4,146 research outputs found
Skewed Pressure Characteristics of Equivalent Load in Double-Arch Tunnel
It is of great importance to reasonably estimate the surrounding rock load of a double-arch tunnel for the design, construction and stability evaluation of the tunnel. Currently, the basic theory on surrounding rock pressure of double-arch tunnels is insufficient for properly making the design and calculations. Generally, simplified calculations based on experience are used, such as the calculation method of Protodyakonov\u27s theory, the building code method and others. Considering the fact that the surrounding rock pressure of double-arch tunnels has skewed distribution characteristics, a computational model of a double-arch tunnel was built using data from an actual excavation of a highway tunnel. Taking some factors into consideration, such as different stress states, different construction methods and different sizes of double-arch tunnels, the pressure evolution of the surrounding rock was analyzed during step-by-step excavation of the double-arch tunnel. The results showed that in each condition the surrounding rock pressure of the double-arch tunnel displayed skewed distribution characteristics. The skewed distribution of the surrounding rock pressure varied with changes in stress state, construction sequence and excavation size. The skewed pressure of the double-arch tunnel was converted to equivalent load. The conversion method and distribution characteristics of the equivalent load are specified. They have important theoretical significance and practical value for similar engineering practices
Warm-Hot Gas in and around the Milky Way: Detection and Implications of OVII Absorption toward LMC X-3
X-ray absorption lines of highly-ionized species such as OVII at about zero
redshift have been firmly detected in the spectra of several active galactic
nuclei. However, the location of the absorbing gas remains a subject of debate.
To separate the Galactic and extragalactic contributions to the absorption, we
have obtained Chandra LETG-HRC and FUSE observations of the black hole X-ray
binary LMC X--3. A joint analysis of the detected OVII and Ne IX Kalpha lines,
together with the non-detection of the OVII Kbeta and OVIII Kalpha lines, gives
the measurements of the temperature, velocity dispersion, and hot oxygen column
density. The X-ray data also allow us to place a 95% confidence lower limit to
the Ne/O ratio as 0.14. The OVII line centroid and its relative shift from the
Galactic OI Kalpha absorption line, detected in the same observations, are
inconsistent with the systemic velocity of LMC X--3 ().
The far-UV spectrum shows OVI absorption at Galactic velocities, but no OVI
absorption is detected at the LMC velocity at significance. Both
the nonthermal broadening and the decreasing scale height with the increasing
ionization state further suggest an origin of the highly-ionized gas in a
supernova-driven galactic fountain. In addition, we estimate the warm and hot
electron column densities from our detected OVII Kalpha line in the LMC X--3
X-ray spectra and from the dispersion measure of a pulsar in the LMC vicinity.
We then infer the O/H ratio of the gas to be ,
consistent with the chemically-enriched galactic fountain scenario. We conclude
that the Galactic hot interstellar medium should in general substantially
contribute to zero-redshift X-ray absorption lines in extragalactic sources.Comment: 11 pages, accepted for publication in Ap
Millimeter Gap Contrast as a Probe for Turbulence Level in Protoplanetary Disks
Turbulent motions are believed to regulate angular momentum transport and
influence dust evolution in protoplanetary disks. Measuring the strength of
turbulence is challenging through gas line observations because of the
requirement for high spatial and spectral resolution data, and an exquisite
determination of the temperature. In this work, taking the well-known HD 163296
disk as an example, we investigated the contrast of gaps identified in high
angular resolution continuum images as a probe for the level of turbulence.
With self-consistent radiative transfer models, we simultaneously analyzed the
radial brightness profiles along the disk major and minor axes, and the
azimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap
contrasts measured from these profiles, we constrained the gas-to-dust scale
height ratio to be , and
for the D48, B67 and B100 regions, respectively. The varying
gas-to-dust scale height ratios indicate that the degree of dust settling
changes with radius. The inferred values for translate into a
turbulence level of in the D48 and
B100 regions, which is consistent with previous upper limits set by gas line
observations. However, turbulent motions in the B67 ring are strong with
. Due to the degeneracy
between and the depth of dust surface density drops, the turbulence
strength in the D86 gap region is not constrained.Comment: 13 pages, 7 figures, accepted for publication in Science China
Physics, Mechanics & Astronom
MyBASE: a database for genome polymorphism and gene function studies of Mycobacterium
<p>Abstract</p> <p>Background</p> <p>Mycobacterial pathogens are a major threat to humans. With the increasing availability of functional genomic data, research on mycobacterial pathogenesis and subsequent control strategies will be greatly accelerated. It has been suggested that genome polymorphisms, namely large sequence polymorphisms, can influence the pathogenicity of different mycobacterial strains. However, there is currently no database dedicated to mycobacterial genome polymorphisms with functional interpretations.</p> <p>Description</p> <p>We have developed a <b>my</b>cobacterial data<b>base </b>(MyBASE) housing genome polymorphism data and gene functions to provide the mycobacterial research community with a useful information resource and analysis platform. Whole genome comparison data produced by our lab and the novel genome polymorphisms identified were deposited into MyBASE. Extensive literature review of genome polymorphism data, mainly large sequence polymorphisms (LSPs), operon predictions and curated annotations of virulence and essentiality of mycobacterial genes are unique features of MyBASE. Large-scale genomic data integration from public resources makes MyBASE a comprehensive data warehouse useful for current research. All data is cross-linked and can be graphically viewed via a toolbox in MyBASE.</p> <p>Conclusion</p> <p>As an integrated platform focused on the collection of experimental data from our own lab and published literature, MyBASE will facilitate analysis of genome structure and polymorphisms, which will provide insight into genome evolution. Importantly, the database will also facilitate the comparison of virulence factors among various mycobacterial strains. MyBASE is freely accessible via <url>http://mybase.psych.ac.cn</url>.</p
Quantum Size Effects on the Chemical Sensing Performance of Two-Dimensional Semiconductors
We investigate the role of quantum confinement on the performance of gas
sensors based on two-dimensional InAs membranes. Pd-decorated InAs membranes
configured as H2 sensors are shown to exhibit strong thickness dependence, with
~100x enhancement in the sensor response as the thickness is reduced from 48 to
8 nm. Through detailed experiments and modeling, the thickness scaling trend is
attributed to the quantization of electrons which favorably alters both the
position and the transport properties of charge carriers; thus making them more
susceptible to surface phenomena
Inverse flux quantum periodicity of magnetoresistance oscillations in two-dimensional short-period surface superlattices
Transport properties of the two-dimensional electron gas (2DEG) are
considered in the presence of a perpendicular magnetic field and of a {\it
weak} two-dimensional (2D) periodic potential modulation in the 2DEG plane. The
symmetry of the latter is rectangular or hexagonal. The well-known solution of
the corresponding tight-binding equation shows that each Landau level splits
into several subbands when a rational number of flux quanta pierces the
unit cell and that the corresponding gaps are exponentially small. Assuming the
latter are closed due to disorder gives analytical wave functions and
simplifies considerably the evaluation of the magnetoresistivity tensor
. The relative phase of the oscillations in and
depends on the modulation periods involved. For a 2D modulation
with a {\bf short} period nm, in addition to the Weiss oscillations
the collisional contribution to the conductivity and consequently the tensor
show {\it prominent peaks when one flux quantum passes
through an integral number of unit cells} in good agreement with recent
experiments. For periods nm long used in early experiments, these
peaks occur at fields 10-25 times smaller than those of the Weiss oscillations
and are not resolved
Search for D to phi l nu and measurement of the branching fraction for D to phi pi
Using a data sample of integrated luminosity of about 33 pb collected
around 3.773 GeV with the BESII detector at the BEPC collider, the semileptonic
decays , and the hadronic
decay are studied. The upper limits of the branching
fractions are set to be 2.01% and 2.04% at the 90% confidence level. The ratio of the
branching fractions for relative to is measured to be . In addition, the
branching fraction for is obtained to be .Comment: 6 pages, 5 figures, to be published in Eur.Phys.J.
Measurements of branching fractions for inclusive K0~/K0 and K*(892)+- decays of neutral and charged D mesons
Using the data sample of about 33 pb-1 collected at and around 3.773 GeV with
the BES-II detector at the BEPC collider, we have studied inclusive K0~/K0 and
K*(892)+- decays of D0 and D+ mesons. The branching fractions for the inclusive
K0~/K0 and K*(892)- decays are measured to be BF(D0 to K0~/K0
X)=(47.6+-4.8+-3.0)%, BF(D+ to K0~/K0 X)=(60.5+-5.5+-3.3)%, BF(D0 to K*-
X)=(15.3+- 8.3+- 1.9)% and BF(D+ to K*- X)=(5.7+- 5.2+- 0.7)%. The upper limits
of the branching fractions for the inclusive K*(892)+ decays are set to be
BF(D0 to K*+ X)<3.6% and BF(D+ to K*+ X) <20.3% at 90% confidence level
Charmless Decays Based on the six-quark Effective Hamiltonian with Strong Phase Effects II
We provide a systematic study of charmless decays (
and denote pseudoscalar and vector mesons, respectively) based on an
approximate six-quark operator effective Hamiltonian from QCD. The calculation
of the relevant hard-scattering kernels is carried out, the resulting
transition form factors are consistent with the results of QCD sum rule
calculations. By taking into account important classes of power corrections
involving "chirally-enhanced" terms and the vertex corrections as well as weak
annihilation contributions with non-trivial strong phase, we present
predictions for the branching ratios and CP asymmetries of decays into
PP, PV and VV final states, and also for the corresponding polarization
observables in VV final states. It is found that the weak annihilation
contributions with non-trivial strong phase have remarkable effects on the
observables in the color-suppressed and penguin-dominated decay modes. In
addition, we discuss the SU(3) flavor symmetry and show that the symmetry
relations are generally respected
Resonances in and
A partial wave analysis is presented of and
from a sample of 58M events in the BES II detector. The
is observed clearly in both sets of data, and parameters of the
Flatt\' e formula are determined accurately: (stat)
(syst) MeV/c, MeV/c, . The data also exhibit a strong peak
centred at MeV/c. It may be fitted with and a
dominant signal made from interfering with a smaller
component. There is evidence that the signal is
resonant, from interference with . There is also a state in with MeV/c and
MeV/c; spin 0 is preferred over spin 2. This state, , is
distinct from . The data contain a strong peak due to
. A shoulder on its upper side may be fitted by interference
between and .Comment: 17 pages, 6 figures, 1 table. Submitted to Phys. Lett.
- âŠ