30 research outputs found
Few-photon single ionization of cold rubidium in the over-the-barrier regime
Photoionization of the rubidium (Rb) atoms cooled in a magneto-optical trap,
characterized by the coexistence of the ground 5 and the excited
5 states, is investigated experimentally and theoretically with the
400 nm femtosecond laser pulses at intensities of W/cm -
W/cm. Recoil-ion momentum distribution (RIMD) of Rb
exhibits rich ring-like structures and their energies correspond to one-photon
ionization of the 5 state, two-photon and three-photon ionizations of
the 5 state, respectively. With the increasing of , we find that
experimental signals near zero-momentum (NZM) in RIMDs resulted from the
5 state enhance dramatically and its peaked Rb momenta dwindle
obviously while that from the 5 state is maintained. Meanwhile, the
ion-yield ratio of the 5 over the 5 states varies from to
as increases. These features indicate a transition from
perturbative ionization to strong-perturbative ionization for the 5
state. Numerical simulations by solving the time-dependent Schr\"odinger
equation (TDSE) can qualitatively explain the measurements of RIMD, photoion
angular distributions, as well as ion-yield ratio. However, some discrepancies
still exist, especially for the NZM dip, which could stem from the
electron-electron correlation that is neglected in the present TDSE simulations
since we have adopted the single-active-electron approximation
Ellipticity-dependent sequential over-barrier ionization of cold rubidium
We perform high-resolution measurements of momentum distribution on Rb
recoil ions up to charge state , where laser-cooled rubidium atoms are
ionized by femtosecond elliptically polarized lasers with the pulse duration of
35 fs and the intensity of 3.310 W/cm in the over-barrier
ionization (OBI) regime. The momentum distributions of the recoil ions are
found to exhibit multi-band structures as the ellipticity varies from the
linear to circular polarizations. The origin of these band structures can be
explained quantitatively by the classical OBI model and dedicated classical
trajectory Monte Carlo simulations with Heisenberg potential. Specifically,
with back analysis of the classical trajectories, we reveal the ionization time
and the OBI geometry of the sequentially released electrons, disentangling the
mechanisms behind the tilted angle of the band structures. These results
indicate that the classical treatment can describe the strong-field multiple
ionization processes of alkali atoms
Halo Properties and Mass Functions of Groups/Clusters from the DESI Legacy Imaging Surveys DR9
Based on a large group/cluster catalog recently constructed from the DESI
Legacy Imaging Surveys DR9 using an extended halo-based group finder, we
measure and model the group-galaxy weak lensing signals for groups/clusters in
a few redshift bins within redshift range . Here, the
background shear signals are obtained based on the DECaLS survey shape catalog
derived with the \textsc{Fourier\_Quad} method. We divide the lens samples into
5 equispaced redshift bins and 7 mass bins, which allow us to probe the
redshift and mass dependence of the lensing signals and hence the resulting
halo properties. In addition to these sample selections, we have also checked
the signals around different group centers, e.g., brightest central galaxy
(BCG), luminosity weighted center and number weighted center. We use a lensing
model that includes off-centering to describe the lensing signals we measure
for all mass and redshift bins. The results demonstrate that our model
predictions for the halo masses, bias and concentrations are stable and
self-consistent among different samples for different group centers. Taking
advantage of the very large and complete sample of groups/clusters, as well as
the reliable estimation of their halo masses, we provide measurements of the
cumulative halo mass functions up to redshift , with a mass precision at
dex.Comment: revised version submitted to Ap
Multi-Objective Immune Optimization of Path Planning for Ship Welding Robot
In order to improve the welding efficiency of the ship welding robot, the path planning of the welding robot based on immune optimization is proposed by taking the welding path length and energy loss as the optimization goals. First, on the basis of the definition of the path planning of the welding robot, the grid modeling of the robotâs working environment and the triangular modeling of the welding weldments are carried out. Then, according to the working process of the welding robot, the length objective function, including the welded seam path and the welding torch path without welding, is constructed, and the energy loss function is constructed based on the kinematics and Lagrange function. Finally, the immune optimization algorithm based on cluster analysis and self-circulation is introduced to realize the multi-objective optimization of the path planning for the ship welding robot. The test results of four kinds of ship welding weldments show that compared with the simple genetic algorithm, immune genetic algorithm, ant colony algorithm, artificial bee colony, particle swarm optimization, and immune cloning optimization, the proposed multi-objective immune planning algorithm is the best in terms of planning path length, energy consumption, and stability. Furthermore, the average shortest path and its standard deviation, the average minimum energy consumption and its standard deviation, and the average lowest convergence generation and its standard deviation are reduced by an average of 9.03%, 54.04%, 8.23%, 19.10%, 27.84%, and 52.25%, respectively, which fully verifies the effectiveness and superiority of the proposed welding robot path planning algorithm
Heat management technology for solidâstate high voltage and high repetitive pulse generators: Towards better effects and reliability
Abstract Solidâstate high voltage high repetitive pulse generators have a broad prospect in various applications. The high power and highâfrequency operation of the pulse generator suffer from the massive heat dissipation problem, which limits the improvement of the output parameters and even affects the lifetime. This article focuses on heat management technology for high voltage high repetitive pulse generators. Firstly, the typical circuit topology of the high repetitive pulse generators was summarised. From the perspective of different application requirements, the demands of the heat management design were concluded. Moreover, the heat generation characteristics and difficulties of solidâstate high voltage high repetitive pulse generators were analysed. Then, the different stateâofâart cooling techniques were reviewed, and their applicability and limitations for the high voltage high repetitive generators were discussed. Finally, a flow chart for heat management design was given
Comprehensive bioinformatics analysis revealed potential key genes and pathways underlying abdominal aortic aneurysm
Abdominal aortic aneurysm (AAA) is a permanent, asymptomatic segmental dilatation of the abdominal aorta, with a high mortality risk upon rupture. Identification of potential key genes and pathways may help to develop curative drugs for AAA. We conducted RNA-seq on abdominal aortic tissues from both AAA patients and normal individuals as a control group. Integrated bioinformatic analysis was subsequently performed to comprehensively reveal potential key genes and pathways. A total of 1148 differential expressed genes (DEGs) (631 up-regulated and 517 down-regulated) were identified in our study. Gene Ontology (GO) analysis revealed enrichment in terms related to extracellular matrix organization, while KEGG analysis indicated enrichment in hematopoietic cell lineage and ECM-receptor interaction. Protein-protein interaction (PPI) network analysis revealed several candidate key genes, and differential expression of 6 key genes (CXCL8, CCL2, PTGS2, SELL, CCR7, and CXCL1) was validated by Gene Expression Omnibus (GEO) datasets. Receiver operating characteristic curve (ROC) analysis demonstrated these genesâ high discriminatory ability between AAA and normal tissues. Immunohistochemistry indicated that several key genes were highly expressed in AAA tissues. Single-cell RNA sequencing revealed differential distribution patterns of these identified key genes among various cell types. 26 potential drugs linked to our key genes were found through DGIdb. Overall, our study provides a comprehensive evaluation of potential key genes and pathways in AAA, which could pave the way for the development of curative pharmacological therapies
Improved Performance of HfxZnyOâBased RRAM and its Switching Characteristics down to 4 K Temperature
Abstract The search for highâperformance resistive randomâaccess memory (RRAM) devices is essential to pave the way for highly efficient nonâVon Neumann computing architecture. Here, it is reported on an alloying approach using atomic layer deposition for a Znâdoped HfOxâbased resistive randomâaccess memory (HfZnO RRAM), with improved performance. As compared with HfOx RRAM, the HfZnO RRAM exhibits reduced switching voltages (>20%) and switching energy (>3Ă), as well as better uniformity both in voltages and resistance states. Furthermore, the HfZnO RRAM exhibits stable retention exceeding 10Â years, as well as write/erase endurance exceeding 105Â cycles. In addition, excellent linearity and repeatability of conductance tuning can be achieved using the constant voltage pulse scheme, achieving â90% accuracy in a simulated multiâlayer perceptron network for the recognition of modified national institute of standards and technology database handwriting. The HfZnO RRAM is also characterized down to the temperature of 4Â K, showing functionality and the elucidation of its carrier conduction mechanism. Hence, a potential pathway for dopedâRRAM to be used in a wide range of temperatures including quantum computing and deepâspace exploration is shown