Life span in online communities.

Recently online communities have attracted great interest and have become an important medium of information exchange between users. The aim of this work is to introduce a simple model of the evolution of online communities. This model describes (a) the time evolution of users' activity in a web service, e.g., the time evolution of the number of online friends or written posts, (b) the time evolution of the degree distribution of a social network, and (c) the time evolution of the number of active users of a web service. In the second part of the paper we investigate the influence of the users' lifespan (i.e., the total time in which they are active in an online community) on the process of rumor propagation in evolving social networks. Viral marketing is an important application of such method of information propagation.

Dynamic phenomena and human activity in an artificial society.

We study dynamic phenomena in a large social network of nearly 3x10;{4} individuals who interact in the large virtual world of a massive multiplayer online role playing game. On the basis of a database received from the online game server, we examine the structure of the friendship network and human dynamics. To investigate the relation between networks of acquaintances in virtual and real worlds, we carried out a survey among the players. We show that, even though the virtual network did not develop as a growing graph of an underlying network of social acquaintances in the real world, it influences it. Furthermore we find very interesting scaling laws concerning human dynamics. Our research shows how long people are interested in a single task and how much time they devote to it. Surprisingly, exponent values in both cases are close to -1 . We calculate the activity of individuals, i.e., the relative time daily devoted to interactions with others in the artificial society. Our research shows that the distribution of activity is not uniform and is highly correlated with the degree of the node, and that such human activity has a significant influence on dynamic phenomena, e.g., epidemic spreading and rumor propagation, in complex networks. We find that spreading is accelerated (an epidemic) or decelerated (a rumor) as a result of superspreaders' various behavior.

Evolution of a social network: the role of cultural diversity.

We present a simple deterministic and based on local rules model of evolving social network, which leads to a network with the properties of a real social system, e.g., small-world topology and assortative mixing. The state of an individual Si is characterized by the values of Q cultural features, drawn from Gaussian distribution with variance sigma. The other control parameter is sociability Ti, which describes the maximal number of connections of an individual. The state of individuals and connections between them evolve in time. As results from numerical computations, an initial diversity of cultural features in a community has an essential influence on an evolution of social network. It was found that for a critical value of control parameter sigma c(Q) there is a structural transition and a hierarchical network with small-world topology of connections and a high clustering coefficient emerges. The emergence of small-world properties can be related to the creation of subculture groups in a community. The power-law relation between the clustering coefficient of a node and its connectivity C(k) approximately k-beta was observed in the case of a scale-free distribution of sociability Ti and a high enough cultural diversity in a population.

Epidemic spreading in a hierarchical social network.

A model of epidemic spreading in a population with a hierarchical structure of interpersonal interactions is described and investigated numerically. The structure of interpersonal connections is based on a scale-free network. Spatial localization of individuals belonging to different social groups, and the mobility of a contemporary community, as well as the effectiveness of different interpersonal interactions, are taken into account. Typical relations characterizing the spreading process, like a range of epidemic and epidemic curves, are discussed. The influence of preventive vaccinations on the spreading process is investigated. The critical value of preventively vaccinated individuals that is sufficient for the suppression of an epidemic is calculated. Our results are compared with solutions of the master equation for the spreading process and good agreement of the character of this process is found.

Localized deficient root development associated with taurodontism: case report.

Dentinal dysplasia type I (DDI) is a rare disturbance in dentin formation. This case report illustrates different radiographic features from other reported DDI cases in that only one quadrant (lower right posterior teeth) has the characteristic of DDI and both right and left upper molars exhibit taurodontism. This finding might be a variation of DDI. However, it is possible that this type of developmental defect could occur because of regionalized abnormalities in cellular function and proliferation as occurs in regional odontodysplasia.

Measuring cardiac output in critically Ill patients: disagreement between thermodilution-, calculated-, expired gas-, and oxygen consumption-based methods.

Calculated values of oxygen consumption have been used to calculate a Fick cardiac output when thermodilution measurements are unreliable and when oxygen consumption measurements are unavailable. To determine the accuracy of these calculations, we measured cardiac output in 20 patients by four methods: (1) a reference Fick cardiac output calculated from metabolic oxygen consumption measurements and arterial-venous oxygen content difference (COmet); (2) thermodilution cardiac output (COtherm), (3) an estimated Fick cardiac output based on calculated oxygen consumption using standard equations (COcalc), and (4) an estimated Fick cardiac output using a bedside measurement of expired carbon dioxide production (COexp). The mean difference +/- 95% limits of agreement between COtherm and COmet was 1.71 +/- 5 liters/min. The mean difference between COcalc and COmet was -0.04 +/- 3.33 liters/min. The mean difference between COexp and COmet was 0.31 +/- 3.01 liters/min. On the basis of these wide confidence intervals, we conclude that (1) thermodilution and metabolic measurements of cardiac output frequently differ in critically ill patients, and (2) estimates of oxygen consumption, based on either standard equations or on expired carbon dioxide production measurements, are poor substitutes for metabolic measurements of oxygen consumption in critically ill subjects and may provide inaccurate estimates of cardiac output.

Pharmacologic characterization of a novel histamine receptor on human eosinophils.

There is increased recognition that lung mast cell mediators not only produce the symptoms of acute asthma, but also result in the recruitment and activation of additional proinflammatory cells, such as eosinophils. Histamine, one of the major mast cell mediators, is known to have numerous effects on eosinophil function. These effects of histamine are mediated by distinct receptors on the surface of eosinophils, only some of which have been characterized. Prior studies have suggested that eosinophils have non-H1, non-H2 histamine receptors which mediate the chemotactic effects of histamine. We observed previously that the histamine-induced increase in cytosolic calcium in human eosinophils could not be blocked by classic H1 or H2 antagonists, but could be inhibited by the H3 antagonist thioperamide. The purpose of this study was to further characterize the pharmacologic properties of this calcium-linked histamine receptor. Using Fura-2 loaded eosinophils to measure the concentration of cytosolic calcium, we examined the effect of additional histamine receptor antagonists and agonists. We found that the pKb for the H3 antagonists thioperamide, impromidine, and burimamide (8.1, 7.6, and 7.2, respectively), were similar to those reported for H3 receptors in the central nervous system, suggesting that the eosinophil histamine receptor was similar to H3 receptors. However, when the known H3 agonists were tested for activity ([R]-alpha-methylhistamine, N alpha-methylhistamine), the potencies of these compounds were much less than the potency of histamine itself, indicating a significant difference between H3 receptors and this eosinophil histamine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of obstructive sleep apnea.

Sleep-disturbed breathing, which includes apneas, hypopneas, and oxygen desaturations, occurs in asymptomatic individuals and increases with age. Obstructive apnea is the most frequent type of respiratory disturbance documented by polysomonography, the gold standard test for assessing sleep-disturbed breathing. Many of the prevalence studies done to date have had one or more methodological weaknesses, including selection biases, varying definitions of obstructive sleep apnea, failure to distinguish types of apneas, failure to control for confounding variables, and small sample size. Although there is consensus on the definitions of sleep-disturbed breathing, the appropriate number of apneas and hypopneas for diagnosing clinically significant obstructive sleep apnea is uncertain. While the cutoff of five or more apneas and hypopneas per hour is historically considered abnormal, the origins of this number are vague, and the longevity of those who have this value on polysomnography is not necessarily reduced. This is particularly true among those without symptoms of obstructive sleep apnea syndrome, which include excessive daytime sleepiness, snoring, nocturnal awakenings, and morning headaches. Investigators should be careful to distinguish symptomatic study subjects from asymptomatic subjects, and to exclude central apneas in calculating their estimates. In addition, various studies have used different definitions of sleep apnea syndrome, making comparisons of point estimates difficult. It would be more appropriate for researchers to estimate morbidity and mortality indices with confidence intervals, using several different cutoff points. Subject selection in all studies should follow a two-stage sampling procedure. All subjects with symptoms compatible with obstructive sleep apnea syndrome and a subsample of asymptomatic individuals should be studied with all-night polysomnography. If portable monitoring is used, the validity and reproducibility of this diagnostic method should be assessed. Subjects with significant comorbidity should be excluded from prevalence studies. Factors that clearly increase the risk of sleep-disturbed breathing and obstructive sleep apnea and its related symptoms include age, structural abnormalities of the upper airway, sedatives and alcohol, and probably family history. Although endocrine changes such as growth hormone, thyroid hormone, and progesterone deficiency also have been suggested as risk factors for exacerbating obstructive sleep apnea syndrome, there is minimal epidemiologic evidence to support this. Case-control studies are recommended to assess the relation of endocrine factors to obstructive sleep apnea syndrome in a rigorous fashion. A limited number of mortality studies have suggested decreased survival in persons with the obstructive sleep apnea syndrome, possibly primarily due to vascular-related disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Sporothrix schenckii fungemia without disseminated sporotrichosis.

Fungemia is a rare complication of Sporothrix schenckii infection and has always been associated with disseminated sporotrichosis. We describe an immunocompetent patient with localized lymphocutaneous sporotrichosis from whose blood the fungus was isolated. A lysis-centrifugation blood culture system may have improved our ability to detect low-level S. schenckii fungemia.

Treatment of superior vena cava thrombosis with recombinant tissue type plasminogen activator.

Thrombotic occlusion of the superior vena cava is an uncommon but serious complication of chronic indwelling venous catheters. Several reports have shown thrombolytic therapy with intravenous streptokinase or urokinase to be effective in the treatment of this condition. We report a case of superior vena cava thrombosis in a 53-year-old woman receiving chemotherapy for breast carcinoma through a subcutaneously implanted venous access catheter who was successfully treated with peripheral infusion of recombinant tissue type plasminogen activator (rtPA).

Alcoholic cardiomyopathy.

The natural course of alcoholic cardiomyopathy is one of progressive left ventricular dysfunction and early demise. The author reports a case of normalization of severe left ventricular dysfunction over a prolonged period in a patient with alcoholic cardiomyopathy who abstained from alcohol.

Survey of noncortical afferent projections to the basilar pontine nuclei: a retrograde tracing study in the rat.

The retrograde transport of the conjugate wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was used in the rat to identify the cell bodies of origin for all subcortical projections to the basilar pontine nuclei (BPN). A parapharyngeal surgical approach was used to allow the injection micropipette to enter the BPN from the ventral aspect of the brainstem and thus avoid any potential for false-positive labeling due to transection and injury-filling of axonal systems located dorsal to the basilar pontine gray. A surprisingly large number of BPN afferent cell groups were identified in the present study. Included were labeled somata in the lumbar spinal cord and a large variety of nuclei in the medulla, pons, and midbrain, as well as labeled cells in diencephalic and telencephalic nuclei such as the zona incerta, ventral lateral geniculate, hypothalamus, amygdala, nucleus basalis of Meynert, and the horizontal nucleus of the diagonal band of Broca. Quite a number of cell groups known to project directly to the cerebellum also exhibited labeled somata in the present study. To explore the possibility that such neurons were labeled because their axons were transected and injury-filled as they coursed through the BPN injection site to enter the cerebellum via the brachium pontis, a series of rats received complete, bilateral lesions of the brachium pontis followed 30-60 minutes later with multiple, diffuse injections of WGA-HRP (12-16 placements per animal) throughout the cerebellar cortex. In another series of animals, the massive cerebellar WGA-HRP injections were not preceded by brachium pontis lesions. In the latter cases, each of the cell groups in question that were known to project directly to the cerebellum exhibited labeled somata. However, when the cerebellar HRP injections were preceded by brachium pontis lesions, each of the cell groups in question continued to exhibit labeled somata in numbers comparable to that observed in the nonlesion cases. This implies that such neurons project to the BPN and the cerebellar cortex and that the axons of these particular neurons do not project to the cerebellum via the brachium pontis.

Collateral branches of cerebellopontine axons reach the thalamus, superior colliculus, or inferior olive: a double-fluorescence and combined fluorescence-horseradish peroxidase study in the rat.

Retrograde double-labeling methods that used two different fluorescent dyes or a fluorescent dye in combination with wheat germ agglutinin horseradish peroxidase were used in the rat to study the collateralization of cerebellopontine fibers to the thalamus, the superior colliculus, or the inferior olive. In cases with combined basilar pontine nuclei and thalamus injections, double-labeled neurons were located in the rostral part of the lateral cerebellar nucleus as well as within the interpositus anterior and interpositus posterior nuclei. These cells are medium to large in size and multipolar-shaped. A much smaller number of double-labeled cells was observed in the combined basilar pontine nuclei and superior colliculus injections. In these cases most of the double-labeled cells were intermediate- to large-sized and either bipolar- or multipolar-shaped. Such neurons were distributed throughout the rostrocaudal extent of the lateral cerebellar nucleus, with only a few double-labeled cells located in the interpositus anterior and posterior nuclei. Finally, in the cases with combined basilar pontine nuclei and inferior olive injections, double-labeled cells were located in interpositus anterior and posterior nuclei and the medial portion of the lateral cerebellar nucleus. The double-labeled cells were relatively small in size and most were spindle-shaped. No double-labeled cells were observed in the medial cerebellar nucleus in any of the three injection combinations. Based upon the observation of double-labeled neurons in the deep cerebellar nuclei in each of the three injection combinations involving the basilar pontine nuclei, we conclude that cerebellar projections to the basilar pons arise in part as collaterals of axons that project to the thalamus, superior colliculus, or the inferior olive.

A review of recent observations concerning the synaptic organization of the basilar pontine nuclei.

Ultrastructural studies are described that have identified in the basilar pontine nuclei (BPN), the synaptic boutons formed by the corticopontine, cerebellopontine, tectopontine, and dorsal column nuclei-pontine afferent projection systems. In addition, immunocytochemical studies visualized neuronal somata, dendrites, and synaptic boutons that contain immunoreactivity for GABA or the synthesizing enzyme glutamic acid decarboxylase (GAD). Based upon differences in the mode of degeneration and postsynaptic locus of degenerative synaptic boutons in the BPN, it is suggested that two types of cortical neurons and three classes of deep cerebellar nuclear cells project to the BPN. For similar reasons, it appears that two types of neurons in the dorsal column nuclei project to the BPN while only one type of afferent synaptic bouton takes origin from the superior colliculus. Furthermore it appears that the population of BPN neurons projecting to the paramedian lobule receives convergent inputs from the cutaneous periphery and the corresponding region of sensorimotor cortex. Studies employing GAD immunohistochemistry indicate that GABA-ergic neurons and axon terminals are present in the BPN and thus support the suggestion that a local inhibitory interneuron is present within the BPN. Taken together these observations suggest that basilar pontine neurons might play a more active role in the integration of various types of information destined for the cerebellar cortex than has previously been recognized.

A double retrograde fluorescent tracing analysis of dorsal column nuclear projections to the basilar pontine nuclei, thalamus, and superior colliculus in the rat.

Injections of the fluorescent dyes Nuclear yellow and True blue were used to determine that the dorsal column nuclei project in collateral fashion to the basilar pontine nuclei (BPN) and the ventral posterolateral nucleus of the thalamus or the BPN and the superior colliculus. Results indicated that relatively few dorsal column nuclear cells project to both the basilar pons and the superior colliculus. In contrast, many dorsal column nuclear cells that project to the BPN also give rise to collateral projections to the thalamus. Thus it is suggested that the latter dorsal column-BPN connections might at least represent in part the anatomical substrate for the electrophysiological demonstration that cerebellar granule cells can be activated at relatively short latency by peripheral tactile receptor stimulation.

Convergence of cortico- and cuneopontine projections onto components of the pontocerebellar system in the rat: an anatomical and electrophysiological study.

Previous studies in the rat have demonstrated that corresponding peripheral tactile and somatosensory cortical inputs converge within the granule cell layer of various cerebellar lobules and further that descending corticopontine projections from the forelimb sensory cortex (FLSCx) partially overlap with the projection zones of ascending basilar pontine afferents from nucleus cuneatus (NC). The present study employed anatomical and electrophysiological procedures to determine whether cortical and dorsal column nuclear afferent projections converge on pontine neurons that, in turn, provide mossy fiber input to the granule cell layer of the paramedian lobule (PML), i.e., that portion of the rodent cerebellum shown to receive forelimb peripheral inputs. The combination of the orthograde and retrograde axonal transport of horseradish peroxidase (HRP) conjugated to wheat germ agglutinin (WGA) was used light microscopically to demonstrate that orthogradely labeled projections from injections of the FLSCx and NC converged with ponto-paramedian projection neurons that were retrogradely labeled from injections of the PML. These studies were also repeated in conjunction with ablations of either the FLSCx or NC which resulted in the ultrastructural identification of degenerating, as well as WGA-HRP labeled axonal boutons of these pontine afferent projections thus confirming that such projections actually formed synaptic contacts with the retrogradely labeled pontoparamedian projection neurons. Single unit recording analyses of neurons in the ventromedial region of the basilar pons following combined electrical stimulation of various regions of the sensorimotor cortex and the contralateral body surface indicated that approximately 40% of all cells recorded responded to electrical stimulation of corresponding regions of the cortex and periphery, particularly the FLSCx and the forepaw. Natural cutaneous stimuli applied to the forepaw that also elicited responses in these same groups of basilar pontine neurons and were associated with relatively small receptive fields. Taken together, these observations indicate that the previously observed convergence of peripheral and somatosensory cortical inputs within the granule cell layer of the cerebellar cortex may be at least partially organized at the level of the basilar pons.

Remodeling of dorsal column nuclear efferents to the basilar pontine gray after cortical ablations in newborn rats.

In view of previous reports documenting corticopontine remodeling in response to neonatal cerebral cortical lesions, we examined possible alterations of ascending pontine afferents from the dorsal column nuclei after the same types of neonatal lesion. Two anterograde tracing techniques, autoradiography and the Fink-Heimer silver degeneration method, were combined to facilitate a topographic analysis. The distribution patterns of cuneo- and gracilopontine terminations appeared expanded in response to neonatal sensorimotor cortical lesions, as compared to non-lesioned animals.

Atypical endocrine tumors of the lung: a histologic, ultrastructural, and clinical study of 19 cases.

Lung cancers are divided by light microscopic criteria into several categories, but only two categories are recognized clinically--small cell and non-small cell carcinomas. Transmission electron microscopy has revealed unexpected complexity within each category, blurring the distinctions between them. The present study was undertaken to determine the incidence of dense-core, neuroendocrine-type granules in lung tumors diagnosed by light microscopy as non-small cell carcinomas, i.e., atypical endocrine tumors, and the clinical significance of their identification. Of 205 consecutive primary and metastatic lung cancers, 19 (9 per cent) diagnosed as non-small cell carcinomas by light microscopy were seen to contain neuroendocrine-type granules by electron microscopy and thus were reclassified as atypical endocrine tumors of the lung. Staining with silver stains, periodic acid-Schiff (PAS), PAS with diastase digestion, and mucicarmine was positive in 18, 15, 14, and eight of the 19 cases, respectively. Electron microscopy revealed glandular differentiation in 12 cases and tonofilaments in eight cases, although none of the tumors met the criteria for identification as squamous cell carcinomas. Clinically, the cancers appeared to resemble non-small cell carcinoma more closely than small cell carcinoma. Median survival (12 months) and response to combination chemotherapy (22 per cent) were in the range reported for non-small cell carcinoma. There were no complete responses, despite the use in some cases of regimens active against small cell carcinoma. However, one patient, the only one to date so treated, had a dramatic response to streptozotocin/5-fluorouracil, suggesting that, as in metastatic carcinoid, this combination may have value in the treatment of atypical endocrine tumors of the lung.

Origin and ultrastructural identification of dorsal column nuclear synaptic terminals in the basilar pontine gray of rats.

The ultrastructural characteristics of HRP-WGA-labeled or degenerating axon terminals arising from neurons in the dorsal column nuclei (DCN) were identified within the contralateral basilar pontine nuclei (BPN) following unilateral HRP-WGA injections or ablations of the DCN. The cells of origin of these projections were also identified through the application of the retrograde tracer HRP-WGA. Two groups of degenerating DCN-pontine terminals were identified. Both formed asymmetrical synaptic contacts with dendritic shafts and/or dendritic appendages of pontine neurons. One group of degenerating terminals contained small, round synaptic vesicles, while the other exhibited a mixture of dense core and pleomorphic vesicles. The former group, which clearly represented the majority of degenerating terminals observed, was interpreted to progress from an early filamentous form of degeneration to a later electron-dense variety and to originate from dorsally located DCN cells distributed primarily at the level of and just caudal to the area postrema. Other DCN-labeled neurons were more ventrally located and were postulated to give rise to those degenerative boutons that contained a mixture of dense core and pleomorphic-shaped vesicles. The present study also identified the cells of origin of two additional projections to the basilar pons: one from cells in the external cuneate nucleus and another from neurons of the medullary reticular formation.