6,342 research outputs found
Variability of crop calendar stage dates
There are no author-identified significant results in this report
Structure and clumping in the fast wind of NGC6543
Far-UV spectroscopy from the FUSE satellite is analysed to uniquely probe
spatial structure and clumping in the fast wind of the central star of the
H-rich planetary nebula NGC6543 (HD164963). Time-series data of the unsaturated
PV 1118, 1128 resonance line P Cygni profiles provide a very sensitive
diagnostic of variable wind conditions in the outflow. We report on the
discovery of episodic and recurrent optical depth enhancements in the PV
absorption troughs, with some evidence for a 0.17-day modulation time-scale.
SEI line-synthesis modelling is used to derive physical properties, including
the optical depth evolution of individual `events'. The characteristics of
these features are essentially identical to the `discrete absorption
components' (DACs) commonly seen in the UV lines of massive OB stars. We have
also employed the unified model atmosphere code CMFGEN to explore spectroscopic
signatures of clumping, and report in particular on the clear sensitivity of
the PV lines to the clump volume filling factor. The results presented here
have implications for the downward revision of mass-loss rates in PN central
stars. We conclude that the temporal structures seen in the PV lines of NGC6543
likely have a physical origin that is similar to that operating in massive,
luminous stars, and may be related to near-surface perturbations caused by
stellar pulsation and/or magnetic fields.Comment: 11 pages, 11 figures. Accepted for publication in MNRA
Gluon Tree Amplitudes in Open Twistor String Theory
We show how the link variables of Arkani-Hamed, Cachazo, Cheung and Kaplan
(ACCK), can be used to compute general gluon tree amplitudes in the twistor
string. They arise from instanton sectors labelled by d, with d=n-1, where n is
the number of negative helicities. Read backwards, this shows how the various
forms for the tree amplitudes studied by ACCK can be grouped into contour
integrals whose structure implies the existence of an underlying string theory.Comment: 36 page
General Rotorcraft Aeromechanical Stability Program (GRASP): Theory manual
The general rotorcraft aeromechanical stability program (GRASP) was developed to calculate aeroelastic stability for rotorcraft in hovering flight, vertical flight, and ground contact conditions. GRASP is described in terms of its capabilities and its philosophy of modeling. The equations of motion that govern the physical system are described, as well as the analytical approximations used to derive them. The equations include the kinematical equation, the element equations, and the constraint equations. In addition, the solution procedures used by GRASP are described. GRASP is capable of treating the nonlinear static and linearized dynamic behavior of structures represented by arbitrary collections of rigid-body and beam elements. These elements may be connected in an arbitrary fashion, and are permitted to have large relative motions. The main limitation of this analysis is that periodic coefficient effects are not treated, restricting rotorcraft flight conditions to hover, axial flight, and ground contact. Instead of following the methods employed in other rotorcraft programs. GRASP is designed to be a hybrid of the finite-element method and the multibody methods used in spacecraft analysis. GRASP differs from traditional finite-element programs by allowing multiple levels of substructure in which the substructures can move and/or rotate relative to others with no small-angle approximations. This capability facilitates the modeling of rotorcraft structures, including the rotating/nonrotating interface and the details of the blade/root kinematics for various types. GRASP differs from traditional multibody programs by considering aeroelastic effects, including inflow dynamics (simple unsteady aerodynamics) and nonlinear aerodynamic coefficients
Generation of bovine transgenics using somatic cell nuclear transfer
The ability to produce transgenic animals through the introduction of exogenous DNA has existed for many years. However, past methods available to generate transgenic animals, such as pronuclear microinjection or the use of embryonic stem cells, have either been inefficient or not available in all animals, bovine included. More recently somatic cell nuclear transfer has provided a method to create transgenic animals that overcomes many deficiencies present in other methods. This review summarizes the benefits of using somatic cell nuclear transfer to create bovine transgenics as well as the possible opportunities this method creates for the future
H - T phase diagram of YbCo2Si2 with H // [100]
We report on the first high-resolution dc-magnetisation () measurements on
a single crystal of \ycs. was measured down to 0.05 K and in fields up to
12 T, with the magnetic field parallel to the crystallographic direction
[100]. Two antiferromagnetic (AFM) phase transitions have been detected in a
field T at K and K, in form of a
sharp cusp and a sudden drop in , respectively. These signatures
suggest that the phase transitions are order at and
order at . The upper transition is suppressed by a critical field
T. The field-dependent magnetisation shows two hysteretic
metamagnetic-like steps at the lowest temperature, followed by a sharp kink,
which separates the AFM region from the paramagnetic one. The magnetic
phase diagram of \ycs has been deduced from the isothermal and isofield curves.
Four AFM regions were identified which are separated by and
order phase-transition lines.Comment: 5 Pages, 3 figure
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