1,145 research outputs found
Universal Behaviour of Metal-Insulator Transitions in the p-SiGe System
Magnetoresistance measurements are presented for a strained p-SiGe quantum
well sample where the density is varied through the B=0 metal-insulator
transition. The close relationship between this transition, the high field Hall
insulator transition and the filling factor =3/2 insulating state is
demonstrated.Comment: 6 pages, 4 figures. Submitted to EP2DS XIII conference 199
Towards the Prediction of User Actions on Exercises with Hints Based on Survey Results
Proceedings of: 6th European Conference of Technology Enhanced Learning, EC-TEL 2011, Palermo, Italy, September 20-23, 2011.The actions a user performs on exercises depending on the different hinting techniques applied, can be used to adapt future exercises. In this paper, we propose a survey for users in order to know their different actions depending on different conditions. The analysis of preliminary results for some questions of the model shows that there is a correlation between some survey questions and the real student actions, but there is a case in which there is not such correlation. For the cases where that correlation exists, this correlation leads to think that some prediction of users actions based on survey results is possible.Work partially funded by the Learn3 project TIN2008-05163/TSI
within the Spanish “Plan Nacional de I+D+I”, and the Madrid regional community
project eMadrid S2009/TIC-1650
Regenerating Nucleus Pulposus of the Intervertebral Disc Using Biodegradable Nanofibrous Polymer Scaffolds
Low back pain is a leading health problem in the United States, which is most often resulted from nucleus pulposus (NP) degeneration. To date, the replacement of degenerated NP relies entirely on mechanical devices. However, a biological NP replacement implant is more desirable. Here, we report the regeneration of NP tissue using a biodegradable nanofibrous (NF) scaffold. Rabbit NP cells were seeded on the NF scaffolds to regenerate NP-like tissue both in vitro and in a subcutaneous implantation model. The NP cells on the NF scaffolds proliferated faster than those on control solid-walled (SW) scaffolds in vitro. Significantly more extracellular matrix (ECM) production (glycosaminoglycan and type II collagen) was found on the NF scaffolds than on the control SW scaffolds. The constructs were then implanted in the caudal spine of athymic rats for up to 12 weeks. The tissue-engineered NP could survive, produce functional ECM, remain in place, and maintain the disc height, which is similar to the native NP tissue.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98480/1/ten%2Etea%2E2011%2E0747.pd
Phonon Hall effect in ionic crystals in the presence of static magnetic field
We study phonon Hall effect (PHE) for ionic crystals in the presence of
static magnetic field. Using Green-Kubo formula, we present an exact
calculation of thermal conductivity tensor by considering both positive and
negative frequency phonons. Numerical results are shown for some lattices such
as hexagonal lattices, triangular lattices, and square lattices. We find that
the PHE occurs on the nonmagnetic ionic crystal NaCl, although the magnitude is
very small which is due to the tiny charge-to-mass ratio of the ions. The
off-diagonal thermal conductivity is finite for nonzero magnetic field and
changes sign for high value of magnetic field at high temperature. We also
found that the off-diagonal thermal conductivity diverges as at low
temperature
Stringy Dark Energy Model with Cold Dark Matter
Cosmological consequences of adding the Cold Dark Matter (CDM) to the exactly
solvable stringy Dark Energy (DE) model are investigated. The model is
motivated by the consideration of our Universe as a slowly decaying D3-brane.
The decay of this D-brane is described in the String Field Theory framework.
Stability conditions of the exact solution with respect to small fluctuations
of the initial value of the CDM energy density are found. Solutions with large
initial value of the CDM energy density attracted by the exact solution without
CDM are constructed numerically. In contrast to the LambdaCDM model the Hubble
parameter in the model is not a monotonic function of time. For specific
initial data the DE state parameter w_{DE} is also not monotonic function of
time. For these cases there are two separate regions of time where w_{DE} being
less than -1 is close to -1.Comment: 15 pages, 6 figures; references adde
What can we learn from a measurement of sin(2 beta + gamma)?
The constraints on the value of the CKM phase gamma that may be achieved by
prospective measurements of sin(2 beta) and sin(2 beta + gamma) are discussed.
Significant constraints require quite small errors, and may depend on
assumptions about strong phases. The measurement of sin(2 beta + gamma)
combined with other experiments could provide valuable limits on new physics in
Bd-Bdbar mixing.Comment: 10 pages, 7 figures, RevTex 4, uses amsmath and graphic
Scoring the EQ-HWB-S: can we do it without value sets? A non-parametric item response theory analysis
Background
Only one pilot value set (UK) is currently available for the EQ Health and Wellbeing Instrument short version (EQ-HWB-S). As an alternative to preference-weighted scoring, we examined whether a level summary score (LSS) is appropriate for the EQ-HWB-S using Mokken scaling analyses.
Methods
Data from patients, carers and the general population collected during the developmental phase of the EQ-HWB-S in Australia, US and UK were used, noting 3 of 9 items have since undergone revision. EQ-HWB-S data fit was examined using R package Mokken scaling’s monotone homogeneity model, utilizing the automated item selection procedure (AISP) as well as Loevinger’s scaling coefficients for items and the scale (HS). Manifest monotonicity was assessed by examining whether the cumulative probability for responses at or above each response level did not decrease across the summary score.
Results
EQ-HWB-S data were available for 3340 respondents: US = 903, Australia = 514 and UK = 1923. Mean age was 50 ± 18 and 1841 (55%) were female. AISP placed all 9 items of the EQ-HWB-S on a single scale when the lower bound was set to < 0.448. Strong scalability (HS = 0.561) was found for the EQ-HWB-S as a single scale. Stronger scales were formed by separating the psychosocial items (n = 6, HS = 0.683) and physical sensation items (n = 3, HS = 0.713). No violations of monotonicity were found except for the items mobility and daily activities for the subgroups with long-term conditions and UK subjects, respectively.
Discussion
As EQ-HWB-S items formed a strong scale and subscales based on Mokken analysis, LSS is a promising weighting-free approach to scoring
Neutrino masses in R-parity violating supersymmetric models
We study neutrino masses and mixing in R-parity violating supersymmetric
models with generic soft supersymmetry breaking terms. Neutrinos acquire masses
from various sources: Tree level neutrino--neutralino mixing and loop effects
proportional to bilinear and/or trilinear R-parity violating parameters. Each
of these contributions is controlled by different parameters and have different
suppression or enhancement factors which we identified. Within an Abelian
horizontal symmetry framework these factors are related and specific
predictions can be made. We found that the main contributions to the neutrino
masses are from the tree level and the bilinear loops and that the observed
neutrino data can be accommodated once mild fine-tuning is allowed.Comment: 18 pages; minor typos corrected. To be published in Physical Review
Cosmological Evolution of a Tachyon-Quintom Model of Dark Energy
In this work we study the cosmological evolution of a dark energy model with
two scalar fields, i.e. the tachyon and the phantom tachyon. This model enables
the equation of state to change from to in the evolution of
the universe. The phase-space analysis for such a system with inverse square
potentials shows that there exists a unique stable critical point, which has
power-law solutions. In this paper, we also study another form of
tachyon-quintom model with two fields, which voluntarily involves the
interactions between both fields.Comment: 17 pages, 10 figure
Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars
Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model
incorporating thermal fluctuations and dipole-dipole interactions (calculated
by the Fast Multipole Method) are presented for systems composed of nanoscale
iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated
under sinusoidally varying fields are obtained, while the coercive field is
estimated to be 1979 14 Oe using linear field sweeps at T=0 K. Thermal
effects are essential to the relaxation of magnetization trapped in a
metastable orientation, such as happens after a rapid reversal of an external
magnetic field less than the coercive value. The distribution of switching
times is compared to a simple analytic theory that describes reversal with
nucleation at the ends of the nanomagnets. Results are also presented for
arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a
separation of 300 nm, where the field from neighboring pillars is only 1
Oe, the interactions have a significant effect on the switching of the magnets.Comment: 19 pages RevTeX, including 12 figures, clarified discussion of
numerical technique
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