3,779 research outputs found
Terrorizing Advocacy and the First Amendment: Free Expression and the Fallacy of Mutual Exclusivity
Traditional free speech doctrine is inadequate to account for modern terrorist speech. Unprotected threats and substantially protected lawful advocacy are not mutually exclusive. This Article proposes recognizing a new hybrid category of speech called “terrorizing advocacy.” This is a type of traditionally protected public advocacy of unlawful conduct that simultaneously exhibits the unprotected pathologies of a true threat. This Article explains why this new category confounds existing First Amendment doctrine and details a proposed model for how the doctrine should be reshaped
The Partially-Split Hall Bar: Tunneling in the Bosonic Integer Quantum Hall Effect
We study point-contact tunneling in the integer quantum Hall state of bosons.
This symmetry-protected topological state has electrical Hall conductivity
equal to and vanishing thermal Hall conductivity. In contrast to the
integer quantum Hall state of fermions, a point contact can have a dramatic
effect on the low energy physics. In the absence of disorder, a point contact
generically leads to a partially-split Hall bar geometry. We describe the
resulting intermediate fixed point via the two-terminal electrical (Hall)
conductance of the edge modes. Disorder along the edge, however, both restores
the universality of the two-terminal conductance and helps preserve the
integrity of the Hall bar within the relevant parameter regime.Comment: 12 pages, 5 figures; v.2: typos fixed and clarified some argument
Experiments with calibrated digital sideband separating downconversion
This article reports on the first step in a focused program to re-optimize
radio astronomy receiver architecture to better take advantage of the latest
advancements in commercial digital technology. Specifically, an L-Band
sideband-separating downconverter has been built using a combination of careful
(but ultimately very simple) analog design and digital signal processing to
achieve wideband downconversion of an RFI-rich frequency spectrum to baseband
in a single mixing step, with a fixed-frequency Local Oscillator and stable
sideband isolation exceeding 50 dB over a 12 degree C temperature range.Comment: 10 pages, 12 figures, to be published in PAS
Quantum Indistinguishability in Chemical Reactions
Quantum indistinguishability plays a crucial role in many low-energy physical
phenomena, from quantum fluids to molecular spectroscopy. It is, however,
typically ignored in most high temperature processes, particularly for ionic
coordinates, implicitly assumed to be distinguishable, incoherent and thus
well-approximated classically. We explore chemical reactions involving small
symmetric molecules, and argue that in many situations a full quantum treatment
of collective nuclear degrees of freedom is essential. Supported by several
physical arguments, we conjecture a "Quantum Dynamical Selection" (QDS) rule
for small symmetric molecules that precludes chemical processes that involve
direct transitions from orbitally non-symmetric molecular states. As we propose
and discuss, the implications of the Quantum Dynamical Selection rule include:
(i) a differential chemical reactivity of para- and ortho-hydrogen, (ii) a
mechanism for inducing inter-molecular quantum entanglement of nuclear spins,
(iii) a new isotope fractionation mechanism, (iv) a novel explanation of the
enhanced chemical activity of "Reactive Oxygen Species", (v) illuminating the
importance of ortho-water molecules in modulating the quantum dynamics of
liquid water, (vi) providing the critical quantum-to-biochemical linkage in the
nuclear spin model of the (putative) quantum brain, among others.Comment: 12 pages, 5 figures. Clarified presentation and figure
Quantum Disentangled Liquids
We propose and explore a new finite temperature phase of translationally
invariant multi-component liquids which we call a "Quantum Disentangled Liquid"
(QDL) phase. We contemplate the possibility that in fluids consisting of two
(or more) species of indistinguishable quantum particles with a large mass
ratio, the light particles might "localize" on the heavy particles. We give a
precise, formal definition of this Quantum Disentangled Liquid phase in terms
of the finite energy density many-particle wavefunctions. While the heavy
particles are fully thermalized, for a typical fixed configuration of the heavy
particles, the entanglement entropy of the light particles satisfies an area
law; this implies that the light particles have not thermalized. Thus, in a QDL
phase, thermal equilibration is incomplete, and the canonical assumptions of
statistical mechanics are not fully operative. We explore the possibility of
QDL in water, with the light proton degrees of freedom becoming "localized" on
the oxygen ions. We do not presently know whether a local, generic Hamiltonian
can have eigenstates of the QDL form, and if it can not, then the non-thermal
behavior discussed here will exist as an interesting crossover phenomena at
time scales that diverge as the ratio of the mass of the heavy to the light
species also diverges.Comment: 14 page
Correlation Effects in Carbon Nanotubes
We consider the effects of Coulomb interactions on single-wall carbon
nanotubes using an on-site Hubbard interaction, u. For the (N,N) armchair tubes
the low energy theory is shown to be identical to a 2-chain Hubbard model at
half-filling, with an effective interaction u_N = u/N. Umklapp scattering leads
to gaps in the spectrum of charge and spin excitations which are exponentially
small for large N. Above the gaps the intrinsic nanotube resistivity due to
these scattering processes is linear in temperature, as observed
experimentally. The presence of "d-wave" superconductivity in the 2-chain
Hubbard model away from half-filling suggests that doped armchair nanotubes
might exhibit superconductity with a purely electronic mechanism.Comment: 4 pages (REVTeX), 5 postscript figures included automatically using
epsf.sty. Complete postscript version also available at
http://www.itp.ucsb.edu/~balents/papers.htm
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