Hierarchy levels in the control of blood flow to the hind limb of the dog

In order to quantitatively assess the dynamic interactions between different levels of the O₂ transport system control hierarchy from the dynamics of the relative contribution by individual cardiovascular and respiratory variables to the response of the system to stress, flow perturbations were introduced in the hind leg of greyhounds by:1) passive motion of the biceps muscle, 2) electrical stimulation (el. stim.) of the muscle nerve, 3) el. stim. of the femoral and sciatic nerve, 4) el. stim. of the proximal end of both nerves, 5) el. stim. of the peripheral end of both nerves, 6) peripheral stimulation after autonomic blockers and 7) peripheral stimulation after Flaxedil. The following variables were continuously measured: upper and lower inflow in the biceps, inflows into the stimulated and the contralateral leg, O₂ saturation of the venous outflow from the muscle and the leg, arterial pressure, heart rate, respiratory rate and tidal volume; and their responses to perturbations were characterized by four parameters [delay time, initial slope, maximum (or minimum) and average response]. Of these, the slope was found to be the most sensitive index of stimulus specificity, while the traditionally measured steady state response, although an important consideration for performance adaptation to stress, does not permit a differentiation between the various control mechanisms which mediate the response. These results indicate that the low frequency dynamics of cardiovascular and respiratory performance contain essential information about the type of control arrangement existing at a given moment. Marked differences in both time course and magnitude of flow responses in vascular beds arranged in parallel and in series were observed with corresponding differences in the changes of the O₂ content of their respective venous outflows. From the ranking of the four parameters a numerical estimate of the overall response as well as of its peripheral and central components was obtained. Between the different experimental conditions the spectrum of the overall responses ranged from predominance of centrally mediated control mechanisms (as judged by the magnitude of the contribution by central indicators) to predominance of locally mediated control mechanism. The latter depended on the presence of increased metabolic activity. If hierarchy levels are defined functionally (rather than structurally) on the basis of the magnitude of the response of the different indicators our results show a complete reversal of the hierarchical ordering between stimulation of the proximal and peripheral end of the sciatic and femoral nerve. An appropriate choice of sufficient and adequate parameters for the characterization of integrated response pattern is a crucial prerequisite for this type of analysis.Supported by Program Project Grant HL 11747 from NHLI.     

中小尺度生态用地规划方法

生态用地指以发挥自然生态功能为主,具有重要生态系统服务功能或生态环境脆弱、生态敏感性较高的土地。它是土地利用与生态建设的直接联系,关系区域生态系统的稳定性和安全性。生态用地的研究有利于建立合理的土地利用系统,完善区域生态安全格局,促进经济社会发展与生态环境相协调。在不同尺度下,生态用地的内涵、性质、主导功能以及规划方法都有所不同,结合我国土地利用规划及城市规划的层次划分,选取市域和中心城区为研究范围,其中市域为中尺度代表范围,中心城区为小尺度代表范围,分别分析了两种尺度下生态用地的内涵及区别,提出了相应的规划方法及侧重点。定量规划方面,中心城区生态用地主要结合国家相关法规、规定、政策等确定;而市域生态用地采取借鉴法、土地利用结构数量优化方法以及情景分析三种方法综合确定。空间规划方面,城区生态用地采取分类规划方法,分别对点线面三类生态用地进行提取,主要步骤为辨识重要生态源,构建面状生态用地;结合水体和交通缓冲区,构建线状生态用地;提取关键节点,构建点状生态用地;生态用地分类。市域生态用地则采取综合规划方法,主要步骤为提取特殊生态用地、基于生态用地结构功能和生态敏感性等的生态建设重要性评价、生态用地空间提取及分类。     

Flow in tubes and arteries--a comparison

The cardiovascular circulatory system of the human body can be compared with a network of tubes. It consists of a pump and a system of branched vessels. The arteries transport the blood to the periphery in a manner similar to that of a water supply network. It is important to know what kind of forces act upon "fittings", bends and bifurcations. It is also essential to assess whether the flow is laminar or turbulent, attached or separated. The flow should be optimized in such a manner as to minimize the drop in pressure. This means that no additional pressure loss due to separation or turbulence should occur, since such losses increase the pump power requirements. The loss appears in heating and acoustic energy. The necessary understanding of blood flow in human vessels is also of great interest to physicians since it is believed that the local flow behavior of blood determines the formation of atherosclerotic plaques. As in tubing systems, deposits in blood vessels are found close to bends and bifurcations. These deposits lead to impaired cerebral circulation and to myocardial infarction. A partial review of recent research into the details of flow behavior (like separation, stagnation and reattachment points) in bends and bifurcations of arterial models is presented. Studies involving steady and pulsatile flow conditions in rigid and elastic models with Newtonian and non-Newtonian fluids are shown here. The most important differences between blood vessels and tubes are discussed. This modern biofluidmechanical approach of detailed flow examination is compared with the more classical hemodynamic approach considering only gross features such as pressure loss coefficients.     

Modeling tree water flow as an unsaturated flow through a porous medium

The electric circuit analogy has had a profound influence on how tree physiologists measure, model and think about tree water flow. For example, previous models that attempt to account for changes in saturation use the electric circuit analogy to define capacitance as the change in saturation per change in pressure. Given that capacitance is constant, this relationship implies that subjecting a block of wood to a pressure of -2.5 MPa for 2 min results in the same change in saturation as subjecting the same block to the same pressure for 2 days. Given the definition of capacitance, it is unclear how the electric circuit analogy could be used to predict changes in saturation separately from changes in pressure. The inadequacies in the electric circuit analogy discussed in this paper necessitate a new theory of tree water flow that recognizes the sapwood as being a porous medium and explicitly deals with the full implications of the unsaturated flow occurring in the sapwood. The theory proposed in this paper combines the Cohesion theory with a mathematical theory of multiphase flow through porous media. Based on this theory, both saturated and unsaturated tree water flow models are presented. Previous partial differential equation models of tree water flow based on the electric circuit analogy are shown to be mathematically equivalent to the model of saturated porous flow. The unsaturated model of tree water flow explicitly models the pressure profile and the rates of change in saturation and specific interfacial area (a measure of how the water in the unsaturated sapwood is partitioned between mobile and immobile components). The unsaturated model highlights the differences between saturated and unsaturated flow and the need to measure the variables governing tree water flow at higher spatial and temporal resolutions.     

Ecology of a Late Silurian fauna of graptolites and associated organisms

The Ludlow Series of Wales and the Welsh Borderland represents an ocean-bordering basin and shelf which received a shoaling sequence of sediments in the late Silurian. Graptolites grade from highest diversity and density in basin areas to lowest diversity and density on the nearshore shelf. By analogy with modern zooplankton, this distribution is attributed to differentiation of surface water masses over basin and shelf. During Ludlow time, the center of graptolite abundance shifted northward, indicating a restriction and seaward movement of the basin water mass. Small nektic cephalopods and phyllocarids parallel distribution trends of the graptolites, as does a fauna of small bivalves and brachiopods which may have lived on floating plants. The water mass model accounts for most distributional patterns of pelagic organisms in this local area, and has broader application to the distribution and evolution of graptolites.     

Numerical simulation of cardiovascular dynamics with different types of VAD assistance

A variety of methods by which mechanical circulatory support (MCS) can be provided have been described. However, the haemodynamic benefits of the different methods have not been adequately quantified. The aim of this paper is to compare the haemodynamic effects of six forms of MCS by numerical simulation. Three types of ventricular assist device (VAD) are studied: positive displacement; impeller and a novel reciprocating-valve design. Similarly, three pumping modes are modelled: constant flow; counterpulsation and copulsation. The cardiovascular system is modelled using an approach developed previously, using the concentrated parameter method by considering flow resistance, vessel elasticity and inertial effects of blood in individual conduit segments. The dynamic modelling of displacement and impeller pumps is represented by VAD inlet/outlet flow-rate changes. The dynamics of the reciprocating-valve pump is modelled with a specified displacement profile. Results show that in each simulation, the physiological variables of mean arterial pressure and systemic flow are adequately maintained. Modulation of the impeller pump flow profile produces a small (5 mmHg) oscillatory component to arterial pressure, whereas the displacement and reciprocating-valve pumps generate substantial arterial pressure and flow pulsatility. The impeller pump requires the least power input, the reciprocating valve pump slightly more, and the displacement pump the most. The in parallel configuration of the impeller and displacement pump designs with respect to the left ventricle provides near complete unloading and can cause the aortic valve to remain closed throughout the entire cardiac cycle with the attendant risk of aortic valve leaflet fusion following prolonged support. The in series configuration of the reciprocating-valve pump avoids this shortcoming but activation must be carefully synchronized to the cardiac cycle to allow adequate coronary perfusion. The reciprocating-valve pump is associated with haemodynamic advantages and a favourable power consumption.     

A bioinspired approach for a multizone temperature control system

Bioinspired design approaches seek to exploit nature in order to construct optimal solutions for engineering problems as uniform temperature control in multizone systems. The ideal free distribution (IFD) is a concept from behavioural ecology, which describes the arrangement of individuals in different habitats such that at equilibrium, all habitats are equally suitable. Here, we relax the IFD's main assumptions using the standing-crop idea to introduce dynamics into the supplies of each habitat. Then, we make an analogy with a multizone thermal system to propose a controller based on the replicator dynamics model, in order to obtain a maximum uniform temperature subject to constant power injection. Besides, we analytically show that the equilibrium point of the controlled system is asymptotically stable. Finally, some practical results obtained with a testbed and comparisons with the theoretical results are presented.     

Rostral Ventrolateral Medulla C1 Neurons and Cardiovascular Regulation

1. The rostral ventrolateral medulla (RVLM) is essential for the normal control of arterial pressure. This region of the brainstem is heterogeneous, and contains spinally projecting neurons that contain phenylethanolamine-N-methyltransferase (C1 neurons) and non-C1 neurons.2. The availability of a toxin, a dopamine--hydroxylase antibody conjugated to saporin, that can selectively destroy C1 neurons within the RVLM allows for the study of cardiovascular regulation in rats following depletion of the C1 neuronal population.3. C1 neurons are not essential for the maintenance of resting blood pressure in anesthetized rats, but do contribute to many cardiovascular responses mediated through the RVLM.4. The depressor response elicited by clonidine injected into the RVLM is dependent upon C1 neurons.5. Studies in rats with selective toxin-induced destruction of RVLM C1 neurons demonstrate that C1 neurons contribute importantly to cardiovascular regulation.     

Water pumping and analysis of flow in burrowing zoobenthos: an overview

Burrowing animals maintain contact with the water above the sediment by pumping water through a tube system and therefore measurements of water pumping rate of burrowing animals is of crucial importance for the study of many processes both within and above the sea floor. This review deals with the measuring of water pumping and the analysis of flow generated by burrowing deposit- and filter-feeding zoobenthos in order to determine the type of pump and mechanisms involved, flow rate, pump pressure, and pumping power. The practical use of fluid mechanical principles is examined, and it is stressed that not only the pump pressure that a burrowing animal can apply is of interest for assessing the energy cost of pumping, but also the distribution of excess pressure along its burrow is of importance for assessing the seepage flow of oxygen-rich water into the sediment surrounding the burrow because this bioirrigation exerts a considerable effect on the chemistry and microbiology of sediments. Dense populations of burrowing filter-feeding zoobenthos also interact with the water above the sediment interface and this is reflected in the development of phytoplankton concentration profiles above the filter-feeding animals. In stagnant situations the near-bottom water may be depleted of food particles, depending on the population filtration rate and the intensity of the biomixing induced by the filtering activity. But moderate currents and the biomixing can presumably generate enough turbulence to facilitate mixing of water layers at the sea bed with the layers above where food particle concentrations are relatively higher. Following a brief summary of types of burrowing benthic animals, common methods for measuring pumping rates are described along with examples. For estimating the required pump pressure, biofluid mechanical theory for flow in tube–pump systems is summarised (elaborated in Appendix A). Specific examples are given to illustrate general principles and to give an idea of typical values of flow rate, pressure drop and power involved. Finally, some flow effects generated by burrowing animals in and above the sediment are described.     

Effects of different nutrients on bacterial growth in a pilot distribution system

The growth of bacterial communities in drinking water distribution systems can lead to the development of problems incompatible with water quality requirements. This study was carried out in order to determine which factors promote bacterial growth in distribution networks. A pilot distribution system was used to perform these experiments. After addition of three different inorganic elements to the network (N, P and S) the results obtained show that they did not contribute to the growth or bacteria either in the circulating water or on the surface of the pipes of the distribution system. However, when organic carbon was added an increase in the number of circulating bacteria was observed though the number of bacteria in the biofilms of the network was constant. These results indicate that in the drinking water of the Barcelona distribution system the factor that controls the growth of bacteria is organic carbon. Moreover, bacteria from the biofilm growing on the surface of the pipes may cause the problems of bacterial growth.     

Cardiac function in neuropeptide Y Y4 receptor-knockout mice

Autonomic control of cardiovascular function in neuropeptide Y (NPY) Y4 receptor-knockout mice was investigated using pancreatic polypeptide (PP), NPY and specific agonists and antagonists for other NPY receptors well characterised in cardiovascular function. Y4 receptor-knockout mice, anaesthetised with sodium pentobarbitone, displayed slower heart rate, indicated by a higher pulse interval and lower blood pressure compared to control mice. After vagus nerves were cut heart rate increased but was still significantly slower than in control mice. PP had no effect on blood pressure or cardiac vagal activity in either group of mice, which was consistent with earlier studies in other species. Injection of NPY evoked an increase in blood pressure but the response was significantly reduced in Y4 receptor-knockout mice compared to the controls. The reduction in pressor activity was not Y1 mediated as the selective Y1 antagonist, BIBP 3226, was effective in blocking NPY pressor activity in knockout mice. In addition, cardiac vagal inhibitory activity evoked by low doses of NPY was also reduced when compared to control responses. As N-acetyl [Leu(28, 31)] NPY 24-36 inhibited vagal activity dose dependently in both groups of mice with no difference in response at any dose, it is unlikely that this effect also is receptor mediated. We propose that the reduced vasoconstrictor and vagal inhibitory activity evoked by NPY in Y4 receptor-knockout mice is due to a lack of adrenergic tone bought about by a proposed reduction in sympathetic activity, possibly resulting from altered NPY activity secondarily affecting adrenergic transmission. We conclude that Y4 receptor deletion disrupts autonomic balance within the cardiovascular system.     

Pentagonal Model of Membrane Channel of Na,K-ATPase. Computer Simulations of Structure and Electrostatic Properties

Computational modeling of the membrane channel of a sodium pump (Na,K-ATPase) is performed and the role of selected amino acids in binding of sodium ions is discussed. The channel is build as a pentameric 10-helix bundle. The transmembrane a-helices are determined from hydropathy calculations. The spatial arrangement of transmembrane a-helices is chosen according to the size of a pore, intersegment loops geometry, and orientation hydrophobicities of transmembrane segments. The latter property provides the numerical estimate of the distribution of the hydrophobic properties at the helical wheels. The model system involves the peptide part and 150 water molecules that soak the pore. The channel structure is submitted to geometry minimization and molecular dynamics relaxation. The relative stability of the channel states with the negatively charged acidic residues belonging to the pore interior decrease in the order Glu-334 > Asp-810 > Glu-785 > Asp-814. The estimated binding energies of 1-3 Na⁺ ions with the channel with the ionized Glu-334 and Glu-785 amino acids are in the range allowing the exothermic complexation.Electronic Supplementary Material available.     

Nematodes as a source of total coliforms in a distribution system

In a distribution system of a large North American city, recurring total coliforms and atypical coliforms were detected at the exit (distribution pumps) of a storage reservoir. The presence of total coliforms and atypical coliforms was noted when the pumps were in operation and the water temperature was higher than 18 degrees C. The total coliform and atypical coliform concentrations at the volute pump casings ranged from 0 to 93.5 colony forming units (cfu)/100 mL. Significant concentrations of nematodes were also detected at this sampling location, averaging 12.0 nematodes/L in 2001 and 17.4 nematodes/L in 2002. The hypothesis that coliforms were released from the nematodes during their transit through the high-pressure pump was tested by recovering nematodes by filtering large volumes of water and grinding the nematodes in the laboratory, using various techniques. Total coliform and heterotrophic bacteria concentrations ranged from 0 to 27 cfu/nematode and 0 to 643 cfu/nematode, respectively. The origin of the nematodes was traced back to the sand filters located at the two water treatment plants. The importance of invertebrates in the distribution system should not be dismissed and the associated health risks, if any, should be assessed.     

The contribution of sensory inputs to the pattern generation of breathing

Current concepts of the basic neural control system and its modulation by afferent inputs are reviewed. It is emphasized that, in analogy with locomotion, the central pattern generator (CPG) for automatic metabolic respiration does not depend on any afferent feedback from receptors sensitive to the movements of the "pump," or the streams of pumped air, for its production of a rhythmic motor output provides the CPG receives some "drive" inputs above threshold and adequate bias. The operation for a variety of reflexes and feedback loops is of fundamental importance, however, for adapting the breathing pattern to the varying requirements for gas exchange to the many behavioural, nonmetabolic demands on the breathing apparatus which are competing with its primary metabolic control functions. The presentation is focussed also on available evidence that the respiratory CPG exerts powerful modulations on the transmission in these reflex pathways controlling the pattern of breathing and adjusting it to the various metabolic and behavioural demands. Mechanisms for "gating," "phasic gain changes," and "phase-dependent reflex reversal" are exemplified.     

Adherence to Mediterranean diet is associated with methylation changes in inflammation-related genes in peripheral blood cells

Epigenetic processes, including DNA methylation, might be modulated by environmental factors such as the diet, which in turn have been associated with the onset of several diseases such as obesity or cardiovascular events. Meanwhile, Mediterranean diet (MedDiet) has demonstrated favourable effects on cardiovascular risk, blood pressure, inflammation and other complications related to excessive adiposity. Some of these effects could be mediated by epigenetic modifications. Therefore, the objective of this study was to investigate whether the adherence to MedDiet is associated with changes in the methylation status from peripheral blood cells. A subset of 36 individuals was selected within the Prevención con Dieta Mediterránea (PREDIMED)-Navarra study, a randomised, controlled, parallel trial with three groups of intervention in high cardiovascular risk volunteers, two with a MedDiet and one low-fat control group. Changes in methylation between baseline and 5 years were studied. DNA methylation arrays were analysed by several robust statistical tests and functional classifications. Eight genes related to inflammation and immunocompetence (EEF2, COL18A1, IL4I1, LEPR, PLAGL1, IFRD1, MAPKAPK2, PPARGC1B) were finally selected as changes in their methylation levels correlated with adherence to MedDiet and because they presented sensitivity related to a high variability in methylation changes. Additionally, EEF2 methylation levels positively correlated with concentrations of TNF-α and CRP. This report is apparently the first showing that adherence to MedDiet is associated with the methylation of the reported genes related to inflammation with a potential regulatory impact.     

Evaluation of water services system through LCA. A case study for Iasi City,Romania

Purpose

The main objective of this paper is to analyse through life cycle assessment (LCA), the entire water services system in Iasi City (Romania): a representative city for the problems faced by the water services sector in Romania. Furthermore, the study is aimed at demonstrating the usefulness of the LCA approach as a support instrument for water resources management.

Methods

The life cycle inventory (LCI) of the Iasi water system was organized considering the water system components, as well as their function related to the water use life cycle: before the tap system as production phase (water abstraction, transport, treatment and distribution) and after the tap section as post-use phase (wastewater collection, treatment and discharge). The foreground data describing the LCI processes were provided directly by the company operating the Iasi water system, while the data for the background processes were sourced or selected from Ecoinvent 2.0 database. The assessment considers the quantification of environmental impacts (according to the CML 2000 baseline and Ecological Scarcity 2006 methodologies) of water supply (abstraction, treatment and distribution) and wastewater disposal (collection and treatment) relative to 1 m³ of tap water.

Results and discussion

For this given system, the results have pointed out that the before the tap system generates higher impacts than the after tap system, mainly due to the energetic effort needed for water supply and the fairly high water losses in the distribution system. However, the after the tap system, specifically the discharge of treated wastewater is still responsible for many of the water-related impact such as Eutrophication (when using CML) or Emissions to surface waters (when using the Ecological Scarcity method). Apart from the LCA approach, this study presents several scenarios for the improvement of the environmental performance of the water services, such as: changing between water sources, improving the distribution system and upgrading the wastewater treatment plant.

Conclusions

This study has demonstrated the usefulness of LCA to describe, compare and predict the environmental performance of complex water services systems (and all its components). The results have provided a reference case for the environmental profile of Iasi city water system, and have enabled the identification of its improvement alternatives. Also, this study, which represents a premiere for Romania, has opened future research directions which may include the development perspectives of the Iasi water services system, as well as improvements of LCIA methodologies to better represent the local specific water-related impacts.     

Risk factors for contamination of domestic hot water systems by legionellae.

To assess risk factors associated with the contamination of the domestic environment by legionellae, 211 houses in the Quebec City area were randomly selected and water samples were collected from the hot water tank, the shower heads, and the most frequently used faucet. After centrifugation, concentrated samples were seeded in triplicate on BCYE and GPV media. Data on the characteristics of the hot water system and plumbing in the house and on the personal habits of the occupants were collected for each house. Among these 211 houses, hot water was provided by either an oil or gas heater in 33 and by an electric heater in 178. Legionellae were isolated from none of the samples from houses with oil or gas heaters and from 39% (69 of 178) of those with electric water heaters (P less than 0.0001). This association remained highly significant after control for water temperature and other variables in a stratified analysis. In the 178 houses with an electric heater, 12% of the faucets, 15% of the shower heads, and 37% of the water heaters were contaminated. Legionella pneumophila serogroups 2 and 4 were the most frequently isolated strains. Logistic regression showed that factors associated with electric water heater contamination were (i) location of the house in older districts of the city (P less than 0.0001), (ii) old age of the water heater (P = 0.003), and (iii) low water temperature (P = 0.05). Contamination of the water heater was the only factor significantly associated with the contamination of peripheral outlets (P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Life cycle assessment of district heat distribution in suburban areas using PEX pipes insulated with expanded polystyrene

Goal, Scope and Background

Combined heat and power (CHP) is a strategy aimed at reducing the impact of the energy sector on the climate by more efficient use of the energy content of the fuel. The implementation of CHP requires the utilisation of the heat produced. Space heating by means of district heating is one possible use for such heat. In countries such as Sweden, where district heating is already extensively used, many multiapartment buildings are connected to district heating. For increased use, the distribution systems will have to expand into suburbs with single family homes. However, the environmental impact and cost of the district heat distribution system increase when the pipe networks are extended into such areas. This is due to the production and installation of longer pipe networks and increased heat losses from the system. Attempts have been made to find new types of pipe constructions in order to lower the costs of connecting single family homes to district heating. These should be evaluated from an environmental perspective. The EPSPEX system is a distribution system intended for suburban areas. This system consists of cross-linked polyethylene (PEX) pipes in insulating blocks of expanded polystyrene (EPS). This paper presents a life cycle assessment of the EPSPEX district heat distribution system. In a second scenario, sub-stations were added. The results indicate areas that require improvement and provide a basis for comparison with other types of district heat distribution systems.

Methods

Production, network construction and use of the district heat system were studied by means of life cycle methodology, employing specific data for the EPSPEX system and generic data for upstream impacts of the materials used. The system constructed in Vråen, Värnamo, Sweden, in 2002 was studied. The district heating used in Vråen is mainly based on biofuels. The functional unit was the use of one metre of an EPSPEX district heating system over a period of one year. The expected system life was 30 years. The results were characterised as global warming potential, acidification potential, eutrophication potential and the use of finite resources, as well as weighted by EPS 2000, ExternE and EcoIndicator 99. No external review was performed, but a reference group of district heating experts familiar with the practice has reviewed the study.

Results

Heat losses are clearly the main environmental impact in all characterisations and weightings (71–92% of the total impact), despite the fact that the heat production studied was mainly based on biomass combustion, generally perceived to be environmentally friendly. Of the system components, the production of EPS insulation blocks had the largest environmental impact.

Discussion

This impact, however, is compensated for by the fact that the need to produce less heat leads to a lower level of emissions. Several characterisation methods revealed that the production and combustion of diesel for excavating the pipe trench has a significant environmental impact. The jointing brass swaged coupling used for the PEX fluid pipes has a surprisingly high impact in terms of acidification and EPS 2000, considering the small amount of brass in the system.

Conclusions

The life cycle environmental impact is dominated by the heat production needed to compensate for heat losses from the system, despite the fact that the EPSPEX system is relatively well insulated compared to a conventional district heating system. It is possible to shut down the heating circuit and only use the hot tap water circuit during the summer months; this reduces the heat losses and is an advantageous feature of the system. The second largest environmental impact of the EPSPEX system arises from the production of the EPS insulation blocks. A decrease in nitrogen oxide emissions, especially those caused by the excavation and filling of pipe trenches, would be beneficial. A rough comparison has been made with available literature data for conventional DN25 twin pipes. The results indicate that the environmental impact of the EPSPEX system is probably lower. However, the pipes are not identical, as the water delivery capacity of the conventional pipe is slightly lower.

Recommendations and Perspectives

In Sweden, new types of pipes are being developed for district heating in suburban areas, and there is a need for an environmental comparison between such new alternatives and previous results for conventional polyurethane insulated steel pipes. This study reveals that biofuels, although perceived to be environmentally friendly, must be used with caution in order to ensure a satisfactory environmental performance. Heat loss from district heating should be minimized also when biofuels are used. The most immediate way to reduce such environmental impact is to increase the insulation. The environmental trade-off between lower heat losses achieved by the use of more insulation and the production of greater amounts of insulation material should be further studied.

     

Biomechanics and energy cost of the amphipod Corophium volutator filter-pump

The integrated function of the setal filter-basket and the pleopodal pump in the burrowing amphipod Corophium volutator was studied by video-microscopy in order to evaluate the energy costs of filter feeding. Video-microscope observations indicated that, in general, nine short, water-pumping beat cycles of the pleopods are succeeded by one slow cycle that coincides with cleaning of the setal filter and transient slowdown of inhalant water velocity. The position of the plumose setal filter on the second pair of gnathopods ensures that all water runs through the filter-basket. The fine V-shaped bristles on the setae enlarge the total filter area so that the velocity of water flowing through the filter is relatively slow, about 2.5 mm s(-1), giving rise to a resistance of about 2.9 mm H(2)O, which is the most important contribution to the total pressure drop in the system. In "standard" individuals of C. volutator with lengths of 3 and 6 mm, the normal operating pump pressure and pumping rate were, respectively, 2.6 and 3.1 mm H(2)O, and 18.3 and 85.5 ml h(-1); the overall pump efficiencies were 5.1% and 11.6%, respectively. These results show that the Corophium filter-pump is comparable to other low-pressure biological pumps in filter-feeding marine invertebrates, such as mussels, polychaetes, ascidians, and bryozoans.     

Risk factors for contamination of domestic hot water systems by legionellae.

To assess risk factors associated with the contamination of the domestic environment by legionellae, 211 houses in the Quebec City area were randomly selected and water samples were collected from the hot water tank, the shower heads, and the most frequently used faucet. After centrifugation, concentrated samples were seeded in triplicate on BCYE and GPV media. Data on the characteristics of the hot water system and plumbing in the house and on the personal habits of the occupants were collected for each house. Among these 211 houses, hot water was provided by either an oil or gas heater in 33 and by an electric heater in 178. Legionellae were isolated from none of the samples from houses with oil or gas heaters and from 39% (69 of 178) of those with electric water heaters (P less than 0.0001). This association remained highly significant after control for water temperature and other variables in a stratified analysis. In the 178 houses with an electric heater, 12% of the faucets, 15% of the shower heads, and 37% of the water heaters were contaminated. Legionella pneumophila serogroups 2 and 4 were the most frequently isolated strains. Logistic regression showed that factors associated with electric water heater contamination were (i) location of the house in older districts of the city (P less than 0.0001), (ii) old age of the water heater (P = 0.003), and (iii) low water temperature (P = 0.05). Contamination of the water heater was the only factor significantly associated with the contamination of peripheral outlets (P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)