4,570 research outputs found
Elastic response of filamentous networks with compliant crosslinks
Experiments have shown that elasticity of disordered filamentous networks
with compliant crosslinks is very different from networks with rigid
crosslinks. Here, we model and analyze filamentous networks as a collection of
randomly oriented rigid filaments connected to each other by flexible
crosslinks that are modeled as worm-like chains. For relatively large
extensions we allow for enthalpic stretching of crosslinks' backbones. We show
that for sufficiently high crosslink density, the network linear elastic
response is affine on the scale of the filaments' length. The nonlinear regime
can become highly nonaffine and is characterized by a divergence of the elastic
modulus at finite strain. In contrast to the prior predictions, we do not find
an asymptotic regime in which the differential elastic modulus scales linearly
with the stress, although an approximate linear dependence can be seen in a
transition from entropic to enthalpic regimes. We discuss our results in light
of the recent experiments.Comment: 10 pages, 11 figure
Giving Voice to Language: Basque Language Activism and the Politics of Education in France, 1969-1994
Over the past several decades there has been a wellspring of political debate in Europe regarding the rights of linguistic minorities in education. Perhaps nowhere has this transnational debate sparked more controversy than in France where the notion of linguistic rights has been negatively construed by many political authorities as antithetical to the republican model of universal public education. Despite such enmity a host of ethnolinguistic activists in France have been laboring for decades to transform education from a site of exclusion into a vehicle of empowerment. In this dissertation I explore the mobilization dynamics that characterized a minority language schooling initiative within the French Basque Country from 1969 to 1994. Drawing on qualitative case study data, I pay particular attention to the struggles, strategies and successes of Basque language activists affiliated with a community-based schooling association known as 'Seaska'. Building on social movement theory, I argue that Seaska gradually accrued the support of reluctant policy-makers by mobilizing an influential repertoire of discursive, organizational and performative strategies. Throughout my discussion I show how these strategic practices allowed Seaska to cope with an enduring tide of political opposition, seize upon several windows of political opportunity and gain increasing levels of recognition within the political arena. By way of conclusion I consider future avenues for conducting comparative research on minority language activism in educational settings beyond the French Basque context
Direct evidence for the magnetic ordering of Nd ions in NdMnSi and NdMnGe by high resolution inelastic neutron scattering
We have investigated the low energy nuclear spin excitations in
NdMnSi and NdMnGe by high resolution inelastic neutron
scattering. Previous neutron diffraction investigations gave ambiguous results
about Nd magnetic ordering at low temperatures. The present element-specific
technique gave direct evidence for the magnetic ordering of Nd ions. We found
considerable difference in the process of the Nd magnetic ordering at low
temperature in NdMnSi and NdMnGe. Our results are consistent
with those of magnetization and recent neutron diffraction measurements
Direct evidence for the magnetic ordering of Nd ions in NdFeAsO by high resolution inelastic neutron scattering
We investigated the low energy excitations in the parent compound NdFeAsO of
the Fe-pnictide superconductor in the eV range by a back scattering
neutron spectrometer. The energy scans on a powder NdFeAsO sample revealed
inelastic peaks at E = 1.600 eV at T = 0.055 K on both energy
gain and energy loss sides. The inelastic peaks move gradually towards lower
energy with increasing temperature and finally merge with the elastic peak at
about 6 K. We interpret the inelastic peaks to be due to the transition between
hyperfine-split nuclear level of the Nd and Nd isotopes with
spin . The hyperfine field is produced by the ordering of the
electronic magnetic moment of Nd at low temperature and thus the present
investigation gives direct evidence of the ordering of the Nd magnetic
sublattice of NdFeAsO at low temperature
Quantum key distribution using non-classical photon number correlations in macroscopic light pulses
We propose a new scheme for quantum key distribution using macroscopic
non-classical pulses of light having of the order 10^6 photons per pulse.
Sub-shot-noise quantum correlation between the two polarization modes in a
pulse gives the necessary sensitivity to eavesdropping that ensures the
security of the protocol. We consider pulses of two-mode squeezed light
generated by a type-II seeded parametric amplification process. We analyze the
security of the system in terms of the effect of an eavesdropper on the bit
error rates for the legitimate parties in the key distribution system. We also
consider the effects of imperfect detectors and lossy channels on the security
of the scheme.Comment: Modifications:added new eavesdropping attack, added more references
Submitted to Physical Review A [email protected]
A simple low-SAR technique for chemical-shift selection with high-field spin-echo imaging
We have discovered a simple and highly robust method for removal of chemical shift artifact in spin-echo MR images, which simultaneously decreases the radiofrequency power deposition (specific absorption rate). The method is demonstrated in spin-echo echo-planar imaging brain images acquired at 7 T, with complete suppression of scalp fat signal. When excitation and refocusing pulses are sufficiently different in duration, and thus also different in the amplitude of their slice-select gradients, a spatial mismatch is produced between the fat slices excited and refocused, with no overlap. Because no additional radiofrequency pulse is used to suppress fat, the specific absorption rate is significantly reduced compared with conventional approaches. This enables greater volume coverage per unit time, well suited for functional and diffusion studies using spin-echo echo-planar imaging. Moreover, the method can be generally applied to any sequence involving slice-selective excitation and at least one slice-selective refocusing pulse at high magnetic field strengths. The method is more efficient than gradient reversal methods and more robust against inhomogeneities of the static (polarizing) field (B0)
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