Analysis of two-dimensional high-energy photoelectron momentum distributions in single ionization of atoms by intense laser pulses

We analyzed the two-dimensional (2D) electron momentum distributions of high-energy photoelectrons of atoms in an intense laser field using the second-order strong field approximation (SFA2). The SFA2 accounts for the rescattering of the returning electron with the target ion to first order and its validity is established by comparing with results obtained by solving the time-dependent Schr\"{o}dinger equation (TDSE) for short pulses. By analyzing the SFA2 theory, we confirmed that the yield along the back rescattered ridge (BRR) in the 2D momentum spectra can be interpreted as due to the elastic scattering in the backward directions by the returning electron wave packet. The characteristics of the extracted electron wave packets for different laser parameters are analyzed, including their dependence on the laser intensity and pulse duration. For long pulses we also studied the wave packets from the first and the later returns.Comment: 12 pages, 10 figure

SciRecSys: A Recommendation System for Scientific Publication by Discovering Keyword Relationships

In this work, we propose a new approach for discovering various relationships among keywords over the scientific publications based on a Markov Chain model. It is an important problem since keywords are the basic elements for representing abstract objects such as documents, user profiles, topics and many things else. Our model is very effective since it combines four important factors in scientific publications: content, publicity, impact and randomness. Particularly, a recommendation system (called SciRecSys) has been presented to support users to efficiently find out relevant articles

Optimising energy efficiency of non-orthogonal multiple access for wireless backhaul in heterogeneous cloud radio access network

This paper studies the downlink problem of a cloud-based central station (CCS) to multiple base stations (BSs) in a heterogeneous cellular network sharing the same time and frequency resources. We adopt non-orthogonal multiple access (NOMA) and propose power allocation for the wireless downlink in the heterogeneous cloud radio access network (HCRAN). Taking into account practical channel modelling with power consumptions at BSs of different cell types (e.g. macro-cell, micro-cell, etc.) and backhauling power, we analyse the energy efficiency (EE) of the practical HCRAN utilising NOMA. Simulation results indicate that the proposed NOMA for the HCRAN outperforms the conventional orthogonal frequency division multiple access (OFDMA) scheme in terms of providing higher EE of up to four times. Interestingly, the results reveal a fact that the EE of the NOMA approach is not always an increasing function of the number of BSs but varies as a quasiconcave function. This motivates us to further introduce an optimisation problem to find the optimal number of BSs that maximises the EE of the HCRAN. It is shown that, with a low power supply at the CCS, a double number of micro BSs can be served by HCRAN providing an improved EE of up to 1.6 times compared to the macro BSs and RRHs, while they achieve the same EE performance with high-power CCS

A Novel 3-Dimensional Culture System as an In Vitro Model for Studying Oral Cancer Cell Invasion

Tissue microenvironment plays a critical role in tumour growth and invasion. This study established a novel 3-dimensional (3-D) cell invasion model for direct microscopic observation of oral cancer cell invasion into the underlying basement membrane and connective tissue stroma. A multilayer cell construct was developed using the OptiCell chamber, consisting of a lower layer of oral mucosa fibroblasts embedded in collagen gel and an overlaying upper layer of oral cancer cells. The two layers are separated by a basement membrane composed of reconstituted extracellular matrix. To verify the applicability of the cell invasion model, multilayer cell constructs of oral squamous cell carcinoma and oral mucosal fibroblasts were exposed to extrinsic urokinase-type plasminogen activator (uPA) or plasminogen activator inhibitor (PAI-1), which are known effectors of cell migration. In addition, the constructs were exposed to both normoxic and hypoxic culture conditions. Microscopic study showed that the presence of uPA enhanced cell invasion, while PAI-1 inhibited cell migration. Western blot and zymographic analysis demonstrated that hypoxia up-regulated uPA and matrix metalloproteinases (MMPs) expression and activity; conversely, PAI-1 level was down-regulated in response to hypoxic challenge as compared to normoxic condition. Our results indicated that the novel 3-D invasion model could serve as an excellent in vitro model to study cancer cell invasion and to test conditions or mediators of cellular migration. © 2005 Blackwell Publishing Ltd

An energy-efficient NOMA for small cells in heterogeneous CRAN under QoS constraints

This paper investigates downlink performance of wireless backhaul in a heterogeneous cloud radio access network (HCRAN) consisting of a cloud-based central station (CCS) and multi-tier small cells. Non-orthogonal multiple access (NOMA) is adopted for the downlink from the CCS to multiple small cells of different types (e.g. microcells, picocells and femtocells). Taking into account practical power consumption at small cells operating within various propagation environment models, we first develop a power allocation for the NOMA, which allows us to derive the energy efficiency (EE) of the wireless backhaul in the practical HCRAN downlink. It is shown that the NOMA is superior to the conventional OFDMA scheme achieving a higher EE of up to six times with the deployment of small cells. The propagation environment is also shown to have a significant impact on the EE performance with a big gap between different cell types when the number of cells is large. Particularly, the EE of the NOMA is shown to not always increase or decrease as a function of the number of cells, while the throughput performance at the cloud edge is strikingly degraded as the number of cells increases. This accordingly motivates us to propose a two-stage algorithm for determining the optimal number of various cells that maximises the EE of the HCRAN while still maintaining the QoS requirement at the cloud edge. Simulation results show that, to meet a target cloud-edge throughput, the same number of femtocells and picocells can be used; however, the femtocells are favourable to the picocells in achieving the maximal EE

Extremely Hot Ambient Temperature and Injury-related Mortality

This pilot study aimed to evaluate the effects of extremely hot ambient temperatures on the total number of fatal injuries. Data were collected from a population-based mortality registry of Thanh Hoa, a province in the North Central region of Vietnam. This study qualified the distributed lag non-linear model and calculated the RR and 95% CI adjusted for long-term trend and absolute humidity. For the entire study population with 3,949 registered deaths due to injuries collected during 2005-2007, after the onset of extremely hot ambient temperatures, an increased risk of death was observed on the 9th day RR (95% CI) = 1.44 (1.06–1.97) and reached the peak on the 12th day RR (95% CI) = 1.58 (1.14–2.17), and at the 15th day RR (95% CI) = 1.49 (1.08–2.06). Men and old adults were identified as the most vulnerable groups. This study confirmed a positive association between hot temperatures and injury-related deaths in the province of 3.6 million people. The findings motivated further investigation into the effect of warm climate changes and the risk of deaths related to other specific causes such as road traffic, work-related injury, and etc

New determination of structure parameters in strong field tunneling ionization theory of molecules

In the strong field molecular tunneling ionization theory of Tong et al. [Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic wavefunction of the molecular orbital from which the electron is removed. The orbital wavefunctions obtained from standard quantum chemistry packages in general are not good enough in the asymptotic region. Here we construct a one-electron model potential for several linear molecules using density functional theory (DFT). We show that the asymptotic wavefunction can be improved with an iteration method and after one iteration accurate asymptotic wavefunctions and structure parameters are determined. With the new parameters we examine the alignment-dependent tunneling ionization probabilities for several molecules and compare with other calculations and with recent measurements, including ionization from inner molecular orbitals

Influence of permanent dipole and dynamic core-electron polarization on tunneling ionization of polar molecules

Citation: Hoang, V. H., Zhao, S. F., Le, V. H., & Le, A. T. (2017). Influence of permanent dipole and dynamic core-electron polarization on tunneling ionization of polar molecules. Physical Review A, 95(2), 8. doi:10.1103/PhysRevA.95.023407We present a detailed theoretical investigation on strong-field ionization of polar (CO and NO) as well as nonpolar molecules (N-2, O-2, and CO2). Our results indicate that accounting for the Stark correction in the molecular tunneling ionization theory leads to overall fairly good agreements with numerical solutions of the time-dependent Schrodinger equation. Furthermore, we show that the effect of dynamic core-electron polarization, in general, has a weak influence on the angle-dependent ionization probability. However, in the case of CO we confirm the recent finding by B. Zhang, J. Yuan, and Z. Zhao [Phys. Rev. Lett. 111, 163001 (2013)] that accounting for dynamic core-polarization is crucial to achieving an overall good agreement with experiments

Operator method in solving non-linear equations of the Hartree-Fock type

The operator method is used to construct the solutions of the problem of the polaron in the strong coupling limit and of the helium atom on the basis of the Hartree-Fock equation. $E_0=-0.1085128052\alpha^2$ is obtained for the polaron ground-state energy. Energies for 2s- and 3s-states are also calculated. The other excited states are briefly discussed.Comment: 7 page