Derivation and validation of a nomogram incorporating modifiable lifestyle factors to predict development of colorectal adenomas after negative index colonoscopy.

This retrospective cohort study aimed to identify baseline patient characteristics involving modifiable lifestyle factors that are associated with the development of colorectal adenomas, and establish and validate a nomogram for risk predictions among high-risk populations with negative index colonoscopy. A total of 83,076 participants who underwent an index colonoscopy at the Tianjin Union Medical Center between 2004 and 2019 were collected. According to meticulous inclusion and exclusion criteria, 249 subjects were enrolled and categorized into the primary and validation cohorts. Based on the primary cohort, we utilized the LASSO-Cox regression and the univariate/multivariate Cox proportional hazards (Cox-PH) regression parallelly to select variables, and incorporated selected variables into two nomogram models established using the multivariate Cox-PH regression. Comparison of the Akaike information criterion and the area under the receiver operating characteristic curve of the two models demonstrated that the nomogram model constituted by four covariates retained by the LASSO-Cox regression, including baseline age, body mass index, physical activity and family history of colorectal cancer (CRC) in first-degree relatives, performed better at predicting adenoma-free survival probabilities. Further validation including the concordance index, calibration plots, decision curve analysis and Kaplan-Meier survival curves also revealed good predictive accuracy, discriminating ability, clinical utility and risk stratification capacity of the nomogram model. Our nomogram will assist high-risk individuals with negative index colonoscopy to prevent colorectal adenoma occurrence and CRC morbidity with improved cost-effectiveness.

Andrographolide sensitizes KRAS-mutant colorectal cancer cells to cetuximab by inhibiting the EGFR/AKT and PDGFRß/AKT signaling pathways.

BACKGROUND: Cetuximab, an inhibitor targeting EGFR, is widely applied in clinical management of colorectal cancer (CRC). Nevertheless, drug resistance induced by KRAS-mutations limits cetuximab's anti-cancer effectiveness. Furthermore, the persistent activation of EGFR-independent AKT is another significant factor in cetuximab resistance. Nevertheless, the mechanism that EGFR-independent AKT drives cetuximab resistance remains unclear. Thus, highlighting the need to optimize therapies to overcome cetuximab resistance and also to explore the underlying mechanism. PURPOSE: This work aimed to investigate whether and how andrographolide enhance the therapeutic efficacy of cetuximab in KRAS-mutant CRC cells by modulating AKT. METHODS: The viabilities of CRC cell lines were analyzed by CCK-8. The intracellular proteins phosphorylation levels were investigated by Human Phospho-kinase Antibody Array analysis. Knockdown and transfection of PDGFRß were used to evaluate the role of andrographolide on PDGFRß. The western blotting was used to investigate Wnt/ß-catenin pathways, PI3K/AKT, and EMT in KRAS-mutant CRC cells. The animal models including subcutaneous tumor and lung metastasis were performed to assess tumor response to therapy in vivo. RESULTS: Andrographolide was demonstrated to decrease the expression of PI3K and AKT through targeting PDGFRß and EGFR, and it enhanced cetuximab effect on KRAS-mutant CRC cells by this mechanism. Meanwhile, andrographolide helped cetuximab to inhibit Wnt/ß-catenin, CRC cell migration and reduced Vimentin expression, while increasing that of E-cadherin. Lastly, co-treatment with cetuximab and andrographolide reduced the growth of KRAS-mutant tumors and pulmonary metastases in vivo. CONCLUSIONS: Our findings suggest that andrographolide can overcome the KRAS-mutant CRC cells' resistance to cetuximab through inhibiting the EGFR/PI3K/AKT and PDGFRß /AKT signaling pathways. This research provided a possible theory that andrographolide sensitizes KRAS-mutant tumor to EGFR TKI.

Colonoscopy compliance and diagnostic yield in a large population-based colorectal cancer screening programme.

OBJECTIVES: With the intention of providing a reference for secondary prevention, our study provides some insight on diagnostic yield of factors influencing compliance with colonoscopy and the presence of advanced adenomas (AA). METHODS: We conducted large-scale CRC screening among local Tianjin residents aged 40-75 years between 2012 and 2019. A high-risk factor questionnaire (HRFQ) was distributed to each participant, followed by the performance of a fecal immunochemical test (FIT). Participants who tested positively for any of these items were advised to undergo a colonoscopy. Relevant basic information was collected from participants during CRC screening, and the screening data were sorted and analysed. RESULTS: A total of 5,670,924 people participated in CRC screening by the end of 2019, including 275,708 people in the high-risk group, and 74,685 (27.1%) people who underwent colonoscopy. The results of the logistic regression model demonstrated that participants with a history of mucous bloody stool (OR = 8.20, 95% CI: 7.92, 8.50, p < 0.001), chronic diarrhea (OR = 5.73, 95% CI: 5.57, 5.89, p < 0.001), and higher level of education (OR = 1.87, 95% CI: 1.80, 1.93, p < 0.001) were more likely to comply with a colonoscopy. Several factors including age (70-75 years old:OR = 3.72, 95% CI: 2.71, 5.10, p < 0.001), and FIT( +) (OR = 1.65, 95% CI: 1.42,1.90, p < 0.001) were identified to be associated with the presence of AA. CONCLUSIONS: Increased compliance with colonoscopy is urgently needed. Our findings can inform the design of future effective large-scale population-based CRC screening programmes.

Marsdenia tenacissima enhances immune response of tumor infiltrating T lymphocytes to colorectal cancer.

Introduction: Tumor-infiltrating T lymphocytes in the tumor microenvironment are critical factors influencing the prognosis and chemotherapy outcomes. As a Chinese herbal medicine, Marsdenia tenacissima extract (MTE) has been widely used to treat cancer in China. Its immunoregulatory effects on tumor-associated macrophages is well known, but whether it regulates tumor-infiltrating T-cell functions remains unclear. Method: We collected 17 tumor samples from MTE-administered colorectal cancer patients, 13 of which showed upregulation of CD3+/CD8+ tumor-infiltrating T cells. Further in vitro and in vivo experiments were performed to investigate the regulatory effects of MTE on tumor-infiltrating T cells and immune escape of tumors. Results: Under single and co-culture conditions, MTE inhibited TGF-ß1 and PD-L1 expression in the colorectal cancer (CRC) cell lines HCT116 and LoVo. In Jurkat cells, MTE inhibited FOXP3 and IL-10 expression, increased IL-2 expression, but had no effect on PD-1 expression. These findings were confirmed in vitro using subcutaneous and colitis-associated CRC mouse models. MTE also increased the density of CD3+/CD8+ tumor-infiltrating T cells and exhibited considerable tumor-suppressive effects in these two tumor mouse models. Conclusions: Our findings suggested that MTE inhibits the immune escape of cancer cells, a precipitating factor increasing the immune response of T lymphocytes.

The accuracy of the FIT in detecting advanced neoplasm is highest in young people aged 40 to 49 years: an analysis based on sex and age.

BACKGROUND: Colorectal cancer (CRC) is one of the most common cancers and is associated with high incidence and mortality rates worldwide. CRC has caused a tremendous loss of human health and wealth. The incidence and mortality of colorectal carcinoma are increasing in young adults. Early cancer detection and prevention are made possible through screening. At present, the faecal immunochemical test (FIT) is a noninvasive method that can be used for the large-scale clinical screening of CRC status. Therefore, this study, based on CRC screening results in Tianjin from 2012 to 2020, was conducted to analyse the major differences in diagnostic performance parameters according to sex and age. METHODS: This study was based on 39,991 colonoscopies performed for individuals in the Tianjin CRC screening program from 2012 to 2020. Of these individuals, they had complete FIT and colonoscopy results. The differences in FIT results were analysed by sex and age. RESULTS: According to this study, males were generally more likely to develop advanced neoplasms (ANs) than females, and the prevalence increased with age. Males with negative FIT results were more likely to have advanced neoplasms than females with positive results. The accuracy of the FIT in detecting ANs in each age group was 54.9%, 45.5%, 48.6% and 49.5% in the 40-49, 50-59, 60-69, and ≥ 70 age groups, respectively. CONCLUSIONS: The FIT detected ANs with highest accuracy in the 40-49 age group. Our research can provide guidance to formulate CRC screening strategies.

Platycodin D represses ß-catenin to suppress metastasis of cetuximab-treated KRAS wild-type colorectal cancer cells.

Cetuximab, an epidermal growth factor receptor (EGFR) inhibitor, is extensively used for clinical therapy in KRAS wild-type colorectal cancer (CRC) patients. However, some patients still cannot get benefit from the therapy, because metastasis and resistance occur frequently after cetuximab treatment. New adjunctive therapy is urgently needed to suppress metastasis of cetuximab-treated CRC cells. In this study, we used two KRAS wild-type CRC cells, HT29 and CaCo2, to investigate whether platycodin D, a triterpenoid saponin isolated from Chinese medicinal herb Platycodon grandifloras, is able to suppress the metastasis of cetuximab-treated CRC. Label-free quantitative proteomics analyses showed that platycodin D but not cetuximab significantly inhibited expression of ß-catenin in both CRC cells, and suggested that platycodin D counteracted the inhibition effect of cetuximab on cell adherence and functioned in repressing cell migration and invasion. Western blot results showed that single platycodin D treatment or combined platycodin D and cetuximab enhanced inhibition effects on expressions of key genes in Wnt/ß-catenin signaling pathway, including ß-catenin, c-Myc, Cyclin D1 and MMP-7, compared to single cetuximab treatment. Scratch wound-healing and transwell assays showed that platycodin D combined with cetuximab suppressed migration and invasion of CRC cells, respectively. Pulmonary metastasis model of HT29 and CaCo2 in nu/nu nude mice consistently showed that combined treatment using platycodin D and cetuximab inhibited metastasis significantly in vivo. Our findings provide a potential strategy to inhibit CRC metastasis during cetuximab therapy by addition of platycodin D.

The comparison of risk factors for colorectal neoplasms at different anatomical sites.

AIM: Both the clinical manifestation and molecular characteristics of colorectal cancer (CRC) vary according to the anatomical site. We explored the risk factors for four groups of colorectal neoplasms (CRN) at different anatomical sites. METHODS: We extracted data from the database of Tianjin Colorectal Cancer Screening Program from 2010 to 2020. According to the CRN anatomical sites, patients were divided into four groups: the proximal colon group, the distal colon group, the rectum group, and the multiple colorectal sites. Binary logistic regression analysis was used to explore the differences in risk factors of CRN at different anatomical sites. RESULTS: The numbers of patients with CRN in the proximal colon, distal colon, rectum, and multiple colorectal sites were 4023, 6920, 3657, and 7938, respectively. Male sex was associated with a higher risk from the proximal colon to the rectum. Advanced age and obesity were also significantly associated with overall colorectal CRN risk, but there were some differences between men and women. Smoking was associated with CRN risk only in the distal colon and rectum in both men and women. Frequent alcohol consumption and family history of CRC in first-degree relatives (FDRs) were associated with the risk of multisite colorectal CRN only in males. CONCLUSIONS: We observed differences in advanced age, obesity, smoking, alcohol consumption, and family history of colorectal cancer at different anatomical sites of colorectal neoplasms. These factors vary by gender.

Young Patients With Colorectal Cancer Have Higher Early Mortality but Better Long-Term Survival.

INTRODUCTION: To define the prognosis of colorectal cancer (CRC) in young patients and to compare their postoperative treatment with that of older patients. METHODS: This multicenter study enrolled 5,457 patients with primary CRC who underwent surgical resection. The overall survival (OS), clinicopathologic characteristics, and postoperative treatment of 253 young patients aged 18-44 years and 5,204 older patients aged 44-80 years were analyzed. RESULTS: The OS rate was 77.1% for young and 74.2% for older patients (P = 0.348). Landmark analysis showed a significant difference in survival between young and older patients, with 63.8% of deaths among young patients being within 25 months of surgery compared with 42.4% among older patients (P = 0.002). Among those who survived more than 25 months, young patients had significantly better survival than older patients (P = 0.009). Multivariable analysis of young patients revealed that the tumor location, perineural invasion, and stage were associated with poor survival within 25 months; after this period, stage was the only prognostic marker. Young patients were more likely to receive chemotherapy, particularly multiagent regimens. For young patients, no significant difference in OS was found based on the chemotherapy regimen, regardless of disease stage (II, III, or IV, all P > 0.05). In addition, unlike in older patients, no difference in OS was found in young patients regardless of the drug regimen administered (all P > 0.05). DISCUSSION: Young-onset CRC may have a unique disease biology that warrants further research and therapy development.

Platycodin D sensitizes KRAS-mutant colorectal cancer cells to cetuximab by inhibiting the PI3K/Akt signaling pathway.

Cetuximab is a monoclonal antibody against epidermal growth factor receptor that blocks downstream signaling pathways of receptor tyrosine kinases, including Ras/Raf/MAPK and PI3K/Akt, thereby inhibiting tumor cell proliferation and inducing cancer cell apoptosis. Owing to KRAS mutations, the effectiveness of cetuximab is usually limited by intrinsic drug resistance. Continuous activation of the PI3K/Akt signaling pathway is another reason for cetuximab resistance. Platycodin-D, a bioactive compound isolated from the Chinese herb Platycodon grandiflorum, regulates Akt in different trends based on tissue types. To investigate whether platycodin-D can sensitize KRAS-mutant colorectal cancer cells to cetuximab by inhibiting the PI3K/Akt signaling pathway, HCT116 and LoVo cells were treated with cetuximab and platycodin-D. LY294002 and SC79 were used to regulate Akt to further evaluate whether platycodin-D sensitizes cells to cetuximab by inhibiting Akt. Our results confirmed that platycodin-D increased the cytotoxic effects of cetuximab, including inhibition of growth, migration, and invasion, via downregulation of PI3K and Akt phosphorylation in HCT116 and LoVo cells both in vitro and in vivo. Given these data, platycodin-D may sensitize KRAS-mutant colorectal cancer cells to cetuximab via inhibition of the PI3K/Akt signaling pathway.

Connexin 43 contributes to the sensitization of colorectal cancer cells to photodynamic therapy through Akt inhibition.

BACKGROUND: Photodynamic therapy could be one approach to treat colorectal cancer though resistance leads to failure of therapy. Akt activation is a cellular survival response to photodynamic therapy and is also a reason for resistance. Thus, inhibition of Akt is a strategy to decrease resistance. Akt interacts with connexin 43, another protein involved in photodynamic therapy resistance. Connexin 43 is widely expressed in different human tissues and has a complex role in tumor development. However, the mechanism of inhibition of Akt by connexin 43 that sensitizes colorectal cancer cells to photodynamic therapy needs further investigation. METHODS: In this study, two colorectal cancer cells with low phosphorylated connexin 43 level were used to explore this mechanism. LY294002 was used as an Akt inhibitor, and connexin 43-pCMV3 was transfected into cells to increase connexin 43 expression. RESULTS: Akt and connexin 43 inhibit each other in both colorectal cancer cell lines. In vitro and in vivo experiments showed that LY294002 and connexin 43 transfection sensitized cells to hematoporphyrin-Photodynamic therapy. LY294002 increased the sensitivity of cells to photodynamic therapy with a pronounced effect in cells with high expression levels of connexin 43. CONCLUSIONS: Connexin 43 should be considered an important factor in increasing the phototoxicity of photodynamic therapy in colorectal cancer through Akt inhibition.

Investigating role of conformational changes of microtubule in regulating its binding affinity to kinesin by all-atom molecular dynamics simulation.

Changes of affinity of kinesin head to microtubule regulated by changes in the nucleotide state are essential to processive movement of kinesin on microtubule. Here, using all-atom molecular dynamics simulations we show that besides the nucleotide state, large conformational changes of microtubule-tubulin heterodimers induced by strong interaction with the head in strongly binding state are also indispensable to regulate the affinity of the head to the tubulin. In strongly binding state the high affinity of the head to microtubule arises largely from mutual conformational changes of the microtubule and head induced by the specific interaction between them via an induced-fit mechanism. Moreover, the ADP-head has a much weaker affinity to the local microtubule-tubulin, whose conformation is largely altered by the interaction with the head in strongly binding state, than to other unperturbed tubulins. This indicates that upon Pi release the ADP-head temporarily has a much weaker affinity to the local tubulin than to other tubulins.

Optimal numbers of residues in linkers of DNA polymerase I, T7 primase and DNA polymerase IV.

DNA polymerase I (PolI), T7 primase and DNA polymerase IV (Dpo4) have a common feature in their structures that the two main domains are connected by an unstructured polypeptide linker. To perform their specific enzymatic activities, the enzymes are required to rearrange the position and orientation of one domain relative to the other into an active mode. Here, we show that the three enzymes share the same mechanism of the transition from the inert to active modes and use the minimum numbers of residues in their linkers to achieve the most efficient transitions. The transition time to the finally active mode is sensitively dependent on the stretched length of the linker in the finally active mode while is insensitive to the position and orientation in the initially inert state. Moreover, we find that for any enzyme whose two domains are connected by an unstructured flexible linker, the stretched length (L) of the linker in the finally active mode and the optimal number (Nopt) of the residues in the linker satisfy relation L ≈ αNopt, with α = 0.24-0.27 nm being a constant insensitive to the system.

Antibacterial activity and kinetics of Litsea cubeba oil on Escherichia coli.

Litsea cubeba oil is extracted from the fresh fruits of Litsea cubeba by distillation. In this study, its chemical constituents, antibacterial activity, kinetics and effects against Escherichia coli were studied. Its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were both 0.125% (v/v) by toxic food method. Moreover, the antibacterial kinetic curves indicated 0.0625% (v/v) of litsea cubeba oil was able to prolong the growth lag phase of E. coli cells to approximate 12 hours while 0.125% (v/v) of litsea cubeba oil was able to kill the cells completely. Furthermore, transmission electron microscope (TEM) observation showed most E. coli cells treated with 0.125% (v/v) of litsea cubeba oil were killed or destroyed severely within 2 hours. The litsea cubeba oil might penetrate and destroy the outer and inner membrane of E. coli cells. Thus many holes and gaps were observed on the damaged cells, which led to their death eventually. The antibacterial effects of litsea cubeba oil mainly attributed to the presence of aldehydes, which accounted for approximately 70% in its whole components analyzed by GC/MS. Based on the antimicrobial properties, litsea cubeba oil would have a broad application in the antimicrobial industry.

Antifungal effect and mechanism of garlic oil on Penicillium funiculosum.

Garlic oil is a kind of fungicide, but little is known about its antifungal effects and mechanism. In this study, the chemical constituents, antifungal activity, and effects of garlic oil were studied with Penicillium funiculosum as a model strain. Results showed that the minimum fungicidal concentrations (MFCs, v/v) were 0.125 and 0.0313 % in agar medium and broth medium, respectively, suggesting that the garlic oil had a strong antifungal activity. The main ingredients of garlic oil were identified as sulfides, mainly including disulfides (36 %), trisulfides (32 %) and monosulfides (29 %) by gas chromatograph-mass spectrometer (GC/MS), which were estimated as the dominant antifungal factors. The observation results by transmission electron microscope (TEM) and scanning electron microscope (SEM) indicated that garlic oil could firstly penetrate into hyphae cells and even their organelles, and then destroy the cellular structure, finally leading to the leakage of both cytoplasm and macromolecules. Further proteomic analysis displayed garlic oil was able to induce a stimulated or weakened expression of some key proteins for physiological metabolism. Therefore, our study proved that garlic oil can work multiple sites of the hyphae of P. funiculosum to cause their death. The high antifungal effects of garlic oil makes it a broad application prospect in antifungal industries.

Antifungal effects of citronella oil against Aspergillus niger ATCC 16404.

Essential oils are aromatic oily liquids obtained from some aromatic plant materials. Certain essential oils such as citronella oil contain antifungal activity, but the antifungal effect is still unknown. In this study, we explored the antifungal effect of citronella oil with Aspergillus niger ATCC 16404. The antifungal activity of citronella oil on conidia of A. niger was determined by poisoned food technique, broth dilution method, and disc volatility method. Experimental results indicated that the citronella oil has strong antifungal activity: 0.125 (v/v) and 0.25 % (v/v) citronella oil inhibited the growth of 5 × 105 spore/ml conidia separately for 7 and 28 days while 0.5 % (v/v) citronella oil could completely kill the conidia of 5 × 105 spore/ml. Moreover, the fungicidal kinetic curves revealed that more than 90 % conidia (initial concentration is 5 × 105 spore/ml) were killed in all the treatments with 0.125 to 2 % citronella oil after 24 h. Furthermore, with increase of citronella oil concentration and treatment time, the antifungal activity was increased correspondingly. The 0.5 % (v/v) concentration of citronella oil was a threshold to kill the conidia thoroughly. The surviving conidia treated with 0.5 to 2 % citronella oil decreased by an order of magnitude every day, and no fungus survived after 10 days. With light microscope, scanning electron microscope, and transmission electron microscope, we found that citronella oil could lead to irreversible alteration of the hyphae and conidia. Based on our observation, we hypothesized that the citronella oil destroyed the cell wall of the A. niger hyphae, passed through the cell membrane, penetrated into the cytoplasm, and acted on the main organelles. Subsequently, the hyphae was collapsed and squashed due to large cytoplasm loss, and the organelles were severely destroyed. Similarly, citronella oil could lead to the rupture of hard cell wall and then act on the sporoplasm to kill the conidia. Nevertheless, the citronella oil provides a potential of being a safe and environmentally friendly fungicide in the future.

[A mobile sensor for remote detection of natural gas leakage].

The detection of natural gas pipeline leak becomes a significant issue for body security, environmental protection and security of state property. However, the leak detection is difficult, because of the pipeline's covering many areas, operating conditions and complicated environment. A mobile sensor for remote detection of natural gas leakage based on scanning wavelength differential absorption spectroscopy (SWDAS) is introduced. The improved soft threshold wavelet denoising was proposed by analyzing the characteristics of reflection spectrum. And the results showed that the signal to noise ratio (SNR) was increased three times. When light intensity is 530 nA, the minimum remote sensitivity will be 80 ppm x m. A widely used SWDAS can make quantitative remote sensing of natural gas leak and locate the leak source precisely in a faster, safer and more intelligent way.

[Study of remote sensing the flux of carbon dioxide gas with tunable diode laser absorption spectroscopy].

Tunable diode laser absorption spectroscopy (TDLAS) technique is a new method to detect trace gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectra in the characteristic absorption region. TDLAS is a highly sensitive, highly selective and fast time response trace gas detection technique. In the present paper, a DFB laser at room temperature was used as the light source, wavelength modulation method was employed, and the second harmonic signal of one absorption line near 1.578 microm of carbon dioxide molecule was measured. A system was built for online monitoring of carbon dioxide concentration within the optical path of more than 700 meters at different heights. Combined with Alonzo Mourning-Obukhov length and characteristic velocity detected by large aperture scintillometer, the flux of carbon dioxide gas calculated by the experiential formula is within -60-60 mg x m(-2) x s(-1). The comparison of the datea detected by TDLAS system and the eddy covariance showed that the change of the data detected by TDLAS had a similar trend to that detected by the eddy covariance, and the best results can be produced by this method, breaking through the phenomenon of only providing the flux of trace gases near the ground at present, and making the measurement of trace gas fluxes within a large area possible.

[Monitoring the flux of carbon dioxide gas with tunable diode laser absorption spectroscopy].

The greenhouse effect exacerbated by the increase of Carbon-containing gases is the more important causes of the climate change, It is very meaningful to the large-scale flux of carbon dioxide detection for the estimate the contributions of the main greenhouse gases in the atmosphere of various errestrial eco-systems. Tunable diode laser absorption spectroscopy (TDLAS) is a highly sensitive, highly selective and fast time response trace gas detection technique. In the present paper, the authors used a DFB laser was used as the light source, and by employing wavelength modulation method, and measuring the second harmonic signal of one absorption line near 1.573 microm of carbon dioxide molecule, the authors built a system for online monitoring of carbon dioxide concentration within the optical path of more than 700 meters at different heights. Combined with Alonzo Mourning -Obukhov length and characteristic velocity detected by large aperture scintillometer, the flux of carbon dioxide gas within one day calculated by the formula is within--1.5-2.5, breaking through the phenomenon of only providing the flux of trace gases near the ground at present, makking the measurement of trace gas fluxes within a large area possible.

[An investigation of temperature compensation of HCL gas online monitoring based on TDLAS method].

HCL, with the character of strong erosion and toxicity, is a kind of chemical material of vital importance. So measuring the HCL in-situ can not only optimize its production process, but also be necessary to reduce the environment pollution. TDLAS (tunable diode laser absorption spectroscopy) technology, and owning the advantage of the tunability and narrow line width of the diode laser, this method can relatively easily select the absorption line of the detected gas without the interference from other gas, thus making the rapid and accurate HCL measurement possible. In the present paper, the HCL measurement system and the implemented experiment are introduced. The impact of the temperature on the measurement as well as the temperature compensation method is emphasized. The final experimental results validated the rationality of the empirical equation and therefore the improvement of the accuracy and feasibility of the TDLAS technology. The system, whose detection limitation reaches 2 ppm, can satisfy the needs of industrial in-sit measurement.

[System design of open-path natural gas leakage detection based on Fresnel lens].

Based on the technology of tunable diode laser absorption spectroscopy (TDLAS) in conjunction with second harmonic wave detection, a long open-path TDLAS system using a 1.65 microm InGaAsP distributed feedback laser was developed, which is used for detecting pipeline leakage. In this system, a high cost performance Fresnel lens is used as the receiving optical system, which receives the laser-beam reflected by a solid corner cube reflector, and focuses the receiving laser-beam to the InGaAs detector. At the same time, the influences of the concentration to the fluctuation of light intensity were taken into account in the process of measurement, and were eliminated by the method of normalized light intensity. As a result, the measurement error caused by the fluctuation of light intensity was made less than 1%. The experiment of natural gas leakage detection was simulated, and the detection sensitivity is 0.1 x 10(-6) (ratio by volume) with a total path of 320 m. According to the receiving light efficiency of the optical system and the detectable minimum light intensity of the detector, the detectable maximal optical path of the system was counted to be 2 000 m. The results of experiment show that it is a feasible design to use the Fresnel lens as the receiving optical system and can satisfy the demand of the leakage detection of natural gas.