bluuebunny/crossref_metadata_2025 huggingface dataset:
Alterations in gastric mucosal lineages induced by acute oxyntic atrophy in wild-type and gastrin-deficient mice
Authors: Nomura Sachiyo , Yamaguchi Hirokazu , Ogawa Masako , Wang Timothy C. , Lee Jeffrey R. , Goldenring James R.
Published: January 2005

In addition to their role in gastric acid secretion, parietal cells secrete a number of growth factors that may influence the differentiation of other gastric lineages. Indeed, oxyntic atrophy is considered the most significant correlate with increased risk for gastric adenocarcinoma. We studied the alterations in gastric mucosal lineages elicited by acute oxyntic atrophy induced by treatment of C57BL/6 and gastrin-deficient mice with the parietal cell protonophore [ S-( R*, S*)]- N-[1-(1,3-benzodioxol-5-yl)butyl]-3,3-diethyl-2-[4-[(4-methyl-1-piperazinyl)carbonyl]phenoxy]-4-oxo-1-azetidinecarboxamide (DMP-777). In both wild-type and gastrin knockout mice, DMP-777 elicited the rapid loss of parietal cells within 2 days of treatment. In wild-type mice, oxyntic atrophy was accompanied by a rapid increase in 5-bromo-2′-deoxyuridine-labeled proliferative cells and attendant increase in surface cell numbers. However, gastrin knockout mice did not demonstrate significant foveolar hyperplasia and showed a blunted proliferative response. After 7 days of treatment in wild-type mice, a second proliferative population emerged at the base of fundic glands along with the development of a mucous cell metaplasia expressing TFF2/spasmolytic polypeptide (SPEM). However, in gastrin knockout mice, SPEM expressing both TFF2 mRNA and protein developed after only 1 day of DMP-777 treatment. In wild-type mice, all changes induced by DMP-777 were reversed 14 days after cessation of treatment. In gastrin-deficient mice, significant SPEM was still present 14 days after the cessation of treatment. The results indicate that foveolar hyperplasia requires the influence of gastrin, whereas SPEM develops in response to oxyntic atrophy independent of gastrin, likely through transdifferentiation of chief cells.
Role of glucose in modulating Mg2+homeostasis in liver cells from starved rats
Authors: Torres Lisa M. , Youngner Jonathan , Romani Andrea
Published: January 2005

α1- and β-Adrenoceptor stimulation elicits Mg2+extrusion from liver cells in conjunction with hepatic glucose output (T. Fagan and A. Romani. Am J Physiol Gastrointest Liver Physiol 279: G943–G950, 2000.). To characterize the role of intrahepatic glucose on Mg2+transport, male Sprague-Dawley rats were starved overnight before being anesthetized and used as organ donors. Perfused livers or collagenase-dispersed hepatocytes were stimulated by α1(phenylephrine)- or β (isoproterenol)-adrenergic agonists. Mg2+extrusion was assessed by atomic absorbance spectrophotometry. In both experimental models, the administration of pharmacological doses of adrenergic agonists did not elicit Mg2+extrusion. The determination of cellular Mg2+indicated an ∼9% decrease in total hepatic Mg2+content in liver cells after overnight fasting, whereas the ATP level was unchanged. Hepatocytes from starved rats accumulated approximately four times more Mg2+than liver cells from fed animals. This enlarged Mg2+accumulation depended in part on extracellular glucose, since it was markedly reduced in the absence of extracellular glucose or in the presence of the glucose transport inhibitor phloretin. The residual Mg2+accumulation observed in the absence of extracellular glucose was completely abolished by imipramine or removal of extracellular Na+. Taken together, these data indicate 1) that hepatic glucose mobilization is essential for Mg2+extrusion by adrenergic agonist and 2) that starved hepatocytes accumulate Mg2+via two distinct pathways, one of which is associated with glucose transport, whereas the second can be tentatively identified as an imipramine-inhibited Na+-dependent pathway.
Neuroendocrine properties of intrinsic cardiac adrenergic cells in fetal rat heart
Authors: Huang M.-H. , Bahl J. J. , Wu Y. , Hu F. , Larson D. F. , Roeske W. R. , Ewy G. A.
Published: January 2005

Intrinsic cardiac adrenergic (ICA) cells in developing rat heart constitute a novel adrenergic signaling system involved in cardiac regulation. Regulatory mechanisms of ICA cells remain to be defined. Immunohistochemical study of fetal rat hearts demonstrated ICA cells with catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). The mRNA of TH and PNMP was also detected in fetal rat hearts before sympathetic innervation. Immunoreactivity of norepinephrine transporter (NET) was localized to ICA cells in rat heart tissue and primary cell culture. For the functional study, the activity of intracellular Ca2+concentration ([Ca2+]i) transients was quantified by a ratio fluorescent spectrometer in cultured ICA cells and myocytes. ICA cells generated spontaneous [Ca2+]itransients that were eliminated by tetrodotoxin or Ca2+-free solutions and showed greatly reduced amplitude with the addition of L-type Ca2+channel blocker nifedipine. [3H]norepinephrine studies demonstrate release and uptake of norepinephrine. Functional interaction between catecholamines produced by the ICA cells and cocultured myocytes was evident by the effect of the β-adrenergic blocker atenolol eliciting a dose-dependent reduction in the amplitude and frequency of [Ca2+]itransients of beating myocytes. Hypoxia inhibited [Ca2+]itransient activity of ICA cells, which subsequently produced a reoxygenation-mediated rebound augmentation of [Ca2+]itransients. We conclude that ICA cells are capable of catecholamine synthesis, release, and uptake. They generate spontaneous [Ca2+]itransient activity that can be regulated by oxygen tension. ICA cells may provide an alternative adrenergic supply to maintain cardiac contractile and pacemaker function at rest and during stress in the absence of sympathetic innervation.
Chronic central infusion of aldosterone leads to sympathetic hyperreactivity and hypertension in Dahl S but not Dahl R rats
Authors: Huang Bing S. , Wang Hao , Leenen Frans H. H.
Published: January 2005

Six-week-old Dahl salt-sensitive (S) and -resistant (R) rats received for 2 wk an intracerebroventricular infusion of aldosterone (Aldo) (22.5 ng/h) or vehicle containing artificial cerebrospinal fluid (aCSF) with 0.15 M Na+. At 8 wk, mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in conscious rats at rest, in response to air stress, and to an intracerebroventricular injection of the α2-adrenoceptor agonists guanabenz or ouabain. Baroreflex control of RSNA and HR was estimated by using intravenous phenylephrine and nitroprusside. In Dahl S but not Dahl R rats, Aldo raised resting MAP by 20–25 mmHg, doubled sympathoexcitatory and pressor responses to air stress and sympathoinhibitory and depressor responses to guanabenz, and impaired baroreflex function. In Dahl S but not Dahl R rats, Aldo significantly increased content of ouabain-like compounds (OLC) in the hypothalamus and attenuated excitatory responses to ouabain. Aldo did not affect water intake, plasma electrolytes, or OLC in plasma and adrenal glands. In another set of three groups of Dahl S rats, Aldo dissolved in aCSF containing 0.16, 0.15, or 0.14 M Na+was infused intracerebroventricularly for 2 wk. CSF Na+concentration ([Na+]) showed only a nonsignificant increase, but resting MAP increased from 111 ± 3 mmHg in rats with Aldo in 0.14 M Na+to 131 ± 3 and 147 ± 3 mmHg with Aldo in 0.15 and 0.16 M Na+, respectively ( P < 0.05 for both). These findings indicate that in Dahl S rats, intracerebroventricular infusion of Aldo causes similar central responses as high salt intake, i.e., increases in brain OLC content, sympathetic hyperreactivity, and hypertension. The extent of the increase in blood pressure (BP) by intracerebroventricular Aldo depends on the [Na+] in the vehicle. In Dahl R rats, intracerebroventricular Aldo did not increase brain OLC, sympathetic reactivity, and BP, suggesting that in this rat strain, a decrease in central responsiveness to mineralocorticoids may contribute to its salt-resistant nature.
Impaired insulin-induced vasodilation in small coronary arteries of Zucker obese rats is mediated by reactive oxygen species
Authors: Katakam Prasad V. G. , Tulbert Christina D. , Snipes James A. , Erdös Benedek , Miller Allison W. , Busija David W.
Published: January 2005

Insulin resistance (IR) and associated hyperinsulinemia are major risk factors for coronary artery disease. Mechanisms linking hyperinsulinemia to coronary vascular dysfunction in IR are unclear. We evaluated insulin-induced vasodilation in isolated small coronary arteries (SCA; ∼225 μm) of Zucker obese (ZO) and control Zucker lean (ZL) rats. Vascular responses to insulin (0.1–100 ng/ml), ACh (10−9–10−5 mol/l), and sodium nitroprusside (10−8–10−4 mol/l) were assessed in SCA by measurement of intraluminal diameter using videomicroscopy. Insulin-induced dilation was decreased in ZO compared with ZL rats, whereas ACh and sodium nitroprusside elicited similar vasodilations. Pretreatment of arteries with SOD (200 U/ml), a scavenger of reactive oxygen species (ROS), restored the vasorelaxation response to insulin in ZO arteries, whereas ZL arteries were unaffected. Pretreatment of SCA with N-nitro-l-arginine methyl ester (100 μmol/l), an inhibitor of endothelial nitric oxide (NO) synthase (eNOS), elicited a vasoconstrictor response to insulin that was greater in ZO than in ZL rats. This vasoconstrictor response was reversed to vasodilation in ZO and ZL rats by cotreatment of the SCA with SOD or apocynin (10 μmol/l), a specific inhibitor of vascular NADPH oxidase. Lucigenin-enhanced chemiluminescence showed increased basal ROS levels as well as insulin (330 ng/ml)-stimulated production of ROS in ZO arteries that was sensitive to inhibition by apocynin. Western blot analysis revealed increased eNOS expression in ZO rats, whereas Mn SOD and Cu,Zn SOD expression were similar to ZL rats. Thus IR in ZO rats leads to decreased insulin-induced vasodilation, probably as a result of increased production of ROS by vascular NADPH oxidase, leading to decreased NO bioavailability, despite a compensatory increase in eNOS expression.
Bone marrow-derived cells contribute to contractile dysfunction in endotoxic shock
Authors: Binck Brian W. , Tsen May F. , Islas Miguel , White D. Jean , Schultz Roger A. , Willis Monte S. , Garcia J. Victor , Horton Jureta W. , Thomas James A.
Published: January 2005

How infection precipitates depressed contractility is incompletely understood but may involve the immune, nervous, and endocrine systems as well as the heart itself. In this study, we examined the role of Toll-like receptor 4 (TLR4) in LPS-induced myocardial contractile depression. Eighteen hours following endotoxin challenge, we compared contractile responses in hearts from wild-type (WT) and TLR4-deficient mice using modified Langendorff preparations. Unlike hearts from WT mice, TLR4-deficient hearts did not reveal significant contractile dysfunction following LPS administration, as measured by decreased responses in maximal left ventricular pressure, +dP/d tmax, and −dP/d tmaxin ex vivo Langendorff preparations. These findings indicate a requirement for TLR4 in LPS-induced contractile depression. To determine the contribution of bone marrow-derived TLR4 function to LPS-induced myocardial dysfunction, we generated TLR4 chimeras using adoptive transfer between histocompatible mouse strains: either TLR4-deficient mice with TLR4+/+ bone marrow-derived cells or TLR4+/+ animals lacking TLR4 in their hematopoietic cells. We then compared the contractile responses of engrafted animals after LPS challenges. Engraftment of TLR4-deficient mice with WT marrow restored sensitivity to the myocardial depressant effects of LPS in TLR4-deficient hearts ( P < 0.05). Inactivation of bone marrow-derived TLR4 function, via transplantation of WT mice with TLR4−/− marrow, however, did not protect against the depressant effect of endotoxin. These findings indicate that bone marrow-derived TLR4 activity is sufficient to confer sensitivity to mice lacking TLR4 in all other tissues. However, because inactivation of marrow-derived TLR4 function alone does not protect against endotoxin-triggered contractile dysfunction, TLR4 function in other tissues may also contribute to this response.
Posttranscriptional regulation of myosin heavy chain expression in the heart by triiodothyronine
Authors: Danzi Sara , Klein Irwin
Published: January 2005

Triiodothyronine (T3) regulates cardiac contractility in part by regulating the expression of several important cardiac myocyte genes. In the rat, the T3-mediated induction of α-myosin heavy chain (MHC) transcription in hypothyroid hearts is rapid, exhibiting zero-order kinetics, whereas the repression of β-MHC in these same hearts is much slower. To elucidate the mechanism for T3transcriptional as well as posttranscriptional regulation of both MHC gene isoforms, we used an RT-PCR-based transcription assay and the RNA polymerase II inhibitor actinomycin D in an in vivo model to simultaneously measure specific α- and β-MHC heterogeneous nuclear RNA (hnRNA), mRNA kinetics, and MHC antisense RNA. In vivo actinomycin D treatment blocked α-MHC transcription in euthyroid rats by >80% at 2 h and suggested a half-life of α-MHC hnRNA of ∼1 h, whereas actinomycin D inhibited β-MHC transcription in hypothyroid rats by >75% at 6 h, suggesting a significantly longer hnRNA half-life of ∼4 h. The effect of actinomycin D on β-MHC transcription was independent of T3. T3treatment in hypothyroid animals caused β-MHC mRNA to decline more rapidly than β-MHC hnRNA, demonstrating, for the first time, a posttranscriptional mechanism(s). The measured change in β-MHC mRNA half-life indicates a T3-mediated destabilization of β-MHC mRNA. To understand the mechanism by which T3destabilizes β-MHC mRNA, we measured β-MHC antisense RNA. β-MHC antisense RNA is present in euthyroid myocytes, but levels are not significant in hypothyroid myocytes. This differential expression may explain some of the effects of T3on MHC posttranscriptional regulation.
Response to selection for photoperiod responsiveness on the density and location of mature GnRH-releasing neurons
Authors: Avigdor Mauricio , Sullivan Shannon D. , Heideman Paul D.
Published: January 2005

Natural variation in neuroendocrine traits is poorly understood, despite the importance of variation in brain function and evolution. Most rodents in the temperate zones inhibit reproduction and other nonessential functions in short winter photoperiods, but some have little or no reproductive response. We tested whether genetic variability in reproductive seasonality is related to individual differences in the neuronal function of the gonadotropin-releasing hormone network, as assessed by the number and location of mature gonadotropin-releasing hormone-secreting neurons under inhibitory and excitatory photoperiods. The experiments used lines of Peromyscus leucopus previously developed by selection from a wild population. One line contained individuals reproductively inhibited by short photoperiod, and the other line contained individuals nonresponsive to short photoperiod. Expression of mature gonadotropin-releasing hormone (GnRH) immunoreactivity in the brain was detected using SMI-41 antibody in the single-labeled avidin-biotin-peroxidase-complex method. Nonresponsive mice had 50% more immunoreactive GnRH neurons than reproductively inhibited mice in both short- and long-day photoperiods. The greatest differences were in the anterior hypothalamus and preoptic areas. In contrast, we detected no significant within-lines differences in the number or location of immunoreactive GnRH neurons between photoperiod treatments. Our data indicate that high levels of genetic variation in a single wild population for a specific neuronal trait are related to phenotypic variation in a life history trait, i.e., winter reproduction. Variation in GnRH neuronal activity may underlie some of the natural reproductive and life history variation observed in wild populations of P. leucopus. Similar genetic variation in neuronal traits may be present in humans and other species.
Exercise improves impaired ventricular function and alterations of cardiac myofibrillar proteins in diabetic dyslipidemic pigs
Authors: Korte F. Steven , Mokelke Eric A. , Sturek Michael , McDonald Kerry S.
Published: January 2005

Chronic diabetes is often associated with cardiomyopathy, which may result, in part, from defects in cardiac muscle proteins. We investigated whether a 20-wk porcine model of diabetic dyslipidemia (DD) would impair in vivo myocardial function and yield alterations in cardiac myofibrillar proteins and whether endurance exercise training would improve these changes. Myocardial function was depressed in anesthetized DD pigs ( n = 12) compared with sedentary controls (C; n = 13) as evidenced by an ∼30% decrease in left ventricular fractional shortening and an ∼35% decrease in +dP/d t measured by noninvasive echocardiography and direct cardiac catheterization, respectively. This depression in myocardial function was improved with chronic exercise as treadmill-trained DD pigs (DDX) ( n = 13) had significantly greater fractional shortening and +dP/d t than DD animals. Interestingly, the isoform expression pattern of the myofibrillar regulatory protein, cardiac troponin T (cTnT), was significantly shifted from cTnT1toward cTnT2and cTnT3in DD pigs. Furthermore, this change in cTnT isoform expression pattern was prevented in DDX pigs. Finally, there was a decrease in baseline levels of cAMP-dependent protein kinase-induced phosphorylation of the myofibrillar proteins troponin I and myosin-binding protein-C in DD animals. Overall, these results indicate that 20 wk of DD lead to myocardial dysfunction coincident with significant alterations in myofibrillar proteins, both of which are prevented with endurance exercise training, implying that changes in myofibrillar proteins may contribute, at least in part, to cardiac dysfunction associated with diabetic cardiomyopathy.
Mechanics, nonlinearity, and failure strength of lung tissue in a mouse model of emphysema: possible role of collagen remodeling
Authors: Ito Satoru , Ingenito Edward P. , Brewer Kelly K. , Black Lauren D. , Parameswaran Harikrishnan , Lutchen Kenneth R. , Suki Béla
Published: January 2005

Enlargement of the respiratory air spaces is associated with the breakdown and reorganization of the connective tissue fiber network during the development of pulmonary emphysema. In this study, a mouse (C57BL/6) model of emphysema was developed by direct instillation of 1.2 IU of porcine pancreatic elastase (PPE) and compared with control mice treated with saline. The PPE treatment caused 95% alveolar enlargement ( P = 0.001) associated with a 29% lower elastance along the quasi-static pressure-volume curves ( P < 0.001). Respiratory mechanics were measured at several positive end-expiratory pressures in the closed-chest condition. The dynamic tissue elastance was 19% lower ( P < 0.001), hysteresivity was 9% higher ( P < 0.05), and harmonic distortion, a measure of collagen-related dynamic nonlinearity, was 33% higher in the PPE-treated group ( P < 0.001). Whole lung hydroxyproline content, which represents the total collagen content, was 48% higher ( P < 0.01), and α-elastin content was 13% lower ( P = 0.16) in the PPE-treated group. There was no significant difference in airway resistance ( P = 0.7). The failure stress at which isolated parenchymal tissues break during stretching was 40% lower in the PPE-treated mice ( P = 0.002). These findings suggest that, after elastolytic injury, abnormal collagen remodeling may play a significant role in all aspects of lung functional changes and mechanical forces, leading to progressive emphysema.
Independent metabolic costs of supporting body weight and accelerating body mass during walking
Authors: Grabowski Alena , Farley Claire T. , Kram Rodger
Published: January 2005

The metabolic cost of walking is determined by many mechanical tasks, but the individual contribution of each task remains unclear. We hypothesized that the force generated to support body weight and the work performed to redirect and accelerate body mass each individually incur a significant metabolic cost during normal walking. To test our hypothesis, we measured changes in metabolic rate in response to combinations of simulated reduced gravity and added loading. We found that reducing body weight by simulating reduced gravity modestly decreased net metabolic rate. By calculating the metabolic cost per Newton of reduced body weight, we deduced that generating force to support body weight comprises ∼28% of the metabolic cost of normal walking. Similar to previous loading studies, we found that adding both weight and mass increased net metabolic rate in more than direct proportion to load. However, when we added mass alone by using a combination of simulated reduced gravity and added load, net metabolic rate increased about one-half as much as when we added both weight and mass. By calculating the cost per kilogram of added mass, we deduced that the work performed on the center of mass comprises ∼45% of the metabolic cost of normal walking. Our findings support the hypothesis that force and work each incur a significant metabolic cost. Specifically, the cost of performing work to redirect and accelerate the center of mass is almost twice as great as the cost of generating force to support body weight.
Accuracy of Subspace Mapping of Spatiotemporal Frequency Domain Visual Receptive Fields
Authors: Nishimoto Shinji , Arai Miki , Ohzawa Izumi
Published: January 2005

Orientation and spatial frequency selectivities are fundamental properties of cells in the early visual cortex. Although they are customarily tested with drifting sinusoidal gratings, a recently developed subspace reverse correlation method may be a better replacement for obtaining a selectivity map in a joint orientation and spatial frequency domain at higher resolution efficiently. These two methods are examined for their accuracy and data compatibility for cells in areas 17 and 18 of anesthetized and paralyzed cats. Peaks and bandwidths of tuning curves from these two methods are highly correlated. However, spatial frequency bandwidths obtained by reverse correlation tend to be slightly narrower for the subspace reverse correlation than those from the drifting grating tests. Consistency between the two methods is improved if the entire duration of data containing signal are taken into account for the subspace reverse correlation rather than using the map only at the optimal correlation delay. Examination of convergence of the subspace mapping process shows that reliable 2-day profiles can be obtained within 5–10 min. for the majority of cells. Temporal dynamics of tuning properties are also examined more directly with the subspace mapping than with the drifting gratings. For many cells, the optimal spatial frequency shifts substantially, measured as a fraction of tuning bandwidth, over the time course of response. In comparison, the optimal orientation remains highly stable throughout the duration of response. Overall, these results suggest that the subspace reverse correlation is a better substitute for the conventional method.
“¿Cuánto tiempo trabajaremos aquí?” Antigüedad en la organización y características de los contratos psicológicos en empleados de call/contact centers
Authors: Alcover Carlos-María , Martínez-Íñigo David , Rodríguez-Mazo Fernando
Published: January 2005

En los últimos años, a la rápida expansión del sector de los call/contact centers (C/CC) se ha asociado la imagen de lugares de trabajo que ofrecen unas condiciones precarias, caracterizadas por la temporalidad, los bajos salarios, unas tareas rutinarias y un elevado control del rendimiento. Sin embargo, el desarrollo de sus actividades les obliga a prestar servicios cada vez más cualificados y complejos, lo que exige una fuerza de trabajo que responda a esta necesidad. En este contexto, se ha considerado que el contrato psicológico (CP) puede resultar un instrumento útil para estudiar si dichas condiciones permiten el establecimiento y desarrollo de orientaciones relacionales o solo transaccionales. Teniendo en cuenta la antigüedad en la organización, en este estudio se han analizado las dos orientaciones mencionadas del CP. Los resultados señalan que la orientación relacional disminuye progresivamente durante los primeros años de contrato hasta llegar a los cinco años de antigüedad, momento a partir del cual la tendencia se invierte, aumentando hasta superar el nivel inicial. De manera inversa, la orientación transaccional aumenta paulatinamente durante los cinco primeros años y a partir de entonces disminuye hasta quedar por debajo del nivel que presentaba al comienzo del contrato. Estos resultados permiten discutir acerca de las implicaciones que los cambios en las orientaciones de los contratos psicológicos pueden tener para los responsables de la gestión de los trabajadores en las empresas del sector de C/CC.
Introducción: perspectivas de futuro para el contrato psicológico
Authors: Topa Gabriela
Published: January 2005

Un dossier dedicado a explorar las aportaciones y la vigencia del contrato psicológico en las organizaciones reconoce, de entrada, la importancia de la obra de Denise Rousseau y, a partir de ahí, elabora teóricamente y explora empíricamente diversos aspectos de interés de esta noción. Quince autores y seis artículos presentan sus aportaciones respectivas. Este número aspira a servir de impulso para posteriores debates sobre la relevancia del contrato psicológico en las organizaciones.
Impacto del feedback negativo sobre los procesos de autorregulación del grupo. La ruptura del contrato grupal relacional
Authors: Tabernero Carmen , Arenas Alicia , Briones Elena
Published: January 2005

El presente trabajo pretende analizar los procesos de creación y ruptura del contrato psicológico en los grupos. Entendemos que estos procesos están ligados a los procesos de autorregulación grupal como la percepción de eficacia grupal, el compromiso, la satisfacción o las metas y expectativas grupales. Ahondando en este objetivo, pretendemos analizar el efecto de la ruptura del contrato psicológico en grupos de trabajo. Concretamente, tratamos de comparar los procesos de autorregulación a nivel individual (66 participantes) y grupal (43 grupos, 129 participantes) ante el desarrollo y la ruptura del contrato psicológico creado por el feedback negativo dado ante el desempeño logrado. Igualmente se pretende contrastar el rendimiento logrado a nivel individual y grupal. Los resultados muestran que en las fases iniciales, donde se desarrolla el contrato de grupo y las normas sociales, tanto los procesos autorreguladores como los resultados logrados son claramente favorables al grupo. Sin embargo, ante un feedback negativo continuado que implica la ruptura del contrato, el individuo mantiene una mayor confianza en su capacidad para afrontar la situación de lo que lo hace el grupo.
Psychological contract ‘breach’: A multiple component perspective to an over-researched construct?
Authors: Cassar Vincent , Briner Rob B.
Published: January 2005

The majority of studies investigating psychological contract breach ask participants to indicate the degree of unfulfillment of an organization's commitment to its employer obligations. However, very little systematic evidence exists about what participants understand by ‘unfulfillment’. This study sought to investigate this aspect. Using a series of in-depth interviews, results indicate that there are at least five component forms that characterize the general notion of unfulfillment: magnitude, delay, type/form, inequity and reciprocal imbalance. These results warrant a multi-dimensional investigation of contract breach. Implications and limitations are also discussed.
Diferencias en el contenido del contrato psicológico en función del tipo de contrato y de la gestión empresarial pública o privada
Authors: Silla Inmaculada , Gracia Francisco-Javier , Peiró José-María
Published: January 2005

El objetivo del presente trabajo es explorar si existen diferencias en el contenido del contrato psicológico en función del tipo de contrato y del tipo de gestión empresarial (pública o privada). Se realizaron ANOVAS 2 × 2 para contrastar las diferencias en las obligaciones del empleador y del empleado respectivamente en función del tipo de contrato: permanente versus temporal y del tipo de gestión empresarial: pública o privada con una muestra de 385 trabajadores. Los resultados proporcionan apoyo a las hipótesis planteadas, indicando que el tipo de contrato y el tipo de gestión empresarial influyen en el contenido del contrato psicológico que se establece entre el empleado y su organización. En el trabajo se analizan las contribuciones de los resultados al debate sobre el cambio del viejo al nuevo contrato psicológico.
Aerosol Characterization and Direct Radiative Forcing Assessment over the Ocean. Part I: Methodology and Sensitivity Analysis
Authors: Costa Maria João , Silva Ana Maria , Levizzani Vincenzo
Published: January 2005

A method based on the synergistic use of low earth orbit (LEO) and geostationary earth orbit (GEO) satellite data for aerosol-type characterization, as well as aerosol optical thickness (AOT) retrieval and monitoring over the ocean, is presented. These properties are used for the estimation of the direct shortwave aerosol radiative forcing at the top of the atmosphere. The synergy serves the purpose of monitoring aerosol events at the GEO time and space scales while maintaining the accuracy level achieved with LEO instruments. Aerosol optical properties representative of the atmospheric conditions are obtained from the inversion of high-spectral-resolution measurements from the Global Ozone Monitoring Experiment (GOME). The aerosol optical properties are input for radiative transfer calculations for the retrieval of the AOT from GEO visible broadband measurements, avoiding the use of fixed aerosol models available in the literature. The retrieved effective aerosol optical properties represent an essential component for the aerosol radiative forcing assessment. A sensitivity analysis is also presented to quantify the effects that changes on the aerosol model may have on modeled results of spectral reflectance, AOT, and direct shortwave aerosol radiative forcing at the top of the atmosphere. The impact on modeled values of the physical assumptions on surface reflectance and vertical profiles of ozone and water vapor are analyzed. Results show that the aerosol model is the main factor influencing the investigated radiative variables. Results of the application of the method to several significant aerosol events, as well as their validation, are presented in a companion paper.
The Role of Airmass Types and Surface Energy Fluxes in Snow Cover Ablation in the Central Appalachians
Authors: Leathers Daniel J. , Graybeal Daniel , Mote Thomas , Grundstein Andrew , Robinson David
Published: January 2005

A one-dimensional snowpack model, a unique airmass identification scheme, and surface weather observations are used to investigate large ablation events in the central Appalachian Mountains of North America. Data from cooperative observing stations are used to identify large ablation events within a 1° latitude × 1° longitude grid box that covers the majority of the Lycoming Creek basin in northern Pennsylvania. All 1-day ablation events greater than or equal to 7.6 cm (3 in.) are identified for the period of 1950 through 2001. Seventy-one events are identified, and these days are matched with a daily airmass type derived using the Spatial Synoptic Classification technique. Average meteorological characteristics on ablation days of each airmass type are calculated in an effort to understand the diverse meteorological influences that led to the large ablation events. A one-dimensional mass and energy balance snowpack model (“SNTHERM”) is used to calculate surface/atmosphere energy fluxes responsible for ablation under each airmass type. Results indicate that large ablation events take place under diverse airmass/synoptic conditions in the central Appalachians. Five airmass types account for the 71 large ablation events over the 52-yr period. Forty-three of the events occurred under “moist” airmass types and 28 under “dry” airmass conditions. Large ablation events under dry airmass types are driven primarily by daytime net radiation receipt, especially net solar radiation. These events tend to occur early and late in the snow cover season when solar radiation receipt is highest and are characterized by relatively clear skies, warm daytime temperatures, and low dewpoint temperatures. Moist airmass types are characterized by cloudy, windy conditions with higher dewpoint temperatures and often with liquid precipitation. During these events sensible heat flux is most often the dominant energy flux to the snowpack during ablation episodes. However, in many cases there is also a significant input of energy to the snowpack associated with condensation. Combinations of high sensible and latent heat fluxes often result in extreme ablation episodes, similar to those witnessed in this area in January 1996.
Estimating Overwater Turbulence Intensity from Routine Gust-Factor Measurements
Authors: Hsu S. A. , Blanchard Brian W.
Published: January 2005

For overwater diffusion estimates the Offshore and Coastal Dispersion (OCD) model is preferred by the U.S. Environmental Protection Agency. The U.S. Minerals Management Service has recommended that the OCD model be used for emissions located on the outer continental shelf. During southerly winds over the Gulf of Mexico, for example, the pollutants from hundreds of offshore platforms may affect the gulf coasts. In the OCD model, the overwater plume is described by the Gaussian equation, which requires the computation of σy and σz, which are, in turn, related to the turbulence intensity, overwater trajectory, and atmospheric stability. On the basis of several air–sea interaction experiments [the Barbados Oceanographic and Meteorological Experiment (BOMEX), the Air-Mass Transformation Experiment (AMTEX), and, most recently, the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE)] and the extensive datasets from the National Data Buoy Center (NDBC), it is shown that under neutral and stable conditions the overwater turbulence intensities are linearly proportional to the gust factor (G), which is the ratio of the wind gust and mean wind speed at height z (Uz) as reported hourly by the NDBC buoys. Under unstable conditions, it is first shown that the popular formula relating the horizontal turbulence intensity (σu,υ/u∗, where u∗ is the friction velocity) to the ratio of the mixing height (h) and the buoyancy length (L) (i.e., h/L) suffers from a self-correlation problem and cannot be used in the marine environment. Then, alternative formulas to estimate the horizontal turbulence intensities (σu,υ/Uz) using G are proposed for practical applications. Furthermore, formulas to estimate u∗ and z/L are fundamentally needed in air–sea interaction studies, in addition to dispersion meteorology.
An Idealized Study of the Structure of Long, Partially Mixed Estuaries*
Authors: Hetland Robert D. , Geyer W. Rockwell
Published: January 2005

Classic models of estuarine circulation are reexamined using a three-dimensional, primitive equation numerical ocean model. The model is configured using an idealized estuary/shelf domain with rectangular cross section, constant vertical mixing, and steady riverine discharge. Tidal dispersion is neglected, so the analysis does apply to well-mixed estuaries and lagoons. Estuarine scales for the length of steady-state salt intrusion, vertical stratification, and estuarine exchange flow estimated from steady-state model results are found to have the same functional relationships to vertical mixing and riverine discharge as the classic analytic solutions. For example, for steady-state conditions, the stratification is found to be virtually independent of the strength of vertical mixing. The estuarine structure was controlled by the interior estuarine circulation, and not by limited exchange at the mouth. Thus, the numerical solutions were not “overmixed,” although the solutions showed a dependence on freshwater flux functionally similar to the overmixed solution. Estuarine adjustment time scales are also estimated from the simulations, and they are related to the steady-state estuarine scales. Two classes of nonsteady solutions are examined: the response to a step change in riverine discharge and estuarine response to changes in vertical mixing. Spring/neap tidal variations are examined by modulating the (spatially constant) vertical mixing with a fortnightly period. Unlike the steady solutions, there is a clear dependence of stratification on mixing rate in the time-dependent solutions. The simulations involving changes in riverine discharge show asymmetries between response to increasing and decreasing river flow that are attributed to quadratic bottom drag.
Evaluation of Interior Circulation in a High-Resolution Global Ocean Model. Part I: Deep and Bottom Waters
Authors: Sen Gupta Alexander , England Matthew H.
Published: January 2005

Global watermass ventilation pathways and time scales are investigated using an “eddy permitting” (¼°) offline tracer model. Unlike previous Lagrangian trajectory studies, here an offline model based on a complete tracer equation that includes three-dimensional advection and mixing is employed. In doing so, the authors are able to meaningfully simulate chlorofluorocarbon (CFC) uptake and assess model skill against observation. This is the first time an eddy-permitting model has been subjected to such an assessment of interior ocean ventilation. The offline model is forced by seasonally varying prescribed velocity, temperature, and salinity fields of a state-of-the-art ocean general circulation model. A seasonally varying mixed layer parameterization is incorporated to account for the degradation of surface convection processes resulting from the temporal averaging. A series of CFC simulations are assessed against observations to investigate interdecadal-time-scale ventilation using a variety of mixed layer criteria. Simulated tracer inventories and penetration depths are in good agreement with observations, especially for thermocline, mode, and surface waters. Deep water from the Labrador Sea is well represented, forming a distinct deep western boundary current that branches at the equator, although concentrations are lower than observed. The formation of bottom water, which occurs around the Antarctic margin, is also generally too weak, although there is excellent qualitative agreement with observations in the region of the Ross and Weddell Seas. Multicentury ventilation of the outflow of North Atlantic Deep Water and bottom water from the Antarctic Margin are investigated using 1000-yr passive tracer experiments with specified interior source regions. The model captures many of the detailed pathways evident from observations, with much of the discrepancy accounted for by differences between actual and modeled topography. A comparison between model-derived “tracer age” and Δ14C “advection age” provides a semiquantitative assessment of model skill at these longer time scales.
A Simple Criterion to Determine the Transition from a Localized Convection to a Distributed Convection Regime*
Authors: Legg Sonya
Published: January 2005

A recent numerical study by Noh et al. of open-ocean deep convection in the presence of a single geostrophic eddy showed that two possible regimes exist: 1) the localized convection regime in which baroclinic instability of the eddy dominates, with slantwise fluxes and restratification, and 2) the distributed convection regime in which vertical mixing dominates. Noh et al. found that localized convection dominates for relatively small buoyancy forcing, strong eddies, and strong surface ambient stratification. Here it is shown that this regime transition can be expressed in terms of a ratio of time scales: the localized convection regime appears when the time scale for lateral fluxes from eddy interior to exterior tL is short in comparison with the time scale for convective erosion of the exterior stratification tc. Scaling arguments give this ratio of time scales as tL/tc ∼ f β2R2B/(A2γ) where f is the Coriolis parameter, R is the radius of the eddy, B is the buoyancy forcing, 1/β is the depth scale of the exponentially decaying surface-intensified stratification, γ is the relative amplitude of the eddy, and Aβ is the value of the surface stratification N20. Comparison with the numerical simulations of Noh et al. shows that this parameter does indeed separate the localized and distributed convection regimes, with the transition occurring at tL/tc ≈ 0.05–0.1.
Identification of the Mechanism of Interdecadal Variability in the North Atlantic Ocean
Authors: te Raa Lianke , Gerrits Jeroen , Dijkstra Henk A.
Published: January 2005

The aim of this paper is to identify the physical mechanism of interdecadal variability in simulations of the North Atlantic Ocean circulation with the Modular Ocean Model of the Geophysical Fluid Dynamics Laboratory. To that end, a hierarchy of increasingly complex model configurations is used. The variability in the simplest case, that of viscous, purely thermally driven flows in a flat-bottom ocean basin with a box-shaped geometry, is shown to be caused by an internal interdecadal mode. The westward propagation of temperature anomalies and the phase difference between the anomalous zonal and meridional overturning that characterize the interdecadal mode are used as “fingerprints” of the physical mechanism of the variability. In this way, the variability can be followed toward a less viscous regime in which the effects of continental geometry and bottom topography are also included. It is shown that, although quantitative aspects of the variability like period and spatial pattern are changing, the physical mechanism of the interdecadal variability in the more complex simulations can be attributed to the same processes as in the simplest model configuration.
The Eddy-Driven Thermocline
Authors: Cessi Paola , Fantini Maurizio
Published: January 2005

The role of baroclinic eddies in transferring thermal gradients laterally, and thus determining the stratification of the ocean, is examined. The hypothesis is that the density differences imposed at the surface by differential heating are a source of available potential energy that can be partially released by mesocale eddies with horizontal scales on the order of 100 km. Eddy fluxes balance the diapycnal mixing of heat and thus determine the vertical scale of penetration of horizontal thermal gradients (i.e., the depth of the thermocline). This conjecture is in contrast with the current thinking that the deep stratification is determined by a balance between diapycnal mixing and the large-scale thermohaline circulation. Eddy processes are analyzed in the context of a rapidly rotating primitive equation flow driven by specified surface temperature, with isotropic diffusion and viscosity. The barotropic component of the eddies is found to be responsible for most of the heat flux, and so the eddy transport is horizontal rather than isopycnal. This eddy transport takes place in the shallow surface layer where eddies, as well as the mean temperature, undergo diabatic, irreversible mixing. Scaling laws for the depth of the thermocline as a function of the external parameters are proposed. In the classical thermocline theory, the depth of the thermocline depends on the diffusivity, the rotation rate, and the imposed temperature gradient. In this study the authors find an additional dependence on the viscosity and on the domain width.
The Motion of a Point Vortex near Large-Amplitude Topography in a Two-Layer Fluid
Authors: White Andrew J. , McDonald N. Robb
Published: January 2005

This work examines the dynamics of point vortices in a two-layer fluid near large-amplitude, sharply varying topography like that which occurs in continental shelf regions. Topography takes the form of an infinitely long step change in depth, and the two-layer stratification is chosen such that the height of topography in the upper layer is a small fraction of the overall depth, enabling quasigeostrophic theory to be used in both layers. An analytic expression for the dispersion relation of free topographic waves in this system is found. Weak vortices are studied using linear theory and, if located in the lower layer, propagate mainly because of their image in the topography. Depending on their sign, they are able to produce significant topographic wave radiation in their wakes. Upper-layer vortices propagate much slower and produce relatively small amplitude topographic wave radiation. Contour dynamics results are used to investigate the nonlinear regions of parameter space. For lower-layer vortices, linear theory is a good approximation, but for upper-layer vortices complicated features evolve and linear theory is only valid for weak vortices.
Mass Flux and Vertical Distribution of Currents Caused by Strong Winds in a Wave Tank
Authors: Ogasawara Toshinori , Yasuda Takashi
Published: January 2005

The velocity fields of wind-driven currents under strong winds were measured in a wind-wave tank with a double bottom. The tank has the characteristics to satisfy partially the continuity of the mass flux and to reduce return-flow effects on the currents. The lower part of the double-bottom tank functions as a duct to circulate the currents, allowing the measurement of the return-flow velocity. The velocity measurements were made on the currents just below the mean water level by using a high-resolution particle image velocimetry (PIV) system and tracking floats and on the currents inside of the duct by using a normal PIV system. Thus, accurate data of the vertical distribution and mass flux of the currents driven by strong winds were obtained from the PIV data. As a result, it is found that the flux in the surface layer with the thickness of 2 times the significant wave height amounts to about 30% of the total mass flux of the currents driven by strong winds with a reference wind speed of 12.0 m s−1.
On the Linear Parameterization of Drag Coefficient over Sea Surface
Authors: Guan Changlong , Xie Lian
Published: January 2005

Combining the logarithmic law with the Charnock relation yields a drag coefficient that is a function of wind speed with the Charnock coefficient as a parameter. It is found that the function is nearly linear within the typically measured range of the drag coefficient. The slope of the linear function is dominated by the Charnock coefficient. When the Charnock relation is extended to a wave age–dependent function, the drag coefficient remains a near-linear function of wind speed after invoking the 3/2 power law. The slope of the linear function is dominated by wave steepness.
Influence of the Surface Heating on Langmuir Circulation
Authors: Min Hong Sik , Noh Yign
Published: January 2005

Large-eddy simulation of the oceanic mixed layer showed that Langmuir circulation (LC) is weakened under the surface heating and is ultimately broken down if the intensity of the surface heating becomes sufficiently strong. The critical condition for the breakdown of LC was mainly determined by the Hoenikker number Ho, and the transition occurs in the range Ho ∼ 1–2. The breakdown of LC leads to a drastic change in the characteristics of the oceanic mixed layer, such as the variation of the rms horizontal velocities with time, the ratio of the horizontal spectra of vertical velocity field, and the pitch. The stability condition for LC suggested by Leibovich was still observed in this simulation. Furthermore, it was found that LC is largely responsible for the formation of a thermocline and the maintenance of a well-mixed layer above it, and the depth of a thermocline was estimated in that case.