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1.
Starting with an elementary problem that appeared in the Putnam mathematics competition, we proceed to discuss some techniques of transcendental number theory and prove the following result. If p, q, r are distinct primes and if c is a real number with the property that pc, qc, rc are integers, then c must be a non-negative integer. The tools used are some linear algebra and complex analysis. The zero-density estimate method discussed here was used by Alan Baker to prove his celebrated theorem on linear forms in logarithms. The question as to whether we can replace three primes by two primes is an open question.  相似文献   

2.
1　Introduction　AmatrixA∈Cn×missaidtobecentrohermitianifA =Jn AJm,andskewcentrohermitianifA =-Jn AJm,where Adenotetheconjugateofthema trixAandJlisthepermutationmatrixoforderlwithonesonthecrossdiagonal(bottomlefttotopright)andzeroselsewhere .ThehermitianToeplitzmatricesformanimportantsubclassofcentrohermi tianmatriceswhichoccurnaturallyindigitalsignalprocessingandotherareas ,seeforinstance[1] andreferencetherein .Thecentrohermitianandrelatedmatricesrecentlyplayanimportantroleinthesolu…  相似文献   

3.
This empirically driven paper is about workplace learning with specific focus on the ‘work’ of consuming practices. By consuming we refer to the eating, and the drinking, and (at times) to the smoking that workers, in most organisations, do on a daily basis. Indeed, it is the quotidian nature of consuming, coupled with its absence from workplace learning research that make them noteworthy practices to explore. In using the term practice we draw on the recent tranche of practice based theorisations: notably Schatzki (1996, Organization Studies, 26(3), 465-484, 2005, Organization Studies, 27(12), 1863-1873, 2006) and Gherardi (Human Relations, 54(1), 131-139, 2001, 2006, Learning Organization, 16(5), 352-359, 2009). The paper frames consuming practices as ‘dispersed’ (general) practices and, illustrated through empirical data from multiple projects, we progressively outline how these contribute to the learning of ‘integrative’ (specialized work) practices. Our overall aim is to (re)position consuming practices from prosaic, to having much relevance for research on workplace learning.  相似文献   

4.
In plants, lipoxygenases (LOXs) play a crucial role in biotic and abiotic stresses. In our previous study, five 13-LOX genes of oriental melon were regulated by abiotic stress but it is unclear whether the 9-LOX is involved in biotic and abiotic stresses. The promoter analysis revealed that CmLOX09 (type of 9-LOX) has hormone elements, signal substances, and stress elements. We analyzed the expression of CmLOX09 and its downstream genes—CmHPL and CmAOS—in the leaves of four-leaf stage seedlings of the oriental melon cultivar “Yumeiren” under wound, hormone, and signal substances. CmLOX09, CmHPL, and CmAOS were all induced by wounding. CmLOX09 was induced by auxin (indole acetic acid, IAA) and gibberellins (GA3); however, CmHPL and CmAOS showed differential responses to IAA and GA3. CmLOX09, CmHPL, and CmAOS were all induced by hydrogen peroxide (H2O2) and methyl jasmonate (MeJA), while being inhibited by abscisic acid (ABA) and salicylic acid (SA). CmLOX09, CmHPL, and CmAOS were all induced by the powdery mildew pathogen Podosphaera xanthii. The content of 2-hexynol and 2-hexenal in leaves after MeJA treatment was significantly higher than that in the control. After infection with P. xanthii, the diseased leaves of the oriental melon were divided into four levels—levels 1, 2, 3, and 4. The content of jasmonic acid (JA) in the leaves of levels 1 and 3 was significantly higher than that in the level 0 leaves. In summary, the results suggested that CmLOX09 might play a positive role in the response to MeJA through the hydroperoxide lyase (HPL) pathway to produce C6 alcohols and aldehydes, and in the response to P. xanthii through the allene oxide synthase (AOS) pathway to form JA.  相似文献   

5.
This study was conducted to investigate the effects of fresh fermented soybean meal (FSM) on the growth performance of nursery piglets, nitrogen excretion in feces, and the concentrations of ammonia (NH3) and particulate matter (PM) in the piggery. A total of 472 nursery piglets (Landrace×Yorkshire, (16.3±0.36) kg body weight) were randomly allocated into two treatments with 236 pigs in each treatment. The pigs were fed the basal diet without fresh FSM (control) or diet containing 10% (100 g/kg) fresh FSM (FSM group), and the crude protein content of the two groups was consistent. The feeding trial lasted for 28 d. The results showed that the pigs fed fresh FSM had increased (P<0.05) average daily gain (ADG) compared with the control. There was no significant difference (P>0.05) in feed to gain ratio (F:G) between the two groups. During the whole experiment, the concentration of NH3 in the piggery decreased (P<0.05) by 19.0%, and the concentrations of PM (PM10 and PM2.5) in the piggery decreased (P<0.05) by 19.9% and 11.6%, respectively, in the FSM group, compared with the control. The ammonia nitrogen and nitrite content in feces increased (P<0.05) by 32.9% and 28.4%, respectively, in the FSM group. The fecal pH declined (P<0.05) significantly in the FSM group compared with the control. At the end of experiment, total protein (TP) concentration was increased (P<0.05) significantly and blood urea nitrogen (BUN) concentration was decreased (P<0.05) for pigs fed the diet with fresh FSM. The results indicated that dietary fresh FSM not only improved the growth performance of nursery piglets, but also reduced the NH3 concentration in the piggery due to nitrogen conversion, and decreased the concentrations of PM10 and PM2.5 in the piggery.  相似文献   

6.
This article examines the productivity of both individuals and institutions, indexed through an examination of five educational psychology journals (Cognition and Instruction, Contemporary Educational Psychology, Educational Psychologist, Educational Psychology Review, and Journal of Educational Psychology) from 2009 to 2014. These results are discussed relative to four previous studies (Hsieh et al. Contemporary Educational Psychology, 29, 333–343, 2004; Jones et al. Contemporary Educational Psychology, 35, 11–16, 2010; Smith et al. Contemporary Educational Psychology, 23, 173–181, 1998; Contemporary Educational Psychology, 28, 422–430, 2003). Vanderbilt University and Fred Paas replaced the University of Maryland and Richard E. Mayer as the top research institution and author, respectively. Sixteen of the top 19 researchers’ institutions were outside the USA, compared to only 10 of the top 32 during 2003–2008 and three of the top 20 during 1991–1996. Educational psychology research continues the trend of becoming more international.  相似文献   

7.
In this study, we aimed to examine the inhibitory effect of PA003, a Pediococcus acidilactici that produces lactic acid and antimicrobial peptides pediocin, on pathogenic biofilm formation on abiotic surfaces. PA003 and pathogens (Escherichia coli, Salmonella enterica serovar Typhimurium, Staphylococcus aureus and Listeria monocytogenes) were used to evaluate auto-aggregation, hydrophobicity, biofilm formation and biofilm formation inhibition on stainless steel, polyvinyl chloride and glass slides in terms of exclusion, displacement and competition. The results showed the highest auto-aggregation abilities were observed for one of the E. coli strains EAggEC (E58595) and the highest hydrophobic strain was observed with EPEC (E2348/69) (51.9%). The numbers of biofilm cells of E. coli, S. Typhimurium, S. aureus and L. monocytogenes on stainless steel, polyvinyl chloride and glass slide coupons were effectively reduced by approximately 4 log CFU/coupon. These results demonstrate that lactic acid bacteria can be used as an alternative to effectively control the formation of biofilms by food-borne pathogens.  相似文献   

8.

Objective

Salmonella enterica remains a major cause of food-borne disease in humans, and Salmonella Typhimurium (ST) contamination of poultry products is a worldwide problem. Since macrophages play an essential role in controlling Salmonella infection, the aim of this study was to evaluate the effect of glycyrrhizic acid (GA) on immune function of chicken HD11 macrophages.

Methods

Chicken HD11 macrophages were treated with GA (0, 12.5, 25, 50, 100, 200, 400, or 800 μg/ml) and lipopolysaccharide (LPS, 500 ng/ml) for 3, 6, 12, 24, or 48 h. Evaluated responses included phagocytosis, bacteria-killing, gene expression of cell surface molecules (cluster of differentiation 40 (CD40), CD80, CD83, and CD197) and antimicrobial effectors (inducible nitric oxide synthase (iNOS), NADPH oxidase-1 (NOX-1), interferon-γ (IFN-γ), LPS-induced tumor necrosis factor (TNF)-α factor (LITAF), interleukin-6 (IL-6), and IL-10), and production of nitric oxide (NO) and hydrogen peroxide (H2O2).

Results

GA increased the internalization of both fluorescein isothiocyanate (FITC)-dextran and ST by HD11 cells and markedly decreased the intracellular survival of ST. We found that the messenger RNA (mRNA) expression of cell surface molecules (CD40, CD80, CD83, and CD197) and cytokines (IFN-γ, IL-6, and IL-10) of HD11 cells was up-regulated following GA exposure. The expression of iNOS and NOX-1 was induced by GA and thereby the productions of NO and H2O2 in HD11 cells were enhanced. Notably, it was verified that nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK) pathways were responsible for GA-induced synthesis of NO and IFN-γ gene expression.

Conclusions

Taken together, these results suggested that GA exhibits a potent immune regulatory effect to activate chicken macrophages and enhances Salmonella-killing capacity.
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9.
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10.
As an easy application of the intermediate value theorem, one can show that for any continuous function f: [0, 1] → ? with f (0) = f (1), there are points a, a + 1/2 both in [0, 1] such that f (a) = f (a + 1/2). In this note, we show that this property holds with 1/2 replaced by any number of the form 1/n for a positive integer n. More interestingly, we show that this is false for every number not of the form 1/n.  相似文献   

11.
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12.
The main purpose of the study is to develop a Facebook Effect Scale on Teacher Quality (FESTQ) based on the pedagogical content knowledge, technological pedagogical content knowledge and lifelong learning frameworks. Study participants comprised 556 teachers. Explanatory factor analysis and confirmatory factor analysis were conducted in the development and testing of the FESTQ. The results showed that the FESTQ is reliable and valid to measure Facebook effect on teacher quality. The FESTQ consists of 40 positive six-point Likert-type items along with six factors, instructional knowledge for in-class applications, general culture knowledge, individual characteristics, instructional knowledge related to student characteristics, instructional knowledge for preparing an assessment tool and special content area knowledge. The psychometric properties of the FESTQ, the study limitations and suggestions for future studies are discussed.  相似文献   

13.
Children as readers of picture books and the ways they respond to, and make meaning from, such texts are the focus of this article, which reports on a small-scale study undertaken in Norway and Wales, UK. The theoretical framing of the research draws on concepts of the multimodal ensemble in picture books and of the reading event as part of a social practice. The research design was developed from the team’s analysis of two texts, Pappa by Svein Nyhus (1998) and What does Daddy Do? by Rachel Bright (2009). Twenty-four children, who were 7 and 8 years old, took part in the study. This was built around two reading events for each book, staged as an immediate response and as a guided response. The data subsequently collected were analysed according to three overarching organisational principles, as book world, real world and play world. For both Daddy and Pappa, the first reading event showed the children’s responses were mainly directed towards exploring the book world. On the second reading event, references to the real world predominated for Daddy, while for Pappa the book world was again dominant. Across both reading events and for both books, the playworld revealed those occasions when the children expanded the meaning of the story, demonstrating an inventive ability to play with the text. Overall, the children’s responses moved fluidly across the three worlds, showing them to be energetically making connections between the reading, their experience of books and their own lives.  相似文献   

14.
The expression of the cell death-inducing DNA fragmentation factor α-like effector (CIDE) family including Cidea, Cideb, and Cidec was significantly increased in mouse and human models of obesity. However, there was less information on these genes’ expression in pigs. Here, we hypothesized that different fat accumulation between lean (Duroc×Landrace×Yorkshire gilts, DLY) and obese (Lantang) pigs was attributed to porcine CIDE-modulating lipid metabolism. Our data showed that Cidea and Cidec were expressed at a high level in adipose tissue, and at a relatively high level in skeletal muscle, whereas Cideb was mainly expressed in the liver in both breeds of pig. Lantang pigs had higher white adipose and skeletal muscle Cidea and Cidec mRNA abundance, and hepatic and muscle Cideb mRNA than DLY pigs. Lipid metabolism-related genes including sterol regulatory element binding protein 1c (SREBP-1c), hepatocyte nuclear factor-4α (HNF-4α), peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), fatty acid synthase (FASN), diacylglycerol O-acyltransferase 1 (DGAT1), and DGAT2 showed a higher expression level in adipose tissue from obese pigs than in that from lean pigs. Lantang pigs exhibited higher mRNA abundance for liver SREBP-1c, HNF-4α, and PGC-1α, and higher skeletal muscle SREBP-1c, HNF-4α, PGC-1α, and DGAT2 expression, as compared with DLY pigs. However, the perlipin2 mRNA levels in adipose tissues, liver, and skeletal muscle were significantly lower in obese pigs than in their lean counterparts. Furthermore, plasma non-esterified fatty acid (NEFA), glucose, and triacylglycerol (TAG) levels were greater in obese pigs than in lean pigs. Finally, data from correlation analysis further found that CIDE mRNA expression was positively correlated with back fat thickness (BFT), abdominal fat mass (AFM), and the levels of NEFA, TAG, and glucose in the two breeds. Collectively, these data revealed that the porcine CIDEs possibly modulated lipid metabolism and contributed to the development of fat deposition and obesity in Lantang pigs.  相似文献   

15.
The purpose of this study was, first, to understand the item hierarchy regarding students’ understanding of scientific models and modeling (USM). Secondly, this study investigated Taiwanese students’ USM progression from 7th to 12th grade, and after participating in a model-based curriculum. The questionnaire items were developed based on 6 aspects of USM, namely, model type, model content, constructed nature of models, multiple models, change of models, and purpose of models. Moreover, 10 representations of models were included for surveying what a model is. Results show that the purpose of models and model type items covered a wide range of item difficulties. At the one end, items for the purpose of models are most likely to be endorsed by the students, except for the item “models are used to predict.” At the other end, the “model type” items tended to be difficult. The students were least likely to agree that models can be text, mathematical, or dynamic. The items of the constructed nature of models were consistently located above the average, while the change of models items were consistently located around the mean level of difficulty. In terms of the natural progression of USM, the results show significant differences between 7th grade and all grades above 10th, and between 8th grade and 12th grade. The students in the 7th grade intervention group performed better than the students in the 7th and 8th grades who received no special instruction on models.  相似文献   

16.
Chlamydia psittaci is an important zoonotic pathogen in birds and may be transmitted to humans and result in severe respiratory disease. To assess the prevalence and genotype of C. psittaci in birds in Kunming, Yunnan, China, a total of 136 specimens of psittacine birds involving 8 species were collected from the city’s zoos (n=60) and pet markets (n=76). The frequency of C. psittaci infection was 19.9% (27/136) in the psittacine birds. The prevalence of C. psittaci was higher in pet birds (26.3%; 20/76) than in zoo birds (11.7%; 7/60) (P=0.034). In particular, among Agapornis fischeri, the C. psittaci infection (50%; 10/20) was significantly more frequent in the pet markets than in the zoos (P=0.006). In addition, the highest prevalence of 41.2% (7/17) was found in Ara ararauna. To determine the genotype of C. psittaci, 23 OmpA gene fragments (about 1.4 kb) in 27 positive samples were successfully amplified and sequenced. Phylogenetic analysis showed that all the 23 strains belonged to genotype A. Our results demonstrate the high prevalence of C. psittaci genotype A infection in psittacine birds in Yunnan Province, suggesting a potential threat to human health in this area. Therefore, it is necessary to take effective measures to prevent the spread of C. psittaci among psittacine birds, as well as among employees and customers.  相似文献   

17.
Microbial attacks during storage are one of the primary causes of product deterioration, and can limit the process of prolonging the shelf-life of harvested food. In this study, sweet potatoes were stored at temperatures of 13, 21, and 29 °C for 4 weeks. Samples were collected during storage and plated on potato dextrose agar, from which axenic mold cultures were obtained and identified using 26S rRNA gene sequences. Physiological changes of potato tubers were assessed with respect to pathogenicity, enzyme activity, and atmospheric storage conditions. Six fungal species were identified, namely Penicillium chrysogenum (P. rubens), P. brevicompactum, Mucor circinelloides, Cladosporium cladosporiodes, P. expansum, and P. crustosum. The following fungal isolates, namely P. expansum, P. brevicompactum, and Rhizopus oryzae, were recovered from the re-infected samples and selected according to their levels of enzyme activity. This study revealed high levels of activity for cellulase and pectinase, which were most notable during the initial three days of testing, and were followed by a steady decrease (P<0.05). Polygalacturonase activity was prominent with values ranging from 12.64 to 56.79 U/mg (P. expansum) and 18.36 to 79.01 U/mg (P. brevicompactum). Spoilage was obvious in the control group, which had a 100% decay at the end of the experimental period compared with samples treated with iprodione and sodium hypochlorite, in which the decay rates were 5% and 55%, respectively. The data for the iprodione- and sodium hypochlorite-treated samples at the end of the 3-month storage period showed that they were significantly different (P=0.041), with the sodium hypochlorite-treated samples producing twice the rate of infection compared to the iprodione-treated samples. The comparative rate of the progression of decay in the treated samples can be expressed as iprodione<sodium hypochlorite<control. This study demonstrates that sweet potato tissue damage is due to the activities of microbial enzymes and, in particular, the pectinases of the organisms isolated from the infected potato tissues, and suggests the advantages of utilizing iprodione as a curing agent for potato tubers before storage.  相似文献   

18.
This research aimed at identifying student profiles of perceptions by means of a clustering method using a validated questionnaire. These profiles describe students’ attraction to science and technology (S&T) studies and careers as a variable driven by school S&T self-concept and interest in school S&T. In addition to three rather predictable student profiles (confident enthusiast, average ambitious, and pessimistic dropout), the fourth fairly well-populated profile called confident indifferent was produced. Our second and third research questions allowed us to describe each profile in terms of the instructional methods to which their population was exposed (including the degree to which they were actively involved) and the instructional methods to which they would like more exposure. An analysis of the evolution of the profiles’ population over time is also presented. The results suggest that pedagogical variety and active involvement in the decision to pursue S&T are important. The perception of the utility and importance of S&T both in and out of school may also play an important role in these decisions. Minor pedagogical preferences were also found in certain age groups.  相似文献   

19.
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20.
The aim of this study was to examine the potential impact of the representational characteristics of models and students’ educational levels on students’ views of scientific models and modeling (VSMM). An online multimedia questionnaire was designed to address three major aspects of VSMM, namely the nature of models, the nature of modeling, and the purpose of models. The three scales of representational characteristics included modality, dimensionality, and dynamics. A total of 102 eighth graders and 87 eleventh graders were surveyed. Both quantitative data and written responses were analyzed. The influence of the representational characteristics seemed to be more salient on the nature of models and the purpose of models. Some interactions between the educational levels and the representational characteristics showed that the high school students were more likely to recognize textual representations and pictorial representations as models, while also being more likely to appreciate the differences between 2D and 3D models. However, some other differences between educational levels did not necessarily suggest that the high school students attained more sophisticated VSMM. For instance, in considering what information should be included in a model, students’ attention to particular affordances of the representation can lead to a more naive view of modeling. Implications for developing future questionnaires and for teaching modeling are suggested in this study.  相似文献   

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