3,487 research outputs found
Deformation Potential Carrier-Phonon Scattering in Semiconducting Carbon Nanotube Transistors
Theoretical calculations of carrier transport in single-walled carbon
nanotubes are compared with recent experiments. Carrier-phonon scattering is
accounted for using the deformation potential approximation. Comparing with
experiments, a deformation potential coupling constant of 14eV is determined
for semiconducting carbon nanotubes. Theory is shown to closely predict the
low-field mobility, on conductance, and on resistance of field-effect
transistors as a function of induced nanotube charge density, diameter, and
temperature. Results indicate that the device conductance is reduced as
multiple subband channels conduct due to strong intersubband scattering.
Comparison with experiment allows identification of the mean free path (Lm) in
semiconducting carbon nanotubes. As the device turns on, Lm is found to
increase significantly. When the device is in the on state, the mean free path
(Lm-ON) varies linearly with tube diameter and inversely with temperature.
Intersubband scattering is found to strongly decrease Lm-ON when a few subbands
are occupied. When 3 subband channels are considered at room temperature, Lm-ON
decreases from 570nm to 200nm for a 4nm diameter tube when intersubband
scattering is included. Since the subband spacing increases with decreasing
tube diameter, the effects of intersubband are reduced for smaller diameters.Comment: 11 pages, 6 figure
Chiral two-loop pion-pion scattering parameters from crossing-symmetric constraints
Constraints on the parameters in the one- and two-loop pion-pion scattering
amplitudes of standard chiral perturbation theory are obtained from explicitly
crossing-symmetric sum rules. These constraints are based on a matching of the
chiral amplitudes and the physical amplitudes at the symmetry point of the
Mandelstam plane. The integrals over absorptive parts appearing in the sum
rules are decomposed into crossing-symmetric low- and high-energy components
and the chiral parameters are finally related to high-energy absorptive parts.
A first application uses a simple model of these absorptive parts. The
sensitivity of the results to the choice of the energy separating high and low
energies is examined with care. Weak dependence on this energy is obtained as
long as it stays below ~560 MeV. Reliable predictions are obtained for three
two-loop parameters.Comment: 23 pages, 4 figures in .eps files, Latex (RevTex), our version of
RevTex runs under Latex2.09, submitted to Phys. Rev. D,minor typographical
corrections including the number at the end of the abstract, two sentences
added at the end of Section 5 in answer to a referee's remar
A systematic review of evidence on the impacts of joint decision-making on community wellbeing - PROTOCOL
No classical limit of quantum decay for broad states
Though the classical treatment of spontaneous decay leads to an exponential
decay law, it is well known that this is an approximation of the quantum
mechanical result which is a non-exponential at very small and large times for
narrow states. The non exponential nature at large times is however hard to
establish from experiments. A method to recover the time evolution of unstable
states from a parametrization of the amplitude fitted to data is presented. We
apply the method to a realistic example of a very broad state, the sigma meson
and reveal that an exponential decay is not a valid approximation at any time
for this state. This example derived from experiment, shows the unique nature
of broad resonances
The Effects of the Type of Skill Test, Choice, and Gender on the Situational Motivation of Physical Education Students
The purpose of this study was to examine the effects of (a) skill test type, (b) choices, and (c) gender on the situational motivation profiles of adolescents during skill testing in physical education. Participants were 507 students (53% male) aged 12–16 years (M = 13.87; SD = 0.94) attending a suburban junior high school in a western state in the U.S. All participants experienced either a norm-referenced, summative or a criterion-referenced, formative skill test with or without choices. The Situational Intrinsic Motivation Scale (SIMS) was administered to assess situational motivation. A 2 (test type) × 2 (choice) × 2 (gender) MANOVA was used to test for significant differences on each of the four SIMS indices. Significant test type and gender and a significant test type by gender interaction were found. These findings suggest practitioners should use criterion-referenced, formative skill tests especially when teaching girls in physical education
Magnetic and Structural Studies of the Quasi-Two-Dimensional Spin-Gap System (CuCl)LaNb2O7
We report magnetization, nuclear magnetic resonance (NMR), nuclear quadrupole
resonance (NQR), and transmission electron microscopy (TEM) studies on the
quasi-two-dimensional spin-gap system (CuCl)LaNb2O7, a possible candidate for
the J1-J2 model on a square lattice. A sharp single NQR line is observed at the
Cu and Cl sites, indicating that both Cu and Cl atoms occupy a unique site.
However, the electric field gradient tensors at the Cu, Cl, and La sites do not
have axial symmetry. This is incompatible with the reported crystal structure.
Thus the J1-J2 model has to be modified. We propose alternative two-dimensional
dimer models based on the NMR, NQR, and TEM results. The value of the hyperfine
coupling constant at the Cu sites indicates that the spin density is mainly on
the d(3z2-r2) orbital (z parallel c). At 1.5 K, Cu- and Nb-NMR signals
disappear above the critical field Bc1 = 10.3 T determined from the onset of
the magnetization, indicating a field-induced magnetic phase transition at Bc1.Comment: 9 pages, 16 figure
The dispersive contribution of decays and X(1576)
We study whether the broad enhancement X(1576) arises from the final state
interaction (FSI) of decays. We
consider both the absorptive and dispersive contribution of the above
amplitudes since the intermediate states are very close to .
The same mechanism leads to a similar enhancement around 1580 MeV in the
spectrum in the channel, which
can be used to test whether X(1576) can be ascribed to the FSI effect of
.Comment: 4 pages, 4 figure
String Theory and Water Waves
We uncover a remarkable role that an infinite hierarchy of non-linear
differential equations plays in organizing and connecting certain {hat c}<1
string theories non-perturbatively. We are able to embed the type 0A and 0B
(A,A) minimal string theories into this single framework. The string theories
arise as special limits of a rich system of equations underpinned by an
integrable system known as the dispersive water wave hierarchy. We observe that
there are several other string-like limits of the system, and conjecture that
some of them are type IIA and IIB (A,D) minimal string backgrounds. We explain
how these and several string-like special points arise and are connected. In
some cases, the framework endows the theories with a non-perturbative
definition for the first time. Notably, we discover that the Painleve IV
equation plays a key role in organizing the string theory physics, joining its
siblings, Painleve I and II, whose roles have previously been identified in
this minimal string context.Comment: 49 pages, 4 figure
Research and education in management of large-scale technical programs
A research effort is reported which was conducted by NASA in conjunction with Drexel University, and which was aimed at an improved understanding of large scale systems technology and management
- …