5,422 research outputs found
Quantum Manifestations of Graphene Edge Stress and Edge Instability: A First-Principles Study
We have performed first-principles calculations of graphene edge stresses,
which display two interesting quantum manifestations absent from the classical
interpretation: the armchair edge stress oscillates with a nanoribbon width,
and the zigzag edge stress is noticeably reduced by spin polarization. Such
quantum stress effects in turn manifest in mechanical edge twisting and warping
instability, showing features not captured by empirical potentials or continuum
theory. Edge adsorption of H and Stone-Wales reconstruction are shown to
provide alternative mechanisms in relieving the edge compression and hence to
stabilize the planar edge structure.Comment: 5figure
The position profiles of order cancellations in an emerging stock market
Order submission and cancellation are two constituent actions of stock
trading behaviors in order-driven markets. Order submission dynamics has been
extensively studied for different markets, while order cancellation dynamics is
less understood. There are two positions associated with a cancellation, that
is, the price level in the limit-order book (LOB) and the position in the queue
at each price level. We study the profiles of these two order cancellation
positions through rebuilding the limit-order book using the order flow data of
23 liquid stocks traded on the Shenzhen Stock Exchange in the year 2003. We
find that the profiles of relative price levels where cancellations occur obey
a log-normal distribution. After normalizing the relative price level by
removing the factor of order numbers stored at the price level, we find that
the profiles exhibit a power-law scaling behavior on the right tails for both
buy and sell orders. When focusing on the order cancellation positions in the
queue at each price level, we find that the profiles increase rapidly in the
front of the queue, and then fluctuate around a constant value till the end of
the queue. These profiles are similar for different stocks. In addition, the
profiles of cancellation positions can be fitted by an exponent function for
both buy and sell orders. These two kinds of cancellation profiles seem
universal for different stocks investigated and exhibit minor asymmetry between
buy and sell orders. Our empirical findings shed new light on the order
cancellation dynamics and pose constraints on the construction of order-driven
stock market models.Comment: 17 pages, 6 figures and 6 table
Global Dynamics of Advection-Dominated Accretion Revisited
We numerically solve the set of dynamical equations describing
advection-dominated accretion flows (ADAF) around black holes, using a method
similar to that of Chakrabarti (1996a). We choose the sonic radius of the flow
and the integration constant in angular momentum equation as free
parameters, and integrate the equations from the sonic point inwards to see if
the solution can extend supersonically to the black hole horizon, and outwards
to see if and where an acceptable outer boundary of the flow can be found. We
recover the ADAF-thin disk solution constructed in Narayan, Kato, & Honma
(1997, NKH97), an representative paper of the previous works on global ADAF
solutions, although in that paper an apparently very different procedure was
adopted. We obtain a complete picture in the form of parameter space
which sums up the situation of ADAF solution at a glance. For comparison we
also present the distribution of global solutions for inviscid flows in the
space, which supports the view that there should be some similarities
between the dynamical behavior of ADAF and that of adiabatic flows, and that
there should be a continuous change from the properties of viscous flows to
those of inviscid ones.Comment: 24 pages with 15 figures, to appear in ApJ Vol. 52
Orthogonal on-rotor sensing vibrations for condition monitoring of rotating machines
Thanks to the fast development of micro-electro-mechanical systems (MEMS) technologies, MEMS accelerometers show great potentialities for machine condition monitoring. To overcome the problems of a poor signal to noise ratio (SNR), complicated modulation, and high costs of vibration measurement and computation using conventional integrated electronics piezoelectric accelerometers, a triaxial MEMS accelerometer-based on-rotor sensing (ORS) technology was developed in this study. With wireless data transmission capability, the ORS unit can be mounted on a rotating rotor to obtain both rotational and transverse dynamics of the rotor with a high SNR. The orthogonal outputs lead to a construction method of analytic signals in the time domain, which is versatile in fault detection and diagnosis of rotating machines. Two case studies based on an induction motor were carried out, which demonstrated that incipient bearing defect and half-broken rotor bar can be effectively diagnosed by the proposed measurement and analysis methods. Comparatively, vibration signals from translational on-casing accelerometers are less capable of detecting such faults. This demonstrates the superiority of the ORS vibrations in fault detection of rotating machines
Emergence of long memory in stock volatility from a modified Mike-Farmer model
The Mike-Farmer (MF) model was constructed empirically based on the
continuous double auction mechanism in an order-driven market, which can
successfully reproduce the cubic law of returns and the diffusive behavior of
stock prices at the transaction level. However, the volatility (defined by
absolute return) in the MF model does not show sound long memory. We propose a
modified version of the MF model by including a new ingredient, that is, long
memory in the aggressiveness (quantified by the relative prices) of incoming
orders, which is an important stylized fact identified by analyzing the order
flows of 23 liquid Chinese stocks. Long memory emerges in the volatility
synthesized from the modified MF model with the DFA scaling exponent close to
0.76, and the cubic law of returns and the diffusive behavior of prices are
also produced at the same time. We also find that the long memory of order
signs has no impact on the long memory property of volatility, and the memory
effect of order aggressiveness has little impact on the diffusiveness of stock
prices.Comment: 6 pages, 6 figures and 1 tabl
Summer and winter living coccolithophores in the Yellow Sea and the East China Sea
This paper describes the distribution of living coccolithophores (LCs) in the
Yellow Sea and the East China Sea in summer and winter, and its relationship
with environmental factors by canonical correspondence analysis (CCA). We
carried out a series of investigations on LCs distribution in the Yellow Sea
and the East China Sea in July and December 2011. 210 samples from different
depths were collected from 44 stations in summer and 217 samples were
collected from 45 stations in winter. Totally 20 taxa belonging to
coccolithophyceae were identified using a polarized microscope at the
1000 × magnification. The dominant species of the two seasons were
Gephyrocapsa oceanica, Emiliania huxleyi, Helicosphaera carteri, and
Algirosphaera robusta. In summer the abundance of coccolithophore cells and
coccoliths ranged 0–176.40 cells mL<sup>−1</sup>, and
0–2144.98 coccoliths mL<sup>−1</sup>, with the average values of
8.45 cells mL<sup>−1</sup>, and 265.42 coccoliths mL<sup>−1</sup>, respectively. And
in winter the abundance of cells and coccoliths ranged
0–71.66 cells mL<sup>−1</sup>, and 0–4698.99 coccoliths mL<sup>−1</sup>, with the
average values of 13.91 cells mL<sup>−1</sup> and 872.56 coccoliths mL<sup>−1</sup>,
respectively. In summer, the LCs in surface layer were mainly observed on the
coastal belt and southern part of the survey area. In winter, the LCs in
surface layer had high value in the continental shelf area of section P. The
comparison among section A, section F, section P and section E indicated
lower species diversity and less abundance in the Yellow Sea than those in
the East China Sea in both seasons. Temperature and the nitrate concentration
may be the major environmental factors controlling the distribution and
species composition of LCs in the studying area based on CCA.
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Abbreviations: LCs: Living Coccolithophores; CCA: canonical correspondence
analysis; DCM: Deep Chlorophyll Maximu
Induction of colonic epithelial cell apoptosis by p47-dependent oxidants11Nucleotide sequence data reported are available in GenBank database under accession # AF540955.
AbstractExogenous oxidants appear capable of initiating both proliferative and death signals, but the role of endogenous oxidants in either tumorigenesis or tumor suppression is unclear. We found that expression of the NAD(P)H oxidase adapter p47phox was suppressed in human colon carcinoma specimens relative to adjacent normal colon. Overexpression of p47phox increased apoptosis in colon cancer cell lines independent of p53 and mismatch-repair competency. p47phox was found to interact with the c-Abl adapter Abl interactor-1 (ABI-1), and p47phox coprecipitated with both ABI-1 and c-Abl. Ectopic expression of p47phox in colon cancer cells increased oxidant production with phosphorylation and activation of nuclear c-Abl and consequent apoptosis. Colonic epithelial p47phox may be specifically targeted to a c-Abl-containing complex that serves a physiologic tumor suppressing function
Singlet Fermionic Dark Matter explains DAMA signal
It has been suggested that, considering channeling effect, the order of a few
GeV dark matters which are elastically scattered from detector nuclei might be
plausible candidates reconciling the DAMA annual modulation signal with the
results of other null experiments. We show that Singlet Fermionic Dark Matter
can be such a dark matter candidate, simultaneously providing the correct
thermal relic density which is consistent with the WMAP data.Comment: 9 pages, 3 figure
A scheme for dense coding in the non-symmetric quantum channel
We investigate the dense coding in the case of non-symmetric Hilbert spaces
of the sender and receiver's particles sharing the quantum maximally entangled
state. The efficiency of classical information gain is also considered. We
conclude that when a more level particle is with the sender, she can get a
non-symmetric quantum channel from a symmetric one by entanglement transfer.
Thus the efficiency of information transmission is improved
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