate. The surface effects tend to align the lamellae parallel to the substrate while the electric field tends to align the lamellae perpendicular to the substrate. Using neutron reflectivity, neutron diffuse scattering, and neutron small-angle scattering, we achieved a quantitative analysis of the internal structure of the films. Film thickness was found to play a non-trivial role in determining the structure of the films. A complete alignment by the surface effects was observed in the thinner films by annealing. The parallel orientation remains stable even if an electric field as strong as 40 V/{mu}m is applied. In the thicker films, a mixed orientation with boundary layers parallel and the central part partially perpendicular to the substrate was observed after annealing. The mixed orientation becomes unstable under a small compressive stress, and will be converted into a completely parallel orientation. The parallel orientation induced by the compressive stress remains stable as long as the electric field is weaker than several ten V/{mu}m. Only a field of about 40 V/{mu}m is able to stabilize the above mentioned mixed orientation. A fully perpendicular orientation was never observed in our experiments. Diffuse scattering shows a mosaic structure in the absence of an electric field, whose mosaicity will be increased by the torque exerted by an electric field. The lateral correlation length of the lamellar domains is estimated as 1-2 {mu}m. Limited by the small q{sub x}-range we have used, a clear statement on the existence of the electric-field-induced structural undulations predicted by the Onuki's theory cannot be made from our experiments. (orig.)
Concept of quasi-periodic undulator - control of radiation spectrum
1995-02-01
A new type of undulator, the quasi-periodic undulator (QPU) is considered which generates the irrational harmonics in the radiation spectrum. This undulator consists of the arrays of magnet blocks aligned in a quasi-periodic order, and consequentially lead to a quasi-periodic motion of electron. A combination of the QPU and a conventional crystal/grating monochromator provides pure monochromatic photon beam for synchrotron radiation users because the irrational harmonics do not be diffracted in the same direction by a monochromator. The radiation power and width of each radiation peak emitted from this undulator are expected to be comparable with those of the conventional periodic undulator.
Robotic System for Precision Assembly of NIF Ignition Targets
2008-08-27
This paper provides an overview of the design and testing of a robotic system developed for assembling the inertial confinement fusion ignition targets (depicted in Figures 1 and 2) that will be fielded on the National Ignition Facility (NIF) laser [1]. The system, referred to as the Final Assembly Machine and shown in Figure 3, consists of six groups of stacked axes that allow manipulating millimeter-sized components with submicron precision, integrated with an optical coordinate measuring machine (OCMM) that provides in-situ metrology. Nineteen motorized axes and ten manual axes are used to control the position and orientation of five objects that are predominantly assembled together in a cubic centimeter work zone. An operator-in-the-loop provides top-level control of the system, making it more similar to a surgical robot than to a programmed computer-controlled machine tool. The operator is provided visual feedback by the vision system of the OCMM, and tactile feedback by force and torque sensors embedded in the tooling that holds the major components being assembled. The vision system is augmented with auxiliary mirrors providing multiple viewing directions, and is used to guide the approach and alignment of the components, and to measure the relative position and orientation of the components. The force and torque sensors are used to guide the final approach, alignment, and mating of the components that are designed to slip-fit together, and to monitor that mating while adhesively bonding those components and attaching the target base.
Molecular Gas in NUclei of GAlaxies (NUGA): IX. The decoupled bars and gas inflow in NGC 2782
2008-02-21
We present CO(1-0) and CO(2-1) maps of the starburst/Seyfert 1 galaxy NGC 2782, obtained with the IRAM interferometer. The CO emission is aligned along the stellar nuclear bar of radius 1 kpc, configured in an elongated structure with two spiral arms at high pitch angle. At the extremity of the nuclear bar, the CO changes direction to trace two more extended spiral features at a lower pitch angle. These are the beginning of two straight dust lanes, which are aligned parallel to an oval distortion, reminiscent of a primary bar, almost perpendicular to the nuclear one. The two embedded bars appear in Spitzer IRAC near-infrared images, and HST color images, although highly obscured by dust in the latter. We compute the torques exerted by the stellar bars on the gas, and find systematically negative average torques down to the resolution limit of the images, providing evidence of gas inflow tantalizingly close to the nucleus of NGC 2782. The observations are well reproduced by numerical simulations, including gas dissipation, which predict the secondary bar decoupling, the formation of an elongated ring at the 1 kpc-radius Inner Lindblad Resonance (ILR) of the primary bar, and the gas inflow to the ILR of the nuclear bar. The presence of molecular gas inside the ILR of the primary bar, transported by a second nuclear bar, is a potential ``smoking gun''; the gas there is certainly fueling the central starburst, and in a second step could fuel directly the AGN.
Polarization of astronomical maser radiation
1991-01-01
The polarization of maser radiation when the source is permeated by an aligned magnetic field is derived for arbitrary angular momenta of the transition states. This generalization is made possible by an analysis of the structure of the propagating waves in a frame aligned with the magnetic axis. The key elements in determining the polarization properties are the assumption of independent and incoherent pump and loss processes for all magnetic sublevels, and the beaming of maser radiation. These solutions are shown to be the most general ones for the dominant rays (those propagating along the longest chords through the source) of steady state beamed masers with arbitrary spins in the relevant domains of parameter space. The beamed nature, and polarization properties, of astronomical maser radiation are established during the unsaturated growth phase, when an increase in ...
Study of Interplanetary Magnetic Field with Atomic Alignment
2010-09-29
We demonstrate a new way of studying interplanetary magnetic field -- atomic alignment. Instead of sending thousands of space probes, atomic alignment allows magnetic mapping with any ground telescope facilities equipped with spectro-polarimeter. The polarization of spectral lines that are pumped by the anisotropic radiation from the sun is influenced by the magnetic alignment, which happens for weak magnetic field (<1G). As a result, the line polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by the specific cases of Io and comet Halley that we consider. Magnetometer data from the Galileo mission Io flyby (2002) were used in order to construct the topology of the magnetic field around Jupiter. So as to the data from the vega mission comet Halley flyby(1986). A uniform density distribution of Na was considered and polarization at each point was then constructed. Both spatial and temporal variations of turbulent magnetic field can be traced with this technique as well. For remote regions like the the boundary with interstellar medium, atomic alignment provides a unique diagnostics of magnetic field, which is crucial for understanding the physical processes like the IBEX ribbons discovered recently.
Storage for radiation-contaminated material container and radiation-contaminated material container
1995-01-01
A storage for radiation-contaminated material container has a cell chamber for containing a plurality of radiation-contaminated material containers. An air ventilation slab is disposed at the lower portion of the cell chamber for placing the radiation-contaminated material containers in an erected state. The air ventilation slab has a plurality of ventilation holes each spaced apart in a horizontal direction and each aligned with the center of the radiation contaminated material container. The radiation contaminated material container has a concrete block in a cylindrical or like other shape. A cooling channel is formed in a hollow portion of the concrete block. The container is disposed to the cooling channel. A canister is contained in the container. Then, spent fuel assemblies as radiation contaminated materials are contained in the canister in a sealed state. (I.N.)
Device for controlling engine torque in vehicle
1989-03-28
A device is described for controlling engine torque in a vehicle which includes an engine and an automatic transmission, and for changing the engine torque during shifting of the automatic transmission by an engine torque change value determined in association with at least engine load, the device comprising: means for detecting intake air pressure of the engine; means for determining the engine torque change value in further association with at least the intake air pressure of the engine; and means for changing engine torque during shifting of the automatic transmission by the determined engine torque change value.
Atomic alignment and Diagnostics of Magnetic Fields in Diffuse Media
2007-11-07
We continue our studies of atomic alignment in diffuse media, in particularly, in interstellar and circumstellar media, with the goal of developing new diagnostics of magnetic fields in these environments. We understand atomic alignment as alignment of atoms or ions in their ground state. Such atoms are sensitive to weak magnetic fields. In particular, we provide predictions of the polarization that arises from astrophysically important aligned atoms (ions) with fine structure of the ground level, namely, OI and SII and Ti II. Unlike our earlier papers which dealt with weak fields only, a substantial part of our current paper is devoted to the studies of atomic alignment when magnetic fields get strong enough to affect the emission from the excited level, i.e. with the regime when the magnetic splitting is comparable to the line-width. This is a regime of Hanle effect modified by the atomic alignment. Using an example of emission and absorption lines of SII ion we demonstrate how polarimetric studies can probe magnetic fields in circumstellar regions and accretion disks. In addition, we show that atomic alignment induced by anisotropic radiation can induce substantial variations of magnetic dipole transitions within the ground state, thus affecting abundance studies based on this emission. Moreover, the radio emission is polarized, provides a new way to study magnetic fields, e.g. at the epoch of Universe reionization.
THz generation by dual-color pulse in prealigned molecules
2010-08-24
We demonstrate that the THz generation in air from a dual-color pulse, composed of the fundamental and second-harmonic waves, can be coherently controlled by field-free molecular alignment. By tuning its time delay to properly match various molecular alignment revivals, the THz generation from the dual-color pulse can be promoted or decreased due to the spatial cross-(de)focusing effect and the alignment-dependent ionization probabilities of the prealigned diatomic molecules of air. For the dual-color pulse of orthogonally polarized fundamental and second-harmonic waves, the polarization of the generated THz radiation can be controlled by the field-free molecular alignment, which functions as a transient dynamic wave-plate for the dual-color pulse with different phase velocities for the orthogonally polarized field components. The plasma effect on the THz generation of the dual-color pulse is also observed, leading to additional intensity and polarization control of the THz radiation.
Estimate of Tilt Instability of Mesa-Beam and Gaussian-Beam Modes for Advanced LIGO
2004-09-21
Sidles and Sigg have shown that advanced LIGO interferometers will encounter a serious tilt instability, in which symmetric tilts of the mirrors of an arm cavity cause the cavity's light beam to slide sideways, so its radiation pressure exerts a torque that increases the tilt. Sidles and Sigg showed that the strength T of this torque is 26.2 times greater for advanced LIGO's baseline cavities -- nearly flat spherical mirrors which support Gaussian beams (``FG'' cavities), than for nearly concentric spherical mirrors which support Gaussian beams with the same diffraction losses as the baseline case -- ``CG'' cavities: T^{FG}/T^{CG} = 26.2. This has motivated a proposal to change the baseline design to nearly concentric, spherical mirrors. In order to reduce thermoelastic noise in advanced LIGO, O'Shaughnessy and Thorne have proposed replacing the spherical mirrors and their Gaussian beams by ``Mexican-Hat'' (MH) shaped mirrors which support flat-topped, ``mesa'' shaped beams. In this paper we compute the tilt-instability torque for advanced-LIGO cavities with nearly flat MH mirrors and mesa beams (``FM'' cavities) and nearly concentric MH mirrors and mesa beams (``CM'' cavities), with the same diffraction losses as in the baseline FG case. We find that the relative sizes of the restoring torques are T^{CM}/T^{CG} = 0.91, T^{FM}/T^{CG} = 96, T^{FM}/T^{FG} = 3.67. Thus, the nearly concentric MH mirrors have a weaker tilt instability than any other configuration. Their thermoelastic noise is the same as for nearly flat MH mirrors, and is much lower than for spherical mirrors.
TRANSIT LIGHTCURVES OF EXTRASOLAR PLANETS ORBITING RAPIDLY ROTATING STARS
2009-01-01
Main-sequence stars earlier than spectral-type approxF6 or so are expected to rotate rapidly due to their radiative exteriors. This rapid rotation leads to an oblate stellar figure. It also induces the photosphere to be hotter (by up to several thousand kelvin) at the pole than at the equator as a result of a process called gravity darkening that was first predicted by von Zeipel. Transits of extrasolar planets across such a non-uniform, oblate disk yield unusual and distinctive lightcurves that can be used to determine the relative alignment of the stellar rotation pole and the planet orbit normal. This spin-orbit alignment can be used to constrain models of planet formation and evolution. Orderly planet formation and migration within a disk that is coplanar with the stellar equator will result in spin-orbit alignment. More violent planet-planet scattering ...
Magnetic resonance imaging. Handbook and atlas Kernspintomographie. Kompendium und Atlas
1999-01-01
Magnetic resonance imaging (MRI) as a diagnostic imaging tool relies on the generation of magnetic fields, whereas the computerized tomography (CT) uses X-radiation. The fundamental principle of MRI is the magnetic resonance of paramagnetic atomic nuclei. These nuclei, as e.g. protons (= hydrogen nuclei), are aligned in required orientation by application of a strong magnetic field. Upon simultaneous application of an electromagnetic high-frequency field perpendicular to the axis of the basic magnetic field, and in response to periodical changing of the electromagnetic field at a given frequency, the originally aligned paramagnetic nuclei are forced into a movement similar to that of a ''whipping top''. When the resonance frequency is shut off, the nuclei return to their former, aligned positions, inducing a weak signal in a coil. The series of signals generated by ...
Intrafraction Geometric Uncertainties in Frameless Image-Guided Radiosurgery
2009-01-01
Purpose: Frameless radiosurgery allows the possibility of intrafraction patient movement. Because radiosurgery delivers the entire radiation dose during one or a few fractions, intrafraction misalignment can result in significant underdosage of the treatment site. This article compares alignment errors and their effect on target coverage for treatments that rely only on initial (fixed) alignment vs. those that make intrafraction corrections (dynamic alignment). Methods and Materials: This study analyzed 577 records of intrafraction patient movement observed during frameless cranial and spinal radiosurgery. For each fraction, the average misalignment per fraction was calculated. Then each fraction was divided into n minifractions and margin formulae developed for hyperfractionated radiotherapy were used to estimate the planning margin that would be ...
Intrafraction Geometric Uncertainties in Frameless Image-Guided Radiosurgery
2009-01-01
Purpose Frameless radiosurgery allows the possibility of intrafraction patient movement. Because radiosurgery delivers the entire radiation dose during one or a few fractions, intrafraction misalignment can result in significant underdosage of the treatment site. This article compares alignment errors and their effect on target coverage for treatments that rely only on initial (fixed) alignment vs. those that make intrafraction corrections (dynamic alignment). Methods and Materials This study analyzed 577 records of intrafraction patient movement observed during frameless cranial and spinal radiosurgery. For each fraction, the average misalignment per fraction was calculated. Then each fraction was divided into n minifractions and margin formulae developed for hyperfractionated radiotherap...
Atomic states and collisional relaxation in plasma polarization spectroscopy: axially symmetric case
1996-10-01
An ensemble of atoms (or ions) is described in terms of the density matrix, and two quantities, population and alignment, are assigned to each atomic level for axially symmetric plasma environment. Collisional relaxation is treated semiclassically as transitions between vectors in the Liouville space and interpreted as elastic or inelastic transitions among the population and the alignment of the levels. A spatially anisotropic velocity distribution of perturbers is expanded in terms of Legendre polynomials, and rate coefficients are defined for the transitions. A set of rate equations are constructed for the system of populations and another set for that of alignments. In the case of an isotropic Maxwellian distribution of perturbers the former reduces to the conventional collisional-radiative model describing the ionizing plasma component of populations. As an example, berylliumlike oxygen in an anisotropic plasma environment is treated by this method. (author)
Radiation properties of pulsar magnetospheres: Observation, theory, and experiment
1995-12-31
In the three decades since their discovery, the accumulated body of observational data from pulsar sources puts constraints on models that seek to explain their periodic radiation. This paper reviews this data, reports on a VLA search for halos predicted by an early model, and reinvestigates a magnetospheric disk-field-aligned-current transmission line system as the origin of the observed radiation, with external wave excitation by as yet an unexplained source. Three dimensional, fully electromagnetic particle-in-cell simulations of the pulsar surface and magnetosphere are used to explore the waveshape and polarization properties of the observed radiation. The multipulse characteristic is consistent with existence of a wave resonator at the lower pulsar ``ionospheric`` boundary.
The origin of polarized blackbody radiation from resistively heated multiwalled carbon nanotubes
2008-07-07
We observed very pronounced polarization of light emitted by highly aligned free-standing multiwall carbon nanotube (MWNT) sheet in axial direction which is turned to the perpendicular polarization when a number of layers are increased. The radiation spectrum of resistively heated MWNT sheet closely follows to the Plank's blackbody radiation distribution. The obtained polarization features can be described by a classical dielectric cylindrical shell model, taking into consideration the contribution of delocalized {pi}-electrons ({pi} surface plasmons). In absorption (emission) the optical transverse polarizability, which is much smaller than longitudinal one, is substantially suppressed by depolarization effect due to screening by induced charges. This phenomenon suggests very simple and precise method to estimate the alignment of nanotubes in bundles or large assemblies.
Radiatively induced flavour violation in the general two-Higgs doublet model with Yukawa alignment
2010-01-01
The most general two-Higgs doublet model contains new sources of flavour violation that are usually in conflict with the experimental constraints. One possibility to suppress the exotic contribution to the flavour changing neutral currents consists on imposing the alignment of the Yukawa couplings. This condition presumably holds at a high-energy scale and is spoiled by the radiative corrections. We compute in this Letter the size of the radiatively induced flavour violating Higgs couplings at the electroweak scale. These also yield the absolute lower bound on the size of the exotic contributions to the flavour changing neutral currents in any two-Higgs doublet model, barring cancellations and the existence of discrete symmetries. We show that these contributions are well below the experim...
Radiatively induced flavour violation in the general two-Higgs doublet model with Yukawa alignment
2010-06-01
The most general two Higgs doublet model contains new sources of flavour violation that are usually in conflict with the experimental constraints. One possibility to suppress the exotic contribution to the flavour changing neutral currents consists on imposing the alignment of the Yukawa couplings. This condition presumably holds at a high-energy scale and is spoiled by the radiative corrections. We compute in this letter the size of the radiatively induced flavour violating Higgs couplings at the electroweak scale. These also yield the absolute lower bound on the size of the exotic contributions to the flavour changing neutral currents in any two Higgs doublet model, barring cancellations and the existence of discrete symmetries. We show that these contributions are well below the experimental bounds in large regions of the parameter space.
Radiatively induced flavour violation in the general two-Higgs doublet model with Yukawa alignment
The most general two-Higgs doublet model contains new sources of flavour violation that are usually in conflict with the experimental constraints. One possibility to suppress the exotic contribution to the flavour changing neutral currents consists on imposing the alignment of the Yukawa couplings. This condition presumably holds at a high-energy scale and is spoiled by the radiative corrections. We compute in this Letter the size of the radiatively induced flavour violating Higgs couplings at the electroweak scale. These also yield the absolute lower bound on the size of the exotic contributions to the flavour changing neutral currents in any two-Higgs doublet model, barring cancellations and the existence of discrete symmetries. We show that these contributions are well below the experimental bounds in large regions of the parameter space.
2010-01-01
A new design concept, called one axis three positions sun-tracking polar-axis aligned CPCs (3P-CPCs, in short), was proposed and theoretically studied in this work for photovoltaic applications. The proposed trough-like CPC is oriented in the polar-axis direction, and the aperture is daily adjusted eastward, southward, and westward in the morning, noon and afternoon, respectively, by rotating the CPC trough, to ensure efficient collection of beam radiation nearly all day. To investigate the optical performance of such CPCs, an analytical mathematical procedure is developed to estimate daily and annual solar gain captured by such CPCs based on extraterrestrial radiation and monthly horizontal radiation. Results show that the acceptance half-angle of 3P-CPCs is a unique parameter to determin...
Vacuum friction in rotating particles
2010-09-22
We study the frictional torque acting on particles rotating in empty space. At zero temperature, vacuum friction transforms mechanical energy into light emission and produces particle heating. However, particle cooling relative to the environment occurs at finite temperatures and low rotation velocities. Radiation emission is boosted and its spectrum significantly departed from a hot-body emission profile as the velocity increases. Stopping times ranging from hours to billions of years are predicted for materials, particle sizes, and temperatures accessible to experiment. Implications for the behavior of cosmic dust are discussed.
The development of radiation-hardened robot for nuclear facility
2000-11-01
The objective of this project is to make a optimal design of differential planetary reducer through the stress analysis. The developed gears are able a high efficiency and manufactured with small size. This reducer of planetary type is able to transmit high rode torque in one stage. This light weight, high efficiency differential planetary reducer, as a new attempt of planetary reducer type, can obtain a high reduction ratio with the simple mechanism which is impossible with the traditional planetary reducer type. 19 refs., 26 figs., 11 tabs. (Author)
An application of a combined charging system on a turbocharged diesel engine
1984-01-01
To improve the low-speed torque characteristics and the fuel economy and to reduce the exhaust gaseous emissions from a 10-liter, turbocharged diesel engines, charge air cooling with a resonant intake system has been introduced. The use of an air-to-air inter-cooler mounted in front of the radiator results in increasing the charge air density and the resonant intake system offers a high volumetric charging efficiencies at low-speed region. Actual engine data show an increase in power of 14 percent, the improvement of specific fuel consumption by 3-7 percent and a decrease in NOx emissions by 33 percent.
A refined model for spinning dust radiation
2008-12-17
We present a comprehensive treatment of the spectrum of electric dipole emission from spinning dust grains, updating the commonly used model of Draine and Lazarian. Grain angular velocity distributions are computed using the Fokker-Planck equation; we revisit the drift and diffusion coefficients for the major torques on the grain, including collisions, grain-plasma interactions, and infrared emission. We use updated grain optical properties and size distributions. The theoretical formalism is implemented in the companion code, SPDUST, which is publicly available. The effect of some environmental and grain parameters on the emissivity is shown and analysed.
2010-01-01
The effects of variable viscosity and thermal conductivity on mixed convection flow of a viscous incompressible fluid past a semi-infinite horizontal permeable surface aligned parallel to a uniform free stream in the presence of thermal radiation have been investigated. The transformed equations have been solved numerically. The effects of various parameters on the velocity and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed.
1996-12-31
A new electronic device to determine the position of the central ray of the radiation beam is proposed. The device aims to provide a perfect alignment of test objects used for evaluating focal spots with this reference axis 7 refs., 1 fig.
1981-07-08
The gamma camera is used to determine the distribution of radio-pharmaceutical preparations in the body (tomography). It has a plate collimator where each gap has a detector from the scintillation plate or photoelement assigned to it. The form of the detectors is matched to the size of gap. The resolution of the gamma camera is improved by the constructional integration of the collimator with the radiation converter parts, because an optimum mutual alignment is guaranteed.
1989-01-01
We have developed image analysis software to facilitate the analysis of optical transition radiation (OTR) patterns generated by the electron beam from the Los Alamos free-electron laser facility. The software can be used for beam alignment, beam profile and angular divergence measurements, and the programs run on an IBM AT microcomputer. The programs and their use are described and some results shown. 2 refs., 17 figs.
The electrodynamic 2-body problem and the origin of quantum mechanics
2005-11-25
We numerically solve the functional differential equations (FDE's) of 2-particle electrodynamics, using the full electrodynamic force obtained from the retarded Lienard-Wiechert potentials and the Lorentz force law. In contrast, the usual formulation uses only the Coulomb force (scalar potential), reducing the electrodynamic 2-body problem to a system of ordinary differential equations (ODE's). The ODE formulation is mathematically suspect since FDE's and ODE's are known to be incompatible; however, the Coulomb approximation to the full electrodynamic force has been believed to be adequate for physics. We can now test this long-standing belief by comparing the FDE solution with the ODE solution, in the historically interesting case of the classical hydrogen atom. The solutions differ. A key qualitative difference is that the full force involves a `delay' torque. Our existing code is inadequate to calculate the detailed interaction of the delay torque with radiative damping. However, a symbolic calculation provides conditions under which the delay torque approximately balances (3rd order) radiative damping. Thus, further investigations are required, and it was prematurely concluded that radiative damping makes the classical hydrogen atom unstable. Solutions of FDE's naturally exhibit an_infinite_ spectrum of _discrete_ frequencies. The conclusion is that (a) the Coulomb force is_not_ a valid approximation to the full electrodynamic force, so that (b) the n-body interaction needs to be reformulated in various current contexts such as molecular dynamics.
Spirality related mechanical properties of single knit fabrics of lincLITE and conventional yarns
2008-01-01
In this study, spirality related mechanical properties such as torque, tensile and snarling tendency and their effect on spirality and skewness are investigated in single jersey structures made from soft and bulkier lincLITE yarns and conventional wool yarns. Twist liveliness, snarling tendency, torque and residual torque, asymmetry of torque and tightness significantly effect the spirality and skewness of single jersey fabrics. Torques and residual torques and snarling tendency have positive and tightness factor has a negative correlation with skewness. Asymmetry of torque appeared to be proportional with an increase of torque and residual torques, but showed a negative correlation with torsional resilience. LincLITE yarns showed better torsional properties nearly in all cases in conc...
Optical measurements of magnetically-aligned asbestos fibers
1989-01-01
The magnetic-alignment behavior of asbestos fibers suspended in water was studied. As the magnetic field rotates, the fibers rotate about their center. Due to viscous drag, the fibers tend to lag the field, with the lag increasing as the rotation rate increases. A theoretical model describing fiber behavior was developed. Experiments measuring the phase lag of individual fibers, experiencing torques of the order of 10{sup {minus}18} Newton-meters were in excellent agreement with the model. For an unknown fiber the phase lag measurement will give the ratio of the length to radius of the fiber. For a known fiber, the cross-sectional size and shape can be determined. This research was undertaken with the intention of laying down the groundwork from which an automatic instrument for monitoring asbestos exposure could be made. Initial investigations involved filtering a liquid dispersion in a one Tesla magnetic-field. The filter contained permanently aligned fibers. The filter was made transparent and scattered-light measurements were made relative to the initial magnetic field direction. Subsequent research focused on measuring light scattered by fibers suspended in water while the fibers followed a rotating magnetic-field. The latter technique proved far more sensitive, being able to detect fiber concentrations of the order of one million fibers per liter with relatively simple equipment. On a mass basis, this sensitivity corresponds to one part in 10{sup 10}. The method did not have the problems associated with the filter itself. Equally important, there is the potential to obtain fiber size information.
Isolated pulsar spin evolution on the P-Pdot Diagram
2010-01-15
We look at two contrasting spin-down models for isolated radio pulsars and, accounting for selection effects, synthesize observable populations. While our goal is to reproduce all of the observable characteristics, in this paper we pay particular attention to the form of the spin period vs. period derivative (P-Pdot) diagram and its dependence on various pulsar properties. We analyse the initial spin period, the braking index, the magnetic field, various beaming models, as well as the pulsar's luminosity. In addition to considering the standard magnetic dipole model for pulsar spin-down, we also consider the recent hybrid model proposed by Contopoulos & Spitkovsky. The magnetic dipole model, however, does a better job of reproducing the observed pulsar population. We conclude that random alignment angles and period dependent luminosity distributions are essential to reproduce the observed P-Pdot diagram. We also consider the time decay of alignment angles, and attempt to reconcile various models currently being studied. We conclude that, in order to account for recent evidence for the alignment found by Weltevrede & Johnston, the braking torque on a neutron star should not depend strongly on the inclination. Our simulation code is publically available and includes a web-based interface to examine the results and make predictions for yields of current and future surveys.
X-ray beam compensation. [filter to flatten energy spectrum and make alignment less critical]
1978-08-22
In an electron accelerator having a target which is exposed to an electron beam for the production of x-ray deceleration radiation, a conical compensating member is arranged centrally within a cone pattern of the x-ray radiation. The compensating member has a decreasing conical shape toward the target and merges into a cylinder portion. Beam paths within the cylinder portion which are additional to those in a conventional purely conical compensating member are compensated by a recess positioned in a base of the compensating member having an appropriately selected depth. In another embodiment, a conically shaped compensating member is arranged within the cone-shaped x-ray pattern such that a tip of the compensating member is aligned away from the target and a base is aligned toward the target. A collimator having a conical passageway surrounding the x-ray radiation has a groove for receiving the base of the compensating member so as to mount the same within the conical passageway of the collimator. 4 figures.
2009-01-01
Objective To evaluate the accuracy, utility, and cost effectiveness of a new electromagnetic patient positioning and continuous, real-time monitoring system, which uses permanently implanted resonant transponders in the target (Calypso® 4D Localization System and Beacon® transponders, Seattle, WA) to continuously monitor tumor location and movement during external beam radiation therapy of the prostate. Materials and methods This clinical trial studied 43 patients at 5 sites. All patients were implanted with 3 transponders each. In 41 patients, the system was used for initial alignment at each therapy session. Thirty-five patients had continuous monitoring during their radiation treatment. Over 1,000 alignment comparisons were made to a commercially available kV X-ray positio...
Optical alignment and diagnostics for the ATF microundulator FEL oscillator
1995-12-31
The microundulator FEL oscillator has a wiggler period of 8.8 mm, and is designed for initial lasing at 0.5 microns with a 50 MeV electron beam. The design and performance of the optical diagnostics and alignment are discussed. A HeNe coalignment laser is mode-matched to the resonator cavity for transverse alignment. Interference fringes are observed in the cavity with a pellicle, allowing an alignment tolerance of +/- 10 micro-radians. The same pellicle is used to produce transition radiation by the electron beam. This enables precise transverse alignment of the electron beam to the resonator axis. The HeNe laser is also used to align the wiggler by backlighting its bore. This method aligns the wiggler to the optic axis to a tolerance of +/- 50 microns. A frequency-doubled,pulsed Nd:YAG laser that produces the electron bunch train is also mode-matched to the FEL cavity. The cavity length is adjusted to resonate with this pulse train. Light from the FEL is transported to the diagnostic room using two separate paths: one for the single pass spontaneous emission, and the second for the multipass cavity output. Several diagnostics (CCD camera, photodiode, photomultiplier tube, joulemeter, spectrometer, and streak camera) are used to characterize the light. These instruments measure light energy per micropulse ranging from 10 femto-Joules to 10 micro-Joules.
Calibration and alignment of the CMS silicon tracking detector
2007-07-15
The Large Hadron Collider (LHC) will dominate the high energy physics program in the coming decade. The discovery of the standard model Higgs boson and the discovery of super-symmetric particles are within the reach at the energy scale explored by the LHC. However, the high luminosity and the high energy of the colliding protons lead to challenging demands on the detectors. The hostile radiation environment requires irradiation hard detectors, where the innermost subdetectors, consisting of silicon modules, are most affected. This thesis is devoted to the calibration and alignment of the silicon tracking detector. Electron test beam data, taken at DESY, have been used to investigate the performance of detector modules which previously were irradiated with protons up to a dose expected after 10 years of operation. The irradiated sensors turned out to be still better than required. The performance of the inner tracking systems will be dominated by the degree to which the positions of the sensors can be determined. Only a track based alignment procedure can reach the required precision. Such an alignment procedure is a major challenge given that about 50000 geometry constants need to be measured. Making use of the novel {chi}{sup 2} minimization program Millepede II an alignment strategy has been developed in which all detector components are aligned simultaneously, as many sources of information as possible are used, and all correlations between the position parameters of the detectors are taken into account. Utilizing simulated data, a proof of concept of the alignment strategy is shown. (orig.)
Torques in atmospheres of rotating planets
2010-04-15
Molecular motion in combination with planetary rotation and gravity causes a torque in gas when seen from a coordinate system fixed in the planet. The torque is caused by the difference in centrifugal forces when gas molecules are moving along or opposite to the planets rotation.
Optical polarization models of quasi-stellar objects and BL Lacertae objects
1976-11-01
A model for optically thin synchrotron radiation from a region of partially aligned magnetic field is compared with optical linear polarization data for QSOs and BL Lacertae objects. The synchrotron theory is treated by considering the magnitude and angle of the field perpendicular to the line of sight to be described by a probability distribution. A quite general argument shows that on such a model the linear polarization should depend much more steeply on the spectral index of the radiation than it does in the case of a perfectly aligned field. For two general classes of field asymmetry, the polarization usually depends linearly or quadratically on the spectral index and on the square of the field alignment, for small values of the alignment. QSO data from the literature together with new observations of BL Lacertae objects are gathered together and compared with this model; a 15--20 percent upper limit for the field alignment is consistent with the polarization of the nonvariable objects and the quiescent polarization of the variables, while the highly polarized bursts of the variables require less than a factor of 2 enhancement in the alignment. For objects with curved spectra, perhaps due to upper energy cutoffs in the electron spectrum, the theory predicts a polarization which rises gradually with frequency. This polarization wavelength dependence is weak over the optical band, but should be easily observable in those BL Lacertae objects with curved spectra, once polarization observations have been extended beyond the optical window. A possible observation of this effect in PKS 0735+17 in the optical on three nights is presented. (AIP)
2008-06-30
DescriptionClouds play a crucial role in the radiation balance of the earth. The radiation properties of ice clouds are very dependent upon the size of the ice particles together with their density and shape and whether their orientation is random or there is a degree of alignment. The presence of thin layers of supercooled liquid clouds also has a profound influence on the radiative properties of clouds and their microphysical evolution. New measurement techniques using polarisation radar and depolarisati [continued...]
Supersymmetry breaking as the origin of flavor
We present an effective flavor model for the radiative generation of fermion masses and mixings based on a SU(5)xU(2) symmetry. We assume that the original source of flavor breaking resides in the supersymmetry breaking sector. Flavor violation is transmitted radiatively to the fermion Yukawa couplings at low energy through finite supersymmetric threshold corrections. This model can fit the fermion mass ratios and CKM matrix elements, explain the non-observation of proton decay, and overcome present constraints on flavor changing processes through an approximate radiative alignment between the Yukawa and the soft trilinear sector.
1996-02-01
A basic consideration has been made of a new undulator not to generate the harmonics of radiation which have integrally factored energies and are harmful in some synchrotron radiation experiments. The undulator has magnetic poles quasi-periodically aligned and generates harmonics with irrational ratios in energy which are not simultaneously diffracted by a crystal monochromator at the same Bragg angle. A combination of the undulator with a high-resolution crystal monochromator is expected to be very useful on beamlines of high energy radiation for which x-ray mirrors would not be suitable because their critical angle of total reflection would be too small. {copyright} {ital 1996 American Institute of Physics.}
Planet migration in three-dimensional radiative discs
2009-08-14
The migration of growing protoplanets depends on the thermodynamics of the ambient disc. Standard modelling, using locally isothermal discs, indicate in the low planet mass regime an inward (type-I) migration. Taking into account non-isothermal effects, recent studies have shown that the direction of the type-I migration can change from inward to outward. In this paper we extend previous two-dimensional studies, and investigate the planet-disc interaction in viscous, radiative discs using fully three-dimensional radiation hydrodynamical simulations of protoplanetary accretion discs with embedded planets, for a range of planetary masses. We use an explicit three-dimensional (3D) hydrodynamical code NIRVANA that includes full tensor viscosity. We have added implicit radiation transport in the flux-limited diffusion approximation, and to speed up the simulations significantly we have newly adapted and implemented the FARGO-algorithm in a 3D context. First, we present results of test simulations that demonstrate the accuracy of the newly implemented FARGO-method in 3D. For a planet mass of 20 M_earth we then show that the inclusion of radiative effects yields a torque reversal also in full 3D. For the same opacity law used the effect is even stronger in 3D than in the corresponding 2D simulations, due to a slightly thinner disc. Finally, we demonstrate the extent of the torque reversal by calculating a sequence of planet masses. Th rough full 3D simulations of embedded planets in viscous, radiative discs we confirm that the migration can be directed outwards up to planet masses of about 33 M_earth. Hence, the effect may help to resolve the problem of too rapid inward migration of planets during their type-I phase.
The Orbital Decay of Embedded Binary Stars
2009-11-09
Young binaries within dense molecular clouds are subject to dynamical friction from ambient gas. Consequently, their orbits decay, with both the separation and period decreasing in time. A simple analytic expression is derived for this braking torque. The derivation utilizes the fact that each binary acts as a quadrupolar source of acoustic waves. The acoustic disturbance has the morphology of a two-armed spiral and carries off angular momentum. From the expression for the braking torque, the binary orbital evolution is also determined analytically. This type of merger may help explain the origin of high-mass stars. If infrared dark clouds, with peak densities up to 10^7 cm^{-3}, contain low-mass binaries, those with separations less than 100 AU merge within about 10^5 yr. During the last few thousand years of the process, the rate of mechanical energy deposition in the gas exceeds the stars' radiative luminosity. Successive mergers may lead to the massive star formation believed to occur in these clouds.
On the role of the current loss in radio pulsar evolution
2006-08-31
The aim of this article is to draw attention to the importance of the electric current loss in the energy output of radio pulsars. We remind that even the losses attributed to the magneto-dipole radiation of a pulsar in vacuum can be written as a result of an Ampere force action of the electric currens flowing over the neutron star surface (Michel, 1991, Beskin et al., 1993). It is this force that is responsible for the transfer of angular momentum of a neutron star to an outgoing magneto-dipole wave. If a pulsar is surrounded by plasma, and there is no longitudinal current in its magnetosphere, there is no energy loss (Beskin et al., 1993, Mestel et al., 1999). It is the longitudinal current closing within the pulsar polar cap that exerts the retardation torque acting on the neutron star. This torque can be determined if the structure of longitudinal current is known. Here we remind of the solution by Beskin, Gurevitch & Istomin (1993) and discuss the validity of such an assumption. The behavior of the recently observed "part-time job" pulsar B1931+24 can be naturally explained within the model of current loss while the magneto-dipole model faces difficulties.
Optical angular momentum transfer to microrotors fabricated by two-photon photopolymerization
2009-01-01
We design, fabricate and test optically driven microrotors a few microns in size. The rotors are trapped and rotated in optical tweezers using an LG02 Laguerre-Gaussian laser beam. We verify that we can accurately measure the total optical torque by measuring the spin angular momentum transfer for three different polarizations, by comparing the optical torque with the optical torque calculated using computational electrodynamics and the viscous drag torque determined from the rotation rate and computational fluid dynamics. The torque agrees with that expected from the design principles and electromagnetic modelling of the torque within the optical trap
Testing isotropy of cosmic microwave background radiation
2008-01-01
ABSTRACT We introduce new symmetry-based methods to test for isotropy in cosmic microwave background (CMB) radiation. Each angular multipole is factored into unique products of power eigenvectors, related multipoles and singular values that provide two new rotationally invariant measures mode by mode. The power entropy and directional entropy are new tests of randomness that are independent of the usual CMB power. Simulated Galactic plane contamination is readily identified. The ILC-WMAP data maps show seven axes well aligned with one another and the direction Virgo. Parameter free statistics find 12 independent cases of extraordinary axial alignment, low power entropy, or both having 5 per cent probability or lower in an isotropic distribution. Isotropy of the ILC maps is ruled out to con...
2009-12-08
Vapor condensation with removing of latent heat by emission of characteristic frequencies allows fast droplets formation in big volumes, which becomes possible with spatial redistribution and spreading of condensation nuclei and ions formed in long lightning traces. Droplets in the vertical Earth electric fields will be polarized and dipoles will be oriented; at movements in the Earth magnetic field they will be torqued into horizontal plane. The estimations show that the teamwork of these phenomena leads to formation of tropic cyclones, which can decay in regions with reduced fields and non supersaturated vapor. The suggested theory can be verified by examination of fields' intensity and radiations: the characteristic, mainly IR radiating of latent heat and emission of the 150 kHz range at approaching of water dipoles to drops.
1983-12-01
The specifications of the flywheel system for momentum storage and vehicle torquing are somewhat dependent upon the attitude control requirements of the space station in orbit. As a ground rule, the flywheel system will be sized large enough to provide all attitude maneuvers, if practical, to avoid or minimize turning on the reaction control system (RCS). The RCS, whenever used, expels expensive mass and tends to contaminate optical surfaces of the vehicle. The vehicle rate and acceleration specifications of 0.10 deg/sec and 0.01 deg/square sec are tentative, and may be reduced if lesser values are more practical for flywheel design. For local vertical attitude hold, the average attitude error should be zero, and not the classical 1 degree, since control moment gyro (CMG) gimbal angles provide an exact reference feedback for gravity gradient momentum. Docking presents a problem for docking transients and attitude alignment which will require use of the RCS.
Hydrostatic shoe bearing eliminates problems for large mills
1982-05-01
The need for grinding mills of ever increasing capacity and greater feed openings has tended toward mill trunnion diameters being beyond the size limits for roller bearings. Hydrodynamic plain bearings need to be wide enough to achieve the necessary bearing pressure in order to obtain an oil film with sufficient carrying capacity at low rotational speeds. This greater width increases edge loading resulting from the deflection of the mill under load. Because of the high surface pressure involved, the life of support rollers and girth rings is often inadequate - fatigue leads to flaking on the contact surfaces. Heat treatment of the girth rings also has its problems. The hydrostatic shoebearing permits unlimited trunnion diameter and a high carrying capacity. The self-aligning shoes compensate automatically for radial deviations and large deformations can be tolerated at the girth ring. The sliding surfaces are completely separated by oil under pressure, enabling negligible starting torque and good damping capacity to be achieved together with low rotational speeds.
Galactic Warps Induced By Cosmic Infall
2006-04-25
Recent ideas for the origin and persistence of the warps commonly observed in disc galaxies have focused on cosmic infall. We present N-body simulations of an idealized form of cosmic infall onto a disc galaxy and obtain a warp that closely resembles those observed. The inner disc tilts remarkably rigidly, indicating strong cohesion due to self-gravity. The line of nodes of the warp inside $R_{26.5} ~ 4.5 \\Rd$ is straight, while that beyond $R_{26.5}$ generally forms a loosely-wound, leading spiral in agreement with Briggs's rules. We focus on the mechanism of the warp and show that the leading spiral arises from the torques from the misaligned inner disc and its associated inner oblate halo. The fact that the line of nodes of most warps forms a leading spiral might imply that the disc mass is significant in the centre. If the line of nodes can be traced to very large radii in future observations, it may reveal information on the mass distribution of the outer halo. The warp is not strongly damped by the halo because the precession rate of the inner disc is slow and the inner halo generally remains aligned with the inner disc. Thus even after the imposed quadrupolar perturbation is removed, the warp persists for a few Gyrs, by which time another infall event can be expected.
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