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- 摘要
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- 实验方案
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Understanding Lasers (An Entry Level Guide, Fourth Edition) || Gas Lasers
摘要： Most gas lasers share some key features. Gas is put into a tube, mirrors are put on the ends, and an electric discharge is passed through the gas to produce a population inversion. The details vary quite a bit. The discharge may pass across the tube or along its length. Some molecular gases emit in the mid to far infrared on vibrational or rotational transitions. Atomic gases tend to emit in or near the visible. Ionized gases may emit in the visible or ultraviolet. One odd family of short-lived molecules emits bright ultraviolet pulses. The result is a varied group of lasers that share important features and can illustrate some important aspects of laser physics. Two families of gas lasers, carbon dioxide (CO2) and excimer lasers, are important commercially, but other gas lasers have become niche products. This chapter will explore the basics of gas lasers and teach you about the most important types.
关键词： gas lasers,CO2 lasers,excimer lasers,electric discharge,population inversion
更新于2025-09-11 14:15:04
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Worldpop - Fusion of Earth and Big Data for Intraurban Population Mapping
摘要： High resolution estimates of human population distributions are very useful for large-scale or national scale analyses in many fields including epidemiology, healthcare, resource distribution, and development. Population densities have long been estimated using remote sensing data, particularly at large spatial scales. However, the accuracy of population density predictions can be very poor in cities, and this is particularly relevant in urban areas in sub-Saharan Africa. Here we map intra-urban population densities for select African cities by disaggregating census data using random forest techniques with remotely-sensed and geospatial data, including bespoke time-series intra-urban built-up data. We produce maps with up to 83% explained variance and find including built-up density layers in urban population models allows for clear improvements in prediction.
关键词： machine learning,population density,census,built-up,Urban areas,Africa
更新于2025-09-10 09:29:36
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[IEEE 2018 10th International Conference on Modelling, Identification and Control (ICMIC) - Guiyang, China (2018.7.2-2018.7.4)] 2018 10th International Conference on Modelling, Identification and Control (ICMIC) - Parameter Estimation of Piezoelectric Transducers Circuit Model Using GA-PSO Algorithm
摘要： The parameters estimation problem for the equivalent admittance circuit model of piezoelectric transducers with high non-linearity near the resonance frequency is studied. A novel Genetic-Particle Swarm Optimization (GA-PSO) algorithm with cascade structure is proposed. The variance of fitness value of population as a criterion is given to evaluate the population convergence, and the population convergence is used as an adaptive switching strategy of Particle Swarm Optimization(PSO) to Genetic Algorithm(GA). The proposed GA-PSO method can also be used for estimating parameters of others. Simulation results are provided to demonstrate the feasibility. Comparison of the proposed GA-PSO method with the existing method is given, which shows that the GA-PSO algorithm is more efficient.
关键词： circuit model,Parameter estimation,GA-PSO,population convergence,piezoelectric transducers
更新于2025-09-10 09:29:36
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Suppression of Dick Effect in Ramsey-CPT Atomic Clock by Interleaving Lock
摘要： The Dick effect is one of the main limitations of short-term frequency stability for most atomic clocks operating in the pulsed mode. Rather than employing better local oscillators with ultralow phase noise, using the interleaving lock technique to eliminate the dead time is a promising approach to suppress the Dick effect. In this paper, we demonstrate the suppression of the Dick effect by the interleaving lock technique in a pulsed Ramsey-coherent population trapping clock with two identical Cs atomic ensembles. The Dick effect is expected to be reduced by a factor of 24 theoretically. The measured short-term Allan deviation is improved from 1.3×10?11 at 1 s to 3.0×10?12 at 1 s. What is even more remarkable is that the Allan deviation curve exhibits 1/τ slope from 0.01 to 2 s.
关键词： Dick effect,Ramsey-coherent population trapping (CPT),interleaving lock
更新于2025-09-10 09:29:36
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ac Stark shifts of dark resonances probed with Ramsey spectroscopy
摘要： The off-resonant ac Stark shift for coherent population trapping (CPT) resonances probed with Ramsey spectroscopy is investigated experimentally and theoretically. Measurements with laser-cooled 87Rb atoms show excellent quantitative agreement with a simple theory. The shift depends on the relative intensity of the two CPT light fields, but depends only weakly on the total intensity. Since the origin of the shift is through couplings of the interrogation light to off-resonant excited-state hyperfine levels, the size and sign of the shift depend on the specific interrogation scheme. The theory also shows that for several commonly used interrogation schemes it is possible to minimize the off-resonant light shift or its dependence on the CPT intensity ratio by properly selecting the system parameters.
关键词： hyperfine levels,laser-cooled atoms,coherent population trapping,ac Stark shift,Ramsey spectroscopy
更新于2025-09-10 09:29:36
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Use of Stokes and anti-Stokes Raman scattering for new applications
摘要： We show the interest in recording both Stokes and anti‐Stokes Raman spectra in two peculiar applications. In one case, the comparison between these two parts of the spectrum, measured at one temperature only, allows to distinguish between first‐ and second‐order phonon bands. In the second example, the difference between Stokes and anti‐Stokes spectra provides separation between vibrational and emission lines. We describe the different stages needed in the measurements and data treatment.
关键词： Stokes and anti‐Stokes Raman scattering,phonon bands,population factor,first‐ and second‐order scattering,luminescence
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Double-Modulation Coherent Population Trapping Clock
摘要： Atomic clocks based on coherent population trapping and constructive polarization modulation are promising for high performance and compact devices. We have demonstrated a cw mode CPT clock with a short-term fractional frequency stability at the level of 3.2 × 10?13/√τ for a few 100 s integration time. This Double-Modulation CPT technology can be reduced to a miniature and robust setup due to its linear architecture. This clock could find future applications in telecommunications, industry, instrumentation, or global navigation satellite systems.
关键词： atomic clock,frequency stability,coherent population trapping
更新于2025-09-10 09:29:36
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The Random Forest-Based Method of Fine-Resolution Population Spatialization by Using the International Space Station Nighttime Photography and Social Sensing Data
摘要： Despite the importance of high-resolution population distribution in urban planning, disaster prevention and response, region economic development, and improvement of urban habitant environment, traditional urban investigations mainly focused on large-scale population spatialization by using coarse-resolution nighttime light (NTL) while few efforts were made to fine-resolution population mapping. To address problems of generating small-scale population distribution, this paper proposed a method based on the Random Forest Regression model to spatialize a 25 m population from the International Space Station (ISS) photography and urban function zones generated from social sensing data—point-of-interest (POI). There were three main steps, namely HSL (hue saturation lightness) transformation and saturation calibration of ISS, generating functional-zone maps based on point-of-interest, and spatializing population based on the Random Forest model. After accuracy assessments by comparing with WorldPop, the proposed method was validated as a qualified method to generate fine-resolution population spatial maps. In the discussion, this paper suggested that without help of auxiliary data, NTL cannot be directly employed as a population indicator at small scale. The Variable Importance Measure of the RF model confirmed the correlation between features and population and further demonstrated that urban functions performed better than LULC (Land Use and Land Cover) in small-scale population mapping. Urban height was also shown to improve the performance of population disaggregation due to its compensation of building volume. To sum up, this proposed method showed great potential to disaggregate fine-resolution population and other urban socio-economic attributes.
关键词： population spatialization,social sensing data,point of interest,ISS photography,Random Forest Regression,urban functional zones
更新于2025-09-10 09:29:36
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[Essentials in Ophthalmology] Advances in Vision Research, Volume II (Genetic Eye Research in Asia and the Pacific) || The Genetics of Inherited Retinal Diseases in the Israeli and Palestinian Populations: A Lesson from Populations with High Rates of Consanguinity
摘要： Inherited retinal diseases (IRDs) are disorders that cause visual loss mainly due to photoreceptor degeneration. The prevalence of IRDs in the Israeli and Palestinian populations was reported to be higher compared to other studied populations. The structures of the Israeli and Palestinian populations are unique mainly because of the large number of ethnic groups. In addition, high rates of consanguinity and intra-community marriages resulted in a high proportion of families with autosomal recessive inheritance patterns. The study of Israeli and Palestinian IRD families resulted so far in the identification of mutations in 74 IRD genes, including 23 novel genes that were identified mainly using the homozygosity mapping and whole exome sequencing techniques. The history and tradition of these populations led to common founder mutations that are usually subpopulation-specific. Such mutations allow a more efficient genetic analysis in searching for the causative gene. However, some founder mutations are shared among different ethnicities and are likely to be the result of a common origin of these ethnic groups, which may have an estimated divergence time of a few thousand years. There is a large variability of retinal phenotypes among patients, while mutations in the same gene can result either in the same phenotype or variable phenotypes that are usually mutation-dependent. There is currently no cure for the vast majority of IRD types; however recent advances bring new hope for curing or at least delaying the degeneration process in the near future.
关键词： Population,Genotype-phenotype correlation,Heterogeneous disease,Mutation,Consanguinity,Retinitis pigmentosa,Gene,Homozygosity mapping
更新于2025-09-10 09:29:36
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A quantum retrograde canon: complete population inversion in <i>n</i> <sup>2</sup> -state systems
摘要： We present a novel approach for analytically reducing a family of time-dependent multi-state quantum control problems to two-state systems. The presented method translates between related n2-state systems and two-state systems, such that the former undergo complete population inversion (CPI) if and only if the latter reach specific states. For even n, the method translates any two-state CPI scheme to a family of CPI schemes in n2-state systems. In particular, facilitating CPI in a four-state system via real time-dependent nearest-neighbors couplings is reduced to facilitating CPI in a two-level system. Furthermore, we show that the method can be used for operator control, and provide conditions for producing several universal gates for quantum computation as an example. In addition, we indicate a basis for utilizing the method in optimal control problems.
关键词： quantum state transfer,quantum computation,coherent control,quantum information,complete population transfer,quantum control
更新于2025-09-09 09:28:46