bluuebunny/crossref_metadata_2025 huggingface dataset:
MDR1 Haplotypes Modify BEN Disease Risk: A Study in Bulgarian Patients with Balkan Endemic Nephropathy Compared to Healthy Controls
Authors: Atanasova S. , von Ahsen N. , Dimitrov T. , Armstrong V. , Oellerich M. , Toncheva D.
Published: January 2004

Background: Balkan endemic nephropathy (BEN) is a slow progressive nephropathy with frequent occurrence of uroepithelial tumors in the upper urinary tract. Genetic factors involved in xenobiotic detoxification mechanisms may cause genetic predisposition to BEN and influence the risk for this disease. Polymorphic MDR1 variants with decreased P-glycoprotein (P-gp) activity modulate the risk for renal neoplasm. We have therefore investigated the impact of MDR1 polymorphisms on BEN manifestation. Methods: The constitutional genotype frequencies of two SNPs (C3435T and G2677T) in the MDR1 gene in 112 healthy control subjects were investigated and compared with those of 96 patients with BEN. Identification of the SNPs was done with rapid cycle real-time PCR and melting curve analysis with allele-specific probes. Results: The frequency of mutant alleles was comparable in both groups. Significant differences were revealed when the MDR1 haplotypes were analyzed. Individuals with a predicted haplotype 12 (2677G/3435T) were less frequent in BEN cases (frequency 7.3%) than in controls (16.1%, p = 0.006). We found that carriers of the haplotype 12 had a decreased risk for BEN (OR = 0.411; 0.21–0.78). Conclusions: The data suggest that haplotype 12 is protective against BEN. There is no clear molecular explanation of the MDR1 haplotype effects on the protein activity, which can explain the modified effect of the haplotype 12 on BEN risk.
Paradigms for Mechanical Signal Transduction in the Intestinal Epithelium
Authors: Basson Marc D.
Published: January 2004

Diverse physical forces including deformation or strain, pressure, and shear stress affect the intestinal mucosa during normal function, and mucosal biology is altered in pathological states in which these forces alter. Taken together with evidence in other tissues and cell types that physical forces can affect cell biology, this has led to the hypothesis that repetitively applied physical forces can initiate intracellular signals that alter intestinal epithelial proliferation and phenotype. This review outlines the nature of such forces and summarizes in vivo and in vitro evidence in support of the paradigm that repetitive force is trophic for the intestinal mucosa via a complex cascade of intracellular signals.
Lung Microvascular Adaptation in Infants with Chronic Lung Disease
Authors: Thibeault Donald W. , Mabry Sherry M. , Norberg Michael , Truog William E. , Ekekezie Ikechukwu I.
Published: January 2004

Microvascular development is critical for normal lung maturation. The aims of this study were (1) to quantitatively and qualitatively assess lung microvascular growth in the human fetus, from 22 to 40 weeks’ gestation, and (2) to compare development in these infants to those with mild, moderate and severe chronic lung disease (CLD). Using 1- and 4-µm thick sections and electron microscopy, lungs were morphometrically assessed for surface density of distal air spaces; volume density of parenchymal vessels having an air-blood barrier (ABB); percent of distal air space wall having an ABB, and capillary loading, defined as ABB/mm2 of epithelial surface area. The percent of vessels with ABB increased in controls during development in parallel with increasing lung parenchyma. Infants with severe CLD had fewer ABBs and less capillary loading than controls up to 34 weeks’ post-conceptional age (PCA), but by 36–40 weeks, showed catch-up growth. Microvasculature vessel diameter, septal thickness, and air sac diameter at 36–40 weeks’ PCA were increased with severe CLD, and vessels were more distant from the air surface. We conclude that infants with severe CLD have both stunted secondary septation and microvascular development, but over time, the primary septal wall adapts by thinning and increasing the number of ABBs, thereby taking on the function of secondary septa.
Correlation between Plasma and Urine Phenylalanine Concentrations
Authors: Boulos Manal , Boulat Olivier , van Melle Guy , Guignard Jean-Pierre , Matthieu Jean-Marie
Published: January 2004

In this pilot study, we show that plasma phenylalanine concentration can be predicted from urine concentration if the age of the patient is taken into consideration. This observation could open the way to a new monitoring of phenylketonuric patients in which painful frequent blood sampling, mandatory to adapt the low phenylalanine diet, could be mostly replaced by urinalysis. Compliance to treatment would be improved and hence also the ultimate mental development. Since this study was based on a small number of patients, validation of the model in a large multicentric survey is needed before it can be recommended.
Relationship of Pregnancy-Associated Plasma Protein-A to Renal Function and Dialysis Modalities
Authors: Fialová L. , Kalousová M. , Soukupová J. , Sulková S. , Merta M. , Jelínková E. , Hořejší M. , Šrámek P. , Malbohan I. , Mikulíková L. , Tesař V. , Zima T.
Published: January 2004

Background: The aim of the study was to determine pregnancy-associated plasma protein-A (PAPP-A), which was recently described as a new marker of cardiovascular events, in patients with chronic renal insufficiency/failure and to find out its relationship to renal function and to prominent markers of oxidative stress (advanced oxidation protein products – AOPP) and inflammation (C-reactive protein – CRP). Methods: The studied group consisted of 36 chronic hemodialysis patients (HD), 10 patients treated with continuous ambulatory peritoneal dialysis (CAPD) and 38 patients with chronic renal insufficiency (CHRI) not yet dialyzed. PAPP-A was measured by Time Resolved Amplified Cryptate Emission technology. Determination of AOPP is based on a spectrophotometric method. Results: PAPP-A levels are statistically significantly elevated in the both groups of dialyzed patients in comparison with healthy subjects (27.0 ± 16.5 mIU/l in HD and 14.07 ± 6.73 mIU/l in CAPD vs. 8.22 ± 2.7 mIU/l in the control group, p < 0.0001 and p < 0.001, respectively, p < 0.05 HD vs. CAPD). The mean serum PAPP-A levels in the CHRI patients not yet dialyzed were not significantly higher in comparison with the control group (9.72 ±4.44 vs. 8.22 ± 2.7 mIU/l, n.s.). In the CHRI not dialyzed patients, we found a significant positive correlation between serum creatinine and PAPP-A levels (r = 0.68, p < 0.05). In comparison with controls, AOPP and CRP levels were significantly higher in HD patients [AOPP 155.0 ± 37.9 µmol/l, p < 0.0001 vs. controls, CRP 10.0 (4.6– 26.9) mg/l (median, interquartile range), p < 0.0001 vs. controls], CAPD patients [AOPP 118.5 ± 25.8 µmol/l, p < 0.0001 vs. controls, CRP 7.7 (2.0–18.8) mg/l, p < 0.01 vs. controls] and AOPP levels in chronic renal failure patients not yet dialyzed (98.5 ± 43.24 µmol/l, p < 0.01 vs. controls). The correlations between PAPP-A and AOPP (r = 0.49, p < 0.05) and PAPP-A and CRP (r = 0.48, p < 0.05) serum concentration were statistically significant in HD patients. In CAPD patients, neither a correlation between PAPP-A and AOPP nor a correlation between PAPP-A and CRP were found. Conclusion: We can conclude that serum PAPP-A levels sensitively reflect the changes in renal function, depend on dialysis modality, and may represent a novel marker associated with inflammation and oxidative stress in chronic renal failure patients.
NOPPAIN: A Nursing Assistant- Administered Pain Assessment Instrument for Use in Dementia
Authors: Snow A. Lynn , Weber Jan B. , O’Malley Kimberly J. , Cody Marisue , Beck Cornelia , Bruera Eduardo , Ashton Carol , Kunik Mark E.
Published: January 2004

The Non-Communicative Patient’s Pain Assessment Instrument (NOPPAIN) is a nursing assistant-administered instrument for assessing pain behaviors in patients with dementia. This study investigated the validity of the NOPPAIN. Twenty-one nursing assistants (NAs) with no prior training in using the NOPPAIN watched six videos, each portraying a bed-bound patient with severe dementia receiving personal care from a nursing assistant and responding with a different level of pain intensity. The NAs completed a NOPPAIN rating for each video. The NAs were also presented with each possible pair of videos and asked to identify the video showing the most pain. Results indicated the NAs were quite accurate in their ratings of the videos, providing excellent preliminary evidence on the use of the NOPPAIN for detecting pain in nursing home patients with dementia.
The First Placebo-Controlled Trial of a Special Butterbur Root Extract for the Prevention of Migraine: Reanalysis of Efficacy Criteria
Authors: Diener H.C. , Rahlfs V.W. , Danesch U.
Published: January 2004

This is an independent reanalysis of a randomised, placebo-controlled parallel-group study on the efficacy and tolerability of a special butterbur root extract (Petadolex®) for the prophylaxis of migraine. The original protocol and analysis had a number of major shortcomings. In order to follow regulatory requirements, an independent reanalysis of the original data was performed. Following a 4-week baseline phase, 33 patients were randomised to treatment with two capsules 25 mg butterbur twice a day and 27 to placebo. The mean attack frequency per month decreased from 3.4 at baseline to 1.8 after 3 months (p = 0.0024) in the verum group and from 2.9 to 2.6 in the placebo group (n.s.). The responder rate (improvement of migraine frequency ≧50%) was 45% in the verum group and 15% in the placebo group. Butterbur was well tolerated. This small trial indicates that butterbur may be effective in the prophylaxis of migraine.
Diffusion-Weighted MRI and 99mTc-HMPAO SPECT in Delayed Relapsing Type of Carbon Monoxide Poisoning: Evidence of Delayed Cytotoxic Edema
Authors: Chu Kon , Jung Keun-Hwa , Kim Han-Joon , Jeong Sang-Wuk , Kang Dong-Wha , Roh Jae-Kyu
Published: January 2004

Background: Carbon monoxide (CO) is a common cause of poisoning, and its sequelae include a progressive (25%) and a delayed relapsing form (75%). We report the diffusion-weighted MRI (DWI) findings in the delayed relapsing form of CO poisoning and characterize the types of edema. Methods: From November 1, 2000 to June 1, 2003, 5 consecutive patients (2 men, 3 women, range of age: 54–67 years), who had the delayed relapsing type of CO poisoning, underwent DWI, conventional MRI, MR angiography and SPECT. CO poisoning was diagnosed by the presence of a typical clinical history, an abnormally increased level of serum carboxyhemoglobin and MRI findings. Apparent diffusion coefficient (ADC) values were measured in all of the abnormal lesions with visual inspection of DWI and T2-weighted echo-planar imaging. Results: DWI showed high signal intensities in bilateral periventricular white matter, in the splenium of the corpus callosum, in internal capsules, and brainstem showing moderately decreased ADC values. In the globus pallidus, the ADC values were rather increased with low signal intensities on DWI. Brain SPECT showed decreased perfusion in bilateral white matter and some parts of the cerebral cortex, which correlated well with the DWI findings. Conclusions: We suggest that prominent, symmetric restricted diffusion can occur in periventricular white matter, brainstem, and corpus callosum after the delayed relapsing type of CO poisoning. Delayed cytotoxic edema can occur in this setting, which provides a new guidance for the pathogenesis of CO poisoning and the differential diagnosis of white matter diseases.
Role of Endothelin-1 in Blood Pressure Regulation in a Rat Model of Visceral Obesity and Hypertension
Authors: da Silva Alexandre A. , Kuo Jay J. , Tallam Lakshmi S. , Hall John E.
Published: January 2004

Endothelial dysfunction has been suggested to play an important role in the development of obesity-induced hypertension. Because endothelin release increases in response to endothelial damage, we examined whether endothelin-1 contributes to increased arterial pressure in a model of visceral obesity produced by feeding Sprague-Dawley rats a high-fat (HF) diet (40% fat w/w, n=6) for 12 months. Arterial and venous catheters were implanted for measurement of mean arterial pressure (MAP) and heart rate (HR) 24 hours per day and intravenous infusions. After a 5-day control period, rats were infused with the selective endothelin-1 type A receptor (ET-A) blocker ABT-627 (2.5 mg/kg per day, IV) for 9 days, followed by a recovery period. Rats fed a standard chow (normal fat, or NF, group: n=6) for 12 months were also infused with ET-A blocker and were used as controls. Compared with NF rats, HF rats had higher MAP (113±4 versus 98±2 mm Hg), increased visceral fat (18.7±2.0 versus 10.8±1.4 g), and 3.2-fold increase in plasma leptin despite similar total body weight gain. Long-term ET-A blockade markedly reduced MAP in HF (−14±3 mm Hg) and NF (−14±2 mm Hg), but it had no effect on HR, GFR, or PRA. These results indicate that a long-term HF diet may cause visceral obesity and increased MAP, even in the absence of major changes in total body weight. Endothelin-1 appears to play an important role in the maintenance of arterial pressure in rats fed HF and NF diets, but it does not appear to contribute to increased MAP in this model of diet-induced hypertension.
Autosomal-Dominant Hypertension With Type E Brachydactyly Is Caused by Rearrangement on the Short Arm of Chromosome 12
Authors: Bähring Sylvia , Rauch Anita , Toka Okan , Schroeder Christoph , Hesse Christiane , Siedler Heike , Fesüs Gabor , Haefeli Walter E. , Busjahn Andreas , Aydin Atakan , Neuenfeld Yvette , Mühl Astrid , Toka Hakan R. , Gollasch Maik , Jordan Jens , Luft Friedrich C.
Published: January 2004

We are studying a Turkish family with autosomal-dominant hypertension and brachydactyly; affected persons die of stroke before 50 years of age. With interphase fluorescence in situ hybridization, we found a chromosome 12p deletion, reinsertion, and inversion in affected persons. This finding suggested that the hypertension could be caused by one or more of 3 genes, the ATP-dependent potassium channel Kir6.1, its regulator the sulfonyl urea receptor SUR2, and the phosphodiesterase PDE3A. We further studied 6 affected and 4 nonaffected persons. Buttocks biopsies were done, small vessels were tested on a myograph, and mRNA was extracted. We performed forearm blood flow studies with intrabrachial artery diazoxide, isoproterenol, and milrinone infusions. Systemic pharmacological testing was done with intravenous diazoxide, nitroprusside, and isoproterenol. PDE3A mRNA was high in vessels from 3 affected subjects, but not high in 3 others. The vessels responded similarly to forskolin, with or without glibenclamide, and to cromakalim. However, there was a suggestion that the dilatation after milrinone might be exaggerated. The forearm infusion studies showed no differences in the responses to diazoxide, isoproterenol, or milrinone. Systemically, affected persons showed a greater blood pressure response to diazoxide and nitroprusside, and a greater heart rate response to isoproterenol than nonaffected persons. The results shed doubt on Kir6.1 and SUR2. The differences in PDE3A expression and responses may be the result of hypertension rather than the cause. Although our 3 candidate genes are no longer likely, the rearrangement we describe greatly enhances the perspectives of this project.
Two Quantitative Trait Loci Affect ACE Activities in Mexican-Americans
Authors: Kammerer Candace M. , Gouin Nicolas , Samollow Paul B. , VandeBerg Jane F. , Hixson James E. , Cole Shelley A. , MacCluer Jean W. , Atwood Larry D.
Published: January 2004

Angiotensin-converting enzyme (ACE) activity is highly heritable and has been associated with cardiovascular disease. We are studying the effects of genes and environmental factors on hypertension and related phenotypes, such as ACE activity, in Mexican-American families. In the current study, we performed multipoint linkage analysis to search for quantitative trait loci (QTLs) that affect ACE activities on data from 793 individuals from 29 pedigrees from the San Antonio Family Heart Study. As expected, we obtained strong evidence (maximum log of the odds [LOD]=4.57, genomic
P
=0.003) that a QTL for ACE activity is located on chromosome 17 near the
ACE
structural locus. We subsequently performed linkage analyses conditional on the effect of this QTL and obtained strong evidence (LOD=3.34) for a second QTL on chromosome 4 near D4S1548. We next incorporated the
ACEIns/Del
genotypes in our analyses and removed the evidence for the chromosome 17 QTL (maximum LOD=0.60); however, we retained our evidence for the QTL on chromosome 4q. We conclude that the QTL on chromosome 17 is tightly linked to
ACE
and is in strong disequilibrium with the insertion/deletion polymorphism, which is consistent with other reports. We also have evidence that an additional QTL affects ACE activity. Identification of this additional QTL might lead to alternate means of prophylaxis.
Decreased Endothelium-Dependent NO-cGMP Vascular Relaxation and Hypertension in Growth-Restricted Rats on a High-Salt Diet
Authors: Payne Jason A. , Alexander Barbara T. , Khalil Raouf A.
Published: January 2004

Low birth weight caused by placental insufficiency increases the risk of hypertension in young adults, particularly while ingesting a high-salt diet; however, the vascular mechanisms involved are unclear. We tested whether intrauterine fetal growth restriction results in salt-sensitive offspring that exhibit impaired endothelium-dependent relaxation, enhanced vascular contraction, and hypertension during high-salt diet feeding. Male offspring of control pregnant rats and pregnant rats with reduced uterine perfusion pressure (intrauterine growth restricted [IUGR]) were fed either a normal-sodium (NS, 1%) or a high-sodium (HS, 8%) diet. Body weight was less in IUGR/NS and IUGR/HS than in NS and HS rats. Arterial pressure was greater in IUGR/NS (144±4 mm|Hg) than in NS (131±3 mm|Hg) rats and far greater in IUGR/HS (171±12 mm|Hg) than in HS (129±2 mm|Hg) rats. In isolated, endothelium-intact aortic strips, phenylephrine (Phe, 10
−5
mol/L) caused an increase in active stress that was greater in IUGR/NS (13.9±0.9 N/m
2
) than in NS (8.5±0.6 N/m
2
) animals and far greater in IUGR/HS (18.2±1.2 N/m
2
) than in HS (9.4±0.8x10
4
N/m
2
) rats. Acetylcholine caused relaxation of the Phe-mediated contraction and induced vascular nitrite/nitrate production that was less in IUGR/NS than in NS animals and far less in IUGR/HS than in HS rats.
N
G
-nitro-
l
-arginine methyl ester, which inhibits nitric oxide (NO) synthase, or ODQ, which inhibits cGMP production in smooth muscle, inhibited acetylcholine relaxations and enhanced Phe contractions in NS and HS rats but not in IUGR/NS or IUGR/HS rats. Endothelium removal enhanced Phe-induced stress in NS and HS rats but not in IUGR/NS or IUGR/HS rats. Thus, endothelium-dependent relaxation via the NO-cGMP pathway is inhibited in systemic vessels of IUGR rats, particularly during intake of an HS diet. This might explain the increased vasoconstriction and arterial pressure in low-birth-weight offspring during ingestion of an HS diet.
Tempol Lowers Blood Pressure and Sympathetic Nerve Activity But Not Vascular O
2
−
in DOCA-Salt Rats
Authors: Xu Hui , Fink Gregory D. , Galligan James J.
Published: January 2004

This study tested the hypothesis that depressor responses caused by tempol are not associated with reductions in vascular O
2
−
levels in urethane-anesthetized deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We compared the effects of intravenous (IV) administration of tempol, apocynin, superoxide dismutase-polyethylene glycol (PEG-SOD), and SOD on mean arterial blood pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA). In DOCA-salt rats, tempol (30 to 300 μmol/kg) dose-dependently decreased RSNA, MAP, and HR. Tempol (300 μmol/kg) decreased MAP from 140±5 to 83±4 mm Hg (
P
<0.05). HR decreased from 435±15 to 390±12 bpm (
P
<0.05). RSNA was reduced by 54%±6% from baseline. However, in the same rats, tempol did not reduce dihydroethidium-induced fluorescent signals in the aorta and vena cava. Apocynin (200 μmol/kg) did not lower MAP (142±5 mm Hg versus 140±6 mm Hg) or HR (428±15 bpm versus 420±13 bpm) and apocynin did not potentiate depressor responses caused by tempol. PEG-SOD (10 000 U/kg, bolus or 5000 U/kg bolus followed by a 30-minutes infusion of 500 U/kg/min) or SOD (25 000 U/kg, bolus or 10 000 U/kg bolus followed by a 30-minutes infusion of 1000 U/kg per minute) did not alter MAP or HR. It is concluded that depressor responses and decreases in HR and RSNA caused by acute tempol treatment are caused by direct sympathetic nerve activity inhibition that is not accompanied by SOD-mimetic action in the aorta or vena cava.
Reduced Endothelial NO-cGMP–Mediated Vascular Relaxation and Hypertension in IL-6–Infused Pregnant Rats
Authors: Orshal Julia M. , Khalil Raouf A.
Published: January 2004

Placental ischemia during pregnancy is associated with increased plasma cytokines such as interleukin-6 (IL-6), which may contribute to increased vascular resistance and hypertension of pregnancy. We tested the hypothesis that an increase in plasma IL-6 during pregnancy is associated with impaired endothelium-dependent relaxation, enhanced vascular contraction, and hypertension. Systolic blood pressure was measured in virgin and pregnant Sprague-Dawley rats non-treated or infused with IL-6 (200 ng/kg per day for 5 days). Isometric contraction was measured in isolated aortic strips, and endothelial nitric oxide (NO) synthase (eNOS) was measured in aortic homogenate using Western blots. Blood pressure was greater in IL-6–infused (146±3) than in control pregnant rats (117±2 mm Hg). In endothelium-intact vascular strips, phenylephrine (Phe) caused greater increase in active stress in IL-6–infused (maximum: 10.6±0.6) than in control pregnant rats (maximum: 4.1±0.3×10
4
N/m
2
). Acetylcholine (ACh)-induced relaxation of Phe contraction and vascular eNOS protein and nitrite/nitrate production were less in IL-6–infused than in control pregnant rats.
N
ω
-nitro-
l
-arginine methyl ester (10
−4
mol/L), inhibitor of NOS, or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (10
−5
mol/L), inhibitor of cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced stress in control but not IL-6–infused pregnant rats. Endothelium removal enhanced Phe-induced stress in control but not in IL-6–infused pregnant rats. The blood pressure and vascular Phe-induced contraction, ACh relaxation, and eNOS protein were not different between control and IL-6–infused virgin rats. Thus, an endothelium-dependent NO-cGMP–mediated relaxation pathway is inhibited in systemic vessels of pregnant rats infused with IL-6. The results support a role for IL-6 as a possible mediator of the increased vascular resistance during hypertension of pregnancy.
Salt Intake, Endothelial Cell Signaling, and Progression of Kidney Disease
Authors: Sanders Paul W.
Published: January 2004

It has been known for decades that increased dietary intake of salt (NaCl) shortens the life span of rats in a dose-dependent fashion. This review focuses specifically on the recently described biological effect and consequences of increased salt ingestion on the endothelium through a mechanism that is independent of blood pressure. Changes in salt intake are recognized by endothelial cells in the vascular tree and glomeruli through a physical process that promotes a series of signaling events involved in transcriptional regulation of genes that include transforming growth factor-β1 (TGF-β1) and the endothelial isoform of nitric oxide synthase (NOS3). A balance is struck between TGF-β1 and NOS3 as salt intake varies and creates a negative feedback loop, because TGF-β1 increased expression of NOS3 and NO inhibited production of TGF-β1 in healthy rats. Changes in this feedback system have been observed in salt-sensitive hypertension and appear to impact end-organ damage, particularly the kidney. The data support an important benefit to reduction of salt intake in the setting of chronic kidney disease.
Diseño y validación de una escala de identidad regional
Authors: Zúñiga Claudia , Asún Rodrigo
Published: January 2004

El objetivo de la presente investigación fue diseñar y validar una escala tipo Likert para medir identidad regional. Para esto se aplicó un instrumento de 38 ítems a 249 estudiantes seleccionados en forma aleatoria de las universidades de la Región de la Araucanía, Chile. Utilizando el análisis de ítems, el cálculo de la fiabilidad del instrumento y análisis factoriales exploratorio y confirmatorio, se eliminó ítems hasta construir una escala final de 13 afirmaciones, las que presentaron altos niveles de discriminación, una adecuada fiabilidad, correlación significativa con criterios externos y una estructura interna coherente con la teoría, aunque no totalmente ajustada a los datos. Finalmente, a partir de esta información, se discute acerca de la estructura de la identidad regional.
Explorando el concepto de exclusión social: diferencias entre la psicología social euronorteamericana y la latinoamericana
Authors: Rodríguez-Kauth Angel
Published: January 2004

Se defiende que el concepto de “exclusión social” tiene un tratamiento diferencial por parte de los psicólogos sociales que se mueven en la órbita euronorteamericana, respecto a los que lo hacen en la latinoamericana. Mientras que los primeros lo consideran como sinónimo de prejuicio, diferenciación social o estereotipia, los segundos lo hacen a partir de consideraciones económicas, políticas y sociales, refiriéndolo básicamente a la pobreza estructural que se vive en estas comarcas.
Internet y desindividuación. Nuevas perspectivas sobre la desindividuación en la red: el modelo de identidad social de los fenómenos de desindividuación (SIDE)
Authors: Moral Félix , Canto Jesús , Gómez-Jacinto Luis
Published: January 2004

Los fenómenos de la desindividuación en psicología social han estado ligados a las situaciones de anonimato y grupo, especialmente en contextos de masa o muchedumbre. La implantación progresiva de las Nuevas Tecnologías en la sociedad está haciendo que, cada vez más, se faciliten un mayor número de servicios mediante el ordenador. Algunos de estos servicios virtuales (chat, correo electrónico, foros, etc.) posibilitan que sus usuarios participen de forma multitudinaria y anónima. Esto ha suscitado el interés por investigar éste nuevo contexto de interacción social, donde pueden ponerse de manifiesto conductas de desindividuación. Ante esta nueva realidad social marcada por la comunicación mediada por ordenador, se presenta el modelo de Identidad Social de los fenómenos de Desindividuación (SIDE), como un modelo explicativo (normativo) y alternativo a las teorías tradicionales de la desindividuación.
Modeling offset‐dependent reflectivity for time‐lapse monitoring of water‐flood production in thin‐layered reservoirs
Authors: Ellison Shelley J. , Imhof Matthias G. , Çoruh Cahit , Fuqua Alan D. , Henry Stephen C.
Published: January 2004

The objective of this case study is to predict whether 5 years of water‐flood production from a thinly layered Gulf of Mexico reservoir will change its seismic amplitude‐variation‐with‐offset (AVO) response in a detectable manner. Density and velocity profiles were computed from in situ wireline logs for 100% oil, gas, and brine saturations and for a 5‐year prediction that was based on a fluid‐flow and production simulation. Analytical AVO curves for simple half‐space models did not match AVO curves extracted from synthetic seismograms computed with a full‐waveform layer‐stack algorithm. Several different amplitude corrections were tried to reduce the AVO curves from the synthetic data to the analytical ones, but, ultimately, none was deemed satisfactory. Instead, AVO change attributes based on relative changes, polarity changes, or ratios were used. Attributes based on the change of AVO gradient were perceived to be most diagnostic of the water flood, but they were also overly sensitive to interference noise and amplitude correction errors. For field data from the study area, a large decrease in intercept magnitude may be the best indicator of the waterfront.
The effect of local distortions on time‐domain electromagnetic measurements
Authors: Hördt Andreas , Scholl Carsten
Published: January 2004

Based on the time‐domain integral equation, we derive expressions for the effect of an anomalous body close to the receiver or close to the transmitter on transient electromagnetic measurements. Similar to magnetotellurics, the distortion of electric fields at late times can be described by a constant distortion tensor relating the secondary electric field to the primary field components that would be obtained in the absence of the body. The distortion of a single electric field transient is a static shift only for particular configurations over a layered half‐space. In the general case, the perturbation is time dependent because the direction of the total electric field vector varies with time. The theory nicely explains spatial variations in electric field transients measured during a high‐redundancy long‐offset transient electromagnetics (LOTEM) survey over an underground gas storage site.

An inversion example with synthetic data illustrates how distortion can be corrected. The elements of the distortion tensor are determined simultaneously with the model parameters. Ambiguity is reduced by a regularization of the distortion parameters. In the example, the background model is recovered well, even for the difficult case where only one transmitter is used. The distortion of the magnetic field time derivatives caused by bodies close to the receiver is proportional to the time derivative of the primary electric step response. The distortion is generally not limited to early times and cannot be neglected in general. Transmitter overprint effects resulting in static shifts of vertical magnetic field time derivatives may also be understood from the theory.
Crosshole IP imaging for engineering and environmental applications
Authors: Kemna Andreas , Binley Andrew , Slater Lee
Published: January 2004

Induced polarization (IP) imaging is a promising tool in engineering and environmental studies. Application of this technique for near‐surface investigations has previously been limited by incomplete understanding of the physicochemical controls on the IP response, together with a lack of appropriate methods for data inversion. As laboratory studies have shown, description of IP in terms of complex electrical conductivity enables access to various structural characteristics pertinent to practical issues such as subsurface lithology definition, hydraulic permeability estimation, or hydrocarbon contaminant mapping. In particular, analysis in terms of real and imaginary conductivity components offers improved lithological characterization, since surface polarization effects are separated from electrolytic and surface conduction effects. An Occam‐type IP inversion algorithm based on complex algebra is described which accounts for these advances in IP interpretation by directly solving for complex conductivity. Results from crosshole applications at two case study sites demonstrate the suitability of the IP imaging approach for subsurface characterization. In the first case study, the imaging results correlate with the observed complex sequence of Quaternary sediments at a waste disposal site. Characterization of the polarizability of these sediments offers significant value in lithological differentiation. In the second case study, the results of IP imaging at a hydrocarbon‐contaminated site illustrate the potential of the method in environmental studies. The hydrocarbon location is clearly evident from the IP image, and a markedly different response is observed at an uncontaminated region of the site. By adopting empirical structural–electrical relationships, images of textural and hydraulic properties are estimated as a step toward improved quantitative characterization. The success of the method for these contrasting applications supports further investigation into understanding the physical and chemical processes that control observed IP.
3D magnetotelluric modeling using the T‐Ω finite‐element method
Authors: Mitsuhata Yuji , Uchida Toshihiro
Published: January 2004

We present a finite‐element algorithm for computing MT responses for 3D conductivity structures. The governing differential equations in the finite‐element method are derived from the T–Ω Helmholtz decomposition of the magnetic field H in Maxwell's equations, in which T is the electric vector potential and Ω is the magnetic scalar potential. The Coulomb gauge condition on T necessary to obtain a unique solution for T is incorporated into the magnetic flux density conservation equation. This decomposition has two important benefits. First, the only unknown variable in the air is the scalar value of Ω. Second, the curl–curl equation describing T is only defined in the earth. By comparison, the system of curl–curl equations for H and the electric field E are singular in the air, where the conductivity σ is zero. Although the use of a small but nonzero value of σ in the air and application of a divergence correction are usually necessary in the E or H formulation, the T–Ω method avoids this necessity. In the finite‐element approximation, T and Ω are represented by the edge‐element and nodal‐element interpolation functions within each brick element, respectively. The validity of this modeling approach is investigated and confirmed by comparing modeling results with those of other numerical techniques for two 3D models.
Finite‐difference modeling of electromagnetic tool response for logging while drilling
Authors: Wang Tsili , Signorelli Jack
Published: January 2004

This paper presents a 3D finite‐difference method for analyzing electromagnetic logging‐while‐drilling (LWD) tool response. The finite‐difference method is formulated with cylindrical coordinates, enabling accurate simulation of a cylindrical tool geometry. The algorithm allows the simulation of inhomogeneous media with arbitrary conductivity and magnetic permeability distributions. With the use of an irregular finite‐difference grid, a complex LWD antenna with cavities and slots is modeled accurately. Our results show that ferrite inserted in antenna slots increases the effective radiating length of the slots. The ferrite also helps reduce the eddy currents in the metal. However, it is unnecessary to use ferrite with a relative magnetic permeability greater than 200 for the particular antenna geometry considered. The slotted antenna exhibits azimuthal field variation that can be neglected for practical purposes because the variation is significant only within a few centimeters from the tool's surface. For typical LWD tool spacings of 1 m or so, the field by a slotted antenna can be well approximated by the field of a dipole antenna.
Elastic impedance inversion of multichannel seismic data from unconsolidated sediments containing gas hydrate and free gas
Authors: Lu Shaoming , McMechan George A.
Published: January 2004

The elastic properties of hydrated sediments are not well‐known, which leads to inaccuracy in the evaluation of the amount of gas hydrate worldwide. Elastic impedance inversion is useful in estimating the elastic properties of sediments containing gas hydrate, or free gas trapped beneath the gas hydrate, from angle‐dependent P‐wave reflections.

We reprocess the multichannel U.S. Geological Survey seismic line BT‐1 from the Blake Ridge off the east coast of North America to obtain migrated common‐angle aperture data sets, which are then inverted for elastic impedance. Two new algorithms to estimate P‐impedance and S‐impedance from the elastic impedance are developed and evaluated using well‐log data from Ocean Drilling Program (ODP) Leg 164; these new algorithms are stable, even in the presence of modest noise in the data.

The Vs/Vpratio, Poisson's ratio, and Lamé parameter terms λρ and λ/μ are estimated from the P‐impedance and S‐impedance. The hydrated sediments have high elastic impedance, high P‐impedance, high S‐impedance, high λρ, slightly higher Vs/Vpratio, slightly lower Poisson's ratio, and slightly lower λ/μ values compared to those of the surrounding unhydrated sediments. The sediments containing free gas have low elastic impedance, low P‐impedance, nonanomalous background S‐impedance, high Vs/Vpratio, low Poisson's ratio, low λρ, and low λ/μ values. We conclude that some parameters such as Vs/Vpratio, Poisson's ratio, and λ/μ, although they help identify the free‐gas charged layers, cannot differentiate between the hydrated sediments and nonhydrated sediments when gas hydrate concentration is low, and cannot differentiate between the hydrated sediments and free‐gas charged sediments when the gas hydrate concentration is high.

Three distinct layers of gas hydrate are interpreted as being caused by gas hydrates with gas of different molecular weights, with correspondingly different stability zones in depth. Free gas appears to be present below the two deeper gas‐hydrate layers, but not below the shallowest one because the lack of a trapping structure. The gas hydrate has an average concentration of ∼3–5.5% by volume, and is highest (9%) at the base of the lower gas hydrate stability zone. The free‐gas concentration ranges from 1 to 8% by volume, and is most developed beneath the local topographic high of the ocean bottom.
Estimating depth and model type using the continuous wavelet transform of magnetic data
Authors: Vallée Marc A. , Keating Pierre , Smith Richard S. , St‐Hilaire Camille
Published: January 2004

The continuous wavelet transform has been proposed recently for the interpretation of potential field anomalies. Using Poisson wavelets, which are equivalent to an upward continuation of the analytic signal, this technique allows one to estimate the depth of burial of homogeneous field sources and to determine the nature of the source in the form of a structural index. Moreau et al. (1999) accomplish this by successively testing the least‐squares misfit on a log–log plot of the wavelet transform amplitude versus the sum of the depth and the dilation (upward continuation height). We extend this methodology by analyzing the ratio of the Poisson wavelet coefficients of the first and second orders. For simple pole sources, this ratio at one dilation is enough to estimate the depth and index uniquely; but for extended sources of finite size, we must analyze the variation of the estimates with dilations. The technique gives good results on synthetic and field examples.
Genetic‐algorithm/neural‐network approach to seismic attribute selection for well‐log prediction
Authors: Dorrington Kevin P. , Link Curtis A.
Published: January 2004

Neural‐network prediction of well‐log data using seismic attributes is an important reservoir characterization technique because it allows extrapolation of log properties throughout a seismic volume. The strength of neural‐networks in the area of pattern recognition is key in its success for delineating the complex nonlinear relationship between seismic attributes and log properties. We have found that good neural‐network generalization of well‐log properties can be accomplished using a small number of seismic attributes. This study presents a new method for seismic attribute selection using a genetic‐algorithm approach. The genetic algorithm attribute selection uses neural‐network training results to choose the optimal number and type of seismic attributes for porosity prediction.

We apply the genetic‐algorithm attribute‐selection method to the C38 reservoir in the Stratton field 3D seismic data set. Eleven wells with porosity logs are used to train a neural network using genetic‐algorithm selected‐attribute combinations. A histogram of 50 genetic‐algorithm attribute selection runs indicates that amplitude‐based attributes are the best porosity predictors for this data set. On average, the genetic algorithm selected four attributes for optimal porosity log prediction, although the number of attributes chosen ranged from one to nine. A predicted porosity volume was generated using the best genetic‐algorithm attribute combination based on an average cross‐validation correlation coefficient. This volume suggested a network of channel sands within the C38 reservoir.
Inversion strategy in crosshole radar tomography using information of data subsets
Authors: Becht Andreas , Tronicke Jens , Appel Erwin , Dietrich Peter
Published: January 2004

Detecting discrete anomalies, such as cavities or tunnels, is an important application of crosshole radar tomography. However, crosshole tomographic inversion results are frequently ambiguous, showing smearing effects and inversion artifacts. These ambiguities lead to uncertainties in interpretation; hence, the size and position of anomalies can only be interpreted with limited accuracy and reliability. We present an inversion strategy for investigating discrete anomalies with crosshole radar tomography. In addition to the full traveltime data set, we use subsets of specified ray‐angle intervals for tomographic inversion. By analyzing inversion results from different ray‐angle intervals, a more accurate interpretation of anomalies is possible. The second step of our strategy is to develop a good inhomogeneous starting model from joint interpretation of the inversion results from different subsets. The third step is to invert the full data set using this new starting model and to evaluate the inversion results by analyzing the distributions of mean square traveltime residuals with respect to the ray angles. We use a synthetic model with two discrete anomalies located roughly at the same depth to demonstrate and evaluate our approach. This inversion strategy is also applied to a field data set collected to investigate karst cavities in limestone. From the inversion results of both examples, we show that horizontal smearing of anomalies can be reduced by eliminating near‐horizontal rays. A good starting model can be obtained based on the joint interpretation of the inversion results of the different subsets; it leads to a high‐resolution final image of the full data set.
Efficient waveform inversion and imaging: A strategy for selecting temporal frequencies
Authors: Sirgue Laurent , Pratt R. Gerhard
Published: January 2004

Prestack migration and/or inversion may be implemented in either the time or the frequency domain. In the frequency domain, it is possible to discretize the frequencies with a much larger sampling interval than that dictated by the sampling theorem and still obtain an imaging result that does not suffer from aliasing (wrap around) in the depth domain. The selection of input frequencies can be reduced when a range of offsets is available; this creates a redundancy of information in the wavenumber coverage of the target. In order to optimize the use of this information, we define a new discretization strategy that depends on the maximum effective offset present in the surface seismic survey: the larger the range of offsets, the fewer frequencies are required.

The strategy, exact in a homogeneous 1D earth, selects frequencies by making use of the well‐known effect of image stretch in normal‐moveout (NMO) correction and in migration (usually considered detrimental for the imaging). The strategy is also useful in more general earth models: we apply it to the 2D Marmousi model and recover a continuous range of wavenumbers using only three input frequencies. The Marmousi inversion result accurately predicts all other data frequencies, demonstrating the redundancy of the data.
Specular ray parameter extraction and stationary‐phase migration
Authors: Chen Jing
Published: January 2004

The Kirchhoff‐type prestack depth migration operator is a diffraction stack of seismic reflection energies over seismic traces. Typically, the diffraction stack is carried out over the full data aperture, producing not only images of reflectors but also aliasing artifacts. Aliasing artifacts often break reflector continuity in images. The stationary‐phase approximation to the migration operator shows that, for image points on reflectors, traces within the neighborhood of specular rays contribute most to the diffraction stack. Traces outside this vicinity introduce aliasing artifacts into the image, especially in the case of coarse trace spacing and aperture truncation. A new migration algorithm, denoted as stationary‐phase migration, is proposed to find the specular ray parameters and then to migrate the specular‐ray energies and reject nonspecular ray energies to yield images with less aliasing.
Velocity model estimation with data‐derived wavefront attributes
Authors: Duveneck Eric
Published: January 2004

Kinematic information for constructing velocity models can be extracted in a robust way from seismic prestack data with the common‐reflection‐surface (CRS) stack. This data‐driven process results, in addition to a simulated zero‐offset section, in a number of wavefront attributes—wavefront curvatures and normal ray emergence angles—associated with each simulated zero‐offset sample. A tomographic inversion method is presented that uses this kinematic information to determine smooth, laterally heterogeneous, isotropic subsurface velocity models for depth imaging. The input for the inversion consists of wavefront attributes picked at a number of locations in the simulated zero‐offset section. The smooth velocity model is described by B‐splines. An optimum model is found iteratively by minimizing the misfit between the picked data and the corresponding modeled values. The required forward‐modeled quantities are obtained during each iteration by dynamic ray tracing along normal rays pertaining to the input data points. Fréchet derivatives for the tomographic matrix are calculated by ray perturbation theory. The inversion procedure is demonstrated on a 2D synthetic prestack data set.
Statistical evaluation of the Fixed Concentration Procedure for acute inhalation toxicity assessment
Authors: Stallard Nigel , Whitehead Anne , Indans Ian
Published: January 2004

The conventional method for the assessment of acute inhalation toxicity (OECD Test Guideline 403, 1981) uses death of animals as an endpoint to identify the median lethal concentration (LC50). A new OECD Testing Guideline called the Fixed Concentration Procedure (FCP) is being prepared to provide an alternative to Test Guideline 403. Unlike Test Guideline 403, the FCP does not provide a point estimate of the LC50, but aims to identify an airborne exposure level that causes clear signs of nonlethal toxicity. This is then used to assign classification according to the new Globally Harmonized System of Classification and Labelling scheme (GHS). The FCP has been validated using statistical simulation rather than byin vivo testing. The statistical simulation approach predicts the GHS classification outcome and the numbers of deaths and animals used in the test for imaginary substances with a range of LC50 values and dose response curve slopes. This paper describes the FCP and reports the results from the statistical simulation study assessing its properties. It is shown that the procedure will be completed with considerably less death and suffering than Test Guideline 403, and will classify substances either in the same or a more stringent GHS class than that assigned on the basis of the LC50 value.