Mechanical behavior of nanorubber reinforced epoxy over a wide strain rate loading

Nanorubber/epoxy composites containing 0,2,6 and 10 wt%nanorubber are subjected to uniaxial compression over a wide range of strain rate from 8×10^(-4) s^(-1) to~2×10^(4) s^(-1).Unexpectedly,their strain rate sensitivity and strain hardening index increase with increasing nanorubber content.Potential mechanisms are proposed based on numerical simulations using a unit cell model.An increase in the strain rate sensitivity with increasing nanorubber content results from the fact that the nanorubber becomes less incompressible at high strain,generating a higher hydro-static pressure.Adiabatic shear localization starts to occur in the epoxy under a strain rate of 22,000 s^(-1) when the strain exceeds 0.35.The presence of nanorubber in the epoxy reduces adiabatic shear localization by preventing it from propagating.

How to Interpret Machine Knowledge

Machine knowledge refers to the knowledge contained in artificial intelligence.This article discusses how to acquire machine knowledge,with a particular focus on the acquisition of causal knowledge.The latter is the process of interpreting machine knowledge.Through the analysis of certain research methods in the fields of physics and artificial intelligence,we propose principles and models for interpreting machine knowledge,and discuss specific methods including the automation of the interpretation process and local linearization.

Generation of high-energy-resolved NH_3 molecular beam by a Stark decelerator with 179 stages

We demonstrate the production of cold, slow NH_3 molecules from a supersonic NH_3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH_3 molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH_3 molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH_3 molecular beam from 333 m/s to 18 m/s, with a final temperature of 29.2 mK.The second is the deceleration-bunch mode, which allows us to decelerate the supersonic NH_3 beam from 333 m/s to 24 m/s,with a final temperature of 2.9 m K. It is clear that the second mode promises to produce colder(high-energy-resolution)molecular samples than the normal mode. Three-dimensional Monte Carlo simulations are also performed for the experiments and they show a good agreement with the observed results. The deceleration-bunch operation mode presented here can find applications in the fields of cold collisions, high-resolution spectroscopy, and precision measurements.

Two types of highly efficient electrostatic traps for single loading or multi-loading of polar molecules

Two novel electrostatic traps named octopole-based disk electrostatic trap(ODET)and tubular-based disk electrostatic trap(TDET)are proposed for trapping cold polar molecules in low-field-seeking states.Using MgF as the target molecule,single loading and multi-loading methods are numerically simulated with varied incident velocities of slow molecular beams in the two types of traps,respectively.In ODET,with an incident velocity of 10 m/s,a highest loading efficiency of 78.4% or 99.9% has been achieved under the single loading or multi-loading operation mode.In TDET,with an incident velocity of 11 m/s,a highest loading efficiency of 81.6% or 106.5% has been achieved using the two loading methods,respectively.With such high loading efficiencies,the trapped cold molecules can be applied in the researches of cold collisions,high precision spectroscopy,and precision measurements.Especially,together with a blue-detuned hollow beam,the new electrostatic traps proposed here offer a new platform for the following gradient-intensity cooling of MgF molecules,which may provide a new way to produce high density ultracold molecules.

A crossed focused vortex beam with application to cold molecules

We report the generation of a crossed,focused,optical vortex beam by using a pair of hybrid holograms,which combine the vortex phase and lens phase onto a spatial light modulator.We study the intensity distributions of the vortex beam in free propagation space,and the relationship of its dark spot size with the incident Gaussian beam’s waist,the lens’s focal length,and its orbital angular momentum.Our results show that the crossed,focused,vortex beam’s dark spot size can be as small as 16.3μm and adjustable by the quantum number of the orbital angular momentum,and can be used to increase the density of trapped molecules.Furthermore,we calculate the optical potential of the blue-detuned,crossed vortex beam for MgF molecules.It is applicable to cool and trap neutral molecules by intensity-gradient-induced Sisyphus cooling,as the intensity gradient of such vortex beam is extremely high near the focal point.

Multiple Kernel Clustering Based on Self-Weighted Local Kernel Alignment

Multiple kernel clustering based on local kernel alignment has achieved outstanding clustering performance by applying local kernel alignment on each sample.However,we observe that most of existing works usually assume that each local kernel alignment has the equal contribution to clustering performance,while local kernel alignment on different sample actually has different contribution to clustering performance.Therefore this assumption could have a negative effective on clustering performance.To solve this issue,we design a multiple kernel clustering algorithm based on self-weighted local kernel alignment,which can learn a proper weight to clustering performance for each local kernel alignment.Specifically,we introduce a new optimization variable-weight-to denote the contribution of each local kernel alignment to clustering performance,and then,weight,kernel combination coefficients and cluster membership are alternately optimized under kernel alignment frame.In addition,we develop a three-step alternate iterative optimization algorithm to address the resultant optimization problem.Broad experiments on five benchmark data sets have been put into effect to evaluate the clustering performance of the proposed algorithm.The experimental results distinctly demonstrate that the proposed algorithm outperforms the typical multiple kernel clustering algorithms,which illustrates the effectiveness of the proposed algorithm.

Information transmission through parallel multi-task-based recognition of high-resolution multiplexed orbital angular momentum

Orbital angular momentums(OAMs)greatly enhance the channel capacity in free-space optical communication.However,demodulation of superposed OAM to recognize them separately is always difficult,especially upon multiplexing more OAMs.In this work,we report a directly recognition of multiplexed fractional OAM modes,without separating them,at a resolution of 0.1 with high accuracy,using a multi-task deep learning(MTDL)model,which has not been reported before.Namely,two-mode,four-mode,and eight-mode superposed OAM beams,experimentally generated with a hologram carrying both phase and amplitude information,are well recognized by the suitable MTDL model.Two applications in information transmission are presented:the first is for 256-ary OAM shift keying via multiplexed fractional OAMs;the second is for OAM division multiplexed information transmission in an eightfold speed.The encouraging results will expand the capacity in future free-space optical communication.

Characteristics investigation of Yb^(3+):YAG crystals for optical refrigeration

Yb^(3+):YAG crystal is one excellent material for developing high-power radiation-balanced lasers(RBLs).An experimental study of the laser cooling performances of YAG crystals with various doping Yb^(3+)concentrations,especially for application of RBLs,is reported here.With improved Yb^(3+)doping concentration in YAG crystal,though the resonance absorption coefficient increases,the corresponding external quantum efficiency has been found to decrease with the average fluorescence wavelength being red shifted,which is detrimental to anti-Stokes fluorescence(ASF)cooling.The decrease of the external quantum efficiency can cause the first zero crossing wavelength to red shift,which is not conducive to RBLs.Based on the comprehensive study of the cooling characteristics of the series of Yb^(3+)-doped YAG crystals,the optimal Yb3+doping concentration for ASF cooling has been suggested.

Simulation of EOM-based frequency-chirped laser slowing of MgF radicals

Here we propose a scheme to slow MgF molecules by using EOM-based frequency-chirped radiation pressure slowing.The scheme well addresses the need for a rapid chirp rate while light molecules are being laser slowed,whose scattering rate and recoil velocity are large.Two EOMs are used to compensate the rapidly changing Doppler shifts arised from the movement of molecules,and to cover the hyperfine energy structure of MgF,respectively.Based the scattering rate maps calculated from an optical Bloch equation model,individual molecule trajectories are simulated by using a semi-classical three-dimensional Monte Carlo approach.We show how the modulation configuration of EOM and the magnetic field influence the slowing results.The study shows that a cryogenic buffer gas-cooled MgF beam source is possible to be slowed down with a number of∼1.4×10^(6)–10^(7),and the final forward speed peaks at∼10 m/s near the capture velocity of a molecular MOT.

Genomic basis of evolutionary adaptation in a warm-blooded fish

Few fishes have evolved elevated body temperatures compared with ambient temperatures,and only in opah(Lampris spp)is the entire body affected.To understand the molecular basis of endothermy,we analyzed the opah genome and identified 23 genes with convergent amino acid substitutions across fish,birds,and mammals,including slc8b1,which encodes the mitochondrial Na+/Ca2+exchanger and is essential for heart function andmetabolic heat production.Among endothermic fishes,44 convergent genes with suggestive metabolic functions were identified,such as glrx3,encoding a crucial protein for hemoglobin maturation.Numerous genes involved in the production and retention of metabolic heat were also found to be under positive selection.Analyses of opah’s unique inner-heat-producing pectoral muscle layer(PMI),an evolutionary key innovation,revealed that many proteins were co-opted from dorsal swimming muscles for thermogenesis and oxidative phosphorylation.Thus,the opah genome provides valuable resources and opportunities to uncover the genetic basis of thermal adaptations in fish.

Machine Knowledge and Human Cognition

Intelligent machines are knowledge systems with unique knowledge structure and function.In this paper,we discuss issues including the characteristics and forms of machine knowledge,the relationship between knowledge and human cognition,and the approach to acquire machine knowledge.These issues are of great significance to the development of artificial intelligence.

A model for real-time computation of fuselage-rotor interference

A simple analytical real-time capable model to account for fuselage-induced velocities at rotor blade elements is described at the example of the Bo105 fuselage.Data of the fuselage-induced flow fields in the volume of rotor operation above the fuselage are first computed by a panel method in the range of angle of attack and sideslip of±90°.The model parameters are then estimated based on these data.The usefulness of the model in combinations of angle of attack and sideslip is demonstrated.

A driven three-dimensional electric lattice for polar molecules

Three-dimensional(3D)driven optical lattices have attained great attention for their wide applications in the quest to engineer new and exotic quantum phases.Here we propose a 3D driven electric lattice(3D-DEL)for cold polar molecules as a natural extension.Our 3D electric lattice is composed of a series of thin metal plates in which two-dimensional square hole arrays are distributed.When suitable modulated voltages are applied to these metal plates,a 3D potential well array for polar molecules can be generated and can move smoothly back and forth in the lattice.Thus,it can drive cold polar molecules confined in the 3D electric lattice.Theoretical analyses and trajectory calculations using two types of molecules,ND3 and PbF,are performed to justify the possibility of our scheme.The 3D-DEL offers a platform for investigating cold molecules in periodic driven potentials,such as quantum computing science,quantum information processing,and some other possible applications amenable to the driven optical lattices.