Additional Temperature Increase Research Articles

Gas flow and heat transfer in granular energy-releasing materials: Novel computational model and important features

In this paper, the process of flowing the coolant gas through granular or porous media with heat-generating sources is considered. Such process takes place in various ruinous objects with energy release sources formed after natural or man-made disasters, e.g., in destroyed power unit of a nuclear power plant like exploded reactor No. 4 of the Chernobyl NPP. Also, this process is typical for some technologies, e.g., for innovative pebble-bed nuclear reactors. The aim of this work is, firstly, to develop a tool for numerical simulation of 3D processes in porous media with energy release sources, which will allow one to get the proper results quickly, and, secondly, to study some important features of these processes. A computational model and OpenFOAM solver have been developed in the work to simulate the fluid flow and heat transfer in granular or porous energy-releasing materials. The proposed mathematical model is based on the assumption of interacting interpenetrating continua, and the developed numerical method is based on the PIMPLE algorithm adapted for the system of governing equations. The novel OpenFOAM solver has been tested on 1D and 2D problems, which were previously solved by known algorithms based on the finite difference method. The new solver is faster by 1–3 orders of magnitude (depending on the number of cells in the mesh) and makes it possible to carry out calculations of 2D and 3D processes without parallelization within reasonable time, in contrast to the previously used numerical methods. The 3D gas flows through porous energy-releasing object have been studied, and some important features of these processes have been revealed. It has been shown that the temperature dependence of the gas dynamic viscosity leads not only to the fact that the gas tends to flow around the hot zones, but also to an additional increase in temperature in the heated area, caused by a drop of the density and velocity of the gas due to increasing the flow resistance force in this region. It has been revealed that if the total intensity of the energy release in the porous object is known a priori, but the relative location of the energy release sources is unknown, it is impossible to predict the maximum temperature of the object.

Impact of Extreme Heatwaves on Population Exposure in China Due to Additional Warming

Extreme heatwaves are among the most important climate-related disasters affecting public health. Assessing heatwave-related population exposures under different warming scenarios is critical for climate change adaptation. Here, the Coupled Model Intercomparison Project phase 6 (CMIP6) multi-model ensemble output results are applied over several warming periods in the Intergovernmental Panel on Climate Change AR6 report, to estimate China’s future heatwave population exposure under 1.5 °C and 2.0 °C warming scenarios. Our results show a significant increase in projected future annual heatwave days (HD) under both scenarios. With an additional temperature increase of 0.5 °C to 2.0 °C of warming, by mid-century an additional 20.15 percent increase in annual HD would occur, over 1.5 °C warming. If the climate warmed from 1.5 °C to 2.0 °C by mid-century, population exposure would increase by an additional 40.6 percent. Among the three influencing elements that cause the changes in population exposure related to heatwaves in China–climate, population, and interaction (e.g., as urbanization affects population redistribution)–climate plays the dominant role in different warming scenarios (relative contribution exceeds 70 percent). Therefore, considering the future heat risks, humanity benefits from a 0.5 °C reduction in warming, particularly in eastern China. This conclusion may provide helpful insights for developing mitigation strategies for climate change.

Investigation of Springtime Cloud Influence on Regional Climate and Its Implication in Runoff Decline in Upper Colorado River Basin

AbstractThe subseasonal features of the annual trends of runoff and other associated hydroclimatic variables in the upper Colorado River basin (UCRB) are examined using multiple data sets from in situ observations, reanalysis, and modeling for early spring (February, March, and April), given that about 58% of annual mean runoff decline from 1980 to 2018 stem from its decreases in the three months. Our analysis suggests that the strong annual trends of hydroclimatic variables in March are more statistically significant than other two months. While recent observational studies attribute the decline of runoff for either annual total or cool and warm seasons to regional warming and precipitation decrease, we suggested, for the first time, that a larger decreasing trend of the runoff in March is caused by the declining cloud optical depth which induces further decrease in precipitation and additional increase in temperature on top of climatic warming. The extra warming can reduce available water resource in the basin likely by enhancing evaporation in March. The recent cloud suppression likely results from stronger subsidence and larger moisture flux divergence over southwestern United States because of abnormal circulation patterns in varying climate, in turn leading to drier atmosphere which is unfavorable for cloud formation/development over the UCRB region. The cloud influence on the runoff in March in the UCRB revealed in this study implies the importance of understanding subseasonal variations of hydroclimate in the changing climate, as well as a need of future studies on the response of circulation patterns to climate change at subseasonal level and its implication on local hydroclimate.

Cavitation dynamics and thermodynamic effects at elevated temperatures in a small Venturi channel

The effects of temperature on hydraulic cavitation dynamics are investigated under various operating conditions, in a close loop cavitation tunnel with a small-scale venturi type section. A systematic study is performed with temperatures varying between 24°C and 85°C, using a high-speed visualization system to observe the cavitating flow. The image processing methods provided in the paper present a quantitative comparison of the cavitation dynamics and structure development. The results show that the increase of the fluid temperature induces the growth of the cavitation volume up to about 55°C, thereafter an additional increase in temperature has the opposite effect. This evolution is interpreted as a competition between a Reynolds effect and the well-known thermal effect. Cavitation is more closely investigated within the temperature range 50°C - 65°C, to analyze the changes in the structure and the cavitation dynamics. For the prediction of thermal suppression head, the thermal effect parameter Σ which can be used empirically, is derived at the maximum cavitation length. This fluid thermodynamic parameter Σ(Ttrans) at the transition peak can be referred to to avoid the maximum cavitation aggressiveness induced vibration or erosion for thermos-fluids around the thermal transition temperature. Finally, the factors influencing cavitation length and shedding frequency are presented and analyzed.

Various Digestion Protocols Within Microplastic Sample Processing—Evaluating the Resistance of Different Synthetic Polymers and the Efficiency of Biogenic Organic Matter Destruction

The digestion of biogenic organic matter is an essential step of sample preparation within microplastic analyses. Organic residues hamper the separation of polymer particles especially within density separation or polymer identification via spectroscopic and staining methods. Therefore, a concise literature survey has been undertaken to identify the most commonly applied digestion protocols with a special focus on water and sediments samples. The selected protocols comprise different solutions, concentrations, and reaction temperatures. Within this study we tested acids (nitric acid and hydrochloric acid), bases (sodium hydroxide and potassium hydroxide), and oxidizing agents [hydrogen peroxide, sodium hypochlorite and Fenton's reagent (hydrogen peroxide 30% in combination with iron(II)sulfate 0.27%)] at different concentrations, temperature levels, and reaction times on their efficiency of biogenic organic matter destruction and the resistance of different synthetic polymers against the applied digestion protocols. Tests were carried out in three parallels on organic material (soft tissue—leaves, hard tissue—branches, and calcareous material—shells) and six polymers (low-density polyethylene, high-density polyethylene, polypropylene, polyamide, polystyrene, and polyethylene terephthalate) in two size categories. Before and after the application of different digestion protocols, the material was weighed in order to determine the degree of digestion efficiency and polymer resistance, respectively. The efficiency of organic matter destruction is highly variable. Calcareous shells showed no to very low reaction to oxidizing agents and bases, but were efficiently dissolved with both tested acids at all concentrations and at all temperatures. Soft and hard tissue were most efficiently destroyed by sodium hypochlorite. However, the other reagents can also have good effects, especially by increasing the temperature to 40–50°C. The additional temperature increase to 60–70°C showed a further but less effective improvement, compared to the initial temperature increase. The resistance of tested polymer types can be rated as good except for polyamide and polyethylene terephthalate. Increasing the concentrations and temperatures, however, results in accelerated degradation of all polymers. This is most evident for polyamide and polyethylene terephthalate, which show losses in weight between 15 and 100% when the digestion temperature is increased. This effect is most pronounced for polyamide in the presence of acids and for polyethylene terephthalate digested with bases. As a concluding recommendation the selection of the appropriate digestion method should be specifically tested within initial pre-tests to account for the specific composition of the sample matrix and the project objectives.

Significant feedbacks of wetland methane release on climate change and the causes of their uncertainty

Emissions from wetlands are the single largest source of the atmospheric greenhouse gas (GHG) methane (CH4). This may increase in a warming climate, leading to a positive feedback on climate change. For the first time, we extend interactive wetland CH4 emissions schemes to include the recently quantified, significant process of CH4 transfer through tropical trees. We constrain the parameterisations using a multi-site flux study, and biogeochemical and inversion models. This provides an estimate and uncertainty range in contemporary, large-scale wetland emissions and their response to temperature. To assess the potential for future wetland CH4 emissions to feedback on climate, the schemes are forced with simulated climate change using a ‘pattern-scaling’ system, which links altered atmospheric radiative forcing to meteorology changes. We perform multiple simulations emulating 34 Earth System Models over different anthropogenic GHG emissions scenarios (RCPs). We provide a detailed assessment of the causes of uncertainty in predicting wetland CH4–climate feedback. Despite the constraints applied, uncertainty from wetland CH4 emission modelling is greater that from projected climate spread (under a given RCP). Limited knowledge of contemporary global wetland emissions restricts model calibration, producing the largest individual cause of wetland parameterisation uncertainty. Wetland feedback causes an additional temperature increase between 0.6% and 5.5% over the 21st century, with a feedback on climate ranging from 0.01 to 0.11 Wm−2 K−1. Wetland CH4 emissions amplify atmospheric CH4 increases by up to a further possible 25.4% in one simulation, and reduce remaining allowed anthropogenic emissions to maintain the RCP2.6 temperature threshold by 8.0% on average.

Annual performance analysis of heat emission in radiator and underfloor heating systems in the European reference room.

In this paper, we investigate the energy usage and emission efficiency of radiator and underfloor heating systems coupled with ON/OFF and PI controls, by performing annual simulations with the IDA ICE software package. Results from measurements carried out in early 2018 at the nZEB test facility near the Tallinn University of Technology are used to calibrate validated emitter and controller models. The calibrated models are then used to assess the energy performance of the systems in a simulation spanning the whole year, using climate data for Strasbourg in the European reference room. The annual simulation is conducted in a specific room with fixed geometry and boundary conditions. As a novelty value of the present study, we impose a non-standard control strategy based on maintaining a specified operative temperature within the room. A single-valued performance indicator, in the form of an increased air temperature set-point, is accordingly obtained for each emitter configuration to be used in further calculations of hourly, monthly or annual heating energy usage. Such a temperature increment accounts for imperfect control, air stratification within the room and the additional temperature increase that is required for achieving a desired operative temperature.

Numerical study on flow characteristics and heat transfer enhancement of oscillatory flow in a spirally corrugated tube

The flow and heat transfer characteristics of oscillatory flow in a smooth tube and two-start spirally corrugated tube were investigated by using a three-dimensional unsteady numerical simulation. The simulation was performed under variable properties, pressure and velocity conditions, with helium (He) as the working medium. The results indicated that longitudinal swirl vortexes were generated with the guidance of a spirally corrugated channel in a two-start spirally corrugated tube in which the fluid flowed spirally forward. The heat absorption (Q) of a two-start spirally corrugated tube exceeded that of a smooth tube (Q0). The difference in the average heat absorption was 561 W and the average of Q/Q0 was 1.36. At the same inlet and wall temperatures of 575 K and 1000 K, the outlet temperature of the smooth and spirally corrugated tube increased by 205 K and 365 K, respectively. Therefore, the spirally corrugated tube presented a superior heat transfer performance when compared to that of the smooth tube. Two types of performance evaluation criterion (PEC) calculation methods in a cycle were used to evaluate the heat transfer enhancement of a spirally corrugated tube. The average value of transient PEC in a cycle was 1.69, and the PEC calculated by average parameters in a cycle was 1.38. When compared with the change of pressure in a MPa level in a heating tube, the pressure drop of hundreds of Pa was negligible. However, the outlet temperature of the heating tube could be subject to an additional temperature increase of hundreds of K with the negligible pressure drop of hundreds of Pa. Thus, the benefits were apparent for the heat transfer enhancement by using spirally corrugated tubes in the heater.

On the transition from hunting-gathering to food production in NE Morocco as inferred from archeological Phorcus turbinatus shells

Processes behind the shift from hunting-gathering to food production lifestyle are multifaceted and not yet completely understood. The Mediterranean coast of NW Africa provides an eclectic transitional pattern, namely, a very hesitant transition to food production. The distribution and abundance of early Neolithic domesticated species is disparate and region specific. Climate and environmental change have been often considered as an important influencing factor for this transition. This hypothesis was tested using archeological shells of the rocky intertidal gastropod Phorcus turbinatus recovered from the Ifri Oudadane site in NE Morocco. The oxygen isotope composition (δ18O) of the shell was used to examine whether the hesitant transition to food production was linked to a local climate shift in the Mediterranean Maghreb. Intrashell δ18O values suggest a marked temperature increase from >7.6 to ~7.0 cal. ka BP, the time when Neolithic innovations first appear on site. An additional increase in temperature from ~7.0 to <6.8 cal. ka BP matches with the beginning of the main occupation phase and the doubtless breakthrough of cultivation at Ifri Oudadane. This apparent warming trend, although considered preliminary, seems to match well with warming tendency observed in several published regional climate proxies. Therefore, a temperature shift may have played a role in the timing and implementation of food production in the area. Last growth episode δ18O values suggest that shellfish were harvested throughout most of the year, with noticeable intensification during the cooler half of the year. This preliminary pattern was fairly consistent throughout the Epipaleolithic and early Neolithic phases, pointing to a probable near year-round site occupation rather than a single season settlement. Future research on Ifri Oudadane and other NW African archeological records are much needed to assess whether these patterns persist in Morocco and other Epipaleolithic and early Neolithic settlements in the western Mediterranean Maghreb.

Negative capacitance in an organic solar cell observed by displacement current measurement

We applied displacement current measurement (DCM) to an organic solar cell (OSC) with a structure of ITO/CuPc/C60/BCP/Al in order to investigate the origin of a negative capacitance (NC). In DCM curve, an anomalous characteristic that the current in backward scan was larger than that in forward scan was observed. We found that this characteristic originates from a gradual increase of an additional current, leading to NC in DCM. The additional current can be explained by the increase of the device temperature owing to a Joule heat and thermal deactivation of the exciton. Moreover, NC value was observed to be enhanced by light irradiation due to an additional temperature increase.

Amplification of global warming through pH dependence of DMS production simulated with a fully coupled Earth system model

Abstract. We estimate the additional transient surface warming ΔTs caused by a potential reduction of marine dimethyl sulfide (DMS) production due to ocean acidification under the high-emission scenario RCP8.5 until the year 2200. Since we use a fully coupled Earth system model, our results include a range of feedbacks, such as the response of marine DMS production to the additional changes in temperature and sea ice cover. Our results are broadly consistent with the findings of a previous study that employed an offline model set-up. Assuming a medium (strong) sensitivity of DMS production to pH, we find an additional transient global warming of 0.30 K (0.47 K) towards the end of the 22nd century when DMS emissions are reduced by 7.3 Tg S yr−1 or 31 % (11.5 Tg S yr−1 or 48 %). The main mechanism behind the additional warming is a reduction of cloud albedo, but a change in shortwave radiative fluxes under clear-sky conditions due to reduced sulfate aerosol load also contributes significantly. We find an approximately linear relationship between reduction of DMS emissions and changes in top of the atmosphere radiative fluxes as well as changes in surface temperature for the range of DMS emissions considered here. For example, global average Ts changes by −0. 041 K per 1 Tg S yr−1 change in sea–air DMS fluxes. The additional warming in our model has a pronounced asymmetry between northern and southern high latitudes. It is largest over the Antarctic continent, where the additional temperature increase of 0.56 K (0.89 K) is almost twice the global average. We find that feedbacks are small on the global scale due to opposing regional contributions. The most pronounced feedback is found for the Southern Ocean, where we estimate that the additional climate change enhances sea–air DMS fluxes by about 9 % (15 %), which counteracts the reduction due to ocean acidification.

Hydroelectric power generation in an Alpine basin: future water-energy scenarios in a run-of-the-river plant

We investigate scenarios of hydroelectric power generation for an Alpine run-of-the-river plant in 2050. To this end, we include a conversion from streamflow to energy in a hydrological model of the basin, and we introduce a set of benchmark climate scenarios to evaluate expected future production. These are a “future-like-present” scenario assuming future precipitation and temperature inputs to be statistically equivalent to those observed during the recent past at the same location, a “warmer-future” scenario, which considers an additional increase in temperature, and a “liquid-only” scenario where only liquid precipitation is admitted. In addition, two IPCC-like climatic scenarios (RCP 4.5 and RCP 8.5) are considered. Uncertainty in glaciers’ volume is accounted by initializing the hydrological model with two different inventories of glaciers. Ensemble results reveal that 1) an average decrease between -40% and -19% of hydroelectric power generation in 2050 is predicted at the plant considered (with respect to present condition); 2) an average decrease between -20% and -38% of cumulative incoming streamflow volume at the plant is also predicted, again with respect to present condition; 3) these effects are associated with a strong average decrease of the volume of glaciers (between -76% and -96%, depending on the initial value considered). However, Monte Carlo simulations show that results are also prone to high uncertainties. Implications of these results for run-of-the-river plants are discussed.

Ballistic impact welding of copper to low carbon steel

A method of ballistic impact welding pure copper to low carbon steel was developed based on the prediction of the critical parameters. The macro profile, microstructure, element distribution across the interface, and the mechanical properties of the welds were studied. It showed that a wavy bond profile was formed at the interface and no intermetallic layer was formed near the interface. The microstructures and the properties exhibited different characteristics in different areas with different distance to the interface for both the copper side and low carbon steel side. Moreover, the additional increase in temperature due to the viscous friction caused by the spinning of projectile between the spinning copper projectile and the low carbon steel results in a recrystallization annealing on the copper side.

The influence of intensity and duration of a painful conditioning stimulation on conditioned pain modulation in volunteers

The aim was to investigate influence from variations in intensity of a painful conditioning stimulation (CS) on early (0-6 min) and prolonged (6-12 min) conditioned pain modulation (CPM) in volunteers during concurrent exposure to test stimuli (TS). CS was applied to either forearm using painful heat with an intensity of 2/10 and 5/10, respectively, rated on a 0-10 numerical pain rating scale. At a second session, CS with an intensity of 7/10 was applied to the arm using a tourniquet. Threshold and suprathreshold painful heat and pressure as well as painful repeated monofilament pricking (RMP) were assessed as TS. Regardless of TS, there was no significant difference in the magnitude of CPM within the same stimulus modality during the various intensities and phases of the CS. Significant modulation of heat pain thresholds (HPTs) was found during the early phase at 5/10 and 7/10, but not at 2/10. Only at 5/10 the prolonged CS resulted in a significant additional increase in HPT. During the early CS phase, CPM of suprathreshold heat pain was found at 2/10 and 5/10. The prolonged CS resulted in a significant additional temperature increase at 5/10. Only during the early phase significant CPM of pressure pain thresholds were found for all three pain intensities in conjunction with a significant CPM of suprathreshold pressure pain at 5/10. There was no CPM of RMP. The CS intensity and the duration of CPM modulated pain sensitivity differentially across TS modalities.

Climate warming over the past three decades has shortened rice growth duration in China and cultivar shifts have further accelerated the process for late rice

An extensive dataset on rice phenology in China, including 202 series broadly covering the past three decades (1980s-2000s), was compiled. From these data, we estimated the responses of growth duration length to temperature using a regression model based on the data with and without detrending. Regression coefficients derived from the detrended data reflect only the temperature effect, whereas those derived from data without detrending represent a combined effect of temperature and confounding cultivar shifts. Results indicate that the regression coefficients calculated from the data with and without detrending show an average shortening of the growth duration of 4.1-4.4 days for each additional increase in temperature over the full growth cycle. Using the detrended data, 95.0% of the data series exhibited a negative correlation between the growth duration length and temperature; this correlation was significant in 61.9% of all of the data series. We then compared the difference between the two regression coefficients calculated from data with and without detrending and found a significantly greater temperature sensitivity using the data without detrending (-2.9 days °C(-1) ) than that derived from the detrended data (-2.0 days °C(-1) ) in the period of emergence to heading for the late rice, producing a negative difference in temperature sensitivity (-0.9 days °C(-1) ). This implies that short-duration cultivars were planted with increase in temperature and exacerbated the undesired phenological change. In contrast, positive differences were detected for the single (0.6 days °C(-1) ) and early rice (0.5 days °C(-1) ) over the full growth cycle, which might indicate that long-duration cultivars were favoured with climate warming, but these differences were insignificant. In summary, our results suggest that a major, temperature induced change in the rice growth duration is underway in China and that using a short-duration cultivar has been accelerating the process for late rice.

Effect Of Temperature On The Electrorotation Behavior Of Human Red Blood Cells

The dielectric parameters of Human Red Blood Cells (HRBCs) were investigated by Electrorotation (ER). Suspended HRBCs were exposed to rotating electric fields in the range from 50 kHz to 250 MHz in a rectangular 4–electrode microchip chamber. ER spectra was recorded at external conductivities ranging from 0.02 – 3.00 S/m. The electrode structures were fabricated on glass chips by laser ablation of a platinum layer. Different measuring temperatures were used. At low conductivities, the temperature of the microscopic stage was kept constant by a thermostat. At higher medium conductivities, the additional temperature increase in the measuring volume due to Joule heating was registered. Measured data in the range from 20 to 35°C were then sorted according to different temperature classes of a width of 5 K. The first and the second characteristic peak frequencies of ER were plotted over medium conductivity and interpreted using an oblate single shell model with a dispersive cytoplasm and temperature dependent electric cell parameters. Key words: Erythrocyte, AC-electrokinetics, impedance, dispersion, ellipsoidal cell model, electric cell properties

Long-term effects of biogeophysical and biogeochemical interactions between terrestrial biosphere and climate under anthropogenic climate change

A complex earth system model, simulating atmosphere and ocean dynamics, marine biogeochemistry, terrestrial vegetation and ice sheets, was used to study feedbacks between the terrestrial biosphere and climate with a set of long-term climate change ensemble experiments. CO 2 emissions were assigned according to historical data and the IPCC SRES scenarios B1, A1B and A2, followed by an exponential decay of the emissions for the period 2100–3000. The experiments give a reasonable reconstruction of the measured CO 2 concentrations between 1750 and 2000. Maximum atmospheric CO 2 concentrations of 520 ppm (B1), 860 ppm (A1B) and 1680 ppm (A2) were reached between 2200 and 2500. Additional experiments were performed with CO 2 emissions and suppressed climate change, as well as an experiment with a prescribed land surface. The experiments were repeated with the vegetation model driven offline, to investigate the effects of climate and CO 2 changes separately. The biogeochemical and biogeophysical interactions between terrestrial biosphere and atmosphere were quantified and compared. A decrease of albedo at high latitudes was the most important biogeophysical change. For the A2 scenario experiment, it causes an additional temperature increase of 1 to 2 K for some high latitude regions by the year 3000, but the changes are minor compared to the heating due to CO 2 increase. The terrestrial biosphere takes up between 15 and 30% of the CO 2 emissions, depending on the scenario and the period considered. The carbon is stored in the tropics and subtropics, where carbon is stored fast, and in the high latitudes, where carbon storage, partly due to forest expansion, is much slower. By the year 3000, the storage of terrestrial carbon results in a decrease of atmospheric CO 2 concentration of 400 ppm, which in turn decreases the global temperature increase by 0.4 K.

Increasing species richness on mountain summits: Upward migration due to anthropogenic climate change or re‐colonisation?

Abstract. Over the last 20 years, several studies comparing recent survey data with historical data from the early 20th century documented an increase in species numbers on high mountain summits of the European Alps. This increase has more or less explicitly been attributed to an upward migration of plant species due to anthropogenic climate warming. However, a reconsideration of the historical and recent data has revealed that more than 90% of the recent species occurrences on mountain summits concern species that were already present at the same or even at higher altitudes within the study region at the time of the historical surveys. This finding suggests that suitable habitats already occurred on these summits under the mesoclimatic conditions prevailing at the beginning of the 20th century and that these habitats were, at least in part, occupied by these plant species. Consequently, the observed increase in species number during the last century does not require the additional temperature increase due to anthropogenic climate change. We therefore consider the phenomenon of increasing species number on high mountain summits to be primarily the result of a natural dispersal process that was triggered by the temperature increase at the end of the Little Ice Age and that is still in progress mostly due to the dispersal limitation of the species involved. Since both the natural dispersal process and a potential upward migration due to anthropogenic climate warming would take place at the same time, we suggest seeding and transplanting experiments in order to assess their respective roles in the increase in species number on mountain summits.

Increasing species richness on mountain summits: Upward migration due to anthropogenic climate change or re-colonisation?

Over the last 20 years, several studies comparing recent survey data with historical data from the early 20th century documented an increase in species numbers on high mountain summits of the European Alps. This increase has more or less explicitly been attributed to an upward migra- tion of plant species due to anthropogenic climate warming. However, a reconsideration of the historical and recent data has revealed that more than 90% of the recent species occurrences on mountain summits concern species that were already present at the same or even at higher altitudes within the study region at the time of the historical surveys. This finding suggests that suitable habitats already occurred on these summits under the mesoclimatic conditions prevailing at the beginning of the 20th century and that these habitats were, at least in part, occupied by these plant species. Consequently, the observed increase in species number during the last century does not require the additional temperature increase due to anthropogenic climate change. We therefore consider the phenomenon of increasing species number on high mountain summits to be primarily the result of a natural dispersal process that was triggered by the temperature increase at the end of the Little Ice Age and that is still in progress mostly due to the dispersal limitation of the species involved. Since both the natural dispersal proc- ess and a potential upward migration due to anthropogenic climate warming would take place at the same time, we sug- gest seeding and transplanting experiments in order to assess their respective roles in the increase in species number on mountain summits.

Fever and autologous blood retransfusion after total knee arthroplasty

The commonest adverse reaction of autotransfusion of drain blood is an increase in temperature, probably due to a cytokine-mediated inflammatory reaction. We recorded body temperature in 21 patients operated on with a total knee prosthesis prospectively during the first 18 postoperative hours. The patients had been given an autotransfusion of autologous filtered drain blood (40 events) within the first 8-9 hours. They all had hypothermia at the end of operation, with a continuous increase in temperature during the first 12 hours whereafter the temperature slowly fell. No additional increase in temperature was seen during the first 2 hours after an autologous retransfusion. Autotransfusion of filtered drain blood within the first 8 postoperative hours after arthroplasty thus did not seem to cause an additional increase in temperature above that due to spontaneous recovery after postoperative hypothermia and surgical trauma.