Quantum control of ultrafast magnetic field in H_(3)^(2+)molecules by tricircular polarized laser pulses

We present a scheme to control the generated ultrafast magnetic field in H_(3)^(2+)molecules using multi-frequency tricircular pulses composed of co-and counter-rotating bicircular pulses.Simulations show that the field amplitude and the wavelength are two significant factors for magnetic field generation by tricircular pulses.Specifically,the strength of the magnetic field is linearly related to the field amplitude atλ_(0)=50 nm,while atλ_(0)=70 nm,the strength first increases and then decreases with the amplitude,this can be attributed to the resonance between the ground and excited states.Moreover,the phase and helicity of bicircular pulses are shown to have important effects on the magnetic field.The dependence of the magnetic field on the phase arises from the interference effect between multiple ionization pathways.These findings illustrate a guiding principle for controlling the magnetic field in molecular systems for future research in ultrafast magneto-optics.

A new digital pulse processing method for 2πa and 2πb emitter measurement

Digital pulse processing has developed rapidly during recent years.Moreover,it has been widely applied in many fields.In this study,we introduce a digital pulse processing method for 2πa and 2πb emitter measurement.Our digital pulse processing method for 2πa and 2πb emitter measurement is comprised of a field-programmable gate-array-based acquisition card and a pulse-height analysis routine.We established two channels(one for the a emitter and one for the b emitter) on an acquisition board using an analog-to-digital converter with a 16-bit resolution at a speed of 100 million samples per second.In this study,we used captured and stored data to analyze emission rate counts and spectrums.The method we established takes into account noise cancelation,dead-time correction,background subtraction,and zero-energy extrapolation.We carefully designed control procedures in order to simplify pulse-width fitting and threshold-level setting.We transmitted data and commands through a universal serial bus between the acquisition board and the computer.The results of our tests prove that our method performs well in pulse reconstruction fidelity and amplitude measurement accuracy.Compared with the current standard method for measuring 2πa and 2πb emission rates,our system demonstrates excellent precision in emission rate counting.

Exploration of magnetic field generation of H_(3)^(2+)by direct ionization and coherent resonant excitation

Coherent electronic dynamics are of great significance in photo-induced processes and molecular magnetism.We theoretically investigate electronic dynamics of triatomic molecule H_(3)^(2+) by circularly polarized pulses,including electron density distributions,induced electronic currents,and ultrafast magnetic field generation.By comparing the results of the coherent resonant excitation and direct ionization,we found that for the coherent resonant excitation,the electron is localized and the coherent electron wave packet moves periodically between three protons,which can be attributed to the coherent superposition of the ground A′state and excited E+state.Whereas,for the direct single-photon ionization,the induced electronic currents mainly come from the free electron in the continuum state.It is found that there are differences in the intensity,phase,and frequency of the induced current and the generated magnetic field.The scheme allows one to control the induced electronic current and the ultrafast magnetic field generation.

Photoelectron momentum distributions of Ne and Xe dimers in counter-rotating circularly polarized laser fields

The strong-field ionization of dimers is investigated theoretically in counter-rotating circularly polarized laser fields.By numerically solving the two-dimensional(2D)time-dependent Schrödinger equation(TDSE)with the single-electron approximation(SEA)frame,we present the photoelectron momentum distributions(PMDs)and photoelectron angular distribution(PADs)of aligned Ne and Xe dimers.It is found that the PMDs and PADs strongly depend on the time delays by counter-rotating circularly polarized laser pulses.The results can be explained by the ultrafast photoionization model and the evolution of electron wave packets for Ne and Xe dimers.Besides,We make a comparison of PMDs between Ne atom and Ne dimer.

Ultrafast photoionization of ions and molecules by orthogonally polarized intense laser pulses: Effects of the time delay

We present the photoelectron momentum distributions(PMDs) and the photoelectron angular distributions(PADs) of He+ ions, aligned H2+ molecules and N2 molecules by intense orthogonally polarized laser pulses. Simulations are performed by numerically solving the corresponding two-dimensional time-dependent Schr?dinger equations(TDSEs) within the single-electron approximation frame. Photoelectron momentum distributions and photoelectron angular distributions present different patterns with the time delays Td, illustrating the dependences of the PMDs and PADs on the time delays by orthogonally polarized laser pulses. The evolution of the electron wavepackets can be employed to describe the intensity of the PADs from the TDSE simulations for N2 molecules.

Effects of initial electronic state on vortex patterns in counter-rotating circularly polarized attosecond pulses

We theoretically investigate the effects of different electronic states as the initial state on the vortex patterns in photoelectron momentum distributions(PMDs)from numerical solutions of the two-dimensional(2D)time-dependent Schrodinger equation(TDSE)of He^(+)with a pair of counter-rotating circularly polarized attosecond pulses.It is found that the number of spiral arms in vortex patterns is equal to the number of the absorbed photons when the initial state is the ground state.However,the number of spiral arms in vortex patterns is always two more than the number of the absorbed photons when the initial state is the excited state.This sensitivity is attributed to the initial electron density distribution.In addition,we have demonstrated the PMDs for different initial electronic states with the same wavelengths and analyzed their corresponding physical mechanisms.It is illustrated that the method presented can be employed to effectively control the distribution of the electron vortices.

Molecular photoelectron momentum and angular distributions of N_(2) molecules by ultrashort attosecond laser pulses

The ultrafast photoionization dynamics of N_(2) molecules by x-ray/XUV laser pulses is investigated.The molecular frame photoelectron momentum distributions(MF-PMDs) and the molecular frame photoelectron angular distributions(MF-PADs) are obtained by numerically solving 2D time-dependent Schrodinger equations within the single-electron approximation(SEA) frame.The results show that the molecular photoionization diffraction appears in 5 nm laser fields.However,when the laser wavelength is 30 nm,the molecular photoionization diffraction disappears and the MF-PMDs show four-lobe pattern.The ultrafast photoionization model can be employed to describe the MF-PMDs and MF-PADs of N_(2) molecules.

Magnetic Resonance Gd？RGD Imaging Study of Hepatocellular Carcinoma with High and Low Metastatic Potential before and after Human Bone Marrow？derived Mesenchymal Stem Cell Intervention

Background： Biotherapy based on human bone marrow-derived mesenchymal stem cells （BMSCs） is currently the focus of research, especially in the field of autologous stem cell transplantation. A novel type of metastasis-associated magnetic resonance （MR） molecular imaging probe was constructed, and the changes in metastasis and proliferation of hepatocellular carcinoma （HCC） before and after BMSC intervention were observed through MR imaging （MRI）. Methods：Metastasis-associatedMRmolecularimagingprobe,integrin αvβ3 ligandcRGD-PEG-DGL-DTPA-Gd （Gd-RGD）,wereconstructed. After human BMSC intervention was performed for 6weeks, tumor weight inhibition rates were calculated, and the RGD molecular probe was imaged through MRI with molecular imaging agent Gd-DTPAas control.The signal-to-noise ratio （SNR） and contrast-to-noise ratio （CNR） in the MRI experiment were used as semi-quantitative indicators. Polymerase chain reaction method was performed to detect proliferation- and metastasis-associated indicators, transforming growth factor β-1 （TGFβ1）, osteopontin （OPN）, and integrin subunit αv and β3. Results： The highest tumor weight inhibition rates were observed 3 weeks after the BMSC transplantation. The MR Gd-RGD in the HCC tissues after the BMSC intervention showed less enhancement than Gd-DTPA. The Gd-DTPAMRI of control group had higher SNR and CNR than Gd-RGD MRI in the experimental groups （P 〈 0.05）. For high metastatic potential hepatocellular carcinoma （MHCC97-H）, significant differenceswereobservedintheSNRsandCNRsofGd-RGDMRIbeforeandaftertheBMSCintervention（P〈0.05）.Forlowmetastaticpotential hepatocellular carcinoma （MHCC97-L）, the CNRs of Gd-RGD MRI were statistically different before and after BMSC intervention （P 〈 0.05）. With regard to MHCC97-H, OPN, β3, and TGFβ1 expression significantly decreased after BMSC intervention （P 〈 0.05）. In MHCC97-L and OPN, β3, TGFβ1, and αv expression after BMSC intervention decreased, and the difference was statistically significant （P 〈 0.05）. Conclusions： The CNR index of MRI is a good indicator for distinguishing high- and low-metastatic potential HCC tissues.After BMSC transplantation of MRI through the two kinds of tracer, the SNR and CNR indexes can distinguish two kinds of high and low metastatic potential HCC tissues, and Gd-RGD imaging is more suitable in distinguishing the metastatic potential changes through BMSC intervention.

SIES:A Novel Implementation of Spiking Convolutional Neural Network Inference Engine on Field-Programmable Gate Array

Neuromorphic computing is considered to be the future of machine learning,and it provides a new way of cognitive computing.Inspired by the excellent performance of spiking neural networks(SNNs)on the fields of low-power consumption and parallel computing,many groups tried to simulate the SNN with the hardware platform.However,the efficiency of training SNNs with neuromorphic algorithms is not ideal enough.Facing this,Michael et al.proposed a method which can solve the problem with the help of DNN(deep neural network).With this method,we can easily convert a well-trained DNN into an SCNN(spiking convolutional neural network).So far,there is a little of work focusing on the hardware accelerating of SCNN.The motivation of this paper is to design an SNN processor to accelerate SNN inference for SNNs obtained by this DNN-to-SNN method.We propose SIES(Spiking Neural Network Inference Engine for SCNN Accelerating).It uses a systolic array to accomplish the task of membrane potential increments computation.It integrates an optional hardware module of max-pooling to reduce additional data moving between the host and the SIES.We also design a hardware data setup mechanism for the convolutional layer on the SIES with which we can minimize the time of input spikes preparing.We implement the SIES on FPGA XCVU440.The number of neurons it supports is up to 4000 while the synapses are 256000.The SIES can run with the working frequency of 200 MHz,and its peak performance is 1.5625 TOPS.