Compact freeform-surface-based Offner imaging spectrometer with both a long-slit and broadband.

Current imaging spectrometers with conventional optical elements face major challenges in achieving a large field of view (FOV), broadband and compact structure simultaneously. In this paper, a compact freeform-surface-based Offner imaging spectrometer with both a long-slit and a broadband (CISLS) is proposed. To keep a long slit and an anastigmatic imaging, the slit off-axis amount of the initial system is within a specific range theoretically. While to achieve a compact structure, the slit off-axis amount should be away from the specific range and as small as possible. Based on the vector aberration theory and the analytical study, Zernike polynomial terms Z5 and Z6 introduce the astigmatism independent of FOV. They are utilized to well balance the astigmatism when the slit off-axis amount is away from the specific range, helping a miniaturization of the system. Other Zernike polynomial terms below the eighth order introduce the astigmatism related to FOV. They contribute to balancing the astigmatism that produced with the increasing of the FOV, thus achieving a wide FOV. The design results show that the proposed CISLS with a high spectral resolution of 2.7 nm achieves a long slit of 30 mm in length but a small size of only 60 mm × 64 mm × 90 mm in volume under a broadband from 400 nm to 1000 nm.

Compact multi-spectral-resolution Wynne-Offner imaging spectrometer with a long slit.

Current imaging spectrometers are developed towards a large field of view (FOV) as well as high resolution to obtain more spatial and spectral information. However, imaging spectrometers with a large FOV and high resolution produce a huge image data cube, which increases the difficulty of spectral data acquisition and processing. In practical applications, it is more reasonable and helpful to identify different targets within a large FOV with different spectral resolutions. In this paper, a compact multi-spectral-resolution Wynne-Offner imaging spectrometer with a long slit is proposed by introducing a special diffraction grating with multi-groove densities at different areas. With the increasing of the groove density and the slit length, the astigmatism of the Wynne-Offner imaging spectrometer increases sharply. Therefore, the relationships between the astigmatism and both the groove density and slit length are studied. Moreover, a holographic grating is introduced. The holographic aberrations produced are utilized to balance the residual astigmatism of the imaging spectrometer. The design results show that the system is only 60m m×115m m×103m m in volume but achieves both a long slit of 20 mm in length and a waveband from 400 nm to 760 nm with three kinds of spectral resolutions of 2 nm, 1 nm, and 0.5 nm. The designed compact multi-spectral-resolution Wynne-Offner imaging spectrometer can be widely applied in the fields of crop classification and pest detection, which require both a large FOV and multiple spectral resolutions.

Ultra-compact dual band imaging spectrometer with freeform prisms.

Wide spectrum and miniaturization are the main challenges in the imaging spectrometer design. In this paper, we propose an ultra-compact dual band imaging spectrometer (CDBIS) with cemented freeform prisms, which works at both the visible-near-infrared (VNIR) from 400 nm to 1000 nm and the shortwave-infrared (SWIR) from 1000 nm to 1700 nm. The imaging spectrometer is only composed of three cemented prisms, a primary prism and two triangular prisms. And a freeform surface characterized by the Zernike polynomial is introduced in each prism. The CDBIS is dispersed by a diffraction grating, which is designed on the second surface of the primary prism. Based on vector aberration theory (VAT), the relationship among the astigmatism generated by the introduced freeform surfaces, the wavelength, and the field of view is studied. Accordingly, a wideband is realized by introducing the freeform surfaces after the diffraction grating. Furthermore, through optimizing the coefficients of Zernike polynomial terms, residual astigmatism at different wavelengths is well balanced. An imaging spectrometer with a volume of only 100c m 3 is obtained, with a spectral resolution of 1.45 nm at VNIR and 2.40 nm at SWIR, respectively. It has a huge potential for broadband space exploration.

Dual-channel snapshot imaging spectrometer with wide spectrum and high resolution.

The comprehensive analysis of dynamic targets brings about the demand for capturing spatial and spectral dimensions of visual information instantaneously, which leads to the emergence of snapshot spectral imaging technologies. While current snapshot systems face major challenges in the development of wide working band range as well as high resolution, our novel dual-channel snapshot imaging spectrometer (DSIS), to the best of our knowlledge, demonstrates the capability to achieve both wide spectrum and high resolution in a compact structure. By dint of the interaction between the working band range and field of view (FOV), reasonable limits on FOV are set to avoid spectral overlap. Further, we develop a dual-channel imaging method specifically for DSIS to separate the whole spectral range into two parts, alleviating the spectral overlap on each image surface, improving the tolerance of the system for a wider working band range, and breaking through structural constraints. In addition, an optimal FOV perpendicular to the dispersion direction is determined by the trade-off between FOV and astigmatism. DSIS enables the acquisition of 53×11 spatial elements with up to 250 spectral channels in a wide spectrum from 400 to 795 nm. The theoretical study and optimal design of DSIS are further evaluated through the simulation experiments of spectral imaging.

Spatial-spectral resolution tunable snapshot imaging spectrometer: analytical design and implementation.

A snapshot imaging spectrometer is a powerful tool for dynamic target tracking and real-time recognition compared with a scanning imaging spectrometer. However, all the current snapshot spectral imaging techniques suffer from a major trade-off between the spatial and spectral resolutions. In this paper, an integral field snapshot imaging spectrometer (TIF-SIS) with a continuously tunable spatial-spectral resolution and light throughput is proposed and demonstrated. The proposed TIF-SIS is formed by a fore optics, a lenslet array, and a collimated dispersive subsystem. Theoretical analyses indicate that the spatial-spectral resolution and light throughput of the system can be continuously tuned through adjusting the F number of the fore optics, the rotation angle of the lenslet array, or the focal length of the collimating lens. Analytical relationships between the spatial and spectral resolutions and the first-order parameters of the system with different geometric arrangements of the lenslet unit are obtained. An experimental TIF-SIS consisting of a self-fabricated lenslet array with a pixelated scale of 100×100 and a fill factor of 0.716 is built. The experimental results show that the spectral resolution of the system can be steadily improved from 4.17 to 0.82 nm with a data cube (N x×N y×N λ) continuously tuned from 35×35×36 to 40×40×183 in the visible wavelength range from 500 to 650 nm, which is consistent with the theoretical prediction. The proposed method for real-time tuning of the spatial-spectral resolution and light throughput opens new possibilities for broader applications, especially for recognition of things with weak spectral signature and biomedical investigations where a high light throughput and tunable resolution are needed.

Design, Synthesis, and Biological Evaluation of Novel Amyl Ester Tethered Dihydroartemisinin-Isatin Hybrids as Potent Anti-Breast Cancer Agents.

A series of novel amyl ester tethered dihydroartemisinin-isatin hybrids 4a-d and 5a-h were designed, synthesized, and evaluated as anti-breast cancer agents. The synthesized hybrids were preliminarily screened against estrogen receptor-positive (MCF-7 and MCF-7/ADR) and triple-negative (MDA-MB-231 and) breast cancer cell lines. Three hybrids 4a,d and 5e not only were more potent than artemisinin and adriamycin against drug-resistant MCF-7/ADR and MDA-MB-231/ADR breast cancer cell lines, but also displayed non-cytotoxicity towards normal MCF-10 A breast cells, and the SI values were >4.15, indicating their excellent selectivity and safety profiles. Thus, hybrids 4a,d and 5e could act as potential anti-breast cancer candidates and were worthy of further preclinical evaluations. Moreover, the structure-activity relationships which may facilitate further rational design of more effective candidates were also enriched.

Novel ester tethered dihydroartemisinin-3-(oxime/thiosemicarbazide)isatin hybrids as potential anti-breast cancer agents: Synthesis, in vitro cytotoxicity and structure-activity relationship.

A series of ester tethered dihydroartemisinin-3-(oxime/thiosemicarbazide)isatin hybrids 7a-p were designed, synthesized, and assessed for their antiproliferative activity against MCF-7, MDA-MB-231, MCF-7/ADR, and MDA-MB-231/ADR breast cancer cell lines. Among them, hybrids 7a,f (IC50 : 1.33-3.84 µM) showed potent activity against triple-negative (MDA-MB-231 and MDA-MB-231/ADR) breast cancer cell lines, and hybrid 7f (IC50 : 3.90 and 10.18 µM) also demonstrated promising activity against estrogen receptor-positive breast cancer cells (MCF-7 and MCF-7/ADR), and the activity was superior to these of artemisinin, dihydroartemisinin, and ADR, revealing their potential to fight against both drug-sensitive and drug-resistant breast cancers. The enriched structure-activity relationships may facilitate further design of more active candidates.

Design, synthesis and anti-breast cancer properties of butyric ester tethered dihydroartemisinin-isatin hybrids.

Fifteen novel butyric ester tethered dihydroartemisinin-isatin hybrids 4a-d and 5a-k were designed, synthesized, and evaluated for cytotoxicity against four human breast cancer cell lines, including MCF-7, MDA-MB-231, MCF-7/ADR and MDA-MB-231/ADR using the MTT method. A significant part of them were active against the four tested cancer cell lines, and the representative hybrid 5b (IC50: 1.27 µM) was 14.88 -> 78.74 times more active than adriamycin (IC50: 18.90 µM), DHA (IC50: 28.28 µM) and ART (IC50: > 100 µM) against MCF-7 breast cancer cells, whereas hybrid 5c (IC50: 2.39 and 3.95 µM) was superior to adriamycin (IC50: 3.38 and >100 µM), DHA (IC50: 48.80 and 82.78 µM) and ART (IC50: >100 and >100 µM) against MDA-MB-231 and MDA-MB-231/ADR breast cancer cell lines. Moreover, the selected hybrids (IC50: >100 µM) displayed non-cytotoxicity towards normal MCF-10A breast cells, and the SI values of hybrids 5b,c were >78.74 and >41.84 respectively, demonstrating their excellent selectivity and safety profiles. Accordingly, hybrids 5b,c could serve as promising anti-breast cancer candidates and deserved further preclinical evaluations.

Analytical design of a cemented-curved-prism based integral field spectrometer (CIFS) with high numerical aperture and high resolution.

Snapshot hyperspectral imaging is superior to scanning spectrometers due to its advantage in dimensionality, allowing longer pixel dwell time and higher data cube acquisition efficiency. Due to the trade-off between spatial and spectral resolution in snapshot spectral imaging technologies, further improvements in the performance of snapshot imaging spectrometers are limited. Therefore, we propose a cemented-curved-prism-based integral field spectrometer (CIFS), which achieves high spatial and high spectral resolution imaging with a high numerical aperture. It consists of a hemispherical lens, a cemented-curved-prism and a concave spherical mirror. The design idea of aplanatic imaging and sharing-optical-path lays the foundation for CIFS to exhibit high-resolution imaging in a compact structure. The numerical model between the parameters of optical elements and the spectral resolution of the system is established, and we analyze the system resolution influenced by the hemispherical lens and the cemented-curved-prism. Thus, the refractive index requirements of the hemispherical lens and the cemented-curved-prism for the optimal spatial and spectral resolution imaging of the system are obtained, providing guidance for the construction of CIFS. The designed CIFS achieves pupil matching with a 1.8 f-number lenslet array, sampling 268 × 76 spatial points with 403 spectral channels in the wavelength band of 400 to 760 nm. The spectral and spatial resolution are further evaluated through a simulation experiment of spectral imaging based on Zemax. It paves the way for developing integral field spectrometers exhibiting high spatial and high spectral resolution imaging with high numerical aperture.

High spectral resolution compact Offner spectrometer based on the aberration-reduced convex holographic gratings recorded by spherical waves under Rowland circle mounting.

High spectral resolution, excellent imaging quality, and compact configuration have become a recent trend in push-broom imaging spectrometers. The concentric Offner imaging spectrometer has become popular due to its high optical performance and compactness. However, astigmatism is the dominant residual aberration in the Offner imaging spectrometer, which makes the meridional and sagittal images unable to be focused well and causes a deterioration in image quality and spectral resolution. In this paper, we present a compact Offner imaging spectrometer with a high resolution based on an aberration-reduced convex holographic grating (ACHG), which is recorded by spherical waves under Rowland circle mounting. The holographic aberration coefficients of ACHG and geometric aberration coefficients of the Offner imaging spectrometer are derived based on the analysis of the light-path function. Furthermore, we analyzed the relationship between holographic aberration coefficients and holographic recording parameters of ACHG under Rowland circle mounting. To balance the geometric aberration of the Offner imaging spectrometer, proper holographic aberration coefficients of the ACHG are achieved through adjusting the holographic recording parameters. The design result indicated that the Offner imaging spectrometer with ACHG provides better images than those with mechanically ruled convex grating (MRCG). Moreover, the spectral resolution is significantly improved. This lays down a theoretical basis for subsequent construction work in the Offner imaging spectrometer with holographic aberration-reduced gratings.

MicroRNA-140 inhibit prostate cancer cell invasion and migration by targeting YES proto-oncogene 1.

Prostate cancer (PCa), which is an aggressive malignancy of the male genitourinary system. In the present study, the effects of microRNA-140 (miR-140) on PCa were determined. We transfected miR-140 mimics or negative control into PCa cells, and we used MTT, wound healing, and Transwell assays for determining the capacities of miR-140 in cell proliferation, migration, and invasion, respectively. We also confirmed the relationship between miR-140 and YES proto-oncogene 1 (YES1) using Luciferase reporter assay. The results showed that miR-140 was downregulated in PCa cells and tissues, and overexpression of miR-140 could significantly suppress their capacities of proliferation, migration, and invasion. Moreover, YES1 was shown to be a direct target of miR-140. Moreover, miR-140 expression is negatively correlated with YES1 levels. miR-140 exhibits significant tumor-suppressive effects in PCa by inhibiting YES1. The study indicated that miR-140 and YES1 could be the potential targets for PCa therapy.

Effect of peptidoglycan amidase MSMEG_6281 on fatty acid metabolism in Mycobacterium smegmatis.

Mycobacterium smegmatis MSMEG_6281, a peptidoglycan (PG) amidase, is essential in maintaining cell wall integrity. To address the potential roles during the MSMEG_6281-mediated biological process, we compared proteomes from wild-type M.smegmatis and MSMEG_6281 gene knockout strain (M.sm-ΔM_6281) using LC-MS/MS analysis. Peptide analysis revealed that 851 proteins were differentially produced with at least 1.2-fold changes, including some proteins involved in fatty acid metabolism such as acyl-CoA synthase, acyl-CoA dehydrogenase, MCE-family proteins, ATP-binding cassette (ABC) transporters, and MmpL4. Some proteins related to fatty acid degradation were enriched through protein-protein interaction analysis. Therefore, proteomic data showed that a lack of MSMEG_6281 affected fatty acid metabolism. Mycobacteria can produce diverse lipid molecules ranging from single fatty acids to highly complex mycolic acids, and mycobacterial surface-exposed lipids may impact biofilm formation. In this study, we also assessed the effects of MSMEG_6281 on biofilm phenotype using semi-quantitative and morphology analysis methods. These results found that M.sm-ΔM_6281 exhibited a delayed biofilm phenotype compared to that of the wild-type M.smegmatis, and the changes were recovered when PG amidase was rescued in a ΔM_6281::Rv3717 strain. Our results demonstrated that MSMEG_6281 impacts fatty acid metabolism and further interferes with biofilm formation. These results provide a clue to study the effects of PG amidase on mycobacterial pathogenicity.

Lack of MSMEG_6281, a peptidoglycan amidase, affects cell wall integrity and virulence of Mycobacterium smegmatis.

Mycolyl-arabinogalactan-peptidoglycan (mAGP) is the major content of the mycobacterium cell wall structure and essential for mycobacterial survival. Peptidoglycan (PG) plays an important role in maintenance of cell division, cell wall integrity and pathogenesis. Mycobacterium smegmatis MSMEG_6281, a peptidoglycan amidase, is vital for mycobacterial cell division. However, the effects of MSMEG_6281on cell wall integrity and mycobacterial virulence remain unknown. In the current study, we demonstrate that MSMEG_6281gene knockout in M.smegmatis alters the microbiological characteristics. Our results revealed that MSMEG_6281gene knockout bacteria (M. sm-ΔM_6281) lost their acid-fastness, increased their sensitivity to lipophilic compounds and presented an abnormal morphology. Our results revealed that MSMEG_6281was related to maintaining the cell wall integrity. Furthermore, we investigated the effects of MSMEG_6281 inactivation on mycobacterial virulence using mice models infected by different M.smegmatis strains. MSMEG_6281 inactivation in the M sm-ΔM_6281 infected group caused less mycobacterial colonization, reduced pathological signs, decreased the anti-microbial enzymes production including iNOS and ß-defensins in mouse lungs. Moreover, IL-1ß and TLR2 expression were significantly down-regulated, while the production of IFN-γ and TNF-α was up-regulated. These findings indicated the diversity of host immune responses induced by different strains of M.smegmatis, suggesting that MSMEG_6281 inactivation impact mycobacterial virulence. In conclusion, the MSMEG_6281 protein plays important roles in maintaining cell wall integrity and mycobacterial virulence.

Pleiotropic Anti-atherosclerotic Effects of PCSK9 InhibitorsFrom Molecular Biology to Clinical Translation.

PURPOSE OF REVIEW: Clinical trials with PCSK9 inhibitors have shown a robust decrease in plasma LDL levels and a significant reduction in the incidence of cardiovascular atherosclerotic events. However, the role of PCSK9 in atherosclerosis is not well investigated and it remains unclear whether PCSK9 inhibition has direct, LDL-independent, anti-atherosclerotic effects. This review outlines the molecular pathways and targets of PCSK9 in atherosclerosis and summarizes the experimental and clinical data supporting the anti-atherosclerotic (pleiotropic) actions of PCSK9 inhibitors. RECENT FINDINGS: PCSK9 is expressed by various cell types that are involved in atherosclerosis (e.g., endothelial cell, smooth muscle cell, and macrophage) and is detected inside human atherosclerotic plaque. Preclinical studies have shown that inhibition of PCSK9 can attenuate atherogenesis and plaque inflammation. Besides increasing plasma LDL, PCSK9 appears to promote the initiation and progression of atherosclerosis. Inhibition of PCSK9 may confer atheroprotection that extends beyond its lipid-lowering effects.

Associations of Prostate-Specific Antigen, Prostate Carcinoma Tissue Gleason Score, and Androgen Receptor Expression with Bone Metastasis in Patients with Prostate Carcinoma.

BACKGROUND Prostate carcinoma (PCa) is often not diagnosed until advanced disease with bone metastasis. Predictive factors for bone metastasis are required to improve patient outcomes. The study aimed to analyze the factors associated with bone metastases in newly diagnosed patients with PCa. MATERIAL AND METHODS This was a retrospective study of 80 patients newly diagnosed with PCa by pathological examination between January 2012 and December 2014. Bone metastases were diagnosed by positron emission computed tomography. Clinical data, serological laboratory results, and pathological examination results were collected. RESULTS Among the 80 patients, 45 (56%) had bone metastases. Age, serum alkaline phosphatase, prostate-specific antigen (PSA), erythrocyte sedimentation rate, PCa tissue Gleason score, androgen receptor (AR) expression, and Ki-67 expression were higher in patients with bone metastasis compared with those without (all P<0.05). Multivariate logistic regression showed that PSA (OR: 1.005; 95%CI: 1.001-1.010; P=0.016), Gleason score (OR: 4.095; 95%CI: 1.592-10.529; P=0.003), and AR expression (OR: 14.023; 95%CI: 3.531-55.6981; P=0.005) were independently associated with bone metastases. Cut-off values for PSA, Gleason score, and AR expression were 67.1 ng/ml (sensitivity: 55.6%; specificity: 97.1%), 7.5 (sensitivity: 75.6%; specificity: 82.9%), and 2.5 (sensitivity: 84.0%; specificity: 91.4%), respectively. CONCLUSIONS PSA, Gleason score, and AR expression in PCa tissues were independently associated with PCa bone metastases. These results could help identifying patients with PCa at high risk of bone metastases.

A Facile Method to Control the Diameter of Monoclinic Vanadium Dioxide Rods.

Nano/submicro vanadium dioxide rods in monoclinic phase (VO2 (M)) were synthesized through hydrothermal reaction combined with subsequent calcinations. The morphology and structure of samples were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The average diameter of VO2 (M) dioxide rods from 210 nm to 1 µm were successfully controlled by adjusting the synthesis conditions including the concentration of Vanadium pentoxide (V2O5) solution and the molar ratio of V2O5 and oxalic acid. Our results reveal that the concentration of V2O5 is the key factor to determine the diameter of VO2 (M) rods, while higher molar ratio favors formation of VO2 rods with narrow diameter distributions. The growth mechanism of vanadium dioxide rods was discussed.

Pressure-induced transformations of onion-like carbon nanospheres up to 48 GPa.

Raman spectra of onion-like carbon nanospheres (OCNSs) have been studied under pressure up to 48 GPa. A transformation related to a change from sp(2) to sp(3) bonding of carbons in OCNSs was observed at pressures above 20 GPa. The Raman spectra exhibit some vibrational features similar to those of the theoretically proposed Z-carbon phase of cold-compressed graphite, while the transition pressure is obviously higher than that for graphite. In contrast to the transformations in compressed graphite, interlayer bonds are formed on the nanoscale between buckled layers in OCNSs under pressure due to the concentric configuration, and sp(2)-sp(3) conversion is incomplete even up to 48 GPa. This is confirmed by TEM observations on the decompressed samples. Moreover, the onion-like carbon structure is extremely stable and can be recovered even after a compression cycle to 48 GPa. This high stability, beyond that of other sp(2) carbon materials, is related to the unique onion-like configuration and to the interlayer bonding. The transformed material should have excellent mechanical properties so that it can sustain very high pressure.

MiR-26a inhibits prostate cancer progression by repression of Wnt5a.

MicroRNAs (miRNAs) are small noncoding RNAs that are involved in different biological processes by suppressing target gene expression. miRNA microarray analysis revealed a significant decrease of miR-26a in prostate cancer tissues versus their normal counterparts, but the role of miR-26a is needed to investigate. In the present study, we found that miR-26a expression was lower in prostate cancer tissues compared with their normal controls, so did the prostate cancer cells. Next, by lentivirus-mediated gain-of-function studies, it was showed that stable miR-26a inhibited cell proliferation, metastasis, and epithelial mesenchymal transition and induced G1 phase arrest in prostate cancer. It was predicted that Wnt5a was a potential target gene of miR-26a by bioinformatics analysis. Then, luciferase assay and Western blot analysis identified that Wnt5a was a new direct target gene of miR-26a and miR-26a inhibited prostate cancer progression via Wnt5a. Altogether, the findings suggested that miR-26a may function as a tumor suppressor in prostate cancer by targeting Wnt5a.

Implementation and validation of aortic remodeling in hypertensive rats.

A computational framework was implemented and validated to better understand the hypertensive artery remodeling in both geometric dimensions and material properties. Integrating the stress-modulated remodeling equations into commercial finite element codes allows a better control and visualization of local mechanical parameters. Both arterial thickening and stiffening effects were captured and visualized. An adaptive material remodeling strategy combined with the element birth and death techniques for the geometrical growth were implemented. The numerically predicted remodeling results in terms of the wall thickness, inner diameter, and the ratio of elastin to collagen content of the artery were compared with and fine-tuned by the experimental data from a documented rat model. The influence of time constant on the material remodeling was also evaluated and discussed. In addition, the geometrical growth and material remodeling were isolated to better understand the contributions of each element to the arterial remodeling and their coupling effect. Finally, this framework was applied to an image-based 3D artery generated from computer tomography to demonstrate its heterogeneous remodeling process. Results suggested that hypertension induced arterial remodeling are quite heterogeneous due to both nonlinear geometry and material adaptation process. The developed computational model provided more insights into the evolutions of morphology and material of the artery, which could complement the discrete experimental data for improving the clinical management of hypertension. The proposed framework could also be extended to study other types of stress-driven tissue remodeling including in-stent restenosis and grafting.

The impact of FDI on industrial structure upgrading and carbon emission under the constraints of environmental regulation.

Foreign direct investment (FDI) plays an important role in promoting industrial structure and curbing carbon emission. The study is based on panel data from 30 provinces in China from 2011 to 2021 and verifies the impact of FDI under environmental regulation on industrial structure upgrading and carbon emission. The empirical results show that FDI under environmental regulation can inhibit carbon emission and promote industrial structure upgrading. The carbon emission reduction effect and industrial structure upgrading effect of FDI show regional heterogeneity, with the strongest effect in the eastern region, followed by the central region, and no significant effect in the western region. The moderating effect examination of environmental regulation illustrates that formal and informal environmental regulation can effectively regulate the relationship between FDI and carbon emission, but due to differences in various factors such as economic development level and population quality, the moderating effect also exhibits regional heterogeneity. In the mechanism test, industrial structure upgrading plays a perfect mediating role in the path of FDI inhibiting carbon emission, and environmental regulation can further enhance the mediating effect of industrial structure upgrading. There is a threshold of industrial structure upgrading between FDI and carbon emission, and FDI can only suppress carbon emission after crossing the threshold of industrial structure upgrading.