Results 1 - 10 of 3179
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[en] Long term observations by Brook et al. reveal that the derivative of rotational frequency of PSR J0738-4042 changed abruptly in 2005. Originally, the spin-down rate was relatively stable, with the rotational frequency derivative being −1.14×10−14 s−2. After September 2005, the derivative began to rise. About 1000 days later, it arrived at another relatively stable value of about −0.98 × 10−14 s−2, indicating that the pulsar is spinning-down relatively slowly. To explain the observed change in spin-down rate, we resort to an asteroid disrupted by PSR J0738-4042. In our model, the orbital angular momentum of the asteroid is assumed to be parallel to that of the rotating pulsar, so that the pronounced reduction in the spin-down rate can be naturally explained as due to the transfer of angular momentum from the disrupted material to the central pulsar. The derived magnetospheric radius is about 7.0 × 109 cm, which is smaller than the tidal disruption radius (8.7 × 1010 cm). Our model is self-consistent. It is shown that the variability in the spin-down rate of PSR J0738-4042 can be quantitatively accounted for by accretion from the asteroid disrupted by the central pulsar. (paper)
[en] Considering sum-frequency generation in an isotropic chiral nonlinear medium, we analyze the transfer of the spin angular momentum of fundamental elliptically polarized Gaussian light beams to the signal beam, which appears as the superposition of two Laguerre–Gaussian modes with both spin and orbital angular momentum. Only for the circular polarization of the fundamental radiation is its angular momentum fully transferred to the sum-frequency beam; otherwise, part of it can be transferred to the medium. Its value, as well as the ratio of spin and orbital contributions in the signal beam, depends on the fundamental frequency ratio and the polarization of the incident beams. Higher energy conversion efficiency in sum-frequency generation does not always correspond to higher angular momentum conversion efficiency. (letter)
[en] Mean values of total and specific orbital angular momenta are systematically analyzed for binary galaxies of various types. The angular momenta of the pairs which include irregular galaxy are considerably smaller than those for pairs of other types. The distribution of orbital angular momenta of the pairs which include Sb galaxy and the distribution of the pairs which do not include Sb galaxy are very different. Most pairs which include Sb galaxy have orbital angular momenta of the order of our Galaxy proper rotation momentum
[en] Total and specific orbital angular momenta of all physical pairs of galaxies from the catalogues of Karachentsev (1972) and Turner (1976) are estimated along with the ratios of the orbital momenta to the total spins. The majority of pairs have orbital momenta of the order of the spin of our Galaxy. Almost all the pairs have specific orbital angular momenta not larger than 4x1030 cm2/s. The angular momentum for pairs of spiral galaxies is nearly uniformly distributed between spins and orbital momentum
[en] In this short note, we report a di-quark model calculation for the spin dependent odderon and demonstrate that the asymmetrical color source distribution in the transverse plane of a transversely polarized hadron plays an essential role in yielding the spin dependent odderon. This calculation confirms the earlier finding that the spin dependent odderon is closely related to the parton orbital angular momentum.
[en] We show that the public experiment held in Venice by Tamburini et al and reported in 2012 New J. Phys. 14 033001 can be regarded as a particular implementation of multiple-input–multiple-output (MIMO) communications and, therefore, has no advantages over established techniques. Moreover, we explain that the use of a ‘vortex’ mode (orbital angular momentum ℓ = 1) at one of the transmit antennas is not necessary to encode different channels since only different patterns—or similarly different pointing angles—of the transmit antennas are required. Finally, we identify why this MIMO transmission allowed the decoding of two signals, despite being line-of-sight. This is due to the large separation between the receiving antennas, which places the transmit antennas in the near-field Fresnel region of the receiving ‘array’. This severely limits the application of this technique in practice, since, for a fixed separation between receiving antennas, the detectable signal power from any additional vortex mode decays at least as 1/r4. (comment)
[en] In this paper, the generation mechanism of arbitrary polarized orbital angular momentum mode using an all-fiber mode selective coupler (MSC), composed of a single mode fiber and a two-mode fiber, are proposed and investigated. Theoretical investigation reveals that no matter which polarization state beam is launched into the MSC, first order arbitrary polarized orbital angular momentum (OAM) mode can be obtained by carefully adjusting a squeezer polarization controller. Additionally, the excitation of first order linearly-polarized and circularly-polarized OAM modes is experimentally demonstrated when the polarization state of input light is changed. (paper)
[en] The Wigner function of a pure continuous-variable quantum state is non-negative if and only if the state is Gaussian. Here we show that for the canonical pair angle and angular momentum, the only pure states with non-negative Wigner functions are the eigenstates of the angular momentum. Some implications of this surprising result are discussed.
[en] We report on the realization of a time-domain 'Stueckelberg interferometer', which is based on the internal-state structure of ultracold Feshbach molecules. Two subsequent passages through a weak avoided crossing between two different orbital angular momentum states in combination with a variable hold time lead to high-contrast population oscillations. This allows for a precise determination of the energy difference between the two molecular states. We demonstrate a high degree of control over the interferometer dynamics. The interferometric scheme provides new possibilities for precision measurements with ultracold molecules