16,049 research outputs found
Planck Constraints on Holographic Dark Energy
We perform a detailed investigation on the cosmological constraints on the
holographic dark energy (HDE) model by using the Planck data. HDE can provide a
good fit to Planck high-l (l>40) temperature power spectrum, while the
discrepancy at l=20-40 found in LCDM remains unsolved in HDE. The Planck data
alone can lead to strong and reliable constraint on the HDE parameter c. At 68%
CL, we get c=0.508+-0.207 with Planck+WP+lensing, favoring the present phantom
HDE at > 2sigma CL. Comparably, by using WMAP9 alone we cannot get interesting
constraint on c. By combining Planck+WP with the BAO measurements from
6dFGS+SDSS DR7(R)+BOSS DR9, the H0 measurement from HST, the SNLS3 and Union2.1
SNIa data sets, we get 68% CL constraints c=0.484+-0.070, 0.474+-0.049,
0.594+-0.051 and 0.642+-0.066. Constraints can be improved by 2%-15% if we
further add the Planck lensing data. Compared with the WMAP9 results, the
Planck results reduce the error by 30%-60%, and prefer a phantom-like HDE at
higher CL. We find no evident tension between Planck and BAO/HST. Especially,
the strong correlation between Omegam h^3 and dark energy parameters is helpful
in relieving the tension between Planck and HST. The residual
chi^2_{Planck+WP+HST}-chi^2_{Planck+WP} is 7.8 in LCDM, and is reduced to 1.0
or 0.3 if we switch dark energy to the w model or the holographic model. We
find SNLS3 is in tension with all other data sets; for Planck+WP, WMAP9 and
BAO+HST, the corresponding Delta chi^2 is 6.4, 3.5 and 4.1, respectively.
Comparably, Union2.1 is consistent with these data sets, but the combination
Union2.1+BAO+HST is in tension with Planck+WP+lensing, corresponding to a Delta
chi^2 8.6 (1.4% probability). Thus, it is not reasonable to perform an
all-combined (CMB+SNIa+BAO+HST) analysis for HDE when using the Planck data.
Our tightest self-consistent constraint is c=0.495+-0.039 obtained from
Planck+WP+BAO+HST+lensing.Comment: 29 pages, 11 figures, 3 tables; version accepted for publication in
JCA
A gauge-invariant and current-continuous microscopic ac quantum transport theory
There had been consensus on what the accurate ac quantum transport theory was
until some recent works challenged the conventional wisdom. Basing on the
non-equilibrium Green's function formalism for time-dependent quantum
transport, we derive an expression for the dynamic admittance that satisfies
gauge invariance and current continuity, and clarify the key concept in the
field. The validity of our now formalism is verified by first-principles
calculation of the transient current through a carbon-nanotube-based device
under the time-dependent bias voltage. Moreover, the previously well-accepted
expression for dynamic admittance is recovered only when the device is a
perfect conductor at a specific potential
A comparative study of mesoporous glass/silk and non-mesoporous glass/silk scaffolds: Physiochemistry and in vivo osteogenesis
Mesoporous bioactive glass (MBG) is a new class of biomaterials with a well-ordered nanochannel structure, whose in vitro bioactivity is far superior than that of non-mesoporous bioactive glass (BG); the material's in vivo osteogenic properties are, however, yet to be assessed. Porous silk scaffolds have been used for bone tissue engineering, but this material's osteoconductivity is far from optimal. The aims of this study were to incorporate MBG into silk scaffolds in order to improve their osteoconductivity and then to compare the effect of MBG and BG on the in vivo osteogenesis of silk scaffolds. MBG/silk and BG/silk scaffolds with a highly porous structure were prepared by a freeze-drying method. The mechanical strength, in vitro apatite mineralization, silicon ion release and pH stability of the composite scaffolds were assessed. The scaffolds were implanted into calvarial defects in SCID mice and the degree of in vivo osteogenesis was evaluated by microcomputed tomography (μCT), hematoxylin and eosin (H&E) and immunohistochemistry (type I collagen) analyses. The results showed that MBG/silk scaffolds have better physiochemical properties (mechanical strength, in vitro apatite mineralization, Si ion release and pH stability) compared to BG/silk scaffolds. MBG and BG both improved the in vivo osteogenesis of silk scaffolds. μCT and H&E analyses showed that MBG/silk scaffolds induced a slightly higher rate of new bone formation in the defects than did BG/silk scaffolds and immunohistochemical analysis showed greater synthesis of type I collagen in MBG/silk scaffolds compared to BG/silk scaffolds
Self-assembly of noble metal nanoparticles into sub-100 nm colloidosomes with collective optical and catalytic properties.
Self-assembly at the nanoscale represents a powerful tool for creating materials with new structures and intriguing collective properties. Here, we report a novel strategy to synthesize nanoscale colloidosomes of noble metals by assembling primary metal nanoparticles at the interface of emulsion droplets formed by their capping agent. This strategy produces noble metal colloidosomes of unprecedentedly small sizes (<100 nm) in high yield and uniformity, which is highly desirable for practical applications. In addition, it enables the high tunability of the composition, producing a diversity of monometallic and bimetallic alloy colloidosomes. The colloidosomes exhibit interesting collective properties that are different from those of individual colloidal nanoparticles. Specifically, we demonstrate Au colloidosomes with well-controlled interparticle plasmon coupling and Au-Pd alloy colloidosomes with superior electrocatalytic performance, both thanks to the special structural features that arise from the assembly. We believe this strategy provides a general platform for producing a rich class of miniature colloidosomes that may have fascinating collective properties for a broad range of applications
Optimizing Batch Linear Queries under Exact and Approximate Differential Privacy
Differential privacy is a promising privacy-preserving paradigm for
statistical query processing over sensitive data. It works by injecting random
noise into each query result, such that it is provably hard for the adversary
to infer the presence or absence of any individual record from the published
noisy results. The main objective in differentially private query processing is
to maximize the accuracy of the query results, while satisfying the privacy
guarantees. Previous work, notably \cite{LHR+10}, has suggested that with an
appropriate strategy, processing a batch of correlated queries as a whole
achieves considerably higher accuracy than answering them individually.
However, to our knowledge there is currently no practical solution to find such
a strategy for an arbitrary query batch; existing methods either return
strategies of poor quality (often worse than naive methods) or require
prohibitively expensive computations for even moderately large domains.
Motivated by this, we propose low-rank mechanism (LRM), the first practical
differentially private technique for answering batch linear queries with high
accuracy. LRM works for both exact (i.e., -) and approximate (i.e.,
(, )-) differential privacy definitions. We derive the
utility guarantees of LRM, and provide guidance on how to set the privacy
parameters given the user's utility expectation. Extensive experiments using
real data demonstrate that our proposed method consistently outperforms
state-of-the-art query processing solutions under differential privacy, by
large margins.Comment: ACM Transactions on Database Systems (ACM TODS). arXiv admin note:
text overlap with arXiv:1212.230
Transmission resonance in a composite plasmonic structure
The design, fabrication, and optical properties of a composite plasmonic
structure, a two-dimentional array of split-ring resonators inserted into
periodic square holes of a metal film, have been reported. A new type of
transmission resonance, which makes a significant difference from the
conventional peaks, has been suggested both theoretically and experimentally.
To understand this effect, a mechanism of ring- resonance induced dipole
emission is proposed.Comment: 14 pages, 4 figure
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