34,746 research outputs found
Stein factors for negative binomial approximation in Wasserstein distance
The paper gives the bounds on the solutions to a Stein equation for the
negative binomial distribution that are needed for approximation in terms of
the Wasserstein metric. The proofs are probabilistic, and follow the approach
introduced in Barbour and Xia (Bernoulli 12 (2006) 943-954). The bounds are
used to quantify the accuracy of negative binomial approximation to parasite
counts in hosts. Since the infectivity of a population can be expected to be
proportional to its total parasite burden, the Wasserstein metric is the
appropriate choice.Comment: Published at http://dx.doi.org/10.3150/14-BEJ595 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Dynamic response of strongly correlated Fermi gases in the quantum virial expansion
By developing a quantum virial expansion theory, we quantitatively calculate
the dynamic density response function of a trapped strongly interacting Fermi
gas at high temperatures near unitarity. A clear transition from atomic to
molecular responses is identified in the spectra when crossing from the BCS to
BEC regimes, in qualitative agreement with recent Bragg spectroscopy
observations. Our virial expansion method provides a promising way to solve the
challenging strong-coupling problems and is applicable to other dynamical
properties of strongly correlated Fermi gases.Comment: 5 pages, 4 figures; published version in Phys. Rev. A. The quantum
virial expansion of single-particle spectral function is discussed in
arXiv:1003.1538 (Phys. Rev. Lett. 104, 240407 (2010)
Radio Frequency Tunable Oscillator Device Based on SmB6 Microcrystal
Radio frequency tunable oscillators are vital electronic components for
signal generation, characterization, and processing. They are often constructed
with a resonant circuit and a 'negative' resistor, such as a Gunn-diode,
involving complex structure and large footprints. Here we report that a piece
of SmB6, 100 micron in size, works as a current-controlled oscillator in the 30
MHz frequency range. SmB6 is a strongly correlated Kondo insulator that was
recently found to have a robust surface state likely to be protected by the
topology of its electronics structure. We exploit its non-linear dynamics, and
demonstrate large AC voltage outputs with frequencies from 20 Hz to 30 MHz by
adjusting a small DC bias current. The behaviors of these oscillators agree
well with a theoretical model describing the thermal and electronic dynamics of
coupled surface and bulk states. With reduced crystal size we anticipate the
device to work at higher frequencies, even in the THz regime. This type of
oscillator might be realized in other materials with a metallic surface and a
semiconducting bulk.Comment: v3 to appear in Physical Review Letter
On Stein‘s factors for Poisson approximation in Wasserstein distance
We provide a probabilistic proof of various Stein's factors for Poisson approximation in terms of the Wasserstein distance
Efficient Synthesis of Narrowly Dispersed Brush Copolymers and Study of Their Assemblies: The Importance of Side Chain Arrangement
Efficient, one-pot preparation of synthetically challenging, high molecular weight (MW), narrowly dispersed brush block copolymers and random copolymers in high conversions was achieved by ring-opening metathesis (co)polymerization (ROMP) of various macromonomers (MMs) using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H_2IMes)(pyr)_2(Cl)_2RuCHPh. A series of random and block copolymers were prepared from a pair of MMs containing polylactide (PLA) and poly(n-butyl acrylate) (PnBA) side chains at similar MWs. Their self-assembly in the melt state was studied by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). In brush random copolymers containing approximately equal volume fractions of PLA and PnBA, the side chains segregate into lamellae with domain spacing of 14 nm as measured by SAXS, which was in good agreement with the lamellar thickness measured by AFM. The domain spacings and order−disorder transition temperatures of brush random copolymers were insensitive to the backbone length. In contrast, brush block copolymers containing approximately equal volume fractions of these MMs self-assembled into highly ordered lamellae with domain spacing over 100 nm. Their assemblies suggested that the brush block copolymer backbone adopted an extended conformation in the ordered state
Performance of Halbach magnetized brushless AC motors
The steady-state performance of Halbach magnetized brushless ac machines when operated in constant torque and flux-weakening modes is investigated both theoretically and experimentally, with particular emphasis on the influence of cross-coupling magnetic saturation on the torque capability
Charge collective modes in an incommensurately modulated cuprate
We report the first measurement of collective charge modes of insulating
Sr14Cu24O41 using inelastic resonant x-ray scattering over the complete
Brillouin zone. Our results show that the intense excitation modes at the
charge gap edge predominantly originate from the ladder-containing planar
substructures. The observed ladder modes (E vs. Q) are found to be dispersive
for momentum transfers along the "legs" but nearly localized along the "rungs".
Dispersion and peakwidth characteristics are similar to the charge spectrum of
1D Mott insulators, and we show that our results can be understood in the
strong coupling limit (U >> t_{ladder}> t_{chain}). The observed behavior is in
marked contrast to the charge spectrum seen in most two dimensional cuprates.
Quite generally, our results also show that momentum-tunability of inelastic
scattering can be used to resolve mode contributions in multi-component
incommensurate systems.Comment: 4+ pages, 5 figure
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