3,563 research outputs found
Collective excitations in quantum Hall liquid crystals: Single-mode approximation calculations
A variety of recent experiments probing the low-temperature transport
properties of quantum Hall systems have suggested an interpretation in terms of
liquid crystalline mesophases dubbed {\em quantum Hall liquid crystals}. The
single mode approximation (SMA) has been a useful tool for the determination of
the excitation spectra of various systems such as phonons in He and in the
fractional quantum Hall effect. In this paper we calculate (via the SMA) the
spectrum of collective excitations in a quantum Hall liquid crystal by
considering {\em nematic}, {\em tetratic}, and {\em hexatic} generalizations of
Laughlin's trial wave function having two-, four- and six-fold broken
rotational symmetry, respectively. In the limit of zero wavevector \qq the
dispersion of these modes is singular, with a gap that is dependent on the
direction along which \qq=0 is approached for {\em nematic} and {\em
tetratic} liquid crystalline states, but remains regular in the {\em hexatic}
state, as permitted by the fourth order wavevector dependence of the
(projected) oscillator strength and static structure factor.Comment: 6 pages, 5 eps figures include
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Attorney General Regulation of Hybrid Entities as Charitable Trusts
In which situations must, should or may state Attorneys General regulate the affairs of for- profit hybrid legal entities on the theory that they hold some or all of their assets in charitable trust? There is a movement afoot in the United States and around the globe – the social enterprise movement. Social enterprises are, generally speaking, organizations that generate revenues and also seek to benefit society in some way. According to the Social Enterprise Alliance, “[s]ocial enterprises are businesses whose primary purpose is the common good. They use the methods and disciplines of business and the power of the marketplace to advance their social, environmental and human justice agendas.” Some social enterprises are set up within the framework of a nonprofit corporation, but more and more for-profit corporations are being established to mix mission and profit
Teasing apart explanations of a developmental delay in binding: experimental evidence from the comparison of SLI and Williams syndrome
This study investigates the knowledge of binding in 21 English-speaking children with SLI, aged 6;08-16;05, compared to 21 children with WS, language- and age-matched, and 21 language-matched control children, aged 4-7;10. Our results demonstrate no difficulties in the interpretation of reflexive or personal pronouns in SLI, revealing an intact knowledge of reflexive binding, as well as spared pragmatic functioning. Children with WS however show difficulties with their interpretation of pronouns, accepting the local binding of a pronoun, indicating impaired pragmatics. Not surprisingly, our language-matched typical controls, aged between 4-7;08 (M=5;03), showed a classic pattern of the Apparent Delay of Principle B Effect (ADPBE). In view of reported pragmatic but not memory deficits in WS, we interpret our results as consistent with the pragmatic deficit explanation but not the memory deficit explanation of the ADPBE
Andreev reflection at point contacts with heavy-fermion UBe13 ?
We comment on a recent Letter by Waelti et al. (PRL 84, 5616 (2000)) on
'Spectroscopic evidence for unconventional superconductivity in UBe13'. We show
- by using the basic Wexler formula - that it is unlikely to observe Andreev
reflection at point contacts between UBe13 and a normal metal. The large
superconducting anomalies usually found for those contacts are mainly due to
the resistive Maxwell resistance vanishing below Tc of UBe13.Comment: 1 page, no figures, RevTeX, submitted to Phys. Rev. Let
Softening of First-Order Phase Transition on Quenched Random Gravity Graphs
We perform extensive Monte Carlo simulations of the 10-state Potts model on
quenched two-dimensional gravity graphs to study the effect of
quenched coordination number randomness on the nature of the phase transition,
which is strongly first order on regular lattices. The numerical data provides
strong evidence that, due to the quenched randomness, the discontinuous
first-order phase transition of the pure model is softened to a continuous
transition, representing presumably a new universality class. This result is in
striking contrast to a recent Monte Carlo study of the 8-state Potts model on
two-dimensional Poissonian random lattices of Voronoi/Delaunay type, where the
phase transition clearly stayed of first order, but is in qualitative agreement
with results for quenched bond randomness on regular lattices. A precedent for
such softening with connectivity disorder is known: in the 10-state Potts model
on annealed Phi3 gravity graphs a continuous transition is also observed.Comment: Latex + 5 postscript figures, 10 pages of text, figures appende
The accuracy of flap thickness and diameter in LASIK using a femtosecond laser
PURPOSE: To evaluate the resultant thickness of the WaveLight FS200 (Alcon Vision, LLC) created LASIK flap compared to intended thickness at the surgical visit, using the WaveLight EX500 (Alcon Vision, LLC) pachymeter and the resultant flap diameter compared to intended diameter.
METHODS: This single arm, prospective, single surgeon study assessed the accuracy of the intended flap thickness and diameter, after successful bilateral LASIK surgery. The WaveLight FS200 femtosecond laser was used to create all flaps with an intended thickness of 120 μm. Flap thickness was calculated by subtracting the stromal bed thickness after flap lift from the preoperative corneal thickness using the WaveLight EX500 on-board optical pachymeter. Flap diameter was determined using digital analysis.
RESULTS: A total of 58 subjects (116 eyes) completed the study. The calculated mean flap thickness was 120.6 ± 9.0 μm (range 102 to 143 μm) using the EX500 pre- and post-flap pachymetry measurements. There was no statistically significant difference between the planned and achieved flap thickness (p \u3e 0.05). The mean difference in flap diameter between planned and actual was 0.02 ± 0.05 mm. Corneal thickness measured by Pentacam at up to 2 months preoperatively versus EX500 just prior to surgery was similar, with EX500 measuring 2 μm less on average than the Pentacam.
CONCLUSION: The results suggest that the WaveLight FS200 laser is reliable for LASIK flap thickness and diameter and accurately created flaps at the intended thickness and the intended diameter
George Huntington: a legacy of inquiry, empathy and hope
On the centenary of George Huntington's death, Wexler et.al. reconsider the setting and the collaborative effort that produced his description of “hereditary chorea,” today Huntington's disease. Tracing the changing identity of this illness, they discuss the legacy of eugenics, the search for the gene, and ongoing research toward a cure
Response to the Letter to the Editor
This paper has attracted interest around the world from the media (both TV
and newspapers). In addition, we have received letters, emails and telephone
calls. One of our favorites was a voicemail message asking us to return a call
to Australia at which point we would learn who really killed JFK. We welcome
the opportunity to respond to the letter to the editor from Mr. Fiorentino. Mr.
Fiorentino claims that our ``statement relating to the likelihood of a second
assassin based on the premise of three or more separate bullets is demonstrably
false.'' In response we would like to simply quote from page 327 of Gerald
Posner's book Case Closed, one of the most well known works supporting the
single assassin theory: ``If Connally was hit by another bullet, it had to be
fired from a second shooter, since the Warren Commission's own reconstructions
showed that Oswald could not have operated the bolt and refired in 1.4
seconds.'' Mr. Fiorentino also claims that the ``second fatal flaw is the use
of a rather uncomplicated formula based on Bayes Theorem.'' Let denote the
evidence and denote the theory that there were just two bullets (and hence
a single shooter). We used Bayes Theorem to hypothetically calculate
from and the prior probability . In order to make ten
times more likely than , the ratio of the prior probabilities
[i.e., ] would have to be greater than 15. Thus, we again
conclude that this casts serious doubt on Dr. Guinn's conclusion that the
evidence supported just two bullets. Sadly, this is far from the first time
that probability has been misunderstood and/or misapplied in a case of public
interest. A notable British example is the Clark case. See Nobles and Schiff
(2005) for details. Finally, we welcome and, in fact, encourage members of the
scientific community to provide alternative analyses of the data.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS154 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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