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1.
Front Microbiol ; 14: 1259103, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37869675

RESUMO

The escalation of harmful pollutants, including heavy metals, due to industrialization and urbanization has become a global concern. To mitigate the negative impacts of heavy metal stress on germination and early plant development, growth regulators have been employed. This study aimed to evaluate the response of mung bean (Vigna radiata L.) to zinc stress in the presence of brassinosteroids, focusing on seedling growth and antioxidant potential. Mung bean seedlings were treated with three concentrations of 24-epibrassinolide (EBL) (0.1, 0.2, and 0.4 PPM) with or without zinc. Results demonstrated that the application of brassinosteroids, combined with zinc stress, significantly enhanced germination percentage (about 47.06, 63.64, and 120%), speed of germination (about 39.13, 50, and 100%), seedling growth (about 38% in case of treatment combined 0.4 PPM 24-EBL and 1.5 mM ZnSO4) and seedling vigor index (204% in case of treatment combined 0.4 PPM 24-EBL and 1.5 mM ZnSO4) compared to zinc-treated seedlings alone after 24 h. The activities of antioxidative enzymes (catalase, ascorbate peroxidase, polyphenol oxidase, and peroxidase) and total soluble protein content decreased, while lipid peroxidation and proline content exhibited a significant increase (p ≤ 0.05) when compared to the control. However, the negative effects induced by heavy metal stress on these parameters were significantly mitigated by EBL application. Notably, the most effective concentration of EBL in overcoming zinc stress was found to be 0.4 PPM. These findings underscore the potential of exogenously applied brassinosteroids as a valuable tool in phytoremediation projects by ameliorating heavy metal stress.

2.
Neurol India ; 71(2): 331-333, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37148064

RESUMO

Spinal epidural abscess (SEA) is a very serious infection of the central nervous system (CNS). It is of very low incidence with a peak age in the geriatric age group. Immunocompromised patients are more susceptible to SEA. It can present with significant neurological deficits, which can be permanent if not identified and treated promptly. In this case report, a 75-year-old immunocompromised patient presented with progressive spastic quadriparesis and septicemia. He was diagnosed with a case of cervical spinal epidural abscess with underlying cord compression. Anterior retropharyngeal approach and button-hole disco-osteotomy of C5-C6 was performed and the cervical SEA was drained, followed by antibiotic saline irrigation (cranially and caudally) was done, total duration of surgery was 70 min. At the time of discharge (7th postoperative day), the patient improved neurologically and sepsis had resolved.


Assuntos
Abscesso Epidural , Masculino , Humanos , Idoso , Abscesso Epidural/complicações , Abscesso Epidural/cirurgia , Abscesso Epidural/diagnóstico , Coluna Vertebral/cirurgia , Antibacterianos/uso terapêutico , Osteotomia , Drenagem
3.
Cureus ; 15(3): e36497, 2023 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-37090396

RESUMO

Currarino syndrome or Currarino triad is a complex condition consisting of congenital anomalies. The triad consists of anterior sacral mass (meningocele, teratoma or dermoid/epidermoid cyst), sacral bone defect (hypoplasia, agenesis ), anorectal malformation/congenital anorectal stenosis. This condition is named after Dr Guido Currarino, an Italian-American paediatric radiologist, who first described it in 1975. This needs a multidisciplinary treatment approach. We describe a case of successfully managed young adult with Currarino syndrome. The latest artificial intelligence tool, Chat Generative Pre-Trained Transformer (ChatGPT), helped to write this case report.

4.
Chaos ; 25(7): 075408, 2015 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-26232981

RESUMO

The discovery of the Horton laws for hydrologic variables has greatly lagged behind geomorphology, which began with Robert Horton in 1945. We define the classical and the generalized Horton laws for peak flows in rainfall-runoff events, which link self-similarity in network geomorphology with river basin hydrology. Both the Horton laws are tested in the Iowa River basin in eastern Iowa that drains an area of approximately 32 400 km(2) before it joins the Mississippi River. The US Geological Survey continuously monitors the basin through 34 stream gauging stations. We select 51 rainfall-runoff events for carrying out the tests. Our findings support the existence of the classical and the generalized Horton laws for peak flows, which may be considered as a new hydrologic discovery. Three different methods are illustrated for estimating the Horton peak-flow ratio due to small sample size issues in peak flow data. We illustrate an application of the Horton laws for diagnosing parameterizations in a physical rainfall-runoff model. The ideas and developments presented here offer exciting new directions for hydrologic research and education.

6.
Indian Heart J ; 65(5): 561-5, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24206880

RESUMO

BACKGROUND: The anatomical variability in patients with anomalous pulmonary venous connection to superior vena cava presents a surgical challenge. The problem is further compounded by the common occurrence of postoperative complications like arrhythmias and obstruction of the superior vena cava or pulmonary veins. We present our experience of managing this subset using the two patch and Warden's techniques. PATIENTS AND METHODS: Between June 2011 and September 2012, 7 patients with APVC to the SVC were operated in our institute. After delineating the anatomy, five of them had a two patch repair and two were managed with Warden's technique. RESULTS: There was no in-hospital mortality or early mortality over a mean follow-up of 9.66 ± 3.88 months (range 6-15 months). All the patients on follow-up had unobstructed pulmonary venous and SVC drainage on echocardiography and all of them were in normal sinus rhythm. CONCLUSIONS: Anomalous pulmonary venous connection to superior vena cava is a challenging subset of patients in whom the surgical management needs to be individualized. The detailed anatomy must be delineated using echocardiography with or without CT angiography before deciding the surgical plan. This entity can be repaired with excellent immediate and early results. However, these patients must be closely followed up for complications like systemic and pulmonary venous obstruction and sinus node dysfunction.


Assuntos
Procedimentos Cirúrgicos Cardíacos/métodos , Veias Pulmonares/cirurgia , Malformações Vasculares/cirurgia , Procedimentos Cirúrgicos Vasculares/métodos , Veia Cava Superior/cirurgia , Adolescente , Angiografia/métodos , Cateterismo Cardíaco/métodos , Criança , Pré-Escolar , Ecocardiografia Doppler/métodos , Feminino , Seguimentos , Humanos , Índia , Lactente , Masculino , Veias Pulmonares/anormalidades , Estudos Retrospectivos , Medição de Risco , Estudos de Amostragem , Esternotomia/métodos , Fatores de Tempo , Tomografia Computadorizada por Raios X/métodos , Resultado do Tratamento , Malformações Vasculares/diagnóstico , Veia Cava Superior/anormalidades , Adulto Jovem
7.
J Card Surg ; 28(4): 433-5, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23627424

RESUMO

Interrupted aortic arch is a rare congenital malformation. We describe the case of an interrupted aortic arch with a bicuspid aortic valve and severe aortic stenosis. The patient underwent a single-stage aortic valve replacement (AVR) and ventral aorta repair through a median sternotomy-laparotomy.


Assuntos
Aorta Torácica/anormalidades , Aorta Torácica/cirurgia , Valva Aórtica/anormalidades , Valva Aórtica/cirurgia , Implante de Prótese de Valva Cardíaca/métodos , Procedimentos Cirúrgicos Vasculares/métodos , Adolescente , Humanos , Laparotomia , Masculino , Esternotomia , Resultado do Tratamento
8.
Biotechnol Appl Biochem ; 60(2): 162-9, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23586605

RESUMO

Polymethyl methacrylate (PMMA) nanofiber membrane (NFM) was synthesized by an electrospinning technique. These membranes were utilized as a support for immobilization of xylanase enzyme to study its pH stability, thermal stability, and reusability. The morphology of aligned NFM was studied by optical microscopy and scanning electron microscopy. The PMMA NFM was functionalized with phenylenediamine and activated with glutaraldehyde to yield an aldehyde group on its surface for covalent immobilization of xylanase. The Fourier transform infrared analysis of the covalently immobilized xylanase confirmed that the enzyme was immobilized on PMMA NFM via amide linkages. The immobilization efficiency of covalently bound xylanase was found experimentally to be 90%. A forward shift in pH optima from 6.0-7.0 (soluble enzyme) to 7.0-9.0 (immobilized enzyme) was observed after xylanase immobilization. The pH and temperature stability of xylanase were enhanced upon its covalent immobilization. The immobilized enzyme was active on repeated use and retained ∼80% of its initial activity after 11 reaction cycles. The improved thermal and operational stability of the covalently immobilized enzyme on PMMA NFM might be advantageous for industrial applications.


Assuntos
Bacillus/enzimologia , Endo-1,4-beta-Xilanases/metabolismo , Membranas Artificiais , Nanofibras , Polimetil Metacrilato/química , Microscopia Eletrônica de Varredura
9.
J Proteome Res ; 11(6): 3259-68, 2012 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-22533410

RESUMO

A synthetic coumarin, N,N,N-triethyl-11-(4-methyl-2-oxo-2H-chromen-7-yloxy)-11-oxoundecan-1-aminium bromide (SCD-1), having potent activity against pathogenic Aspergilli (MIC90 15.62 µg/mL), was investigated to identify its molecular targets in the pathogen. The proteome of Aspergillus fumigatus was developed after treatment with sublethal doses of compound and analyzed. The results demonstrated 143 differentially expressed proteins on treatment with SCD-1. The expression of four proteins, namely cell division control protein, ubiquitin-like activating enzyme, vacuolar ATP synthase catalytic subunit A, and UTP-glucose-1-phosphate uridylyltransferase of A. fumigatus, was completely inhibited, whereas there were 13 newly expressed and 96 overexpressed proteins, mainly belonging to stress pathway. The treatment of A. fumigatus with SCD-1 also led to attenuation of proteins involved in cell replication and other important biosynthetic processes, including riboflavin biosynthesis, which has been pathogen-specific. In addition to key enzymatic players and antioxidants, nine hypothetical proteins were also identified, seven of which have been novel, being described for the first time. As no cellular functions have yet been described for these hypothetical proteins, their alteration in response to SCD-1 provides significant information about their putative roles in pathogen defense.


Assuntos
Antifúngicos/farmacologia , Cumarínicos/farmacologia , Proteínas Fúngicas/metabolismo , Compostos de Amônio Quaternário/farmacologia , Aspergilose/tratamento farmacológico , Aspergillus fumigatus/efeitos dos fármacos , Aspergillus fumigatus/metabolismo , Humanos , Redes e Vias Metabólicas/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Terapia de Alvo Molecular , Mapas de Interação de Proteínas , Transporte Proteico/efeitos dos fármacos , Proteoma/metabolismo , Proteômica
10.
Proteome Sci ; 9: 5, 2011 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-21294899

RESUMO

BACKGROUND: Hepatitis E is endemic to resource-poor regions, where it manifests as sporadic cases and large waterborne outbreaks. The disease severity ranges from acute self-limited hepatitis with low mortality to fulminant hepatic failure with high mortality. It is believed that the host response plays an important role in determining the progression and outcome of this disease. We profiled the plasma peptidome from hepatitis E patients to discover suitable biomarkers and understand disease pathogenesis. RESULTS: The peptidome (< 10 kDa) fraction of plasma was enriched and analyzed by mass spectrometry. A comparative analysis of the peptide pattern of hepatitis E patients versus healthy controls was performed using ClinPro Tools. We generated a peptide profile that could be used for selective identification of hepatitis E cases. We have identified five potential biomarker peaks with m/z values of 9288.6, 7763.6, 4961.5, 1060.572 and 2365.139 that can be used to reliably differentiate between hepatitis E patients and controls with areas under the receiver operating characteristic curve (AUROC) values of 1.00, 0.954, 0.989, 0.960 and 0.829 respectively. A number of proteins involved in innate immunity were identified to be differentially present in the plasma of patients compared to healthy controls. CONCLUSIONS: Besides the utility of this approach for biomarker discovery, identification of changes in endogenous peptides in hepatitis E patient plasma has increased our understanding of disease pathogenesis. We have identified peptides in plasma that can reliably distinguish hepatitis E patients from healthy controls. Results from this and an earlier proteomics study are discussed.

11.
Cardiol Young ; 21(2): 121-9, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21205419

RESUMO

BACKGROUND AND AIM: Congenital tricuspid regurgitation is an extremely rare condition. The morphologic heterogeneity makes it difficult to derive any conclusions regarding the best strategy for management of this condition. METHODS: We analysed the published literature on "congenital tricuspid regurgitation" using MEDLINE. In addition, the reference sections of all relevant articles were searched to identify additional cases. Studies published till June 2009 are included. RESULTS: As far as we could establish, there were 123 cases of congenital tricuspid regurgitation. Of these, 63 were documented during surgery, 38 during autopsy, and 22 were diagnosed by echocardiography or cardiac catheterisation. The mean age was 22.57 years, with a standard deviation of 23.42 years, and the age ranged from 1 day to 80 years, with a median of 16 years. There was a male predominance, with a male-to-female ratio of approximately 3:2. CONCLUSION: Congenital tricuspid regurgitation is an uncommon clinical entity with wide anatomical variations. The severity of disease dictates the presentation in infancy, childhood, or adulthood. Tricuspid valve repair is the ideal treatment whenever feasible, especially in children. We propose a new classification for congenital tricuspid regurgitation, which not only includes the anatomical variations, but can also help the surgeon in deciding on the best strategy for management.


Assuntos
Insuficiência da Valva Tricúspide , Valva Tricúspide/anormalidades , Humanos , Prevalência , Insuficiência da Valva Tricúspide/classificação , Insuficiência da Valva Tricúspide/congênito , Insuficiência da Valva Tricúspide/epidemiologia , Estados Unidos/epidemiologia
12.
J Proteome Res ; 9(11): 5517-29, 2010 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-20828163

RESUMO

The secreted proteomes of a three week old culture of an Indian (190/96) and a German (DAYA) Aspergillus fumigatus isolate were investigated for reactivity with IgG and/or IgE antibodies derived from pooled allergic broncho-pulmonary aspergillosis (ABPA) patients' sera. Two dimensional Western blotting followed by mass spectrometric analysis of the reactive protein spots revealed 35 proteins from the two A. fumigatus strains. There were seven known A. fumigatus allergens among them (Asp f1-4, Asp f9, Asp f10, and Asp f13/15), whereas three proteins displaying significant sequence similarity to known fungal allergens have been assigned as predicted allergens (Dipeptidyl-peptidase-V precursor, Nuclear transport factor 2, and Malate dehydrogenase, NAD-dependent). Eight IgG and IgE reactive proteins were common in both strains; however, 12 proteins specifically reacted in 190/96 and 15 in DAYA. Further testing with sera of 5 individual ABPA patients demonstrated that 12 out of 20 immunoreactive proteins of 190/96 strain of A. fumigatus had consistent reactivity with IgE. Seven of these proteins reacted with IgG also. The 25 of 35 identified proteins are novel with respect to immuno-reactivity with ABPA patients' sera and could form a panel of molecules to improve the currently existing less-sensitive diagnostic methods. Through expressing recombinantly, these proteins may also serve as a tool in desensibilization strategies.


Assuntos
Alérgenos/sangue , Antígenos de Fungos/análise , Aspergilose Broncopulmonar Alérgica/imunologia , Aspergillus fumigatus/imunologia , Proteínas Fúngicas/imunologia , Proteoma/imunologia , Anticorpos Antifúngicos/sangue , Humanos , Imunoglobulina E/sangue , Imunoglobulina G/sangue , Proteoma/metabolismo
13.
J Bronchology Interv Pulmonol ; 17(3): 266-8, 2010 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23168899

RESUMO

Tracheobronchial defects may occur intraoperatively because of surgical trauma after resection of thoracic tumors. The repair of large, circumferential tracheobronchial defects with tissue loss may pose a major challenge. In an effort to solve this problem, different techniques have been used with little success. Attempts with foreign materials, nonviable tissues, autogenous noncartilaginous tissues, tissue engineering, and allotransplantation have all been associated with disappointing or suboptimal results. In each category, biologic problems are noted. Hence, the reconstruction and substitution of large, circumferential tracheobronchial defects has so far remained an unsolved surgical dilemma. We report a unique case in which an airway defect in the bronchus, made inadvertently intraoperatively, was repaired using autologous bronchial cartilage obtained from the resected specimen. In the literature, autologous bronchial cartilage has never been used before in reconstructing a large tracheobronchial defect.

14.
Proteome Sci ; 7: 39, 2009 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-19860894

RESUMO

BACKGROUND: Hepatitis E, caused by the hepatitis E virus (HEV), is endemic to developing countries where it manifests as waterborne outbreaks and sporadic cases. Though generally self-limited with a low mortality rate, some cases progress to fulminant hepatic failure (FHF) with high mortality. With no identified predictive or diagnostic markers, the events leading to disease exacerbation are not known. Our aim is to use proteomic tools to identify biomarkers of acute and fulminant hepatitis E. RESULTS: We analyzed proteins in the plasma and urine of hepatitis E patients and healthy controls by two-dimensional Differential Imaging Gel Electrophoresis (DIGE) and mass spectrometry, and identified over 30 proteins to be differentially expressed during acute hepatitis E. The levels of one plasma protein, transthyretin, and one urine protein, alpha-1-microglobulin (alpha1m), were then quantitated by enzyme immunoassay (EIA) in clinical samples from a larger group of patients and controls. The results showed decreased plasma transthyretin levels (p < 0.005) and increased urine alpha1m levels (p < 0.001) in acute hepatitis E patients, compared to healthy controls. Preliminary results also showed lower urine zinc alpha glycoprotein levels in fulminant hepatitis E compared to acute disease; this remains to be confirmed with more fulminant cases. CONCLUSION: Our results demonstrate the utility of characterizing plasma and urine proteomes for signatures of the host response to HEV infection. We predict that plasma transthyretin and urine alpha1m could be reliable biomarkers of acute hepatitis E. Besides the utility of this approach to biomarker discovery, proteome-level changes in human biofluids would also guide towards a better understanding of host-virus interaction and disease.

15.
World J Gastroenterol ; 14(23): 3693-709, 2008 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-18595136

RESUMO

AIM: To evaluate the protective effect of 2'-p-hydroxybenzoylmussaenosidic acid [negundoside (NG), against carbon tetrachloride (CCl(4))-induced toxicity in HuH-7 cells. METHODS: CCl(4) is a well characterized hepatotoxin, and inducer of cytochrome P450 2E1 (CYP2E1)-mediated oxidative stress. In addition, lipid peroxidation and accumulation of intracellular calcium are important steps in the pathway involved in CCl(4) toxicity. Liver cells (HuH-7) were treated with CCl(4), and the mechanism of the cytoprotective effect of NG was assessed. Silymarin, a known hepatoprotective drug, was used as control. RESULTS: NG protected HuH-7 cells against CCl(4) toxicity and loss of viability without modulating CYP2E1 activity. Prevention of CCl(4) toxicity was associated with a reduction in oxidative damage as reflected by decreased generation of reactive oxygen species (ROS), a decrease in lipid peroxidation and accumulation of intracellular Ca(2+) levels and maintenance of intracellular glutathione homeostasis. Decreased mitochondrial membrane potential (MMP), induction of caspases mediated DNA fragmentation and cell cycle arrest, as a result of CCl(4) treatment, were also blocked by NG. The protection afforded by NG seemed to be mediated by activation of cyclic adenosine monophosphate (cAMP) synthesis and inhibition of phospholipases (cPLA2). CONCLUSION: NG exerts a protective effect on CYP2E1-dependent CCl(4) toxicity via inhibition of lipid peroxidation, followed by an improved intracellular calcium homeostasis and inhibition of Ca(2+)-dependent proteases.


Assuntos
Antioxidantes/farmacologia , Cálcio/metabolismo , Tetracloreto de Carbono/toxicidade , Hepatócitos/efeitos dos fármacos , Iridoides/farmacologia , Vitex , Antioxidantes/isolamento & purificação , Apoptose/efeitos dos fármacos , Caspase 3/metabolismo , Inibidores de Caspase , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , AMP Cíclico/metabolismo , Citocromo P-450 CYP2E1/metabolismo , Citocromos c/metabolismo , Citoproteção , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Glutationa/metabolismo , Hepatócitos/enzimologia , Hepatócitos/metabolismo , Hepatócitos/patologia , Humanos , Glicosídeos Iridoides , Iridoides/isolamento & purificação , Peroxidação de Lipídeos/efeitos dos fármacos , Potencial da Membrana Mitocondrial/efeitos dos fármacos , Mitocôndrias Hepáticas/efeitos dos fármacos , Mitocôndrias Hepáticas/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Fosfolipases A2 Citosólicas/antagonistas & inibidores , Fosfolipases A2 Citosólicas/metabolismo , Folhas de Planta , Espécies Reativas de Oxigênio/metabolismo , Silimarina/farmacologia , Vitex/química
16.
J Paediatr Child Health ; 43(7-8): 571-2, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17635690

RESUMO

Pyridoxine dependency is a rare autosomal-recessive disorder causing intractable seizures in neonates and infants. Life-long therapy with pyridoxine is required for prevention of seizure recurrence and for an optimum intellectual outcome. With the availability of newer biochemical confirmatory tests, the conventional pyridoxine-withdrawal test is being used less frequently for diagnosis. This report describes an infant whose parents were non-compliant with pyridoxine therapy and proposes that pyridoxine-withdrawal test may be useful in demonstrating to parents the need for life-long pyridoxine therapy, thereby reducing non-compliance.


Assuntos
Piridoxina/uso terapêutico , Convulsões/tratamento farmacológico , Humanos , Índia , Lactente , Masculino , Cooperação do Paciente , Piridoxina/deficiência , Convulsões/congênito , Resultado do Tratamento
17.
Viral Immunol ; 20(1): 56-65, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17425421

RESUMO

Hepatitis E virus (HEV) causes acute viral hepatitis and is endemic in the developing world. Few data are available on cellular immune responses in HEV infection. Using flow cytometry, we studied the frequencies of peripheral blood CD4(+) /CD8(+) T cells secreting interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-4 in 21 patients with acute hepatitis E and 18 healthy controls, after stimulation with the HEV capsid (ORF2) protein. Cytokine levels in serum specimens and culture supernatants of ORF2-stimulated peripheral blood mononuclear cells (PBMCs) were estimated in enzyme-linked immunosorbent assays. In addition, cytokine mRNA transcripts were measured in PBMCs by reverse transcription-polymerase chain reaction. In patients with acute hepatitis E, although the total CD4(+) population was expanded, the proportions of CD4(+)/CD69(+) and CD8(+) /CD69(+) cells producing IFN-gamma, TNF-alpha, and IL-4 in response to HEV ORF2 stimulation were unchanged. However, IFN-gamma levels in the supernatants and IFN-gamma mRNA transcripts in cells were elevated in ORF2-stimulated PBMCs in acute hepatitis E; levels of IL-2 or TNF-alpha were unchanged. Our findings suggest that CD4(+) IFN-gamma-secreting cells, which do not belong either to the helper T cell type 1 or type 2 phenotype, as is the case with natural killer T cells, may be involved in the pathogenesis of hepatitis E. Further, the limited immune reactivity we detected in peripheral blood cells may be related to the sequestration of immune events to the intrahepatic compartment, which is the major disease site.


Assuntos
Hepatite E/imunologia , Proteínas Virais/imunologia , Doença Aguda , Citocinas/biossíntese , Citocinas/sangue , Citocinas/genética , Feminino , Humanos , Ionomicina/farmacologia , Masculino , RNA Mensageiro/análise , Linfócitos T/imunologia , Acetato de Tetradecanoilforbol/farmacologia
18.
Phys Rev E Stat Nonlin Soft Matter Phys ; 68(1 Pt 2): 016123, 2003 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-12935216

RESUMO

We examine the appearance of power-law behavior in rooted tree graphs in the context of river networks. It has long been observed that the tails of statistical distributions of upstream areas in river networks, measured above every link, obey a power-law relationship over a range of scales. We examine this behavior by considering a subset of all links, defined as those links which drain complete Strahler basins, where the Strahler order defines a discrete measure of scale, for self-similar networks with both deterministic and random topologies. We find an excellent power-law structure in the tail probabilities for complete Strahler basin areas, over many ranges of scale. We show analytically that the tail probabilities converge to a power law under the assumptions of (1) simple scaling of the distributions of complete Strahler basin areas and (2) application of Horton's law of stream numbers. The convergence to a power law does not occur for all underlying distributions, but for a large class of statistical distributions which have specific limiting properties. For example, underlying distributions which are exponential and gamma distributed, while not power-law scaling, produce power laws in the tail probabilities when rescaled and sampled according to Horton's law of stream numbers. The power-law exponent is given by the expression phi=ln(R(b))/ln(R(A)), where R(b) is the bifurcation ratio and R(A) is the Horton area ratio. It is commonly observed that R(b) approximately equal R(A) in many river basins, implying that the tail probability exponent for complete Strahler basins is close to 1.0.

19.
Philos Trans R Soc Lond B Biol Sci ; 357(1421): 619-26, 2002 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-12079523

RESUMO

Underlying the diversity of life and the complexity of ecology is order that reflects the operation of fundamental physical and biological processes. Power laws describe empirical scaling relationships that are emergent quantitative features of biodiversity. These features are patterns of structure or dynamics that are self-similar or fractal-like over many orders of magnitude. Power laws allow extrapolation and prediction over a wide range of scales. Some appear to be universal, occurring in virtually all taxa of organisms and types of environments. They offer clues to underlying mechanisms that powerfully constrain biodiversity. We describe recent progress and future prospects for understanding the mechanisms that generate these power laws, and for explaining the diversity of species and complexity of ecosystems in terms of fundamental principles of physical and biological science.


Assuntos
Ecossistema , Fractais , Modelos Teóricos , Natureza
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