Multiple-Input Multiple-Output Gaussian Broadcast Channels with Common and Confidential Messages

This paper considers the problem of the multiple-input multiple-output (MIMO) Gaussian broadcast channel with two receivers (receivers 1 and 2) and two messages: a common message intended for both receivers and a confidential message intended only for receiver 1 but needing to be kept asymptotically perfectly secure from receiver 2. A matrix characterization of the secrecy capacity region is established via a channel enhancement argument. The enhanced channel is constructed by first splitting receiver 1 into two virtual receivers and then enhancing only the virtual receiver that decodes the confidential message. The secrecy capacity region of the enhanced channel is characterized using an extremal entropy inequality previously established for characterizing the capacity region of a degraded compound MIMO Gaussian broadcast channel.Comment: Submitted to the IEEE Transactions on Information Theory, July 200

Lambda polarization in pp -> p\Lambda K^+ \pi^+\pi^-\pi^+\pi^-

We show that there is a correlation between the invariant mass of the produced \Lambda K^+, \Lambda K^+\pi^+\pi^- or \Lambda K^+ \pi^+\pi^-\pi^+\pi^- system in the exclusive reaction pp\to p\Lambda K^+\pi^+\pi^-\pi^+\pi^- and the longitudinal or transverse momentum of $\Lambda$. Together with the longitudinal and transverse momentum dependence of Lambda polarization observed in inclusive reactions, such a correlation implies a dependence of Lambda polarization on these invariant masses. The qualitative features of this dependence are consistent with the recent observation by E766 collaboration at BNL. A quantitative estimation has been made using an event generator for $pp$ collisions. A detailed comparison with the data is made.Comment: 10 pages with 3 figures, submitted to J. Phys.

Cerebrospinal fluid flow behaviour in lumbar spinal stenosis - a computational fluid dynamic study based on magnetic resonance imaging

Introduction Degenerative lumbar spinal stenosis (LSS) is a pathology characterized by compression of neural elements and vascular structures due to a narrowed lumbar spinal canal. The main clinical presentation is neurogenic claudication. The pathophysiology is not entirely understood. Often, the clinical manifestation is not corresponding to the finding in magnetic resonance images (MRI). Objective The aim of this study is to determine the behaviour of cerebrospinal fluid (CSF) flow in degenerative LSS by using computational fluid dynamic (CFD) simulation through the qualitative and quantitative prediction of fluid flow and comparing with the flow in the normal spine. Methods This cross-sectional study evaluated the selected 34 MRI images, which had fulfilled the inclusion and exclusion criteria. The T2 weighted MRI images were used to assess the level and degree of stenosis. These images were transferred electronically to MIMIC and SOLIDWORKS for model generation and then to ANSYS FLUENT for the CFD simulations with the predetermined boundary condition. Lastly, the results were extracted according to the region of interest (ROI). Results The mean velocity in stenosis groups at L3/L4 disc level and L4/L5 disc level was relatively lower than the normal group, but it was higher at the L5/S1 disc level for the stenosis groups. This study revealed an insignificant difference between the normal groups and the stenosis groups at L3/L4 disc level. However, significant differences between the stenosis group and the normal group at L4/L5 disc level (p < 0.001) and L5/S1 disc level (p < 0.001) were reported. This study demonstrated the severity of stenosis did not carry a great influence toward the CSF velocity. The mean pressure of the CSF reduced from L3/L4 disc level to L5/S1 disc level. The mean pressure in the normal group was ranging from 981.47 Pa to 982.29 Pa, but for stenosis group was ranging from 981.00 Pa to 983.00 Pa, depending on the stenosis level. The mean wall shear stress (WSS) in normal group was 0.019 Pa, and stenosis group was ranging 0.014 Pa to 0.024 Pa at L3/L4 disc level. However, indifferent mean WSS was showed at the L4/L5, and L5/S1 disc level revealed the (0.011 Pa and 0.007 Pa, respectively) for both normal and stenosis groups. All the streamlines demonstrated a laminar flow pattern regardless the normal spine or stenotic spine with their Reynold’s number ranging from 326.2 to 1312.57. Conclusion The mean velocity in degenerative LSS did not differ significantly in stenosis group compared to the normal group at L3/L4 disc leve, but the study showed the mean velocity differ significantly for L4/L5 disc level and L5/S1 disc level. The degree of stenosis did not influence significantly on the mean velocity. The mean pressure reduced when flowed caudally, and showed insignificant different. Insignificant different was showed in the mean WSS as well as the flow pattern between the normal groups and degenerative LSS groups

Exploring Boarding Strategies for High-Speed Railway

In light of the increasing demand for passenger transportation on high-speed railway (HSR), the pedestrian flow at HSR stations has become quite crowded in many countries, which has attracted researchers to study the HSR boarding behavior. In this paper, we propose three boarding strategies based on the features of the boarding behavior at an origin HSR station; we then use a cellular automaton (CA) model to study the impacts of boarding strategies on each passenger’s motion during the boarding process at HSR station. The simulation results indicate that some of the three strategies can optimize some passengers’ boarding time and relieve the congestion degree, and the positive impacts on the boarding process are the most prominent when the three strategies are used simultaneously. The results can help administrators to effectively organize the boarding process at the origin HSR station

Connected and Disconnected Sea Partons from CT18 Parametrization of PDFs

The separation of the connected and disconnected sea partons, which were uncovered in the Euclidean path-integral formulation of the hadronic tensor, is accommodated with an alternative parametrization of the non-perturbative parton distribution functions in the CT18 global analysis. This is achieved with the help of the distinct small $x$ behaviours of these two sea partons and the constraint from the lattice calculation of the ratio of the strange momentum fraction to that of the $\bar u$ or $\bar d$ in the disconnected insertion. The whole dataset of CT18 is used in this CT18CS fit. The impact of the recent SeaQuest data on the $\bar{d}(x)-\bar{u}(x)$ distribution of CT18CS is also discussed. The separate momentum fractions for the valence, the connected sea and disconnected sea of $u$ and $d$, the strange and the gluon partons are presented at $\mu =1.3$ GeV for the first time. They can be compared term-by-term with systematic error controlled lattice calculations.Comment: Revised manuscript accepted for publication in PR