3,768 research outputs found
Liquid-to-liquid phase transition in pancake vortex systems
We study the thermodynamics of a model of pancake vortices in layered
superconductors. The model is based on the effective pair potential for the
pancake vortices derived from the London approximation of a version of the
Lawrence-Doniach model which is valid for extreme type-II superconductors.
Using the hypernetted-chain (HNC) approximation, we find that there is a
temperature below which multiple solutions to the HNC equations exist. By
explicitly evaluating the free energy for each solution we find that the system
undergoes a first-order transition between two vortex liquid phases. The
low-temperature phase has larger correlations along the field direction than
the high-temperature phase. We discuss the possible relation of this phase
transition to the liquid-to-liquid phase transition recently observed in
Y-Ba-Cu-O superconductors in high magnetic fields in the presence of disorder.Comment: 7 pages, 6 figure
Teleportation via thermally entangled state of a two-qubit Heisenberg XX chain
We find that quantum teleportation, using the thermally entangled state of
two-qubit Heisenberg XX chain as a resource, with fidelity better than any
classical communication protocol is possible. However, a thermal state with a
greater amount of thermal entanglement does not necessarily yield better
fidelity. It depends on the amount of mixing between the separable state and
maximally entangled state in the spectra of the two-qubit Heisenberg XX model.Comment: 5 pages, 1 tabl
The RNA Helicase DDX6 Controls Cellular Plasticity by Modulating P-Body Homeostasis
Post-transcriptional mechanisms have the potential to influence complex changes in gene expression, yet their role in cell fate transitions remains largely unexplored. Here, we show that suppression of the RNA helicase DDX6 endows human and mouse primed embryonic stem cells (ESCs) with a differentiation-resistant, “hyper-pluripotent” state, which readily reprograms to a naive state resembling the preimplantation embryo. We further demonstrate that DDX6 plays a key role in adult progenitors where it controls the balance between self-renewal and differentiation in a context-dependent manner. Mechanistically, DDX6 mediates the translational suppression of target mRNAs in P-bodies. Upon loss of DDX6 activity, P-bodies dissolve and release mRNAs encoding fate-instructive transcription and chromatin factors that re-enter the ribosome pool. Increased translation of these targets impacts cell fate by rewiring the enhancer, heterochromatin, and DNA methylation landscapes of undifferentiated cell types. Collectively, our data establish a link between P-body homeostasis, chromatin organization, and stem cell potency
Valence band photoemission from the GaN(0001) surface
A detailed investigation by one-step photoemission calculations of the
GaN(0001)-(1x1) surface in comparison with recent experiments is presented in
order to clarify its structural properties and electronic structure. The
discussion of normal and off-normal spectra reveals through the identified
surface states clear fingerprints for the applicability of a surface model
proposed by Smith et al. Especially the predicted metallic bonds are confirmed.
In the context of direct transitions the calculated spectra allow to determine
the valence band width and to argue in favor of one of two theoretical bulk
band structures. Furthermore a commonly used experimental method to fix the
valence band maximum is critically tested.Comment: 8 pages, 11 eps files, submitted to PR
Shaking Table Test of the Taiwanese Traditional Dieh-Dou Timber Frame
This article attempts to explore the dynamic behavior of traditional Dieh-Dou timber structure under different combinations of structural forms and vertical loads. Using time-history record (TCU 084) from the Chi-Chi earthquake, two semi full-scale specimens (Symmetric and Asymmetric) were tested. Results showed that the Symmetric specimen tends to be damaged more easily and faster than the Asymmetric one. Damage pattern generally begins from the bottom Dou members and subsequently spreading upwards to the upper Dou, horizontal Gong members, and adjoining Shu members. Friction force between the contact surfaces is crucial towards the maintenance of overall structure. Increase vertical loadings have significant effect on the natural frequencies and global stiffness of the structure. Using the Single-Degree-Of-Freedom (SDOF) system, the derived stiffness is generally in good agreement with the dynamic results of both forms. This study suggests that the effects of increasing vertical loadings should be taken into consideration for future evaluation
Resonance phenomena in ultracold dipole-dipole scattering
Elastic scattering resonances occurring in ultracold collisions of either
bosonic or fermionic polar molecules are investigated. The Born-Oppenheimer
adiabatic representation of the two-bodydynamics provides both a qualitative
classification scheme and a quantitative WKB quantization condition that
predicts several sequences of resonant states. It is found that the
near-threshold energy dependence of ultracold collision cross sections varies
significantly with the particle exchange symmetry, with bosonic systems showing
much smoother energy variations than their fermionic counterparts. Resonant
variations of the angular distributions in ultracold collisions are also
described.Comment: 19 pages, 6 figures, revtex4, submitted to J. Phys.
Structural behavior of traditional Dieh-Dou timber main frame
Under different combinations of horizontal and vertical loads, a total of three static cyclic tests
were conducted to investigate the in-plane structural behaviour of the traditional Dieh-Dou timber
frame. Typical deformation patterns include column rocking, joint rotation around the primary
beam-column and column Dou-column regions, vertical shear around the upper and lower end of
column mortise, embedment around primary beam-column regions and vertical shearing around
the mortise regions of the Dou members. Visible deformation generally began from 1/30 rad
onwards. Column restoring force contributed mainly to the main frame’s moment resistance when
displacement is small. When frame deformation exceeds 1/50 rad, bending moment from the
primary beam dominated the frame’s global restoring force. Hence, column restoring force and
the primary beam-column connection generally undertake the primary moment-resisting
mechanism while the complex bracket structures above the primary beam play a secondary role.
Base on embedment theory and semi-rigid spring model, a new theoretical model was developed
to estimate the global behaviour for the global system of Dieh-Dou main frame. The current
model can only estimate the initial and secondary stiffness as the spring stiffness are assumed to
behave bi-linearly. Hence, it is unable to predict the out-of-plane failure phenomena and ultimate
failure load at this moment. Although the prediction tends to be on the conservative side, the
predicted model is generally in good agreement with observed results
Nonparametric nonlinear model predictive control
Model Predictive Control (MPC) has recently found wide acceptance in industrial applications, but its potential has been much impeded by linear models due to the lack of a similarly accepted nonlinear modeling or databased technique. Aimed at solving this problem, the paper addresses three issues: (i) extending second-order Volterra nonlinear MPC (NMPC) to higher-order for improved prediction and control; (ii) formulating NMPC directly with plant data without needing for parametric modeling, which has hindered the progress of NMPC; and (iii) incorporating an error estimator directly in the formulation and hence eliminating the need for a nonlinear state observer. Following analysis of NMPC objectives and existing solutions, nonparametric NMPC is derived in discrete-time using multidimensional convolution between plant data and Volterra kernel measurements. This approach is validated against the benchmark van de Vusse nonlinear process control problem and is applied to an industrial polymerization process by using Volterra kernels of up to the third order. Results show that the nonparametric approach is very efficient and effective and considerably outperforms existing methods, while retaining the original data-based spirit and characteristics of linear MPC
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