Persistence of social signatures in human communication.

The social network maintained by a focal individual, or ego, is intrinsically dynamic and typically exhibits some turnover in membership over time as personal circumstances change. However, the consequences of such changes on the distribution of an ego's network ties are not well understood. Here we use a unique 18-mo dataset that combines mobile phone calls and survey data to track changes in the ego networks and communication patterns of students making the transition from school to university or work. Our analysis reveals that individuals display a distinctive and robust social signature, captured by how interactions are distributed across different alters. Notably, for a given ego, these social signatures tend to persist over time, despite considerable turnover in the identity of alters in the ego network. Thus, as new network members are added, some old network members either are replaced or receive fewer calls, preserving the overall distribution of calls across network members. This is likely to reflect the consequences of finite resources such as the time available for communication, the cognitive and emotional effort required to sustain close relationships, and the ability to make emotional investments.

Suppressing cascades of load in interdependent networks.

Understanding how interdependence among systems affects cascading behaviors is increasingly important across many fields of science and engineering. Inspired by cascades of load shedding in coupled electric grids and other infrastructure, we study the Bak-Tang-Wiesenfeld sandpile model on modular random graphs and on graphs based on actual, interdependent power grids. Starting from two isolated networks, adding some connectivity between them is beneficial, for it suppresses the largest cascades in each system. Too much interconnectivity, however, becomes detrimental for two reasons. First, interconnections open pathways for neighboring networks to inflict large cascades. Second, as in real infrastructure, new interconnections increase capacity and total possible load, which fuels even larger cascades. Using a multitype branching process and simulations we show these effects and estimate the optimal level of interconnectivity that balances their trade-offs. Such equilibria could allow, for example, power grid owners to minimize the largest cascades in their grid. We also show that asymmetric capacity among interdependent networks affects the optimal connectivity that each prefers and may lead to an arms race for greater capacity. Our multitype branching process framework provides building blocks for better prediction of cascading processes on modular random graphs and on multitype networks in general.

Improving community detection in networks by targeted node removal.

How a network breaks up into subnetworks or communities is of wide interest. Here we show that vertices connected to many other vertices across a network can disturb the community structures of otherwise ordered networks, introducing noise. We investigate strategies to identify and remove noisy vertices ("violators") and develop a quantitative approach using statistical breakpoints to identify when the largest enhancement to a modularity measure is achieved. We show that removing nodes thus identified reduces noise in detected community structures for a range of different types of real networks in software systems and in biological systems.

Origin of compartmentalization in food webs.

The response of an ecosystem to perturbations is mediated by both antagonistic and facilitative interactions between species. It is thought that a community's resilience depends crucially on the food web--the network of trophic interactions--and on the food web's degree of compartmentalization. Despite its ecological importance, compartmentalization and the mechanisms that give rise to it remain poorly understood. Here we investigate several definitions of compartments, propose ways to understand the ecological meaning of these definitions, and quantify the degree of compartmentalization of empirical food webs. We find that the compartmentalization observed in empirical food webs can be accounted for solely by the niche organization of species and their diets. By uncovering connections between compartmentalization and species' diet contiguity, our findings help us understand which perturbations can result in fragmentation of the food web and which can lead to catastrophic effects. Additionally, we show that the composition of compartments can be used to address the long-standing question of what determines the ecological niche of a species.

Community structure in directed networks.

We consider the problem of finding communities or modules in directed networks. In the past, the most common approach to this problem has been to ignore edge direction and apply methods developed for community discovery in undirected networks, but this approach discards potentially useful information contained in the edge directions. Here we show how the widely used community finding technique of modularity maximization can be generalized in a principled fashion to incorporate information contained in edge directions. We describe an explicit algorithm based on spectral optimization of the modularity and show that it gives demonstrably better results than previous methods on a variety of test networks, both real and computer generated.

Mixture models and exploratory analysis in networks.

Networks are widely used in the biological, physical, and social sciences as a concise mathematical representation of the topology of systems of interacting components. Understanding the structure of these networks is one of the outstanding challenges in the study of complex systems. Here we describe a general technique for detecting structural features in large-scale network data that works by dividing the nodes of a network into classes such that the members of each class have similar patterns of connection to other nodes. Using the machinery of probabilistic mixture models and the expectation-maximization algorithm, we show that it is possible to detect, without prior knowledge of what we are looking for, a very broad range of types of structure in networks. We give a number of examples demonstrating how the method can be used to shed light on the properties of real-world networks, including social and information networks.

Vertex similarity in networks.

We consider methods for quantifying the similarity of vertices in networks. We propose a measure of similarity based on the concept that two vertices are similar if their immediate neighbors in the network are themselves similar. This leads to a self-consistent matrix formulation of similarity that can be evaluated iteratively using only a knowledge of the adjacency matrix of the network. We test our similarity measure on computer-generated networks for which the expected results are known, and on a number of real-world networks.

Oncogenic osteomalacia: imaging studies.

X-ray und NMR imaging studies of a 34-year-old patient with tumor-induced hypophosphatemic osteomalacia (OM) are presented. Besides typical features of OM, periosteal new bone formation was noticed initially. After 17 months of conservative treatment with supplements of inorganic phosphorus and 1,25-dihydroxyvitamin D, bone density had increased but Looser's zones were still present, while periosteal new bone formation was strikingly less evident. At this time a tumor in the first left metatarsal space became palpable, was surgically excised and proved to be a low-grade synovial sarcoma with hypervascular and partially calcified structures. Six months later an X-ray survey showed no more signs of metabolic osteopathy. Preoperatively, the pronounced vascularity of the tumor could be demonstrated by angiography and NMR scanning.

[Sphincter-preserving radiotherapy of anal carcinoma]. / Sphinktererhaltende Strahlentherapie des Analkarzinoms.

During the last decade radiotherapy, in combination with chemotherapy, has become the treatment of choice in cure of anal carcinoma with preservation of anal function, and has replaced abdominoperineal resection (APR). From 1979-1990 54 patients with anal carcinoma were treated by radiotherapy. 24 patients received radiotherapy after APR (12 adjuvant, 12 after recurrence). 11 received palliative radiotherapy without prior APR. 19 patients were treated curatively, 17 of whom received a combination of external irradiation followed by interstitial iridium implantation in a split course regimen. 11 of the 19 patients received short simultaneous chemotherapy (mitomycin C and 5-fluorouracil). All 19 patients had a complete remission. 18/19 patients had no local recurrence after mean 14 months' follow-up. 2 patients developed regional recurrence. 3 patients died of other causes. Colostomy was necessary in 5/19 patients with anal necrosis which was dose-related. The maximum tolerated dose was 71.4 Gy. Our results support the recommendation in the literature of primary, curative, radiotherapy and chemotherapy of anal carcinoma with preservation of the anal sphincter.

[Cardiac function and the skin microcirculation in acromegaly]. / Kardiale Funktion und kutane Mikrozirkulation bei Akromegalie.

The microcirculation was measured by nail-fold capillary video microscopy in 21 patients (12 men, 9 women; mean age 54.7 [29-74] years) with acromegaly. Levels of growth hormone (12.0-71.7 microU/ml) and of somatomedin C (2.4-10.5 IU/ml) were elevated in 10 patients, despite preceding treatment. Eleven patients had an increase in myocardial thickness and nine had impairment of left ventricular function, although only slight in most. Left ventricular hypertrophy was demonstrable even in the absence of hypertension. No patient had evidence of coronary heart disease. Nail-fold capillary video microscopy (capillary density, torque index, reactive hyperaemia, epidermal blood flow) failed to distinguish between successfully treated patients and those with persistently elevated growth hormone concentrations or disease duration of over 5 years. There was no evidence of inadequate capillary blood flow as a cause of abnormal function in hypertrophied organs.

Hypomagnesaemia-induced hypocalcaemia: concentrations of parathyroid hormone, prolactin and 1,25-dihydroxyvitamin D during magnesium replenishment.

Three patients with hypomagnesaemia-induced hypocalcaemia were investigated during the phase of magnesium replenishment. Before treatment, serum levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were at the lower limit of normal. In spite of a rapid rise of parathyroid hormone (PTH) after intravenous administration of magnesium, a reactive increase in 1,25-dihydroxyvitamin D in serum was absent or delayed. The increase of serum calcium into the normal range occurred before any consistent change in the concentrations of this vitamin D metabolite. The rise of serum prolactin in response to the increase in PTH was blunted or absent, and is a further example of a transient PTH resistance during the phase of magnesium replenishment.

Mechanisms of hypocalcaemia in the clinical form of severe magnesium deficit in the human.

Severe magnesium depletion leading to hypocalcaemia has been described in a variety of clinical settings. Inadequately low concentrations of parathyroid hormone (PTH) are a constant feature of hypomagnesaemic hypocalcaemia (HMHC), while target organ resistance to PHT in kidneys and bone may be demonstrated in the majority of these patients. The failure of membrane-bound adenylate cyclase in the parathyroids, kidneys and bone, thought to be the most important molecular mechanism in HMHC, cannot explain the concomitant resistance to vitamin D and its metabolites. In recent years, information has accumulated on further magnesium-dependent intracellular events and alternative pathways of transcellular signalling. This may eventually allow the identification of one or more further biochemical mechanisms leading to hypocalcaemia in severe magnesium deficiency.

Development of a luminescence immunoassay for follitropin suitable for clinical routine.

We developed a luminescence immunoassay (LIA) for follitropin, based on the synthesis of a follitropin-N-(4-aminobutyl)-N-ethylisoluminol conjugate. The luminescence tracer was purified by gel chromatography. Antibody-bound and non-bound tracer fractions were separated by using a second antibody reagent bound to magnetic particles. The assay can be performed within 24 hours and is sufficiently sensitive for the measurement of all clinically relevant follitropin concentrations including the subnormal range.

Tumor-induced osteomalacia: pre- and postoperative biochemical findings.

A patient with late-onset hypophosphatemic osteomalacia was treated with oral supplements of phosphate (1.5 g/day) and calcitriol (1.5-3.0 micrograms/day) for 17 months, before a slowly growing tumor in the first metatarsal space became evident. Before treatment concentrations of inorganic phosphate (Pi) and calcitriol in serum and tubular reabsorption of phosphate (TRP) were very low, calcium and parathyroid hormone (PTH) in serum were normal, urinary cyclic adenosine monophosphate (cAMP) was strongly elevated. During the first weeks of conservative treatment urinary cAMP returned to normal; concomitantly there was a transient slight fall in PTH. Serum calcium was in the low normal range and did not significantly change during conservative therapy. During the further course PTH rose to pretreatment values, but urinary cAMP remained normal. When the dose of calcitriol was elevated to 3 x 1.0 micrograms/day, leading to slightly elevated serum concentrations of this substance, Pi in serum rose to the low normal range, but TRP remained low and bone pain, although improved, did not subside. The tumor was locally excised. Postoperatively calcitriol concentration became elevated within 48 hours and remained so for several weeks. The rise in calcitriol concentration preceded the elevation of Pi in serum, not, however, the increase of TRP. The elevation of urinary cyclic AMP before therapy may have been due to a direct action of the substance secreted by the tumor.

[Hypomagnesemia-induced hypocalcemia: functional hypoparathyroidism, parathyroid hormone- and vitamin D-resistant]. / Die Hypomagnesiaemie-bedingte Hypocalciaemie: Funktioneller Hypoparathyreoidismus, Parathormon- und Vitamin D-Resistenz.

In four patients with severe hypomagnesemia, hypocalcemia, and functional hypoparathyroidism (three patients with shortened bowel, one with alcoholism), sequential measurements of parameters of calcium metabolism were performed before and during intravenous administration of magnesium. Parathyroid hormone was immeasurably or inadequately low in all patients before magnesium injection, but rapidly rose to elevated values thereafter. Even without calcium supplements, serum calcium rose to normal levels within 2-5 days, although 1,25(OH)2-Vitamin D levels did not rise significantly. In the patient with alcoholism, hypophosphatemia developed during the first days after admission; the rise of serum calcium preceded the elevation of cyclic adenosine monophosphate in urine. A transient rise of urinary calcium was observed in two patients after initiation of magnesium therapy, with a subsequent fall to subnormal levels in spite of normal serum calcium concentrations. The findings were considered to be due to partial parathyroid hormone resistance during the phase of magnesium replenishment.

[Familial nonneoplastic inappropriate thyrotropin secretion]. / Familiäre, nicht-neoplastische inadäquate Thyreotropin-Inkretion.

A follicular thyroid carcinoma was suspected in a 62-year-old woman after the fifth goitre excision for non-neoplastic inappropriate thyrotropin secretion. Small-follicular adenoma could not be excluded histologically. After an attempt at thyrotropin suppression with L-thyroxine, triiodothyronine, D-thyroxine with L-thyroxine, and bromocriptine had failed, lasting if partial decrease in the maximally elevated TSH levels was achieved with triiodothyroacetic acid (TRIAC). One of the patient's three daughters also has non-neoplastic inappropriate thyrotropin secretion and has had two goitre excisions. It is most likely a familial form of inappropriate TSH secretion.

Tumoral calcinosis. Observations during six years.

Findings of a 56 year old woman suffering from tumoral calcinosis, who was treated for 6 years, are presented. Under conditions known to lead to negative calcium-phosphorus balance, a reduction in tumor size was seen. Transient hypercalcemia was attributed to immobilization. The process of tumor reduction was not definitely accelerated by treatment with ethane-hydroxy-diphosphonate (EHDP; 500 mg/day for 20 months). Nephrotic syndrome as a consequence of amyloidosis developed. Amyloidosis seems to have resulted from the aseptic histiocytic inflammatory process in the tumors. The possible importance of high cholesterol in very low density lipoproteins in the serum of the patient is discussed.

Functional difference between "classical" neurosecretory material and vasopressin-like substances of the outer layer of the median eminence.

In female Wistar rats the influence of adrenalectomy and NaCl administration on the amount of "classical" neurosecretory material (cNSM) in the supraoptico-hypophysial system and on vasopressin-like substance-containing granules (vlG) in the outer layer of the median eminence has been studied. In conjunction with appropriate sodium replacement, adrenalectomy induces an increase in the amount of vlG but does not alter the amount of cNSM. Administration of hypertonic saline diminishes cNSM but has not or only little influence on the amount of vlG. From the findings it is concluded that cNSM and vlG, in spite of their identical histochemical and immunohistochemical properties, have different functions. The functional significance of the vlG is discussed.

Tumoral calcinosis: accumulation of bone-seeking tracers in the calcium deposits.

Rapid and preferential uptake of 47 calcium 87m Strontium by the multinodular calcareous masses was seen in a patient with tumoral calcinosis. Using 87m Strontium, scintigraphic imaging of the tumors was achieved, while the skeleton was barely visible. More intense accumulation of 87m Sr. in one tumor suggested a higher rate of calcium depostion. This was in agreement with the observation that this tumor showed less tendency to decrease in size during calcium and phosphorus deprivation therapy. Quantitative measurements of the uptake of bone seeking tracers by the tumors may be of value in estimating calcium turnover in the calcified masses.