36,439 research outputs found
Plane-wave impulse approximation extraction of the neutron magnetic form factor from quasielastic ^3He(e,e') at Q^2=0.3 to 0.6 (GeV/c)^2
A high precision measurement of the transverse spin-dependent asymmetry A_T' in ^3He(e,e') quasielastic
scattering was performed in Hall A at Jefferson Lab at values of the squared four-momentum transfer, Q^2,
between 0.1 and 0.6 (GeV/c)^2. A_(T') is sensitive to the neutron magnetic form factor, G_M^n . Values of G_M^n at
Q^2 = 0.1 and 0.2 (GeV/c)^2, extracted using Faddeev calculations, were reported previously. Here, we report
the extraction of G_M^n for the remaining Q^2 values in the range from 0.3 to 0.6 (GeV/c)^2 using a plane-wave
impulse approximation calculation. The results are in good agreement with recent precision data from experiments
using a deuterium target
Time-efficient geometrically non-linear finite element simulations of thin shell deployable structures
Isogeometric analysis of thin shells can provide higher continuity and exact geometric description. It is shown in the existing literature that isogeometric analysis converges with fewer degrees of freedom than Câ°-continuous finite elements that use Langrange polynomial shape functions, but the speed of the solutions has not been previously assessed. In this research, the geometrically nonlinear bending of a thin shell deployable structure, a tape spring is studied, using both NURBS-based and Câ°-continuous finite elements. The complex deformation of a tape spring makes it a perfect case study to compare the computational efficiency of the mentioned techniques. The simulations are carried out in the commercial software ABAQUS and LS-DYNA, and it is found that isogeometric analysis is at least three times slower than the Câ°-continuous finite element methods
Submillimetre observations of a sample of broad absorption line quasars
The broad absorption line (BAL) features seen in a small fraction of quasar
optical/UV spectra are attributed to bulk outflows away from the quasar core.
Observational evidence suggests that dust plays a key role in these systems,
although whether the inferred dust properties are a signature of orientation
effects or whether they are indicative of an evolutionary sequence remains an
outstanding issue. Submillimetre (submm) detections of BAL quasars (BALQSOs),
which would clearly help to resolve this issue, have so far been sparse. This
paper reports on new submm observations of seven BALQSOs. The strongest
influence on the observed flux is found to be the redshift, with the two
highest redshift sources appearing intrinsically more submm-luminous than the
lower redshift ones. Since this trend is also seen in other high redshift AGN,
including non-BAL quasars it implies that the dust emission properties of these
systems are no different from those of the general AGN population, which is
difficult to reconcile with the evolutionary interpretation of the BAL
phenomenon.Comment: 5 Pages, to appear in ApJ Letter
Demonstration of the Zero-Crossing Phasemeter with a LISA Test-bed Interferometer
The Laser Interferometer Space Antenna (LISA) is being designed to detect and
study in detail gravitational waves from sources throughout the Universe such
as massive black hole binaries. The conceptual formulation of the LISA
space-borne gravitational wave detector is now well developed. The
interferometric measurements between the sciencecraft remain one of the most
important technological and scientific design areas for the mission.
Our work has concentrated on developing the interferometric technologies to
create a LISA-like optical signal and to measure the phase of that signal using
commercially available instruments. One of the most important goals of this
research is to demonstrate the LISA phase timing and phase reconstruction for a
LISA-like fringe signal, in the case of a high fringe rate and a low signal
level. We present current results of a test-bed interferometer designed to
produce an optical LISA-like fringe signal previously discussed in the
literature.Comment: find minor corrections in the CQG versio
Experimental investigation of the asymmetric spectroscopic characteristics of electron- and hole-doped cuprates
Quasiparticle tunneling spectroscopic studies of electron- (n-type) and hole-doped (p-type) cuprates reveal that the pairing symmetry, pseudogap phenomenon and spatial homogeneity of the superconducting order parameter are all non-universal. We compare our studies of p-type YBa2Cu3O7-delta and n-type infinite-layer Sr(0.9)Ln(0.1)CuO(2) (Ln = La, Gd) systems with results from p-type Bi2Sr2CaCu2Ox and n-type one-layer Nd1.85Ce0.15CuO4 cuprates, and attribute various non-universal behavior to different competing orders in p-type and n-type cuprates
Simulation of a finishing operation : milling of a turbine blade and influence of damping
Milling is used to create very complex geometries and thin parts, such as turbine blades. Irreversible geometric defects may appear during finishing operations when a high surface quality is expected. Relative vibrations between the tool and the workpiece must be as small as possible, while tool/workpiece interactions can be highly non-linear. A general virtual machining approach is presented and illustrated. It takes into account the relative motion and vibrations of the tool and the workpiece. Both deformations of the tool and the workpiece are taken into account. This allows predictive simulations in the time domain. As an example the effect of damping on the behavior during machining of one of the 56 blades of a turbine disk is analysed in order to illustrate the approach potential
First passage time for subdiffusion: The nonextensive entropy approach versus the fractional model
We study the similarities and differences between different models concerning
subdiffusion. More particularly, we calculate first passage time (FPT)
distributions for subdiffusion, derived from Greens' functions of nonlinear
equations obtained from Sharma-Mittal's, Tsallis's and Gauss's nonadditive
entropies. Then we compare these with FPT distributions calculated from a
fractional model using a subdiffusion equation with a fractional time
derivative. All of Greens' functions give us exactly the same standard relation
which characterizes subdiffusion
(), but generally FPT's are not equivalent to one another. We will
show here that the FPT distribution for the fractional model is asymptotically
equal to the Sharma--Mittal model over the long time limit only if in the
latter case one of the three parameters describing Sharma--Mittal entropy
depends on , and satisfies the specific equation derived in this paper,
whereas the other two models mentioned above give different FTPs with the
fractional model. Greens' functions obtained from the Sharma-Mittal and
fractional models - for obtained from this particular equation - are very
similar to each other. We will also discuss the interpretation of subdiffusion
models based on nonadditive entropies and the possibilities of experimental
measurement of subdiffusion models parameters.Comment: 12 pages, 8 figure
Precision Measurement of the Spin-Dependent Asymmetry in the Threshold Region of ^3He(e, e')
We present the first precision measurement of the spin-dependent asymmetry in the threshold region of ^3He(e,eâ˛) at Q^2 values of 0.1 and 0.2(GeV/c)^2. The agreement between the data and nonrelativistic Faddeev calculations which include both final-state interactions and meson-exchange current effects is very good at Q^2 = 0.1(GeV/c)^2, while a small discrepancy at Q^2 = 0.2(GeV/c)^2 is observed
Transverse Asymmetry A_TⲠfrom the Quasielastic ^3He(e,eâ˛) Process and the Neutron Magnetic Form Factor
We have measured the transverse asymmetry A_TⲠin ^3He(e,eâ˛) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q^2 values from 0.1 to 0.6 (GeV/c)^2. The neutron magnetic form factor GMn was extracted based on Faddeev calculations for Q^2 = 0.1 and 0.2 (GeV/c)^2 with an experimental uncertainty of less than 2%
- âŚ