Periods Of Insolation Research Articles

Energy partitioning and its controls over a heterogeneous semi‐arid shrubland ecosystem in the Lake Naivasha Basin, Kenya

AbstractThis paper reports on the energy balance and partitioning analysed from 3‐year micrometeorological flux measurements of energy and water fluxes over a heterogeneous semi‐arid shrubland ecosystem in Lake Naivasha basin. The measurements enabled the characterization of the seasonal and interannual variability of the energy and water fluxes of the ecosystem covering two wet years (2012 and 2013) and one drought year (2014). On an annual scale, more than 60% of net radiation (Rn) was partitioned as latent (LE) and sensible (H) energy flux, with the latter being the larger consumer of Rn (~34%) and dominant for most months. The transition from H to LE dominance occurred from early noon to late afternoon in the wettest months of April and May. The residual energy balance closure term (C) accounted for between 25 and 40% of the Rn with the imbalance tending to be highest during periods of high insolation. Annual evapotranspiration was estimated at 873 mm, 632 mm and 537 mm for year 2012, 2013 and 2014 respectively. This accounted for at least 80% of the annual precipitation received for the respective years. Surface conductance (gs) scaled significantly with leaf expansion and Priestley–Taylor α coefficient, but was limited during periods of drought because of inadequate soil moisture suggesting that, change in LE was paralleled by changes in green leaf area index. Low values of decoupling coefficient (Ω) during these periods indicated that evapotranspiration was strongly controlled by gs and vapour pressure deficit (VPD). However, under non‐limiting moisture conditions evapotranspiration was decoupled from the atmosphere. This suggested that during the dry seasons and periods of prolonged drought, a lack of moisture in combination with high VPD leads to significant decreases in stomatal conductance that eventually limits partitioning of available energy into LE in the semi‐arid ecosystem part of the Lake Naivasha basin. However, during wet season these factors are non‐limiting and radiation is the dominant control of energy partitioning into LE in the ecosystem. The coupling and decoupling pattern provide insights towards formulating models that quantify evapotranspiration for ecosystems that experience seasonal shifts in controlling factors. Copyright © 2016 John Wiley & Sons, Ltd.

Modeling subcanopy incoming longwave radiation to seasonal snow using air and tree trunk temperatures

AbstractData collected at three Swiss alpine forested sites over a combined 11 year period were used to evaluate the role of air temperature in modeling subcanopy incoming longwave radiation to the snow surface. Simulated subcanopy incoming longwave radiation is traditionally partitioned into that from the sky and that from the canopy, i.e., a two‐part model. Initial uncertainties in predicting longwave radiation using the two‐part model resulted from vertical differences in measured air temperature. Above‐canopy (35 m) air temperatures were higher than those within (10 m) and below (2 m) canopy throughout four snow seasons (December–April), demonstrating how the forest canopy can act as a cold sink for air. Lowest model root‐mean‐square error (RMSE) was using above‐canopy air temperature. Further investigation of modeling subcanopy longwave radiation using above‐canopy air temperature showed underestimations, particularly during periods of high insolation. In order to explicitly account for canopy temperatures in modeling longwave radiation, the two‐part model was improved by incorporating a measured trunk view component and trunk temperature. Trunk temperature measurements were up to 25°C higher than locally measured air temperatures. This three‐part model reduced the RMSE by up to 7.7 W m−2 from the two‐part air temperature model at all sensor positions across the 2014 snowmelt season and performed particularly well during periods of high insolation when errors from the two‐part model were up to 40 W m−2. A parameterization predicting tree trunk temperatures using measured air temperature and incoming shortwave radiation demonstrate a simple method that can be applied to provide input to the three‐part model across midlatitude coniferous forests.

Performance assessment of integrated PV/T and solid desiccant air-conditioning systems for cooling buildings using Maisotsenko cooling cycle

Hot summer days coincide with high solar insolation periods and high peak demands in the UAE. Solid desiccant air conditioning systems are capable of utilizing low-grade sources of energy such as solar energy. In this paper, two new air conditioning systems combining solid desiccant and Maisotsenko coolers are examined for use in humid climates such as the UAE. Solar energy in the form of a solar PV/T module is selected as the primary source of energy to operate the desiccant air cooling systems while an auxiliary heater is devised for supplementary air heating. A detailed thermodynamic analysis is performed to illustrate and evaluate the proposed air conditioning systems’ performance in the UAE under different operating conditions. A comparative analysis is carried out to signify the advantages and disadvantages of integrating the Maisotsenko cooler with conventional desiccant air conditioning units. In addition, a seasonal analysis is conducted to examine the performance of the proposed systems throughout a summer day in Abu Dhabi. Average COP for two proposed configurations during the investigated period are 0.2495 and 0.2713. Furthermore, their corresponding solar shares are 32.2% and 36.5%, respectively. Finally, with PV/T module collectors’ area of 681.0m2 and 656.3m2, annual electricity generation of 145.0MWh and 139.7MWh are reported, respectively.

THE LEVEL OF VITAMIN D IN PEOPLE OLDER THAN 50 YEARS RESIDING IN THE REPUBLIC OF BASHKORTOSTAN IN THE PERIOD OF MAXIMUM INSOLATION

Aim. To study the vitamin D levels in the period of maximal sun exposure in individuals older than 50 years residing in the Republic of Bashkortostan, to compare them with the levels during the period of the minimum insolation. Materials and methods. In the period of high insolation in 175 people aged over 50 years residing in the city (Ufa) and rural areas of the Republic of Bashkortostan, we investigated the levels of 25 (OH) D and parathyroid hormone (PTH) by the indirect ELISA. Results. We show that the senior age groups of the population of the Republic of Bashkortostan even in the period of the maximum insolation are characterized by the high frequency of hypovitaminosis and deficiency of vitamin D. The level of vitamin D is higher in the period of the maximum insolation, and in rural areas, this increase is more prominent. Levels of vitamin D and PTH in the period of the maximum insolation do not depend on male or female sex, and do not differ in rural and urban population. Conclusions. In general, our results show that the problem of deficiency of vitamin D for senior citizens remains of high relevance even in the period of the maximum insolation.

Indian monsoon variations during three contrasting climatic periods: The Holocene, Heinrich Stadial 2 and the last interglacial–glacial transition

In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the North Atlantic, Eurasia or the Indian Ocean.

Sustainable synthesis of a high performance inter-polymer anion exchange membrane employing concentrated solar radiation in a crucial functionalization step

Preparation of an anion exchange membrane (AEM) from polymethylstyrene-co-divinylbenzene/polyethylene (Pp-MSt-co-DVB/PE) inter-polymer film (IPF) was reported recently. Functionalization of the above IPF was achieved through photo-thermochemical benzylic bromination with N-bromosuccinimide. The end result was the same as that achieved through chloromethylation of conventional styrene-DVB IPF, while avoiding use of carcinogenic chloromethyl ether. The present study reports the optimum process for preparation of the Pp-MSt-co-DVB/PE IPF and a new protocol for its efficient bromination employing concentrated solar radiation. No chemical initiator was necessary in the new process. Over the 4h period of peak solar insolation, the bromination yield of a 1.18m×0.12m strip of IPF (Pp-MS content, 31.88% w/w; film thickness, 80±11µm) was 87.1±3.5%. Cross-sectional analysis showed reasonable uniformity of bromination across the film thickness. The AEM obtained upon quaternization exhibited an anion exchange capacity of 1.60±0.04meqg−1, bulk resistivity of 4.52±0.47Ωm, and chloride transport numbers (EMF method) of 0.941±0.003 and 0.981±0.002 employing HCl and NaCl, respectively, as electrolytes. The performance of the synthesized AEM was compared with that of IONSEP-HC-A, a commercial AEM.

Modelling Greenland ice sheet inception and sustainability during the Late Pliocene

Understanding the evolution and dynamics of ice sheet growth during past warm periods is a very important topic considering the potential total removal of the Greenland ice sheet. In this regard, one key event is the full glaciation of Greenland that occurred at the end of the Pliocene warm period, which remains partially unexplained. Previous modelling studies succeeded in reproducing this full glaciation either by imposing an unrealistically low CO2 value or by imposing a partial ice sheet over the surface of Greenland. Although they highlight some fundamental mechanisms, none of these studies are fully satisfactory because they do not reflect realistic conditions occurring during the Late Pliocene. Through a series of simulations with the IPSL-CM5A coupled climate model used to force the GRISLI ice sheet model, we show that a drop in CO2 levels does not lead to an abrupt inception of the Greenland ice sheet. High ablation rates in central and northern Greenland combined with low accumulation prevent such an abrupt inception. Ice sheet inception occurs when low summer insolation and CO2 levels below modern values are combined, the Greenland ice sheet being restricted to the southeast region, where high topography favours this build-up. This ice sheet experiences only partial melting during summer insolation maxima combined with high CO2 levels. Further growth of the ice sheet with recoupling experiments is important at 360 and 280 ppm during insolation minima. Thus, the full glaciation at 2.6 Ma could be the result of a cumulative build-up of the Greenland ice sheet over several orbital cycles, leading to progressively more intense glaciations during low summer insolation periods. Although this result could be a shortcoming of the modelling framework itself, the gradual glacial inception interpreted from the oxygen isotope record could support our scenario.

The role of CO2 decline for the onset of Northern Hemisphere glaciation

The Pliocene–Pleistocene Transition (PPT), from around 3.2 to 2.5 million years ago (Ma), represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern Eurasia and North America. Paleo evidence indicates that the PPT was accompanied and possibly caused by a decrease in atmospheric CO2, but the temporal resolution of CO2 reconstructions is low for this period of time and uncertainties remain large. Therefore, instead of applying existent CO2 reconstructions we solved an ‘inverse’ problem by finding a schematic CO2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records. To this end, we performed an ensemble of transient simulations with an Earth system model of intermediate complexity from which we derived a best guess transient CO2 scenario for the interval from 3.2 to 2.4 Ma that gives the best fit between the simulated and reconstructed benthic δ18O and global sea surface temperature evolution. Our data-constrained CO2 scenarios are consistent with recent CO2 reconstructions and suggest a gradual CO2 decline from 375–425 to 275–300 ppm, between 3.2 and 2.4 Ma. In addition to a gradual decline, the best fit to paleoclimate data requires the existence of pronounced CO2 variability coherent with the 41-kyr (1 kyr = 1000 years) obliquity cycle. In our simulations the long-term CO2 decline is accompanied by a relatively abrupt intensification of Northern Hemisphere glaciation at around 2.7 Ma. This is the result of a threshold behaviour of the ice sheets response to gradual CO2 decrease and orbital forcing. The simulated Northern Hemisphere ice sheets during the early Pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m. Both ice volume and benthic δ18O are dominated by 41-kyr cyclicity. Our simulations suggest that before 2.7 Ma Greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation. A fully glaciated Greenland comparable to its present-day ice volume is modelled only during glacial maxima after 2.7 Ma and more continuously after 2.5 Ma.

Role of seasonal transitions and westerly jets in East Asian paleoclimate

The summer rainfall climate of East Asia underwent large and abrupt changes during past climates, in response to precessional forcing, glacial–interglacial cycles as well as abrupt changes to the North Atlantic during the Last Glacial. However, current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity, and do not account for the known complexity in the seasonal evolution of East Asian rainfall, which exhibits sharp transition from the Spring regime to the Meiyu, and then again from the Meiyu to the Summer regime.We explore the interpretation that East Asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes. Following previous suggestions we focus on role of the westerly jet over Asia, namely that its latitude relative to Tibet is critical in determining the stepwise transitions in East Asian rainfall seasons. In support of this linkage, we show from observational data that the interannual co-variation of June (July–August) rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the Meiyu (Summer), and with more northward-shifted westerlies for earlier transitions.We similarly suggest that East Asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions, in particular the transition of the jet from south of the Plateau to the north that determines the seasonal transition from Spring rains to the Meiyu. In an extreme scenario – which we speculate the climate system tended towards during stadial (cold) phases of D/O stadials and periods of low Northern Hemisphere summer insolation – the jet does not jump north of the Plateau, essentially keeping East Asia in prolonged Spring conditions.We argue that this hypothesis provides a viable explanation for a key paleoproxy signature of D/O stadials over East Asia, namely the heavier mean δ18O of precipitation as recorded in speleothem records. The southward jet position prevents the low-level monsoonal flow – which is isotopically light – from penetrating into the interior of East Asia; as such, precipitation there will be heavier, consistent with speleothem records. This hypothesis can also explain other key evidences of East Asian paleoclimate changes, in particular the occurrence of dusty conditions during North Atlantic stadials, and the southward migration of the Holocene optimal rainfall.

Comparison of decentralised and centralised grid‐compatible battery storage systems in distribution grids with high PV penetration

AbstractBecause of the high amount of installed solar power systems in Europe and especially Germany, the low‐voltage distribution grids reach their maximum capacities during periods of high insolation. As an alternative to grid reinforcement, local battery storage systems can be used to store the surplus generation and limit the feed‐in power of the solar power systems. For this purpose, decentralised photovoltaic (PV) home storages in single households and larger stationary battery systems supplying a whole local grid area can be called into action. In this paper, a grid‐compatible storage operational strategy is simulated using standard load profiles and statistically generated realistic load profiles for use with both storage types. The goal of this research is to investigate a grid‐compatible and also economic storage operation when using centralized large‐scale batteries instead of PV home storage systems in a low‐voltage distribution grid with a high degree of decentralised PV generation. Results show that large‐scale systems provide advantages regarding grid‐related operation and economic feasibility and therefore represent a useful alternative to home storage systems. Additionally, it can be shown that depending on which storage type is simulated, different requirements are imposed. The simulation of decentralised home storages needs real load profiles in order to receive realistic results, while the operation of large‐scale battery storages can be simulated using standard load profiles. Copyright © 2014 John Wiley & Sons, Ltd.

Modeling erosion of ice-rich permafrost bluffs along the Alaskan Beaufort Sea coast

The Arctic climate is changing, inducing accelerating retreat of ice-rich permafrost coastal bluffs. Along Alaska's Beaufort Sea coast, erosion rates have increased roughly threefold from 6.8 to 19 m yr−1 since 1955 while the sea ice-free season has increased roughly twofold from 45 to 100 days since 1979. We develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice-free season, sea level, water temperature, nearshore wavefield, and permafrost temperature in controlling erosion rates in this setting. The model captures the processes of erosion observed in short-term monitoring experiments along the Beaufort Sea coast, including evolution of melt notches, topple of ice wedge-bounded blocks, and degradation of these blocks. Model results agree with time-lapse imagery of bluff evolution and time series of ocean-based instrumentation. Erosion is highly episodic with 40% of erosion is accomplished during less than 5% of the sea ice-free season. Among the formulations of the submarine erosion rate we assessed, we advocate those that employ both water temperature and nearshore wavefield. As high water levels are a prerequisite for erosion, any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion. The certain increases in sea level and potential changes in storminess will both contribute to this effect. As water temperature also influences erosion rates, any further expansion of the sea ice-free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates.

Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka

Abstract. We investigate changes in the delivery and oceanic transport of Amazon sediments related to terrestrial climate variations over the last 250 ka. We present high-resolution geochemical records from four marine sediment cores located between 5 and 12° N along the northern South American margin. The Amazon River is the sole source of terrigenous material for sites at 5 and 9° N, while the core at 12° N receives a mixture of Amazon and Orinoco detrital particles. Using an endmember unmixing model, we estimated the relative proportions of Amazon Andean material ("%-Andes", at 5 and 9° N) and of Amazon material ("%-Amazon", at 12° N) within the terrigenous fraction. The %-Andes and %-Amazon records exhibit significant precessional variations over the last 250 ka that are more pronounced during interglacials in comparison to glacial periods. High %-Andes values observed during periods of high austral summer insolation reflect the increased delivery of suspended sediments by Andean tributaries and enhanced Amazonian precipitation, in agreement with western Amazonian speleothem records. Increased Amazonian rainfall reflects the intensification of the South American monsoon in response to enhanced land–ocean thermal gradient and moisture convergence. However, low %-Amazon values obtained at 12° N during the same periods seem to contradict the increased delivery of Amazon sediments. We propose that reorganizations in surface ocean currents modulate the northwestward transport of Amazon material. In agreement with published records, the seasonal North Brazil Current retroflection is intensified (or prolonged in duration) during cold substages of the last 250 ka (which correspond to intervals of high DJF or low JJA insolation) and deflects eastward the Amazon sediment and freshwater plume.

Operational Strategies for Battery Storage Systems in Low-voltage Distribution Grids to Limit the Feed-in Power of Roof-mounted Solar Power Systems

Due to the high amount of installed solar power systems in Germany, the low-voltage distribution grids reach their maximum capacities in periods of high insolation. In order to ensure a proper integration of today's and especially the prospective solar energy, grid reinforcement is a common method to increase the transmission capacity. As an alternative to this costly and intricate approach, local battery storage systems can be used to store the surplus generation and limit the feed-in power of the solar power systems. In this paper, two different operational strategies for battery storage systems together with solar power systems for self-consumption are presented and evaluated. Results show that the feed-in power can be distinctly reduced without generating significant losses for the system-owner.

Sea surface temperature and salinity reconstruction based on stable isotopes and Mg/Ca of planktonic foraminifera in the western Pacific Warm Pool during the last 155 ka

Changes in sea surface temperature (SST), seawater oxygen isotope (δ18Osw), and local salinity proxy (δ18Osw-ss) in the past 155 ka were studied using a sediment core (MD06-3052) from the northern edge of the western Pacific Warm Pool (WPWP), within the flow path of the bifurcation of the North Equatorial Current. Our records reveal a lead-lag relationship between paired Mg/Ca-SST and δ18O during Termination II and the last interglacial period. Similarity in SST between our site and the Antarctic temperature proxy and in CO2 profile showed a close connection between the WPWP and the Antarctic. Values of δ18O sw exhibited very similar variations to those of mean ocean δ18Osw, owing to the past sea-level changes on glacial-interglacial timescale. Calculated values of δ18Osw-ss reflect a more saline condition during high local summer insolation (SI) periods. Such correspondence between δ18Osw-ss and local SI in the WPWP may reflect complex interaction between ENSO and monsoon, which was stimulated by changes in solar irradiance and their influence on the local hydrologic cycle. This then caused a striking reorganization of atmospheric circulation over the WPWP.

Mitigation of Rooftop Solar PV Impacts and Evening Peak Support by Managing Available Capacity of Distributed Energy Storage Systems

A high penetration of rooftop solar photovoltaic (PV) resources into low-voltage (LV) distribution networks creates reverse power-flow and voltage-rise problems. This generally occurs when the generation from PV resources substantially exceeds the load demand during high insolation period. This paper has investigated the solar PV impacts and developed a mitigation strategy by an effective use of distributed energy storage systems integrated with solar PV units in LV networks. The storage is used to consume surplus solar PV power locally during PV peak, and the stored energy is utilized in the evening for the peak-load support. A charging/discharging control strategy is developed taking into account the current state of charge (SoC) of the storage and the intended length of charging/discharging period to effectively utilize the available capacity of the storage. The proposed strategy can also mitigate the impact of sudden changes in PV output, due to unstable weather conditions, by putting the storage into a short-term discharge mode. The charging rate is adjusted dynamically to recover the charge drained during the short-term discharge to ensure that the level of SoC is as close to the desired SoC as possible. A comprehensive battery model is used to capture the realistic behavior of the distributed energy storage units in a distribution feeder. The proposed PV impact mitigation strategy is tested on a practical distribution network in Australia and validated through simulations.

Triple cycle for solar thermal power system adapted to periods with varying insolation

In the current study, a new solar-driven triple cycle is proposed to allow power generation during low insolation periods. This triple cycle integrates the solar gas-turbine top cycle, the steam Rankine cycle, and the Kalina bottom cycle. During the top cycle of the proposed system, compressed air was heated to 1000 °C or higher in the solar tower receiver. The heated compressed air was then used to drive the gas turbine to generate electricity. A Rankine cycle with a back-pressure steam turbine was utilized to recover waste heat from the gas turbine, thereby generating electricity through the steam turbine. The bottom cycle is the Kalina cycle, which comprises another back-pressure turbine and utilizes ammonia–water mixture as working fluid. After driving the steam Rankine cycle, the flue gas from the gas turbine sequentially heats the ammonia–water mixture to produce power. A new operational strategy was presented to generate electricity during low insolation period without the backup of fossil fuel. In middle insolation periods, the air is heated by the solar field and then directly drives the steam Rankine cycle, bypassing the gas turbine. In low insolation periods, the heated air directly drive the Kalina cycle, bypassing the Brayton cycle and the steam Rankine cycle. The off-design performance was investigated and the irreversibility was disclosed with the aid of the energy-utilization diagram method. Thus, the proposed system can utilize low insolation to generate electricity. This study provides a possibility to improve the solar–electric efficiency.

Formación de espeleotemas en el noreste peninsular y su relación con las condiciones climáticas durante los últimos ciclos glaciares

Speleothem growing is closely linked to warm climates with a positive hydrological balance. Mild temperatures and hydrological availability are conditions that tend to stimulate soil CO2 production due to denser vegetation cover and higher microbial activity. In such situations, waters enriched with dissolved carbonate are common and can infiltrate in the karstic system. This study compiles 158 dates from 34 speleothems collected in nine caves in the Northeastern Iberia to distinguish the time intervals with speleothem formation. A clear connection of speleothem growth and interglacial periods is established but precesssional influence is also observed, being periods of maxima insolation those with ideal conditions to produce karstic formations such as speleothems. The Holocene is without doubt the best represented period in the available records. However, last centuries were not characterized by an important development of speleothems in the studied caves.

PREVALENCE OF VITAMIN D DEFICIENCY IN PEOPLE OVER 50 YEARS OLD RESIDING IN REPUBLIC OF BASHKORTOSTAN IN PERIODS OF LOW INSOLATION

Objectives. To study the vitamin D levels in the period of minimal sun exposure in individuals older than 50 years residing in the Republic of Bashkortostan. Materials and methods. In the period of low insolation (March) in 188 people (68 men and 120 women) aged over 50 years (mean age 66,1 ± 0,75 years) residing in the city (Ufa) and rural areas of the Republic of Bashkortostan we investigated the levels of 25 (OH) D and parathyroid hormone (PTH) by the indirect ELISA. Level of 25 (OH) D 25-50 nmol/l were considered as mild vitamin D deficiency; 12,5-25 nmol/l-as moderate deficiency, and levels below 12.5 nmol/l - as a severe vitamin D deficiency. Results. The average level of 25 (OH) D was 33,55 ± 1,28 nmol/l; in urban area 43,48 ± 1,59 nmol/l; in rural area 21,25 ± 1,06 nmol/l; 36,29±2,43 nmol/l in men; 32,28± 1,47 nmol/l in women. The levels of vitamin D in the urban population were twice as high as in rural areas. A statistically significant difference by gender in terms of the levels of vitamin D was not found. We saw normal levels of vitamin D only in 18 % of subjects (in the city- 30 %, in the rural areas - 2 %), 43 % of people had a mild vitamin D deficiency (in the city - 59 %, in rural areas - 24 %), 33 % - a moderate deficiency of vitamin D (in the city -11 %, in the rural areas - 60 %), and 6 % of the patients had a severe vitamin D deficiency (in the city - 0 %, in rural areas -14 %). Moderate to severe vitamin D deficiency in rural areas was significantly more prevalent (74 %) than in urban (11 %). Gender was not found to be a risk factor for the development of vitamin D deficit in people over 50 years. There was a negative correlation between vitamin D levels and patient age (r=-0,356, p <0,001) and between levels of vitamin D andPTH (r =-0,313, p <0.001).

Heating season performance of a full-scale heat pipe assisted solar wall

Previous computer simulations and bench-scale experiments showed that the heat pipe assisted solar wall had the potential for significantly improved performance relative to conventional passive space heating systems. To further test this potential, a full-scale prototype of the heat pipe system was designed, built and installed in a classroom on the University of Louisville campus in Louisville, KY. During the spring heating season of 2010 (January–April), maximum daily peak thermal efficiency was 83.7% and average daily peak thermal efficiency was 61.4%. The maximum hourly average room gain achieved during the season was 163W/m2. On days with good solar insolation, the thermal storage was heated to temperatures sufficient to provide significant energy to the classroom – even during the coldest days of the season. During the longest period (4 days) of low insolation during the season, average hourly heat delivery to the room from storage remained positive, and was never less than 16.6W/m2. During good insolation days following a period of consecutive low insolation days, thermal storage temperature was quickly restored to levels comparable to those obtained during consecutive good insolation days. Estimated heat removal factor * transmittance absorptance product FR(τα) and heat removal factor * overall loss coefficient FRUL values for the system were comparable to those for glazed liquid active collectors.

A data mining approach: Analyzing wind speed and insolation period data in Turkey for installations of wind and solar power plants

Wind and solar power plant installations have been recently increased rapidly with respect to the depletion of fossil-based fuels all over the world. Due to stochastic nature of meteorological conditions, wind and solar energies have a non-schedulable nature and they require several installation analyses to determine the location and the capacities of wind and solar power to be produced.This paper focuses on the similarity, feasibility and numerical analyses of 75 cities in Turkey based on the monthly average wind speed and insolation period data. The nearest and the farest neighbor algorithms are used as agglomerative hierarchical clustering methods with Euclidean, Manhattan and Minkowski distance metrics in the stage of making the similarity and feasibility analyses. The maximum cophenetic correlation coefficient is achieved by the nearest neighbor algorithm with the Minkowski distance metric in the similarity and feasibility analyses. On the other hand, graphical representations of the monthly average wind speed and insolation period data are utilized for making the numerical analysis. The highest annual average wind speed and insolation period are obtained as 3.88m/s and 8.45h/day, respectively. Overall, many inferences were achieved in acceptable and efficient limits for wind and solar energy.