Please note, due to essential maintenance online transactions will not be possible between 02:30 and 04:00 BST, on Tuesday 17th September 2019 (22:30-00:00 EDT, 17 Sep, 2019). We apologise for any inconvenience.
To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
We have constructed the foundations to a series of diagnostics methods to probe the jet phenomena in young stars as observed at various optical forbidden lines and radio wavelengths. We calculate and model in a self-consistent manner the physical and radiative processes, which arise within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk of a sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. Such approach can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between complex numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST, Adaptic Optics, and radio interferometry.
Recent observations have revealed that young stellar objects are associated with jet-like structures and Herbig-Haro objects emitting at wavelengths ranging from optical lines to radio continua. These phenomena are similar in morphologies, and have mostly comparable energetics, dynamics, and kinematics. Probing such phenomena observed at various wavelengths with self-consistent physical and radiative processes arising within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk is a challenge for confronting theory and observation of outflows. How such early outflow phase may play a role in forming planetary materials may help solve puzzles posed by meteorites. We will discuss the relevant observations, theoretical foundations for modelling approaches, magnetic structures and dynamical effects, and the connection to the early solar system.
We review the theory of x-winds in young stellar objects (YSOs). In particular, we consider how a model where the central star does not corotate with the inner edge of the accretion disk may help to explain the enhanced emission of X-rays from embedded protostars. We argue, however, that the departure from corotation is not large, so a mathematical formulation that treats the long-term average state as steady and axisymmetric represents a useful approximation. Magnetocentrifugally driven x-winds of this description collimate into jets, and their interactions with the surrounding molecular cloud cores of YSOs yield bipolar molecular outflows.
How large, 100-AU scale, rotationally supported disks form around protostars remains unsettled, both observationally and theoretically. In this contribution, we discuss the theoretical difficulties with disk formation in the presence of a dynamically significant magnetic field and their possible resolutions. These difficulties are caused by the concentration of magnetic field lines close to the forming star by protostellar collapse, and the strong magnetic braking associated with the concentrated field. Possible resolutions include magnetic field-rotation axis misalignment, non-ideal MHD effects, and turbulence. The field-rotation misalignment has been shown to promote disk formation, especially when the field is relatively weak and the misalignment angle is relatively large. Non-ideal MHD effects can enable the formation of small disks at early times. How such disks grow at later times remains to be fully quantified. Turbulence has been found to enable disk formation in a number of simulations, but the exact reason for its beneficial effect is debated.
Wiggling structures in a bipolar outflow may be attributed to orbital motion of a binary system or precession of an accretion disk perturbed by a companion. The shocked knots along the outflow axis display a morphology with either mirror symmetry due to the orbital motion or point symmetry resulted from disk precession. Using the Submillimeter Array (SMA), our CO (2-1) and SiO (5-4) observations show wiggling structures in the collimated bipolar outflow driven by the NGC 1333 IRAS 2A Class 0 protostar (d ~ 200 pc). By fitting the peak positions of emission knots, we can examine the lateral displacement of the molecular jet to constrain parameters of the unresolved binary system, such as the binary separation and total binary mass. With an angular resolution of ~3″, we have determined the knot positions in SiO (5–4)(Fig. 1) and CO (2–1). As a first attempt, we consider the scenario of orbital motion in a binary system and estimate a total binary mass of ~ 1M⊙ and a binary separation of roughly ~ 20 AU, corresponding to ~ 0.1″. Such a small separation makes it challenging to resolve this hypothesized proto-binary system, which is thought to be responsible for the large-scale quadrupolar outflow nearly perpendicular with each other in CO (1–0).
Perovskite KNbO3 thin films were epitaxially grown on (001) MgO by sequential deposition of ultrathin layer (<10Å) single component (KOx and NbOy) species. By engineering the first overlayer species from NbOy to KOx, on (001) MgO, a 45° in-plane rotation of the epitaxial KNbO3 films was observed. This 45° rotation is a result of minimization of the electrostatic energy within the KNbO3/MgO interface. Transmission electron microscopy was employed to characterize these epitaxial KNbO3 films.
Three subjects are covered in this paper. First, a set of criteria are established to explain how epitaxial growth can be achieved for sol-gel processed ferroelectric thin films. These criteria describe the conversion of amorphous films to epitaxial films. Second, we report the microstructures of ion beam sputtered buffer layers, (100) MgO on (100) Si, and epitaxial bottom electrodes, (100) Pt on (100) MgO and (111) Pt on (0001) A12O3, for the integration of ferroelectric films with various types of substrates. Third, microstructures of the multilayered epitaxial films, (001) YBa2Cu307-δ on (100) KNbO3/(100) MgO and (100) KNbO3 on (100) MgO/(100) Si, are characterized. The results indicate that high quality epitaxial multilayered films can be obtained under the proper processing conditions.
Email your librarian or administrator to recommend adding this to your organisation's collection.