ObjectiveTo establish the specific chromatogram and quantitative analysis of multi-components by single-marker（QAMS） based on linear calibration using two reference substances（LCTRS）， explore the consistency between Hedyotis Herba dispensing granules and standard decoction， and evaluate the quality of the dispensing granules. MethodsHigh performance liquid chromatography（HPLC） specific chromatogram was established based on 15 batches of Hedyotis Herba standard decoction and 10 batches of the dispensing granules， and LCTRS was used to locate chromatographic peaks. The actual retention times of 7 characteristic peaks in the specific chromatogram was measured on 24 different types of C₁₈ columns， taking deacetyl asperulosidic acid and asperulosidic acid as the dual standard compounds， the retention times of the other 5 characteristic peaks were predicted and validated. Based on this， QAMS was developed to determine the contents of four components（deacetyl asperulosidic acid， deacetyl asperulosidic acid methyl ester， asperulosidic acid， and p-coumaric acid）. Then， the relative correction factors of deacetyl asperulosidic acid， deacetyl asperulosidic acid methyl ester and p-coumaric acid were calculated using the reference peak of asperulosidic acid in the dual standard compounds， and each component was quantified accordingly. Finally， the consistency between the dispensing granules and standard decoction was assessed by taking extract rate of the standard decoction， consistency of the specific chromatograms， contents and transfer rates of the indicator components as indexes， and the quality of the dispensing granules was evaluated. ResultsThere were 7 common peaks in the characteristic chromatogram of samples of Hedyotis Herba standard decoction and the dispensing granules， and four of them were identified by reference standards， namely deacetyl asperulosidic acid（peak 1）， deacetyl asperulosidic acid methyl ester（peak 3）， asperulosidic acid（peak 6） and p-coumaric acid（peak 7）. The similarity between the dispensing granules and the standard decoction was >0.9. The absolute deviation in the predicted retention time for each component by LCTRS was lower than that of the relative retention time method. The extract rate of the 15 batches of Hedyotis Herba standard decoction ranged from 7.89% to 14.60%， the contents of deacetyl asperulosidic acid， deacetyl asperulosidic acid methyl ester， asperulosidic acid and p-coumaric acid were 6.62-19.70， 3.83-17.99， 1.57-6.69， 1.62-4.52 mg·g^-1， and the transfer rates of these components from decoction pieces to the standard decoction were 22.89%-39.60%， 34.03%-62.24%， 24.25%-43.70%， and 40.58%-73.71%， respectively. The extract rate， index component contents and transfer rates from decoction pieces to the three batches of Hedyotis Herba dispensing granules（P1-P3）， produced by manufacturer A， were similar to those of the standard decoction prepared from the same batch of decoction pieces， and all fell within the specified range. The contents of the 4 indicator components in 7 batches of the dispensing granules（P4-P10） from manufacturers B-E were all within the range of the content converted from the standard decoction based on the quantity of the dispensing granules. ConclusionThe established specific chromatogram and QAMS based on LCTRS are reasonable and reliable. Based on the evaluation indicators of standard decoction yield， consistency of specific chromatograms， contents and transfer rates of the four index components， the 10 batches of Hedyotis Herba dispensing granules from various manufacturers have exhibited good consistency with the standard decoction， indicating that the current production process is relatively reasonable.

ObjectiveTo establish the specific chromatogram of Chuanxiong Rhizoma dispensing granules（CRdg）， and to evaluate its quality by chemometrics and two reference substances for determination of multiple components（TRSDMC）. MethodsHigh performance liquid chromatography（HPLC） specific chromatograms were established using 13 batches of CRdg from 7 manufacturers， and preliminary quality evaluation was performed by similarity evaluation and chemometrics analysis. Eight characteristic peaks in the specific chromatogram of CRdg were measured on 22 different types of C₁₈ columns， and the actual retention times were recorded. Taking chlorogenic acid（peak 1） and senkyunolide A（peak 8） as double standard compounds， the retention times of the eight characteristic peaks were predicted by linear calibration using two reference substances（LCTRS）， and the method was validated on three other columns of different brands. Taking chlorogenic acid as reference peak， the relative correction factor method（RCFM） was used to quantify cryptochlorogenic acid， caffeic acid， ferulic acid， senkyunolide I and senkyunolide A， and the results were compared with the external standard method（ESM）. ResultsThe similarities of specific chromatograms of 13 batches of CRdg were all >0.90， and a total of 8 characteristic peaks were calibrated， and six of them were identified， including chlorogenic acid（peak 1）， cryptochlorogenic acid（peak 2）， caffeic acid（peak 3）， ferulic acid（peak 5）， senkyunolide I（peak 6） and senkyunolide A（peak 8）. Through chemometric analysis， it was found that ferulic acid， chlorogenic acid， senkyunolide I and cryptochlorogenic acid were the main components causing quality difference in CRdg， and the accuracy of LCTRS in predicting the retention time of 8 characteristic peaks was superior to that of the relative retention time method（RRT）. Further comparison of the results obtained from RCFM and ESM showed that there was no statistically significant difference between the two methods. ConclusionA quality evaluation method for CRdg based on HPLC specific chromatogram and TRSDMC is established， its qualitative accuracy is better than that of RRT， the quantitative accuracy is similar to that of ESM， and 4 quality-differentiated components among different manufacturers are found. This method is stable and reliable， and has reference value for the quality evaluation of other dispensing granules.

ObjectiveTo establish the specific chromatogram of Chuanxiong Rhizoma dispensing granules（CRdg）， and to evaluate its quality by chemometrics and two reference substances for determination of multiple components（TRSDMC）. MethodsHigh performance liquid chromatography（HPLC） specific chromatograms were established using 13 batches of CRdg from 7 manufacturers， and preliminary quality evaluation was performed by similarity evaluation and chemometrics analysis. Eight characteristic peaks in the specific chromatogram of CRdg were measured on 22 different types of C₁₈ columns， and the actual retention times were recorded. Taking chlorogenic acid（peak 1） and senkyunolide A（peak 8） as double standard compounds， the retention times of the eight characteristic peaks were predicted by linear calibration using two reference substances（LCTRS）， and the method was validated on three other columns of different brands. Taking chlorogenic acid as reference peak， the relative correction factor method（RCFM） was used to quantify cryptochlorogenic acid， caffeic acid， ferulic acid， senkyunolide I and senkyunolide A， and the results were compared with the external standard method（ESM）. ResultsThe similarities of specific chromatograms of 13 batches of CRdg were all >0.90， and a total of 8 characteristic peaks were calibrated， and six of them were identified， including chlorogenic acid（peak 1）， cryptochlorogenic acid（peak 2）， caffeic acid（peak 3）， ferulic acid（peak 5）， senkyunolide I（peak 6） and senkyunolide A（peak 8）. Through chemometric analysis， it was found that ferulic acid， chlorogenic acid， senkyunolide I and cryptochlorogenic acid were the main components causing quality difference in CRdg， and the accuracy of LCTRS in predicting the retention time of 8 characteristic peaks was superior to that of the relative retention time method（RRT）. Further comparison of the results obtained from RCFM and ESM showed that there was no statistically significant difference between the two methods. ConclusionA quality evaluation method for CRdg based on HPLC specific chromatogram and TRSDMC is established， its qualitative accuracy is better than that of RRT， the quantitative accuracy is similar to that of ESM， and 4 quality-differentiated components among different manufacturers are found. This method is stable and reliable， and has reference value for the quality evaluation of other dispensing granules.

ObjectiveTo study the effect of Taikong Yangxin Pills on the metabolism of simulated weightless rats based on metabolomics and discuss the metabolism mechanism. MethodsIn the simulated space capsule environment on the ground， the rat model of simulated weightlessness was established by the tail suspension method. Rats were randomly grouped as follows： out-of-capsule control， in-capsule control， model， and high （3.0 g·kg^-1） and low （1.5 g·kg^-1） doses of Taikong Yangxin Pills， and they were administrated with corresponding drugs by gavage for 28 days. The serum levels of endogenous metabolites in rats were determined by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry （UPLC-Q-TOF/MS）. The obtained data were processed by principal component analysis （PCA） and orthogonal partial least squares-discriminant analysis （OPLS-DA） to screen for differential metabolites and potential biomarkers. MetaboAnalyst 5.0 was used for pathway enrichment analysis to explain the metabolic regulation mechanism of the drug. ResultsCompared with the out-of-capsule control group， the in-capsule control group showed elevated levels of thirteen metabolites， including 14-hydroxyhexadecanoic acid， linoleic acid， and α-linolenic acid （P<0.05）， which suggested that the space capsule environment mainly affected the metabolism of α-linolenic acid and linoleic acid in the rats. Compared with the in-capsule control group， the model group showed lowered levels of fourteen metabolites， including 4-imidazolone-5-propionic acid， isocitric acid/citric acid， and L-tyrosine （P<0.05）， which were recovered after the treatment with Taikong Yangxin pills （P<0.05）. The pathway enrichment analysis revealed that weightlessness induced by tail suspension and drug intervention mainly involved the phenylalanine， tyrosine， and tryptophan biosynthesis， tyrosine metabolism， histidine metabolism， and citric acid cycle. ConclusionThe simulated space capsule environment and simulated weightlessness induced by tail suspension can both affect the metabolism level of rats. Taikong Yangxin pills can ameliorate the metabolic abnormality in the rat model of weightlessness by regulating various amino acids and energy metabolism-related pathways.

Objective This study aims to investigate the effects of varying durations of light exposure on body weight and learning and memory abilities of pubertal NIH mice. Methods Forty pubertal NIH mice, evenly split by gender and with similar initial weights, were subjected to a 12 h light-dark cycle for one week. They were then randomly assigned to groups with daily light exposure durations of 0, 6, 12, 18, and 24 hours, with 8 mice in each group. The experimental period lasted for 7 weeks, with the first 5 weeks as the feeding phase under different light exposure conditions, and the last 2 weeks as the behavioral testing phase. Their body weight was monitored, and learning and memory abilities were assessed using the T-maze, object location test, and eight-arm maze tests. Results During the light exposure period, there were no significant differences in body weight among groups (P>0.05). However, the weight gain of mice in the 24 h group was significantly higher than that of the 0 h group and the 6 h group during the second and third weeks of light exposure (P<0.05). After five weeks of light exposure, in the T-maze test, the latency time of the 0 h light exposure group was significantly longer than that of the 12 h group (P<0.01), and the latency time of the 24 h light exposure group was significantly longer than that of the 12 h group (P<0.05). In the object location test, the mice in 12 h group exhibited a higher discrimination index and spent more time observing the new location compared to the other groups, with significant differences in comparison to the 18 h group (P<0.01) and the 24 h group (P<0.05). In the eight-arm maze test, the time to find food, the reference memory error rate, and the working memory error rate in the 12 h group were all lower than those in the 0 h group, with significant differences (P<0.05). Moreover, the working memory error rate in the 24 h group was higher than that in the 12 h group, with significant differences (P<0.05). Conclusion Continuous 24 h light exposure affects body weight gain, while light exposure durations exceeding 18 h or below 6 h per day weaken the learning and memory abilities of NIH mice.

ObjectiveTo establish the quality standards for Sennae Folium（Cassia angustifolia） dispensing granules based on standard decoctions. MethodsHigh performance liquid chromatography（HPLC） specific chromatograms were established for 15 batches of Sennae Folium（C. angustifolia） standard decoctions and 10 of Sennae Folium（C. angustifolia） dispensing granules from different manufacturers， and the similarity evaluation， hierarchical cluster analysis（HCA） and principal component analysis（PCA） were performed. Linear calibration with two reference substances（LCTRS） and quantitative analysis of multi-components by single-marker（QAMS） were established for the common peaks in the specific chromatograms to determine the contents of main components in the decoction pieces， standard decoctions and dispensing granules， and to calculate their transfer rates from decoction pieces to standard decoctions and dispensing granules. ResultsThe similarities of specific chromatograms of 15 batches of Sennae Folium（C. angustifolia） standard decoctions and 10 batches of Sennae Folium（C. angustifolia） dispensing granules were all greater than 0.95， and a total of 8 characteristic peaks were calibrated， and five of them were identified， including kaempferol-3，7-O-diglucoside， apigenin-6，8-di-C-glucoside， quercetin-3-O-gentianoside， sennoside B and sennoside A. HCA and PCA results showed that there were certain differences in the composition of different batches of standard decoctions， but no clustering was observed in the production area. As the standard decoctions， the extract rate of 15 batches of samples was 26.54%-45.38%， the contents of kaempferol-3，7-O-diglucoside， apigenin-6，8-di-C-glucoside， quercetin-3-O-gentianoside， sennoside B and sennoside A were 12.16-19.26， 2.57-4.94， 3.27-5.11， 6.75-11.39， 4.69-7.79 mg·g^-1， and their transfer rates from decoction pieces to standard decoctions were 45.41%-79.02%， 29.12%-55.07%， 40.52%-67.90%， 24.72%-49.12%， 27.54%-49.34%， respectively. The extract rates of Sennae Folium（C. angustifolia） dispensing granules（C8-C10） were 38.10%-39.50%， the transfer rates of the above five components from decoction pieces to dispensing granules were 72.85%-73.58%， 53.43%-53.94%， 40.19%-40.74%， 24.62%-25.00%， 28.65%-29.11%， respectively， which were generally consistent with the transfer rates from decoction pieces to standard decoctions. ConclusionCompared with the relative retention time method， LCTRS has higher prediction accuracy and is more suitable for chromatographic columns. The established quality control standard of Sennae Folium（C. angustifolia） dispensing granules based on standard decoction is reasonable and reliable， and all indicators of samples from different manufacturers are within the range specified based on the standard decoction， which can provide reference for the quality control and process research of this dispensing granules.

ObjectiveTo explore the characteristics of ecological niche and interspecific relationships of mosquitoes in different habitats in Dongcheng District, Beijing, and to provide a basis for mosquito ecological monitoring, control and the development or optimization of prevention and control strategies for related mosquito-borne diseases. MethodsFrom May to October 2023, the ecological monitoring in residential areas, parks, tourist attractions and medical institutions in Dongcheng District of Beijing was carried out using the carbon dioxide (CO₂) mosquito trapping method, and the ecological niche characteristics and interspecific relationships of mosquitoes in different habitats were analyzed using Levins ecological niche breadth index, Pinaka ecological niche overlap index and ecological niche similarity coefficients. ResultsThe temporal ecological niche of Culex pipiens pallens (10.62) was higher than that of Aedes albopictus (8.29) in different habitats in Dongcheng District of Beijing, and the temporal ecological niche overlap index of the two mosquitoes was as high as 0.87. The ecological niche breadth of Culex pipiens pallens was higher than that of Aedes albopictus in different monitoring habitats, and the order of the ecological niche breadth of Culex pipiens pallens in different monitoring habitats was, from high to low, as follows: residential areas (11.09) > tourist attractions (10.25) > medical institutions (9.15) > parks (9.07), while the ecological niche breadth of Aedes albopictus in different habitats was, in descending order, residential areas (8.56) > medical institutions (7.68) > parks (7.44) > tourist attractions (5.73). The results of niche overlap analysis showed that the overlap index between Culex pipiens pallens and Aedes albopictus was the largest in residential areas (0.86), as for in other habitats, which was, in descending order, parks (0.81) > medical institutions (0.68) > tourist attractions (0.60). Besides, the ecological similarity coefficients further verified that similarity coefficients, between the two mosquito species, were highest in residential areas (0.712), lowest in tourist attractions (0.497), and which were 0.675 in parks and 0.598 in medical institutions, respectively. ConclusionIn different monitoring habitats in Dongcheng District of Beijing, Culex albopictus pallens demonstrates a stronger spatio-temporal resource utilization ability than Aedes albopictus, and the two species exhibit more similar spatio-temporal resource utilization patterns in residential areas. Corresponding control strategies targeting the characteristics of ecological niches and interspecific relationships of these two mosquito species in different habitats should be developed to enhance the prevention and control effect.

Objective:To investigate the impact of Tumor-Infiltrating Lymphocytes (TILs) density in the tumor stroma on the long-term prognosis of hepatocellular carcinoma (HCC) liver transplant patients meeting the Hangzhou criteria.Methods:This study is a retrospective cohort study. The clinical data of 83 patients with hepatocellular carcinoma who met the Hangzhou criteria and underwent allogeneic liver transplantation from January 2018 to December 2023 in the Department of Hepatobiliary Surgery, Beijing Chaoyang Hospital affiliated to Capital Medical University were collected and analyzed. Hematoxylin and Eosin (HE) staining was used to study the density of TILs in the resected liver grafts. Patients were divided into TILs-negative group (TILs<10%, n=31) and TILs-positive group (TILs≥10%, n=52) based on whether the TILs density exceeded 10%. Clinical and pathological characteristics were analyzed, and the significance of alpha-fetoprotein (AFP), TILs density, and microvascular invasion on the prognosis of HCC patients who met the Hangzhou criteria was studied. Measurement data with normal distribution were expressed as mean±standard deviation ( ± s) and compared between groups using t-test. Measurement data with skewed distribution were expressed as M ( Q1, Q3) and compared using rank-sum tests. Categorical data were compared using chi-square test. Kaplan-Meier method was used to study the relationship between various observation indicators and overall survival, and survival curves were plotted. Log-rank test was used to compare the survival rates between groups, and multivariate Cox regression model was used to adjust for the distribution of risk factors between groups. Results:The preoperative AFP level in the TILs-negative group was (15.69±1.21) U/mL, and in the TILs-positive group was (12.17±0.13) U/mL, with a statistically significant difference between the two groups ( P<0.05). In the TILs-negative group, 8 cases had microvascular invasion, and the number of low, moderate, and high differentiation tumors was 8, 23, and 0, respectively. In the TILs-positive group, 3 cases had microvascular invasion, and the number of low, moderate, and high differentiation tumors was 2, 31, and 19, respectively. The results indicated that patients in the TILs-negative group were more likely to have microvascular invasion and poorer tumor differentiation ( P<0.05). All patients were regularly followed up, and the 1-, 2-, and 3-year survival rates in the TILs-negative group and TILs-positive group were 84.0%, 77.6%, 69.8%, and 94.7%, 91.7%, 86.6%, respectively ( P<0.01). Cox proportional hazards model indicated that microvascular invasion ( RR=4.474, 95% CI: 1.172-17.072, P=0.028) and TILs-negative status ( RR=5.081, 95% CI: 1.420-18.184, P=0.012) were independent risk factors for the long-term prognosis of HCC patients who met the Hangzhou criteria. Conclusions:Among HCC patients meeting the Hangzhou criteria, the density of TILs in the tumor stroma is related to AFP levels, tumor differentiation, and the presence of microvascular invasion. TILs-negative status indicates a poorer prognosis for these patients.

Objective:To evaluate the role of sphingosine-1-phospho-1 receptor 1 (S1PR1) in remifentanil-induced hyperalgesia in rats with incisional pain and the relationship with KCNQ2/3 potassium channels in the dorsal root ganglia (DRG).Methods:Forty-eight male Sprague-Dawley rats with successful caudal vein catheterization, aged 2-3 months, weighing 260-280 g, were divided into 6 groups ( n=8 each) using a random number table method: control group (group C), S1PR1 inhibitor group (FTY720) group (group F), remifentanil group (group R), remifentanil + S1PR1 inhibitor (FTY720) group (group RF), remifentanil + incision pain group (group RI) and remifentanil + incision pain + S1PR1 inhibitor (FTY720) group (group RIF). In group C, normal saline 0.1 ml· kg -1·min -1 was intravenously infused for 60 min. In group F, FTY720 3 nmol was intrathecally injected at 10 min before normal saline injection, and 0.1 ml · kg -1·min -1 normal saline was infused into the caudal vein for 60 min. Remifentanil 1.0 μg· kg -1·min -1 was infused for 60 min through the caudal vein in group R. In RF group, FTY720 (3 nmol) was intrathecally injected, and 10 min later remifentanil 1.0 μg· kg -1·min -1 was infused via the caudal vein for 60 min. The incisional pain model was established, and remifentanil 1.0 μg· kg -1·min -1 was infused via the caudal vein for 60 min in RI group. In RIF group, FTY720 3 nmol was intrathecally injected at 10 min before remifentanil infusion, then the incisional pain model was developed, and remifentanil 1.0 μg· kg -1·min -1 was infused via the caudal vein at the same time for 60 min. The mechanical paw withdraw threshold (MWT) and thermal paw withdraw latency (TWL) were measured at 24 h before remifentanil or normal saline infusion (T 0) and 2, 6, 24 and 48 h after remifentanil or normal saline infusion (T 1-4). The rats were sacrificed after the last measurement of pain threshold, and the L 4-6 segments of the DRG were taken for determination of the expression of S1PR1, KCNQ2 and KCNQ3 protein and mRNA in the DRG by Western blot and real-time polymerase chain reaction. Results:Compared with group C, the MWT was significantly decreased, and the TWL was shortened at T 1-4, the expression of S1PR1 protein and mRNA in the DRG was up-regulated, the expression of KCNQ2 and KCNQ3 protein and mRNA in the DRG was down-regulated ( P<0.05), and no significant change was found in each parameter in R and RI groups ( P>0.05). Compared with group R, the MWT was significantly decreased, and the TWL was shortened at T 1-4, the expression of S1PR1 protein and mRNA in the DRG was up-regulated, and the expression of KCNQ2 and KCNQ3 protein and mRNA in the DRG was down-regulated in group RI, and the MWT was significantly increased, and the TWL was prolonged at T 1-4, the expression of S1PR1 protein and mRNA in the DRG was down-regulated, and the expression of KCNQ2 and KCNQ3 protein and mRNA in the DRG was up-regulated in group RF ( P<0.05). Compared with group RI, the MWT was significantly increased, and the TWL was prolonged at T 1-4, the expression of S1PR1 protein and mRNA in the DRG was down-regulated, and the expression of KCNQ2 and KCNQ3 protein and mRNA in the DRG was up-regulated in group RIF ( P<0.05). Conclusions:S1PR1 is involved in the process of remifentanil-induced hyperalgesia in rats with incisional pain, which is related to the inhibition of KCNQ2/3 potassium channel expression in the DRG.

Objective:To analyze the effect of lateral decubitus hand position pad on tumor micrometastasis and trauma response in patients with non-small cell lung cancer.Methods:Seventy-eight patients with non-small cell lung cancer (45 patients in stage Ⅰ, and 33 cases in stage Ⅱ) admitted to Zhejiang Jinhua Guangfu Cancer Hospital from January 2020 to January 2022 and performed single-aperture thoracoscopic radical resection of non-small cell lung cancer was retrospectively selected, and they were divided into control group (38 cases, adopted traditional body positioning) and study group (40 cases, adopted lateral decubitus hand position pad). Postural indicators, expression levels of metastatic genes, tumor markers, pain degree and stress response indicators were compared between the two groups.Results:The success rate of one position placement in the study group was higher than that in the control group: 100.00%(40/40) vs. 78.95%(30/38); the incidence of surgical skin compression and limb discomfort were lower than those in the control group: 2.50%(1/40) vs. 26.32%(10/38), 5.00%(2/40) vs. 28.95%(11/38); the position placement time was short than that in the control group: (8.47 ± 1.38) min vs.(12.42 ± 2.03) min, there were statistical differences ( P<0.05). Three months after surgery, the expressions of tumor necrosis factor receptor-associated protein 1(TRAP1), matrix metalloproteinase-9 (MMP-9) in the study group were lower than those in the control group: 0.56 ± 0.07 vs. 0.85 ± 0.10, 0.32 ± 0.04 vs. 0.54 ± 0.06, the expressions of E-cadherin and Kruppel-like factor 4(KLF4) in the study group were higher than those in the control group: 1.69 ± 0.22 vs. 1.36 ± 0.17, 2.25 ± 0.37 vs. 1.98 ± 0.20, there were statistical differences ( P<0.05). Three months after surgery, the levels of carcinoembryonic antigen (CEA), cytokeratin (CYFRA21-1) in the study group were lower than those in the control group: (36.89 ± 4.12) μg/L vs. (41.72 ± 5.34) μg/L, (7.25 ± 0.81) μg/L vs. (8.01 ± 1.34) μg/L, there were statistical differences ( P<0.05). At 1-day after surgery, the levels of prostaglandin E2 (PGE2), cortisol (Cor) and substance P (SP) in the study group were lower than those in the control group: (110.47 ± 10.12) pg/L vs. (138.88 ± 14.42) pg/L, (60.37 ± 7.18) ng/L vs. (71.34 ± 8.01) ng/L, (6.26 ± 0.81) μg/L vs. (8.25 ± 1.17) μg/L, there were statistical differences ( P<0.05). Conclusions:The application of lateral decubitus hand position pad in single-aperture thoracoscopic radical resection of non-small cell lung cancer can improve the patient′s position and improve the surgical effect, thus reducing the trauma reaction and effectively inhibiting tumor micrometastasis.