A basis for the synthesis of quasicrystals

It has been established that quasicrystals with icosahedral point group symmetry occur in a rapidly solidified Mg32 (Al, Zn)49 alloy chosen on the basis of its equilibrium crystal structure. This alloy has a natural tendency to form icosahedral atomic clusters stabilised by size difference amongst constituent atoms. Results highlight the relationship between equilibrium crystal structure and the tendency to form quasicrystals

Modeling impacts of climate change scenario over Turkey

Bu çalışmada izlenen yöntem, Türkiye ve çevresi üzerinde, günümüz ve gelecek için NASA-Sonlu Hacim Genel Dolaşım Modeli (fvGCM) tarafından üretilen projeksiyonların, ICTP-Bölgesel İklim Modeli (RegCM3) kullanılarak dinamik olarak ölçek küçültülmesidir. Günümüz (1961-1990, RF) ve gelecek (2071-2100, A2) simülasyonları için, Hükümetlerarası İklim Değşikliği Paneli (IPCC) tarafından belirlenmiş sera gazları emisyon senaryoları dikkate alınmıştır. A2 ve RF simülasyonlarının sıcaklık ve yağış için yapılan mevsimsel analizleri Türkiye’nin iklimsel bölgeleri üzerinde alansal ortalama alınarak ayrı ayrı incelenmiştir. A2 simülasyonuna göre, Türkiye üzerinde sıcaklıklardaki en dramatik değişim yaz mevsiminde Ege Bölgesi üzerindeki 5 ila 6 °C’ler arasındaki artıştır. Kış ayları dışındaki mevsimlerde artış, 3-4 °C arasında değişmektedir. Gelecek simülasyonundaki minimum artış, kış mevsiminden 2-3 °C olarak hesaplanmıştır. Yine A2 simülasyonunda, Doğu Karadeniz dağları boyunca uzanan bölgede kış yağışlarıdaki artış, rüzgar paterninin değişmesiyle orografik etkinin güçlenmesine bağlıdır. Türkiye’nin güneyi üzerinde de rüzgar paterninin güneyli değişimine bağlı olarak kış yağışlarında çok ciddi azalmalar (% 34) model sonuçlarında ortaya çıkmıştır. Sonbahar meviminde ise Güneydoğu Anadolu Bölgesinde yağışlarda % 50’lere varan artışlar görülmüştür. Bu artışların ana nedeni değişen rüzgar akımlarının taşıdığı nem olabilir. Gelecek iklim senaryosunda Fırat ve Dicle su havzalarını kapsayan alandaki kış yağışlarında yaşanan azalmalarla, küresel ısınmaya paralel sıcaklık artışının buharlaşmaya etkisiyle birlikte değerlendirildiğinde, model sonuçlarının hidrolojik analizlerinin önemi daha çok ortaya çıkmaktadır. Anahtar Kelimeler: İklim değişimi, bölgesel iklim modellemesi, ölçek küçültme.The Earth's climate has changed many times and fluctuated between the glacial and the interglacial periods since its formed. These changes related to natural forcings like volcanic eruptions, intense tectonic activity, solar activity and variation of Earth's orbital parameters, were sometimes very dramatic. Today, the global change we face to is different than the natural changes occurred in the past. Human-induced climate change has been taken into consideration extensively within the last decade more than ever. Recent advances in both climate observing systems and methodologies to detect the climate change, as well as broader global coverage of observations help scientists to better understand the climate system. Scientific studies which are led by IPCC (Intergovernmental Panel on Climate Change) showed that dominance of anthropogenic effect on global warming is indisputable (IPCC, 2007). Regional climate change modeling has been applied to many different areas such as agriculture, seasonal forecasting, hydrology applications, paleoclimate and climate projections. Because of its ability to resolve sharp gradients and contrasts in the surface conditions, the regional climate modeling approach yields more accurate and spatially detailed information. In this study,  the ICTP-Regional Climate Model version 3 (RegCM3) has been used to downscale present and future scenario simulations generated by the NASA-Finite Volume General Circulation Model (fvGCM) over Turkey and its surroundings. The present-day (1961-1990, RF) and the future climate change simulations (2071-2100, A2) are based on the IPCC Greenhouse Gases emissions, which are CO2, CH4, N2O, and CFC11- CFC12. Emission scenarios for these gases have been implemented into the radiation scheme for the simulations and, relatively high resolution of 30 km is adopted to resolve the complex topography of the domain. The role of the domain characteristics such as complex land-sea distribution determines the sub-regional climatic features and spatial climate variability. This diverse climatic structure of the region brings great challenge for regional climate modeling. Levantine Sea, Aegean Sea and Black Sea are main moisture sources of the Turkey and its surrounding regions. A2 simulation results which correspond future climate indicate that warming over Turkey's climatic zones is in the range of 2-5 °C. Summer temperature changes are more dominant in the A2 scenario. This pattern has also been observed for neighboring countries. Summer heat wave conditions over Aegean region (5 °C increase) are more obvious in the area averages than in the spatial pattern based model results. The difference between the summer and winter change is about 3 °C and it could play an important role in contributing to temporal shifts of the transition seasons. In addition, warming in winter over eastern and southeastern of Turkey which have higher altitudes are nearly 1 °C higher than for Marmara and Aegean regions which have lower altitudes. Autumn temperature changes for all regions are affected by the extension of the summer season extension due to the global warming. Most significant precipitation changes in A2 scenario have been occurred over the Mediterranean region of Turkey in winter and over the Southeastern of Turkey in autumn. Our analyses show a 34% decrease over Mediterranean region and it is related to the change in the atmospheric circulation which in turn causes reduced orographic forcing. The same circulation change also enhanced orographic forcing especially over the east of the Black Sea region and results in significant precipitation increase. Decreases over the Aegean and Southeastern regions are around 20% in winter. Autumn precipitation over Southeastern region increased as high as 48%. Flow pattern changes which also affected Iraq and Syria are consistent with enhanced moisture availability over this region which may account for the major precipitation increase. All precipitation changes in winter and autumn are also statistically significant. The amount of precipitation over Turkey in summer season is very little except eastern Black Sea region. Therefore, percent changes for summer precipitation over all of regions could not be meaningful to discuss. Analyses of A2 simulation show that combined effect of precipitation decrease and evapotranspiration increase related to temperature increase could play major role to reduce water resources over Turkey. Especially, there could be significant problems over Euphrates-Tigris basin because of the decreasing water availability in future scenario. Keywords: Climate change, regional climate modeling, downscaling scenarios

Normal coordinate analysis of the in-plane vibrations of o, m, p-fluorochloro and fluorobromo benzenes

A normal coordinate analysis of the in-plane vibrations of o, m, p-fluorochloro and fluorobromo benzenes was made dividing the six molecules into two sets. Some of the assignments of these molecules made by earlier workers were revised. The frequencies of the assigned fundamentals of each set of fluorochloro and fluorobromo benzenes were then fitted by the method of damped least-squares employing a 19 parameter modified Urey-Bradley force field

A study of the icosahedral phase: Mg<SUB>32</SUB> (Al,Zn)<SUB>49</SUB>

Homogeneous single phase Mg32Al19Zn30 was melt spun to form flakes suitable for TEM examination. The nodular structure gave diffraction patterns with 5.3.2 icosahedral point group symmetry. The formation of the icosahedral phase is rationalized in terms of the Mg (AlZn)49 equilibrium structure. This structure is a Frank-Kasper phase. It has previously been established how such icosahedral order can be anticipated in the Frank-Kasper phases

A new quasi-crystalline phase in rapidly solidified Mg4CuAl6

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Revised Franck-Condon factors for the ionization transition of O<SUB>2</SUB> and the second negative band system of O<SUP>+</SUP><SUB>2</SUB>

Franck-Condon factors are calculated for the ionization transition of O<SUB>2</SUB> and the second negative bands of O<SUP>+</SUP><SUB>2</SUB> using revised molecular constants for the ground state of O<SUP>+</SUP><SUB>2</SUB>. The potential functions of the various states considered are constructed by the RKR method using an exact technique presented by Zeleznik