[Objective]The paper was to investigate the dynamics of essential metal elements(Ca,Mg,Fe,Mn,Zn and Cu)contents in winter oilseed rape(Brassica napus L.)during cold acclimation,and to reveal the effects and mechan...[Objective]The paper was to investigate the dynamics of essential metal elements(Ca,Mg,Fe,Mn,Zn and Cu)contents in winter oilseed rape(Brassica napus L.)during cold acclimation,and to reveal the effects and mechanisms of essential elements in cold resistance of oilseed rape.[Method]Three varieties with different cold resistance including Zhongshuang No.11(ZS,freezing sensitive variety),Ganyouza No.1(GY)and Jinyuyou No.1(JYY,freezing tolerant varieties)were used in the study,and the changes of necessary metal elements in these oilseed rapes during cold acclimation were studied.[Result]The concentration of metal elements in oilseed rape had significant changes during cold acclimation,and the difference between varieties was significant.In plant roots,the concentrations of Ca,Mg,Fe,Mn,Zn and Cu were significantly increased,this might because that low temperature made the transpiration decreased,thus blocking the upward transport of elements.In plant shoots,the concentrations of Ca,Mg and Zn were significantly decreased,while the concentrations of Fe and Mn were significantly increased;the change extent of various elements in ZS variety was the largest.[Conclusion]Maintaining the stability of Ca,Mg and Zn concentrations and increasing Fe,Mn and Cu concentrations in plant shoots might be benefit for increasing the cold tolerance of winter oilseed rape.展开更多
Breast cancer is the second leading cancer in the world. <span style="font-family:Verdana;">The long-term</span><span style="font-family:Verdana;"> exposure </span><span ...Breast cancer is the second leading cancer in the world. <span style="font-family:Verdana;">The long-term</span><span style="font-family:Verdana;"> exposure </span><span style="font-family:Verdana;">of</span><span style="font-family:Verdana;"> some metallic compounds induces different forms of cancer, including breast cancer. Trace elements are essential metals for the physiological functions of the cell on a molecular level and also contribute </span><span style="font-family:Verdana;">in</span> <span style="font-family:Verdana;">treatment</span><span style="font-family:Verdana;"> of many diseases. </span><span style="font-family:Verdana;">The aim of study was</span><span style="font-family:Verdana;"> to compare the level of essential trace elements, sodium, potassium, calcium, iron, and zinc in breast cancer patients with normal healthy adult women. Total forty-five patients (age range from 25</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">-</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">73 years) were included in this study and divided into three groups according to three different stages of breast cancer including tumor-II, tumor-III </span><span style="font-family:Verdana;">and</span><span style="font-family:Verdana;"> tumor-IV. Blood was collected from all participants after taking history, clinical data </span><span style="font-family:Verdana;">and</span><span style="font-family:Verdana;"> taking consent. However, about fifteen non-cancer healthy women in </span><span style="font-family:Verdana;">age</span><span style="font-family:Verdana;"> range from 26</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">-</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">69 years were subjected to this study. The elemental concentrations were determined through atomic absorption spectrophotometer </span><span style="font-family:Verdana;">subsequent to</span><span style="font-family:Verdana;"> microwave-induced acid digestion. The results of Na, K, Zn, Fe, Ca, were observed </span></span><span style="font-family:Verdana;">to </span><span style="font-family:Verdana;">decrease in blood samples of breast cancer patients as compared to non-cancer subjects. The results are reliable with other numerous literature reported studies, the efficiency, and deficiency of these trace metals may contribute </span><span style="font-family:Verdana;">an </span><span style="font-family:Verdana;">important</span><span style="font-family:Verdana;"> role in the progress of breast cancer.</span>展开更多
A survey was carried out with the aim of assessing the level of the total phenolic compounds (TPC), essential (Na, K, Ca, Mg, Cu, Zn) and toxic (Cd and Pb) elements in 10 Latvian whole grain rye and/or wheat flo...A survey was carried out with the aim of assessing the level of the total phenolic compounds (TPC), essential (Na, K, Ca, Mg, Cu, Zn) and toxic (Cd and Pb) elements in 10 Latvian whole grain rye and/or wheat flour bread samples, obtained from the local market. The quantities of the TPC were determined by spectrophotometry. Mineral content was determined by flame photometry, flame atom absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAA) after wet digestion in concentrated HNO3. The values were comparable to the literature data. The average content in all the samples was (on a basis of weight of the product) 547 ± 28 mg/100 g for Na; 280 ±20 mg/100 g for K; 32 ± 2 mg/100 g for Ca; 88 ±5 mg/100 g for Mg; 0.49 ± 0.09 mg/100 g for Cu; 1.6 ±0.2 mg/100 g for Zn. Both Pb and Cd were determined below the limit of detection (LOD 5 0.10 mg/100 g). The LOD values were determined for each element. The TPC content in defatted samples was slightly lower than the non-defatted ones, showing the dependence on the sample preparation. The calculated average levels of the elements were compared with the maximum levels recommended or regulated by the national legislation.展开更多
The objective of the present study was to evaluate the relation between maternal blood levels of selected toxic and potentially toxic elements (manganese (Mn), copper (Cu), zinc (Zn), arsenic (As), selenium ...The objective of the present study was to evaluate the relation between maternal blood levels of selected toxic and potentially toxic elements (manganese (Mn), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), lead (Pb) and mercury (Hg)) and birth weight of their new-borns in a Slovenian population, taking into account maternal socio-demographic characteristics and dietary habits. 535 women from 12 regions of Slovenia were recruited at delivery. Maternal blood was collected at 1.5 months after birth. Associations between birth weight and a) predictors obtained through the questionnaires and b) levels of selected elements were tested using bivariate tests and multiple linear regression. Multiple regression models revealed maternal age as an additional predictor for birth weight and confirmed pre-pregnancy body mass, estimated gestational age and gender of the baby as the main predictors for birth weight. Mn in maternal blood was significantly and positively associated with birth weight. The positive association observed between birth weight and Mn in maternal blood could be explained by the essentiality of Mn in foetal development as an important cofactor in enzymereactions in bone formation and in metabolic regulation for amino acid, lipid, protein and carbohydrate levels.展开更多
September 2017 Contents Preface Ensuring People’s Right to Health Based on China’s Conditions Continuous Improvement of Health Environment and Conditions Public Health Service Capability Improving Steadily Great Imp...September 2017 Contents Preface Ensuring People’s Right to Health Based on China’s Conditions Continuous Improvement of Health Environment and Conditions Public Health Service Capability Improving Steadily Great Improvement in the Quality of Medical and Health Services Improvement of the National Medical Security System展开更多
The paper studies an effective way for Chinese enterprises to implement Total Productive Maintenance (TPM) to cut cost and increase efficiency under the impact of financial crisis. It first reviews the definition an...The paper studies an effective way for Chinese enterprises to implement Total Productive Maintenance (TPM) to cut cost and increase efficiency under the impact of financial crisis. It first reviews the definition and objectives of TPM, clarifies how TPM supports lean objectives, and suggests seven steps and essential elements for Chinese enterprises to implement TPM systematically and successfully. The paper also puts the steps and essential elements into practice in a Chinese enterprise, which are proven effective and we hope the proposals are helpful for Chinese enterprises to change their extensive operation in equipment management.展开更多
Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining o...Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining of Lakhra coal mining was evaluated in detail. The biological samples (scalp hair and blood) of 270 workers of Lakhra coal mining {official and control subjects} (indoor and outdoor) 18 to 55 years age group and 70 referent subjects of same age-groups were examined. The biological samples (blood and scalp hair) of workers of Lakhra coal mining and referent subjects were analyzed for calcium (Ca) and lead (Pb). Flame atomic absorption spectrometry was applied for the determination of the Ca in digested samples of studied subjects by the microwave oven whereas, the Pb contents were measured by electrothermal atomic absorption spectrometry. The validity of the methodology was checked by using the certified human hair material (BCR 397) and lyophilized human blood (Clincheck). The results indicated the higher contents of Pb in biological samples of indoor and outdoor mining workers than referents. However, the levels of Ca were found to be lower in indoor and outdoor mining workers than those of referents. It can be concluded that immediate action should be taken by recommended authorities to improve the ventilation and hygiene practices inside the industries, mines, and other workplaces.展开更多
Purpose: It is well known that trace elements and heavy metals play a significant role in human health and disease. These elements play an important role in different metabolic pathways of cells and tissues. Trace ele...Purpose: It is well known that trace elements and heavy metals play a significant role in human health and disease. These elements play an important role in different metabolic pathways of cells and tissues. Trace element deficiency or excess is implicated in the development or progression of some cancers. We present a study which investigates serum/ plasma levels of trace-heavy elements in metastatic colon cancer patients and healthy subjects. Methods: Blood samples were collected from 29 healthy subjects and 40 patients with metastatic colon cancer in Oncology Department of Medical School of Yuzuncu Yil University. In both groups, the serum levels of copper (Cu), magnesium (Mg), lead (Pb), chromium (Cr), zinc (Zn) selenium (Se), manganese (Mn), and cadmium (Cd) were determined. Results: Higher levels of Cu, Mg, Pb, Cr, Zn, Mn and Cd were seen in patients with metastatic colon cancer compared to healthy subjects and these findings were statistically significant (p 0.05). Se levels were noted to be lower in patients with colon cancer in comparison to healthy subjects and this finding was also statistically significant (p 0.05). Conclusions: According to our findings there was significant diffence in trace elements and heavy metals levels between healthy subjects and metastatic colon cancer patients. Therefore heavy metal and trace elements may have prognostic significance in complex disorders including colon cancer. However, further comprehensive studies are needed in order to advance our understanding of the relationship between heavy metal and trace elements and their role in cancers.展开更多
<strong>Background:</strong> Recently, Coronavirus Disease 2019 (COVID-19) has been affected by the extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has developed important global health a...<strong>Background:</strong> Recently, Coronavirus Disease 2019 (COVID-19) has been affected by the extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has developed important global health anxiety. At this time, the treatment options for this disease are only moderately successful. Smoking has been related to COVID-19 and its mortality, and it has the potential to affect bacteriological and viral conversion, clinical effects, and treatment outcomes. <strong>Methods:</strong> The aim of this study was to determine the relationship between critical essential trace {zinc (Zn), iron (Fe), and copper (Cu)} and toxic {cadmium (Cd) and nickel (Ni)} elements in human biological samples such as scalp hair, serum, saliva, blood, nasal fluid, and sputum of smoking and nonsmoking male COVID-19 patients (n = 139, age range 25 - 38 years) from Hyderabad, Pakistan. For comparative purposes, the biological specimens of referent persons (n = 83), pulmonary Tuberculosis (T.B) patients (n = 67), Pneumonia (n = 56) of the same age groups were also be analyzed. Microwave oven mediated digestion method was employed, and digestion of samples was carried out with the help of 2:1 mixture solution of HNO<sub>3</sub> (65%) and H<sub>2</sub>O<sub>2</sub> (30%). Atomic absorption spectrometry was employed for the determination of elemental concentrations from the microwave oven employed digested samples. <strong>Results:</strong> The found average of essential elements (Zn, Fe, and Cu) in biological specimens of smoker and nonsmoker male COVID-19, T.B, and Pneumonia patients was found to lower, whilst cadmium and nickel were found to be higher when compared with samples from referents (p < 0.001). <strong>Conclusions:</strong> Improved elemental (Cu, Fe, Zn) concentrations may also decrease the risk of bacterial co-infection by enhancing the mucociliary clearance and respiratory epithelial barrier function, in addition to providing direct antibacterial effects against <i>S. pneumoniae</i>. Our findings also suggest that higher Cd and Ni concentrations are linked to cigarette smoking, which could lead to COVID-19 and other lung-infected diseased recurrences. However, further clinical and experimental research is required.展开更多
In this paper, which is a continuation of our previous paper [T. Albu, M. Iosif, A. Tercan, The conditions (Ci) in modular lattices, and applications, J. Algebra Appl. 15 (2016), http: dx.doi.org/10.1142/S0219498...In this paper, which is a continuation of our previous paper [T. Albu, M. Iosif, A. Tercan, The conditions (Ci) in modular lattices, and applications, J. Algebra Appl. 15 (2016), http: dx.doi.org/10.1142/S0219498816500018], we investigate the latticial counterparts of some results about modules satisfying the conditions (Cll) or (C12). Applications are given to Grothendieck categories and module categories equipped with hereditary torsion theories.展开更多
基金Supported by Special Funds for Public Welfare Industry(Agricul-ture)Study of China(200903003)Subjects of Special Funds of Public Welfare Institutes of China(1610172011016)~~
文摘[Objective]The paper was to investigate the dynamics of essential metal elements(Ca,Mg,Fe,Mn,Zn and Cu)contents in winter oilseed rape(Brassica napus L.)during cold acclimation,and to reveal the effects and mechanisms of essential elements in cold resistance of oilseed rape.[Method]Three varieties with different cold resistance including Zhongshuang No.11(ZS,freezing sensitive variety),Ganyouza No.1(GY)and Jinyuyou No.1(JYY,freezing tolerant varieties)were used in the study,and the changes of necessary metal elements in these oilseed rapes during cold acclimation were studied.[Result]The concentration of metal elements in oilseed rape had significant changes during cold acclimation,and the difference between varieties was significant.In plant roots,the concentrations of Ca,Mg,Fe,Mn,Zn and Cu were significantly increased,this might because that low temperature made the transpiration decreased,thus blocking the upward transport of elements.In plant shoots,the concentrations of Ca,Mg and Zn were significantly decreased,while the concentrations of Fe and Mn were significantly increased;the change extent of various elements in ZS variety was the largest.[Conclusion]Maintaining the stability of Ca,Mg and Zn concentrations and increasing Fe,Mn and Cu concentrations in plant shoots might be benefit for increasing the cold tolerance of winter oilseed rape.
文摘Breast cancer is the second leading cancer in the world. <span style="font-family:Verdana;">The long-term</span><span style="font-family:Verdana;"> exposure </span><span style="font-family:Verdana;">of</span><span style="font-family:Verdana;"> some metallic compounds induces different forms of cancer, including breast cancer. Trace elements are essential metals for the physiological functions of the cell on a molecular level and also contribute </span><span style="font-family:Verdana;">in</span> <span style="font-family:Verdana;">treatment</span><span style="font-family:Verdana;"> of many diseases. </span><span style="font-family:Verdana;">The aim of study was</span><span style="font-family:Verdana;"> to compare the level of essential trace elements, sodium, potassium, calcium, iron, and zinc in breast cancer patients with normal healthy adult women. Total forty-five patients (age range from 25</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">-</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">73 years) were included in this study and divided into three groups according to three different stages of breast cancer including tumor-II, tumor-III </span><span style="font-family:Verdana;">and</span><span style="font-family:Verdana;"> tumor-IV. Blood was collected from all participants after taking history, clinical data </span><span style="font-family:Verdana;">and</span><span style="font-family:Verdana;"> taking consent. However, about fifteen non-cancer healthy women in </span><span style="font-family:Verdana;">age</span><span style="font-family:Verdana;"> range from 26</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">-</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">69 years were subjected to this study. The elemental concentrations were determined through atomic absorption spectrophotometer </span><span style="font-family:Verdana;">subsequent to</span><span style="font-family:Verdana;"> microwave-induced acid digestion. The results of Na, K, Zn, Fe, Ca, were observed </span></span><span style="font-family:Verdana;">to </span><span style="font-family:Verdana;">decrease in blood samples of breast cancer patients as compared to non-cancer subjects. The results are reliable with other numerous literature reported studies, the efficiency, and deficiency of these trace metals may contribute </span><span style="font-family:Verdana;">an </span><span style="font-family:Verdana;">important</span><span style="font-family:Verdana;"> role in the progress of breast cancer.</span>
文摘A survey was carried out with the aim of assessing the level of the total phenolic compounds (TPC), essential (Na, K, Ca, Mg, Cu, Zn) and toxic (Cd and Pb) elements in 10 Latvian whole grain rye and/or wheat flour bread samples, obtained from the local market. The quantities of the TPC were determined by spectrophotometry. Mineral content was determined by flame photometry, flame atom absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAA) after wet digestion in concentrated HNO3. The values were comparable to the literature data. The average content in all the samples was (on a basis of weight of the product) 547 ± 28 mg/100 g for Na; 280 ±20 mg/100 g for K; 32 ± 2 mg/100 g for Ca; 88 ±5 mg/100 g for Mg; 0.49 ± 0.09 mg/100 g for Cu; 1.6 ±0.2 mg/100 g for Zn. Both Pb and Cd were determined below the limit of detection (LOD 5 0.10 mg/100 g). The LOD values were determined for each element. The TPC content in defatted samples was slightly lower than the non-defatted ones, showing the dependence on the sample preparation. The calculated average levels of the elements were compared with the maximum levels recommended or regulated by the national legislation.
文摘The objective of the present study was to evaluate the relation between maternal blood levels of selected toxic and potentially toxic elements (manganese (Mn), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), lead (Pb) and mercury (Hg)) and birth weight of their new-borns in a Slovenian population, taking into account maternal socio-demographic characteristics and dietary habits. 535 women from 12 regions of Slovenia were recruited at delivery. Maternal blood was collected at 1.5 months after birth. Associations between birth weight and a) predictors obtained through the questionnaires and b) levels of selected elements were tested using bivariate tests and multiple linear regression. Multiple regression models revealed maternal age as an additional predictor for birth weight and confirmed pre-pregnancy body mass, estimated gestational age and gender of the baby as the main predictors for birth weight. Mn in maternal blood was significantly and positively associated with birth weight. The positive association observed between birth weight and Mn in maternal blood could be explained by the essentiality of Mn in foetal development as an important cofactor in enzymereactions in bone formation and in metabolic regulation for amino acid, lipid, protein and carbohydrate levels.
文摘September 2017 Contents Preface Ensuring People’s Right to Health Based on China’s Conditions Continuous Improvement of Health Environment and Conditions Public Health Service Capability Improving Steadily Great Improvement in the Quality of Medical and Health Services Improvement of the National Medical Security System
文摘The paper studies an effective way for Chinese enterprises to implement Total Productive Maintenance (TPM) to cut cost and increase efficiency under the impact of financial crisis. It first reviews the definition and objectives of TPM, clarifies how TPM supports lean objectives, and suggests seven steps and essential elements for Chinese enterprises to implement TPM systematically and successfully. The paper also puts the steps and essential elements into practice in a Chinese enterprise, which are proven effective and we hope the proposals are helpful for Chinese enterprises to change their extensive operation in equipment management.
文摘Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining of Lakhra coal mining was evaluated in detail. The biological samples (scalp hair and blood) of 270 workers of Lakhra coal mining {official and control subjects} (indoor and outdoor) 18 to 55 years age group and 70 referent subjects of same age-groups were examined. The biological samples (blood and scalp hair) of workers of Lakhra coal mining and referent subjects were analyzed for calcium (Ca) and lead (Pb). Flame atomic absorption spectrometry was applied for the determination of the Ca in digested samples of studied subjects by the microwave oven whereas, the Pb contents were measured by electrothermal atomic absorption spectrometry. The validity of the methodology was checked by using the certified human hair material (BCR 397) and lyophilized human blood (Clincheck). The results indicated the higher contents of Pb in biological samples of indoor and outdoor mining workers than referents. However, the levels of Ca were found to be lower in indoor and outdoor mining workers than those of referents. It can be concluded that immediate action should be taken by recommended authorities to improve the ventilation and hygiene practices inside the industries, mines, and other workplaces.
文摘Purpose: It is well known that trace elements and heavy metals play a significant role in human health and disease. These elements play an important role in different metabolic pathways of cells and tissues. Trace element deficiency or excess is implicated in the development or progression of some cancers. We present a study which investigates serum/ plasma levels of trace-heavy elements in metastatic colon cancer patients and healthy subjects. Methods: Blood samples were collected from 29 healthy subjects and 40 patients with metastatic colon cancer in Oncology Department of Medical School of Yuzuncu Yil University. In both groups, the serum levels of copper (Cu), magnesium (Mg), lead (Pb), chromium (Cr), zinc (Zn) selenium (Se), manganese (Mn), and cadmium (Cd) were determined. Results: Higher levels of Cu, Mg, Pb, Cr, Zn, Mn and Cd were seen in patients with metastatic colon cancer compared to healthy subjects and these findings were statistically significant (p 0.05). Se levels were noted to be lower in patients with colon cancer in comparison to healthy subjects and this finding was also statistically significant (p 0.05). Conclusions: According to our findings there was significant diffence in trace elements and heavy metals levels between healthy subjects and metastatic colon cancer patients. Therefore heavy metal and trace elements may have prognostic significance in complex disorders including colon cancer. However, further comprehensive studies are needed in order to advance our understanding of the relationship between heavy metal and trace elements and their role in cancers.
文摘<strong>Background:</strong> Recently, Coronavirus Disease 2019 (COVID-19) has been affected by the extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has developed important global health anxiety. At this time, the treatment options for this disease are only moderately successful. Smoking has been related to COVID-19 and its mortality, and it has the potential to affect bacteriological and viral conversion, clinical effects, and treatment outcomes. <strong>Methods:</strong> The aim of this study was to determine the relationship between critical essential trace {zinc (Zn), iron (Fe), and copper (Cu)} and toxic {cadmium (Cd) and nickel (Ni)} elements in human biological samples such as scalp hair, serum, saliva, blood, nasal fluid, and sputum of smoking and nonsmoking male COVID-19 patients (n = 139, age range 25 - 38 years) from Hyderabad, Pakistan. For comparative purposes, the biological specimens of referent persons (n = 83), pulmonary Tuberculosis (T.B) patients (n = 67), Pneumonia (n = 56) of the same age groups were also be analyzed. Microwave oven mediated digestion method was employed, and digestion of samples was carried out with the help of 2:1 mixture solution of HNO<sub>3</sub> (65%) and H<sub>2</sub>O<sub>2</sub> (30%). Atomic absorption spectrometry was employed for the determination of elemental concentrations from the microwave oven employed digested samples. <strong>Results:</strong> The found average of essential elements (Zn, Fe, and Cu) in biological specimens of smoker and nonsmoker male COVID-19, T.B, and Pneumonia patients was found to lower, whilst cadmium and nickel were found to be higher when compared with samples from referents (p < 0.001). <strong>Conclusions:</strong> Improved elemental (Cu, Fe, Zn) concentrations may also decrease the risk of bacterial co-infection by enhancing the mucociliary clearance and respiratory epithelial barrier function, in addition to providing direct antibacterial effects against <i>S. pneumoniae</i>. Our findings also suggest that higher Cd and Ni concentrations are linked to cigarette smoking, which could lead to COVID-19 and other lung-infected diseased recurrences. However, further clinical and experimental research is required.
文摘In this paper, which is a continuation of our previous paper [T. Albu, M. Iosif, A. Tercan, The conditions (Ci) in modular lattices, and applications, J. Algebra Appl. 15 (2016), http: dx.doi.org/10.1142/S0219498816500018], we investigate the latticial counterparts of some results about modules satisfying the conditions (Cll) or (C12). Applications are given to Grothendieck categories and module categories equipped with hereditary torsion theories.