New Internet of Things (IoT) technologies such as Long Range (LoRa) are emerging which enable power efficient wireless communication over very long distances. Devices typically communicate directly to a sink node which removes the need of constructing and maintaining a complex multihop network. Given the fact that a wide area is covered and that all devices communicate directly to a few sink nodes a large number of nodes have to share the communication medium. LoRa provides for this reason a range of communication options (centre frequency, spreading factor, bandwidth, coding rates) from which a transmitter can choose. Many combination settings are orthogonal and provide simultaneous collision free communications. Nevertheless, there is a limit regarding the number of transmitters a LoRa system can support. In this paper we investigate the capacity limits of LoRa networks. Using experiments we develop models describing LoRa communication behaviour. We use these models to parameterise a LoRa simulation to study scalability. Our experiments show that a typical smart city deployment can support 120 nodes per 3.8 ha, which is not sufficient for future IoT deployments. LoRa networks can scale quite well, however, if they use dynamic communication parameter selection and/or multiple sinks.

We define semihyperbolicity, a condition which describes non‐positive curvature in the large for an arbitrary metric space. This property is invariant under quasi‐isometry. A finitely generated group is said to be weakly semihyperbolic if when endowed with the word metric associated to some finite generating set it is a semihyperbolic metric space. Such a group is of type FPx and satisfies a quadratic isoperimetric inequality. We define a group to be semihyperbolic if it satisfies a stronger (equivariant) condition. We prove that this class of groups has strong closure properties. Word‐hyperbolic groups and biautomatic groups are semihyperbolic. So too is any group which acts properly and cocompactly by isometries on a space of non‐positive curvature. A discrete group of isometries of a 3‐dimensional geometry is not semihyperbolic if and only if the geometry is Nil or Sol and the quotient orbifold is compact. We give necessary and sufficient conditions for a split extension of an abelian group to be semihyperbolic; we give sufficient conditions for more general extensions. Semihyperbolic groups have a solvable conjugacy problem. We prove an algebraic version of the flat torus theorem; this includes a proof that a polycyclic group is a subgroup of a semihyperbolic group if and only if it is virtually abelian. We answer a question of Gersten and Short concerning rational structures on Zn.

SUMMARYMost studies from Argentina have focused on toxocariasis as an environmental problem of big cities, and there are no available data about children infection from small or middle-sized cities. In order to assess the prevalence of anti-Toxocara antibodies in infantile population, 206 children from Resistencia, of both sexes, aged 1-14 years old were studied by Elisa testing with E/S T. canis L 2 antigens. Hematological parameters and immunoglobulin levels were determined; five days' stool samples were studied and epidemiological data were obtained by means of a questionnaire to parents. Results showed that 73% of the children had one or more dogs living at home, 57% reported geophagia and 37.9% were positive for Toxocara serology, but there was no significant difference in prevalence neither for boys and girls, nor concerning age. An increased risk of infection was observed in age groups 5-6 and 7-8 for boys, and in age groups 3-4 and 5-6 for girls. KEYWORDS: Toxocariasis; Toxocara canis; Visceral larva migrans; SeroprevalenceHuman toxocariasis is probably one of the most widely spread zoonotic nematode infection. Toxocara eggs acquired by hand-to-mouth contact hatch in the stomach and the larvae migrate through human soft tissues leading to visceral larva migrans (VLM) or ocular larva migrans (OLM) 8 . As the parasite does not develop in man until adulthood, the examination of fecal specimens is not helpful; thus the diagnosis of toxocariasis as well as the assessment of its importance in population, can only be achieved through serological tests. In developed countries, VLM has been referred to as the second most common type of helminthic infection; in developing countries, although other helminthiasis are highly prevalent, human toxocariasis is likely to be also very frequent 14 .Most of the studies from Argentina have focused on toxocariasis as an environmental problem of big cities 13,15 ; there are few reports about human infection, particularly in children, and there are no available data from small or middle-sized cities where urban contamination presents different characteristics from those in big ones, due to the particular relationship that its inhabitants establish with the surrounding environment 5 . All these circumstances have led us to assess the prevalence of anti-Toxocara antibodies in a middle-sized subtropical city's infantile population in Argentina.A survey was carried out in Resistencia, a city located in the northeast of Argentina (27º10' S, 58º58' W, and at 53 m above sea level), and characterized by a subtropical climate with hot and humid summers and moderately mild and dry winters (average annual temperature of 20.5 º C; mean annual rainfall of 1350 mm). The city has more than 350,000 inhabitants and people live predominantly in individual houses with front gardens, backyards, and wide sidewalks with a narrow paved area, the rest being bare ground or partially covered by grass. Only 20% of the urban area has paved streets, about 70% of the families own dogs and stray dogs are qui...

No abstract

No abstract

The effect of acute or short-term hypoxia on fetal cardiovascular hemodynamics has been well known; however, little is known about the effect of long-term hypoxemia. To determine the fetal hemodynamic responses to this stress we studied two groups of animals: 1) pregnant ewes (n = 20) at 110-115 days of gestation subjected to hypoxia for up to 28 days and 2) pregnant ewes (n = 4) that served as normoxic controls. We chronically catheterized the fetal brachiocephalic artery and vein. Five to 6 days after surgery, control measurements were made of mean arterial blood pressure, heart rate, arterial PO2, O2 saturation, hemoglobin, hematocrit, blood volume, and the concentrations of erythropoietin, cortisol, epinephrine, and norepinephrine. The next day the ewes were placed in a chamber with an inspired O2 fraction of 12-13%. Within a few minutes fetal arterial PO2 decreased from control value of 29.7 +/- 2.1 to 19.1 +/- 2.1 Torr, where it remained. Hemoglobin increased from 10.0 +/- 1.0 to 12.9 +/- 1.9 g/dl by day 7, where it remained. This was associated with an increase of erythropoietin from 22.8 +/- 2.2 to 144 +/- 37 mU/ml within 24 h, but by day 7 it had returned to levels slightly above normal. Epinephrine also increased moderately and remained elevated throughout the study. However, values of mean arterial pressure and heart rate did not differ from controls. Perhaps surprisingly, these fetuses were able to compensate so that at term their body weights were normal, 3.77 +/- 0.2 kg.

Eiiergy conservation plays a crucial in wireless sensor networks since such networks are designed to be placed in hostile and non-accessible areas. While battery-driven sensors will run out of battery sooner or late< the use of renewable energy sources such as solar power or gravitation may extend the lifetime of a sensor network. We propose to utilize solar power in wireless sensor networks and extend LEACH a well-known cluster-based protocol for sensor networks to become solar-aware. The presented simulation results show that making LEACH solar-aware significantly extends the lifetime of sensor networks.

Wireless sensor networks are based on the collaborative efforts of many small wireless sensor nodes, which collectively are able to form networks through which sensor information can be gathered. Such networks usually cannot operate in complete isolation, but must be connected to an external network to which monitoring and controlling entities are connected. As TCP/IP, the Internet protocol suite, has become the de-facto standard for large-scale networking, it is interesting to be able to connect sensornets to TCP/IP networks. In this paper, we discuss three different ways to connect sensor networks with TCP/IP networks: proxy architectures, DTN overlays, and TCP/IP for sensor networks. We conclude that the methods are in some senses orthogonal and that combinations are possible, but that TCP/IP for sensor networks currently has a number of issues that require further research before TCP/IP can be a viable protocol family for sensor networking.