Your browser doesn't support javascript.
loading
Шоу: 20 | 50 | 100
Результаты 1 - 17 de 17
Фильтр
1.
Psicol. reflex. crit ; 37: 7, 2024. tab, graf
Статья в английский | LILACS-Express | LILACS, INDEXPSI | ID: biblio-1558774

Реферат

Abstract Background This study explored the effects of attention shifting on Chinese children's word reading. Objective The sample consisted of 87 fourth-grade children from Shaoxing City, China. Methods The students completed measures of the attention shifting task, reading accuracy test, reading fluency test, and rapid automatized naming test. Results The results showed that reading fluency was significantly correlated with attention shifting scores, specifically with tag1 and tag6 (ps < 0.05). The reading accuracy score was also significantly correlated with tag6 (p < 0.05). According to the regression analysis of attention shifting on word reading, even when controlling for rapid automatic naming, attention shifting significantly affected word reading fluency at approximately 600 ms (p = .011). Attention shifting did not affect children's word reading accuracy. Short conclusion These findings suggest that attention shifting is significantly associated with children's word reading. Educators should focus on developing children's attention shifting to improve their word reading ability.

2.
Rev. Assoc. Med. Bras. (1992, Impr.) ; Rev. Assoc. Med. Bras. (1992, Impr.);68(8): 1115-1119, Aug. 2022. tab, graf
Статья в английский | LILACS-Express | LILACS | ID: biblio-1406614
3.
Digital Chinese Medicine ; (4): 253-263, 2022.
Статья в английский | WPRIM | ID: wpr-973528

Реферат

@#Objective To propose two novel methods based on deep learning for computer-aided tongue diagnosis, including tongue image segmentation and tongue color classification, improving their diagnostic accuracy. Methods LabelMe was used to label the tongue mask and Snake model to optimize the labeling results. A new dataset was constructed for tongue image segmentation. Tongue color was marked to build a classified dataset for network training. In this research, the Inception + Atrous Spatial Pyramid Pooling (ASPP) + UNet (IAUNet) method was proposed for tongue image segmentation, based on the existing UNet, Inception, and atrous convolution. Moreover, the Tongue Color Classification Net (TCCNet) was constructed with reference to ResNet, Inception, and Triple-Loss. Several important measurement indexes were selected to evaluate and compare the effects of the novel and existing methods for tongue segmentation and tongue color classification. IAUNet was compared with existing mainstream methods such as UNet and DeepLabV3+ for tongue segmentation. TCCNet for tongue color classification was compared with VGG16 and GoogLeNet. Results IAUNet can accurately segment the tongue from original images. The results showed that the Mean Intersection over Union (MIoU) of IAUNet reached 96.30%, and its Mean Pixel Accuracy (MPA), mean Average Precision (mAP), F1-Score, G-Score, and Area Under Curve (AUC) reached 97.86%, 99.18%, 96.71%, 96.82%, and 99.71%, respectively, suggesting IAUNet produced better segmentation than other methods, with fewer parameters. Triplet-Loss was applied in the proposed TCCNet to separate different embedded colors. The experiment yielded ideal results, with F1-Score and mAP of the TCCNet reached 88.86% and 93.49%, respectively. Conclusion IAUNet based on deep learning for tongue segmentation is better than traditional ones. IAUNet can not only produce ideal tongue segmentation, but have better effects than those of PSPNet, SegNet, UNet, and DeepLabV3+, the traditional networks. As for tongue color classification, the proposed network, TCCNet, had better F1-Score and mAP values as compared with other neural networks such as VGG16 and GoogLeNet.

4.
Psicol. reflex. crit ; 35: 27, 2022. tab, graf
Статья в английский | LILACS, INDEXPSI | ID: biblio-1406426

Реферат

The study explored the mediating effect of number sense between nonverbal intelligence and children's mathematical performance. The sample consisted of 131 pupils in Shaoxing City of China from grades 1, 3, and 5. The students completed measures of nonverbal intelligence, number sense, basic arithmetic ability, mathematical performance, rapid automatized naming, and working memory. Results show that although all variables significantly relate with each other (all p < .01), only nonverbal intelligence, number sense, and basic arithmetic ability significantly affect children's mathematical performance (all p < .01). According to multiple-mediation model, nonverbal intelligence significantly predicts children's mathematical performance through number sense and basic arithmetic ability. These findings suggest that domain-specific mathematical skills play a prominent role in children's mathematical performance in primary school, rather than domain-general cognitive functions. Educators should pay attention to develop children's number sense in order to improve children's mathematical ability. (AU)


Тема - темы
Humans , Male , Female , Child , Cognition , Intelligence , Learning , Mathematics , Memory, Short-Term , China , Education, Primary and Secondary
5.
Rev. bras. pesqui. méd. biol ; Braz. j. med. biol. res;54(8): e10940, 2021. graf
Статья в английский | LILACS | ID: biblio-1285675

Реферат

Recently, an increasing number of studies have reported that dysregulation of circular RNA (circRNA) expression plays critical roles in the progression of several cancers, including colorectal cancer (CRC). However, the detailed molecular mechanisms of circRNAs involvement in CRC remain largely unknown. Here, we confirmed that the level of circEGFR was significantly increased in CRC tissues compared to matched adjacent non-tumor tissues, and a high level of circEGFR was correlated with poor clinicopathological characteristics and poor prognosis in patients with CRC. Moreover, increased circEGFR expression promoted CRC cell proliferation, migration, and invasion in vitro. Mechanistically, circEGFR acted as a ceRNA for miR-106a-5p to relieve the repressive effect of miR-106a-5p on DDX5 mRNA. Moreover, circEGFR enhanced DDX5 expression, thereby upregulating p-AKT levels. Together, these findings showed that circEGFR promoted CRC cell proliferation, migration, and invasion through the miR-106a-5p/DDX5/AKT axis, and may serve as a promising diagnostic marker and therapeutic target for CRC patients.


Тема - темы
Humans , Colorectal Neoplasms/genetics , MicroRNAs/genetics , Gene Expression Regulation, Neoplastic , Cell Movement/genetics , Cell Line, Tumor , Cell Proliferation/genetics , DEAD-box RNA Helicases , RNA, Circular
6.
Clinics ; Clinics;76: e2671, 2021. tab, graf
Статья в английский | LILACS | ID: biblio-1339706

Реферат

OBJECTIVES: To investigate the predictive value of long non-coding RNA (lncRNA) H19 and the ten-eleven translocation enzyme 1 (TET1) transcriptional expression in postoperative recurrence of uterine fibroids (UFs). METHODS: Seventy-five patients with UF, who underwent surgical treatment, were enrolled in the treatment group, and 60 healthy individuals were enrolled in the control group. The relative expression levels of lncRNA H19 and TET1 mRNA in the serum and UF tissues were analyzed. The patients were further divided into a better curative (BC) group and a poor efficacy (PE) group to analyze the predictive value of lncRNA H19 and TET1 and the independent risk factors affecting the recurrence of UF. RESULTS: Compared with the control group, lncRNA H19 expression levels were significantly higher, while TET1 expression levels were significantly lower in the treatment group (p<0.001). The area under the receiver operating characteristic (ROC) curve (AUC) values of the two indicators for diagnostic importance were found to be 0.872 and 0.826, respectively. Compared with the PE group, lncRNA H19 expression levels were significantly lower, while TET1 expression levels were significantly higher in the BC group (p<0.001). The AUC values of the two indicators for their predictive efficacy were 0.788 and 0.812, respectively. Logistic regression analysis showed that age, menarche age, maximum diameter of UFs, number of UFs, lncRNA H19 levels, and TET1 levels were independent risk factors affecting UF recurrence. The AUC values of lncRNA H19 and TET1 for their predictive value for postoperative recurrence were 0.814 and 0.765, respectively. CONCLUSIONS: The lncRNA H19 and TET1 have high diagnostic and predictive efficacy for determining the postoperative recurrence of UFs.


Тема - темы
Humans , Female , RNA, Long Noncoding/genetics , Leiomyoma , RNA, Messenger , ROC Curve , Proto-Oncogene Proteins , Mixed Function Oxygenases , Neoplasm Recurrence, Local
7.
Clinics ; Clinics;75: e1656, 2020. graf
Статья в английский | LILACS | ID: biblio-1133444

Реферат

OBJECTIVES: Mesenchymal stem cells (MSCs) are potentially ideal for type 2 diabetes treatment, owing to their multidirectional differentiation ability and immunomodulatory properties. Here we investigated whether the stem cells from human exfoliated deciduous teeth (SHED) in combination with hyperbaric oxygen (HBO) could treat type 2 diabetic rats, and explored the underlying mechanism. METHODS: SD rats were used to generate a type 2 diabetes model, which received stem cell therapy, HBO therapy, or both together. Before and after treatment, body weight, blood glucose, and serum insulin, blood lipid, pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-6), and urinary proteins were measured and compared. After 6 weeks, rats were sacrificed and their organs were subjected to hematoxylin and eosin staining and immunofluorescence staining for insulin and glucagon; apoptosis and proliferation were analyzed in islet cells. Structural changes in islets were observed under an electron microscope. Expression levels of Pdx1, Ngn3, and Pax4 mRNAs in the pancreas were assessed by real-time quantitative polymerase chain reaction (RT-qPCR). RESULTS: In comparison with diabetic mice, those treated with the combination or SHE therapy showed decreased blood glucose, insulin resistance, serum lipids, and pro-inflammatory cytokines and increased body weight and serum insulin. The morphology and structure of pancreatic islets improved, as evident from an increase in insulin-positive cells and a decrease in glucagon-positive cells. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining of islet cells revealed the decreased apoptosis index, while Ki67 and proliferating cell nuclear antigen staining showed increased proliferation index. Pancreatic expression of Pdx1, Ngn3, and Pax4 was upregulated. CONCLUSION: SHED combined with HBO therapy was effective for treating type 2 diabetic rats. The underlying mechanism may involve SHED-mediated increase in the proliferation and trans-differentiation of islet β-cells and decrease in pro-inflammatory cytokines and apoptosis of islets.


Тема - темы
Humans , Animals , Male , Mice , Rats , Mesenchymal Stem Cell Transplantation , Diabetes Mellitus, Experimental/therapy , Diabetes Mellitus, Type 2/therapy , Insulin-Secreting Cells , Hyperbaric Oxygenation/methods , Stem Cells , Tooth, Deciduous , China , Rats, Sprague-Dawley , Diabetes Mellitus, Type 2/chemically induced , Mesenchymal Stem Cells , Insulin
8.
Статья в английский | WPRIM | ID: wpr-773628

Реферат

Diabetic nephropathy (DN) is one of the common microvascular complications of diabetes mellitus. Renal fibrosis is closely related to the deterioration of renal function. The present study aimed to investigate protective effect of Taxus chinensis on high-fat diet/streptozotocin-induced DN in rats and explore the underlying mechanism of action. The rat DN model was established via feeding high fat diet for 4 weeks and subsequently injecting streptozotocin (30 mg·kg body weight) intraperitoneally. The rats with blood glucose levels higher than 16.8 mmol·L were selected for experiments. The DN rats were treated with Taxus chinensis orally (0.32, 0.64, and 1.28 g·kg) once a day for 8 weeks. Taxus chinensis significantly improved the renal damage, which was indicated by the decreases in 24-h urinary albumin excretion rate, blood serum creatinine, and blood urea nitrogen. Histopathological examination confirmed the protective effect of Taxus chinensis. The thickness of glomerular basement membrane was reduced, and proliferation of mesangial cells and podocytes cells and increase in mesangial matrix were attenuated. Further experiments showed that Taxus chinensis treatment down-regulated the expression of TGF-β1 and α-SMA, inhibited phosphorylation of Smad2 and Smad3. These results demonstrated that Taxus chinensis alleviated renal injuries in DN rats, which may be associated with suppressing TGF-β1/Smad signaling pathway.


Тема - темы
Animals , Humans , Male , Rats , Albumins , Blood Glucose , Metabolism , Creatinine , Blood , Diabetic Nephropathies , Blood , Drug Therapy , Genetics , Urine , Drugs, Chinese Herbal , Kidney , Metabolism , Phosphorylation , Rats, Sprague-Dawley , Signal Transduction , Smad Proteins , Genetics , Metabolism , Taxus , Chemistry , Transforming Growth Factor beta1 , Metabolism
9.
Статья в английский | WPRIM | ID: wpr-812418

Реферат

Diabetic nephropathy (DN) is one of the common microvascular complications of diabetes mellitus. Renal fibrosis is closely related to the deterioration of renal function. The present study aimed to investigate protective effect of Taxus chinensis on high-fat diet/streptozotocin-induced DN in rats and explore the underlying mechanism of action. The rat DN model was established via feeding high fat diet for 4 weeks and subsequently injecting streptozotocin (30 mg·kg body weight) intraperitoneally. The rats with blood glucose levels higher than 16.8 mmol·L were selected for experiments. The DN rats were treated with Taxus chinensis orally (0.32, 0.64, and 1.28 g·kg) once a day for 8 weeks. Taxus chinensis significantly improved the renal damage, which was indicated by the decreases in 24-h urinary albumin excretion rate, blood serum creatinine, and blood urea nitrogen. Histopathological examination confirmed the protective effect of Taxus chinensis. The thickness of glomerular basement membrane was reduced, and proliferation of mesangial cells and podocytes cells and increase in mesangial matrix were attenuated. Further experiments showed that Taxus chinensis treatment down-regulated the expression of TGF-β1 and α-SMA, inhibited phosphorylation of Smad2 and Smad3. These results demonstrated that Taxus chinensis alleviated renal injuries in DN rats, which may be associated with suppressing TGF-β1/Smad signaling pathway.


Тема - темы
Animals , Humans , Male , Rats , Albumins , Blood Glucose , Metabolism , Creatinine , Blood , Diabetic Nephropathies , Blood , Drug Therapy , Genetics , Urine , Drugs, Chinese Herbal , Kidney , Metabolism , Phosphorylation , Rats, Sprague-Dawley , Signal Transduction , Smad Proteins , Genetics , Metabolism , Taxus , Chemistry , Transforming Growth Factor beta1 , Metabolism
10.
Zhonghua nankexue ; Zhonghua nankexue;(12): 221-225, 2018.
Статья в Китайский | WPRIM | ID: wpr-689773

Реферат

<p><b>Objective</b>To study the expression of CLAUDIN-11 in the testis tissue of non-obstructive azoospermia (NOA) patients with different severities and investigate its clinical significance.</p><p><b>METHODS</b>Sixty-two NOA patients were divided into a hypospermatogenesis (HS) group (n = 30) and a Sertoli cell only syndrome (SCO) group (n =32). The expression of CLAUDIN-11 in the testicular tissue of the patients was detected by immunohistochemistry, that of CLAUDIN-11 mRNA determined by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR), and the levels of serum reproductive hormones measured by chemiluminescent immunoassay.</p><p><b>RESULTS</b>Immunohistochemistry showed that the expression of CLAUDIN-11 was mainly in the cytoplasm of the Sertoli cells around the seminiferous tubule wall in the HS group, but diffusely distributed in the membrane of the Sertoli cells in the SCO group. RT-qPCR revealed a significantly lower expression of CLAUDIN-11 mRNA in the HS than in the SCO group (0.008 ± 0.001 vs 0.013 ± 0.002, t = 10.616, P<0.01). The level of serum luteotropic hormone (LH) was also markedly lower in the HS than in the SCO group ([3.62 ± 1.34] vs [4.96 ± 3.10] IU/L, P<0.05) and so was that of follicle-stimulating hormone (FSH) ([5.36 ± 2.80] vs [10.65 ± 9.18] IU/L, P<0.05).</p><p><b>CONCLUSIONS</b>The up-regulated expression of CLAUDIN-11 in Sertoli cells may play an important role in the development and progression of spermatogenic dysfunction in NOA patients.</p>


Тема - темы
Humans , Male , Azoospermia , Genetics , Metabolism , Claudins , Metabolism , Follicle Stimulating Hormone , Metabolism , Oligospermia , Genetics , Metabolism , RNA, Messenger , Metabolism , Seminiferous Tubules , Metabolism , Sertoli Cell-Only Syndrome , Genetics , Metabolism , Sertoli Cells , Metabolism , Spermatogenesis , Testis , Metabolism
11.
Indian J Dermatol Venereol Leprol ; 2016 May-June; 82(3): 339-342
Статья в английский | IMSEAR | ID: sea-178216
12.
Zhonghua nankexue ; Zhonghua nankexue;(12): 568-570, 2012.
Статья в Китайский | WPRIM | ID: wpr-286461

Реферат

<p><b>OBJECTIVE</b>To investigate the efficacy and action mechanism of Shengjing Tablets in the treatment liquefaction.</p><p><b>METHODS</b>We randomly assigned 150 patients with semen non-liquefaction to receive Shengjing Tablets group, n = 100) and vitamin E capsules (control group, n = 50) for 2 courses of 45 days each, followed by observation liquefaction time and other semen parameters.</p><p><b>RESULTS</b>After the first course, 68 of the patients in the treatment group 20 responded and 12 failed to respond; and after the second course, 84 were cured, 9 responded and 7 failed to respond, effective rate of 93.0%. In comparison, only 8 of the controls were cured, 8 responded and 34 failed to respond after medication. There were statistically significant differences between the two groups (P < 0.01). Meanwhile, the treatment showed obvious improvement in sperm motility and concentration.</p><p><b>CONCLUSION</b>Shengjing Tablets may shorten the time liquefaction, and can be used as a safe and effective therapy for semen non-liquefaction.</p>


Тема - темы
Adult , Humans , Male , Young Adult , Drugs, Chinese Herbal , Therapeutic Uses , Infertility, Male , Drug Therapy , Phytotherapy , Semen , Sperm Count , Treatment Outcome
13.
Zhonghua nankexue ; Zhonghua nankexue;(12): 514-517, 2012.
Статья в Китайский | WPRIM | ID: wpr-286471

Реферат

<p><b>OBJECTIVE</b>To investigate the role of the TEKT4 protein in the pathogenesis of idiopathic asthenozoospermia.</p><p><b>METHODS</b>We separated and purified the ejaculated sperm from idiopathic asthenozoospermia patients and normozoospermic men by Percoll discontinuous density gradients, and detected the distribution and the expressions of TEKT4 mRNA and TEKT4 protein by RT-PCR and Western blot.</p><p><b>RESULTS</b>RT-PCR revealed that the expression of TEKT4 mRNA was significantly lower in the sperm of the idiopathic asthenozoospermia patients than in those of the normozoospermic men (0.59 +/- 0.13 vs 0.75 +/- 0.15, t = 4.325, P < 0.05), and Western blot confirmed the results of RT-PCR (0.48 +/- 0.14 vs 0.69 +/- 0.13, t = 5.939, P < 0.05).</p><p><b>CONCLUSION</b>The expression of TEKT4 is significantly decreased in the ejaculated sperm of idiopathic asthenozoospermia patients, which might be one of the causes of idiopathic asthenozoospermia.</p>


Тема - темы
Adult , Humans , Male , Asthenozoospermia , Metabolism , Blotting, Western , Case-Control Studies , Cytoskeletal Proteins , Metabolism , RNA, Messenger , Genetics , Sperm Motility , Spermatozoa , Metabolism
14.
Zhonghua nankexue ; Zhonghua nankexue;(12): 110-114, 2011.
Статья в Китайский | WPRIM | ID: wpr-266204

Реферат

<p><b>OBJECTIVE</b>To investigate the role of the cation channel of sperm 1 (CatSper1) protein in the pathogenesis of idiopathic asthenozoospermia.</p><p><b>METHODS</b>Sperm samples from patients with idiopathic asthenozoospermia were separated by Percoll discontinuous density gradients, and the distribution and expression of the CatSper1 protein were determined by immunocytochemistry. Western blotting was used to detect the different expressions of CatSper1 in the ejaculated sperm from the normal control, mild asthenozoospermia, moderate asthenozoospermia and severe asthenozoospermia groups, followed by statistical analyses.</p><p><b>RESULTS</b>The expression of CatSper1, located in the principle piece of the sperm tail, was reduced significantly in the samples from the idiopathic asthenozoospermia patients as compared with the normal controls (t = 2.188, P = 0.042). The relative contents of the CatSper1 protein in the sperm of the control, mild asthenozoospermia, moderate asthenozoospermia and severe asthenozoospermia groups were 0.806 +/- 0.266, 0.669 +/- 0.207, 0.505 +/- 0.214 and 0.295 +/- 0.162, respectively, significantly decreased in the asthenozoospermia patients in comparison with the normal controls (P <0.05). There was a positive correlation between the percentage of progressively motile sperm and the relative content of the CatSper1 protein (r = 0.633, P = 0.000).</p><p><b>CONCLUSION</b>The decreased or abnormal expression of the CatSper1 protein may be a factor involved in the pathogenesis of idiopathic asthenozoospermia.</p>


Тема - темы
Adult , Humans , Male , Young Adult , Asthenozoospermia , Metabolism , Calcium Channels , Metabolism , Case-Control Studies , Spermatozoa , Metabolism
15.
Zhonghua nankexue ; Zhonghua nankexue;(12): 699-702, 2011.
Статья в Китайский | WPRIM | ID: wpr-305804

Реферат

<p><b>OBJECTIVE</b>To investigate the role of the SEPT4 protein in the pathogenesis of idiopathic asthenozoospermia.</p><p><b>METHODS</b>Samples of ejaculated sperm from idiopathic asthenozoospermia patients and normozoospermic men were separated and purified by Percoll discontinuous density gradients, the distribution and expression of SEPT4 in the sperm samples were determined by immunocytochemistry, and the expressions of SEPT4 mRNA and SEPT4 protein were detected by RT-PCR and Western blot.</p><p><b>RESULTS</b>Immunocytochemistry showed that the expression of SEPT4, located in the annulus, was significantly reduced in the sperm of the idiopathic asthenozoospermia patients (t = 3.452, P < 0.01). RT-PCR revealed that the expression of SEPT4 mRNA was significantly lower in the sperm of the idiopathic asthenozoospermia patients than in those of the normozoospermic men (t = 3.521, P < 0.05). Western blot confirmed the results of RT-PCR (t = 5.872, P < 0.05).</p><p><b>CONCLUSION</b>The expression of SEPT4 is significantly decreased in the ejaculated sperm of idiopathic asthenozoospermia patients, which might be one of the causes of idiopathic asthenozoospermia.</p>


Тема - темы
Adult , Humans , Male , Young Adult , Asthenozoospermia , Metabolism , Case-Control Studies , Septins , Metabolism , Sperm Motility , Spermatozoa , Metabolism
16.
Zhonghua nankexue ; Zhonghua nankexue;(12): 356-359, 2007.
Статья в Китайский | WPRIM | ID: wpr-297723

Реферат

Hypoxia-inducible factor 1 (HIF-1) has a close relation with prostate cancer. It is involved not only in angiogenesis, cell proliferation/survival and glucose metabolism but also in p53, p21 and signal transduction pathway in prostate cancer. Further studies of HIF-1 may yield new approaches to the diagnosis and treatment of prostate cancer. We present a review of the structure and biological functions of HIF-1 and its relation with prostate cancer.


Тема - темы
Humans , Male , Hypoxia-Inducible Factor 1 , Physiology , Prostatic Neoplasms , Diagnosis , Metabolism , Therapeutics
17.
Zhonghua nankexue ; Zhonghua nankexue;(12): 1095-1098, 2006.
Статья в Китайский | WPRIM | ID: wpr-289071

Реферат

<p><b>OBJECTIVE</b>To construct a eukaryotic expression vector carrying human VEGF RNAi and to study the effect of RNA interference on VEGF expression in prostate carcinoma.</p><p><b>METHODS</b>VEGF RNAi was synthesized, inserted into the RNA interference eukaryotic expression vector, and confirmed by the result sequencing. The vector was transfected into prostate cancer PC-3, the VEGF expression detected by Western blot and the cell inhibiting rate determined by MTT.</p><p><b>RESULTS</b>The VEGF RNAi eukaryotic expression vector was successfully constructed. Compared with the empty vector group and the control group, the amount of VEGF protein expression was obviously decreased in the VEGF RNAi group. The inhibiting rates were 23.5% , 33. 5% and 40. 8% at 24, 48 and 72 h respectively.</p><p><b>CONCLUSION</b>VEGF RNAi can inhibit the protein expression and growth of PC-3, which provides an experimental base for the biological therapy of prostate cancer.</p>


Тема - темы
Humans , Male , Cell Line, Tumor , Gene Expression , Neoplasms, Hormone-Dependent , Genetics , Metabolism , Prostatic Neoplasms , Genetics , Metabolism , RNA Interference , Transfection , Vascular Endothelial Growth Factor A , Genetics
Критерии поиска