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We demonstrate a novel flat-field, dual-optic imaging EUV-soft X-ray spectrometer and monochromator that attains an unprecedented throughput efficiency exceeding 60% by design, along with a superb spectral resolution of λ/Δλ > 200 accomplished without employing variable line spacing gratings. Exploiting the benefits of the conical diffraction geometry, the optical system is globally optimized in multidimensional parameter space to guarantee optimal imaging performance over a broad spectral range while maintaining circular and elliptical polarization states at the first, second, and third diffraction orders. Moreover, our analysis indicates minimal temporal dispersion, with pulse broadening confined within 80 fs tail-to-tail and an FWHM value of 29 fs, which enables ultrafast spectroscopic and pump-probe studies with femtosecond accuracy. Furthermore, the spectrometer can be effortlessly transformed into a monochromator spanning the EUV-soft X-ray spectral region using a single grating with an aberration-free spatial profile. Such capability allows coherent diffractive imaging applications to be conducted with highly monochromatic light in a broad spectral range and extended to the soft X-ray region with minimal photon loss, thus facilitating state-of-the-art imaging of intricate nano- and bio-systems, with a significantly enhanced spatiotemporal resolution, down to the nanometer-femtosecond level.

This article examines the impacts of mode hopping on the sensing performance of optical frequency domain reflectometry (OFDR) and explores the potential for developing economical OFDR interrogators employing low-cost distributed feedback (DFB) lasers. By conducting numerical simulations, this study reveals that mode hopping has minimal effects on distance sensing measurements in free space due to the limited duration of beat interference signal at the incorrect frequency within the coherence length. Additionally, the simulations indicate that mode hopping only slightly affects the distributed strain sensing of OFDR, resulting in an error range of less than ± 1 µ ε when 100 µ ε is applied to the sensing fiber. These findings highlight the potential of using low-cost DFB lasers with a 1-nm wavelength sweep range and a 1-MHz linewidth as tunable laser sources in OFDR while maintaining reliable and accurate sensing performance. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the altered brain areas activated in functional magnetic resonance imaging before and after escitalopram antidepressant treatment in patients with major depressive disorder. Functional magnetic resonance studies showed abnormal activity in brain regions such as prefrontal cortex， cingulate cortex and striatum in patients prior to treatment， meantime， the abnormal activation of anterior cingulate， dorsolateral prefrontal and thalamus reflected the outcomes of escitalopram antidepressant therapy. Following the treatment with escitalopram， the fMRI activation of brain areas returned to normal， and those changes were significantly correlated with the improvement of depressive symptoms. So this paper provides a review of the brain functional activity changes in patients with major depressive disorder before treatment and at different time point of medication， as well as the correlation between altered brain functional activity and clinical symptoms.

Energy management strategies for hydrogen fuel cell hybrid electric vehicles (FCHEVs) are a key factor in achieving real-time vehicle energy optimization control, vehicle driving economy, and fuel cell durability. In this paper, for an FCHEV equipped with a fuel cell and supercapacitor, the quantitative information, logic rules, and operational constraints are transformed into linear integer inequalities according to its different operating modes, and the Hysdel language is used to establish its mixed logic dynamic model (MLD). Then, the energy management strategy based on model predictive control (MPC) is developed using the MLD model as the prediction model and the equivalent hydrogen consumption and the performance degradation of the fuel cell as the optimization performance indexes. Finally, under the World Light Vehicle Test Cycle, a joint simulation was carried out with Advisor and Simulink to verify the proposed strategy's superiority by comparing it with the power following control strategy (PFCS) and the compound fuzzy control strategy (CFCS). The results show that the strategy not only ensures real-time FCHEV energy control, but also reduces hydrogen consumption by 10.98% and 1.98% and the number of start/stop times of a fuel cell by six and four, compared to PFCS and CFCS, respectively, which improves the economy of the whole vehicle as well as the durability of the fuel cell. [ABSTRACT FROM AUTHOR]

In this letter, a portable trace carbon dioxide (CO2) measurement instrument based on photoacoustic spectroscopy (PAS) was proposed and designed. The nonresonance PA cell (PAC) including a cooper tube with 251.2 μl was designed. Two condenser microphones were used to measure the PA signal simultaneously. The center wavelength of the distributed feedback laser was chosen to 2004 nm. Within 1 s integral time, the detection limit for CO2 reached 12.7 ppm. The normalized noise‐equivalent absorption coefficient was calculated to be 4.8468 × 10−9 cm−1W/Hz1/2. With Allan‐Werle deviation analysis, the measurement detection limit for CO2 improved to 4 ppm with 30 s integration time. As a result, the trace CO2 instrument based on PAS shows a good performance in long‐term detection. [ABSTRACT FROM AUTHOR]

Transformation circle theory is simpler than other methods for analyzing laser resonators. In our analysis only a circles and simple mathematical knowledge are used to analyze the stability and calculate the parameters of the laser resonator, which further simplifies the transformation theory. The results agree well with the well-known matrix theory. Two- and three-mirror (including a thermal lens) laser resonators are used as examples to present the stability formula and the Gaussian beam dimensions at the mirrors. Furthermore, we apply the commonly used example in which the laser medium is close to the cavity mirror. OCIS codes: 080.2720, 140.3410, 140.4780.

The influence of composition on the photorefractive effect in pure LiNbO3 crystals at low light intensity was investigated. The experimental results indicate that different defects dominate the photorefractive centers of pure LiNb[O.sub.3] with various compositions. Bipolarons are considered to be responsible for the enhanced photovoltaic field in reduced near-stoichiometric LiNbO3, and their bulk photovoltaic constant K is estimated to be ~6.95 x [10.sup.-32] [m.sub.3]/V. Q polarons (composed of two bipolarons) are introduced to explain the photorefractive effect of congruent LiNb[O.sub.3] at both low and high light intensities.

A method of measuring the refractive indices of minute samples by analyzing capillary interferometry is introduced. With the interference theory of light, the intensity distribution of an interference fringe pattern formed by a cylindrical tube of a capillary is obtained, and the influence of some parameters on the fringes are discussed. The measurement accuracy and its relative problems are analyzed. OCIS codes: 120.3180, 120.5710, 260.3160.