15,024 research outputs found
Non-spectator Contributions To The Lifetime of
In this work, we evaluate the contributions of non-spectator effects to the
lifetimes of and B-mesons. Based on the well-established models and
within a reasonable range of the concerned parameters, the contributions can
reduce the lifetime of by compared to that of B-mesons
which are not significantly affected. This might partly explain the measured
ratio \cite{Data}, which has been a
long-standing discrepancy between theory and experimental data
Large-Scale Spectroscopic Mapping of the Ophiuchi Molecular Cloud Complex I. The CH to NH Ratio as a Signpost of Cloud Characteristics
We present 2.5-square-degree CH N=1-0 and NH J=1-0 maps of the
Ophiuchi molecular cloud complex. These are the first large-scale maps
of the Ophiuchi molecular cloud complex with these two tracers. The
CH emission is spatially more extended than the NH emission. One
faint NH clump Oph-M and one CH ring Oph-RingSW are identified
for the first time. The observed CH to NH abundance ratio
([CH]/[NH]) varies between 5 and 110. We modeled the CH
and NH abundances with 1-D chemical models which show a clear decline
of [CH]/[NH] with chemical age. Such an evolutionary trend is
little affected by temperatures when they are below 40 K. At high density
(n 10 cm), however, the time it takes for the abundance
ratio to drop at least one order of magnitude becomes less than the dynamical
time (e.g., turbulence crossing time 10 years). The observed
[CH]/[NH] difference between L1688 and L1689 can be explained by
L1688 having chemically younger gas in relatively less dense regions. The
observed [CH]/[NH] values are the results of time evolution,
accelerated at higher densities. For the relative low density regions in L1688
where only CH emission was detected, the gas should be chemically younger.Comment: Accepted by ApJ, 45 pages, 10 figure
Diffusion of Colloidal Rods in Corrugated Channels
In many natural and artificial devices diffusive transport takes place in
confined geometries with corrugated boundaries. Such boundaries cause both
entropic and hydrodynamic effects, which have been studied only for the case of
spherical particles. Here we experimentally investigate diffusion of particles
of elongated shape confined into a corrugated quasi-two-dimensional channel.
Elongated shape causes complex excluded-volume interactions between particle
and channel walls which reduce the accessible configuration space and lead to
novel entropic free energy effects. The extra rotational degree of freedom also
gives rise to a complex diffusivity matrix that depends on both the particle
location and its orientation. We further show how to extend the standard
Fick-Jacobs theory to incorporate combined hydrodynamic and entropic effects,
so as, for instance, to accurately predict experimentally measured mean first
passage times along the channel. Our approach can be used as a generic method
to describe translational diffusion of anisotropic particles in corrugated
channels.Comment: 12 pages and 4 figure
Adsorption of Ions at the Interface of Clay Minerals and Aqueous Solutions
Adsorption of ions at the interface of clay minerals and aqueous solutions plays a critical role in a wide spectrum of colloidal, chemical, physical, and geological processes. Owing to the particular complexity of related systems and the femtosecond scale of related processes, the direct experimental observations often become a challenging task. As a contrast, computer simulations have proven to be a competent and powerful approach therein and already realized fruitful and significant contributions. In this chapter, we attempt to draw a relatively comprehensive picture of the interfacial adsorption of ions mainly within the context of computer simulations. As elaborated, quantum mechanics (QM) and molecular dynamics (MD), two popular simulation techniques currently used, have respective advantages, and with their collaborative efforts, we are striding toward the in-depth and systematic understanding of adsorption configuration, distribution, stability, reaction thermodynamics and mechanism, dynamics, diffusivity as well as electric double layer and other fundamental issues that are closely associated with the adsorption of ions at the interface of clay minerals and aqueous solutions. In addition, we demonstrate that investigation of the interfacial adsorption of ions greatly helps to unravel the origin and mechanism of ion-specific effects, whose importance has been explicitly suggested to be no less than Gregor Mendel’s work to genetics
Application of Density Functional Theory in Soil Science
Soil is the basis for life and soil science is regarded as the final frontier; however, as compared to chemistry, physics, biology, and other disciplines, soil science undergoes an obviously slower development and remains almost stagnant in the past few decades, mainly due to two reasons: (1) wrong and outdated perceptions for a large portion of soil researchers; (2) complexity of soil systems that are difficult to characterize by current experimental techniques. Computer simulations have unique advantages to handle complex systems while currently, its role during soil researches is far from being recognized. In this chapter, several examples are given with respect to application of density functional theory (DFT) calculations to soil science, focusing on the adsorption of uranyl ion and SO2 onto mineral surfaces and reaction mechanisms to form acid rain. In this way, insightful clues at the atomic level are provided for the adsorption, interaction, and reactions regarding soil systems. We believe that computer simulations including DFT are the right key to unravel the complicated processes occurring in soils. More efforts of computer simulations are anticipated for soil science with aim to decipher the experimental results and probe the uncharted principles that may result in a revolutionary in the near future
Instantaneous Bethe-Salpeter Equation and Its Exact Solution
We present an approach to solve a Bethe-Salpeter (BS) equation exactly
without any approximation if the kernel of the BS equation exactly is
instantaneous, and take positronium as an example to illustrate the general
features of the solutions. As a middle stage, a set of coupled and
self-consistent integration equations for a few scalar functions can be
equivalently derived from the BS equation always, which are solvable
accurately. For positronium, precise corrections to those of the Schr\"odinger
equation in order (relative velocity) in eigenfunctions, in order in
eigenvalues, and the possible mixing, such as that between () and
() components in () states as well, are
determined quantitatively. Moreover, we also point out that there is a
problematic step in the classical derivation which was proposed first by E.E.
Salpeter. Finally, we emphasize that for the effective theories (such as NRQED
and NRQCD etc) we should pay great attention on the corrections indicated by
the exact solutions.Comment: 4 pages, replace for shortening the manuscrip
Similarities and differences of functional connectivity in drug-naïve, first-episode adolescent and young adult with major depressive disorder and schizophrenia
Major depressive disorder (MDD) and schizophrenia (SZ) are considered two distinct psychiatric disorders. Yet, they have considerable overlap in symptomatology and clinical features, particularly in the initial phases of illness. The amygdala and prefrontal cortex (PFC) appear to have critical roles in these disorders; however, abnormalities appear to manifest differently. In our study forty-nine drug-naïve, first-episode MDD, 45 drug-naïve, first-episode SZ, and 50 healthy control (HC) participants from 13 to 30 years old underwent resting-state functional magnetic resonance imaging. Functional connectivity (FC) between the amygdala and PFC was compared among the three groups. Significant differences in FC were observed between the amygdala and ventral PFC (VPFC), dorsolateral PFC (DLPFC), and dorsal anterior cingulated cortex (dACC) among the three groups. Further analyses demonstrated that MDD showed decreased amygdala-VPFC FC and SZ had reductions in amygdala-dACC FC. Both the diagnostic groups had significantly decreased amygdala-DLPFC FC. These indicate abnormalities in amygdala-PFC FC and further support the importance of the interaction between the amygdala and PFC in adolescents and young adults with these disorders. Additionally, the alterations in amygdala-PFC FC may underlie the initial similarities observed between MDD and SZ and suggest potential markers of differentiation between the disorders at first onset
Microstructure evolution and mechanical property response of TC11 titanium alloy under electroshock treatment
© 2020 The Authors This work investigated the effects of electroshock treatment (EST) on the microstructure variation and mechanical properties of TC11 alloy. The average hardness of the specimens decreased from 358 HV to 328 HV after EST of 0.04 s, then increased to 396 HV after EST of 0.06 s. After EST, the yield strength of specimen declined from 959 MPa to 797 MPa after EST of 0.04 s, and then increased to 1265 MPa after EST of 0.06 s, but the fracture strain decreased continuously. The variation in mechanical properties was closely related to the phase transition from the secondary α (αs) to β phase, and the precipitation of refined needlelike α martensite (αM). The diffusion of atoms accompanied by broaden αs/β boundary from 11.2 nm to 27.6 nm due to the phase transformation after EST by 0.04 s and the dislocation pileup at the boundary to form defects, which resulted the decrease in strength. While increasing the EST time to 0.06 s, the width of αM/β boundary decreased to 5.91 nm. All results indicated that the EST is an effective method for optimizing the microstructure and mechanical properties of titanium alloys in a short time
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