An investigation of artificial pasture establishment under dryland conditions

This study was conducted to determine the suitable mixtures of perennial forage species for the stablishment of artificial pasture under dry conditions in Karapinar-Konya between 2004 and 2006. In this study, complex mixtures of crested wheatgrass (Agropyron cristatum (L.) Gaertner), tall wheatgrass (Agropyron elongatum (Host) Beauv.), intermediate wheatgrass (Agropyron intermedium (Host) Beauv.), smooth brome (Bromus inermis Layss), sheep fescue (Festuca ovina L.), tall oatgrass (Arrhenatherum elatius (L.) Presl.), alfalfa (Medicago sativa L.), sainfoin (Onobrychis sativa Lam.) and garden burnet (Poterium sanguisorba L.) were used. The experiment design was conducted in a randomized block design with three replications. The highest fresh forage yields were obtained from crested wheatgrass, garden burnet and alfalfa mixtures in 2005 and 2006 (1708.1 and 1763.6 kg ha-1, respectively) and the highest dry matter yield was obtained in 2006 (933.9 kg ha-1). The results showedthat mixtures of crested wheatgrass, garden burnet and alfalfa may be used to establish artificial pasture under dryland conditions in similar ecology of Karapýnar-Konya.Key words: Artificial pasture, dryland conditions, crested wheatgrass, garden burnet, alfalfa

Theoretical modeling of the doping process in polypyrrole by calculating UV/vis absorption spectra of neutral and charged oligomers

Changes in absorption spectra during doping of oligopyrroles were investigated with time-dependent density functional theory on optimized structures of neutral, singly, and doubly charged pyrrole oligomers with up to 24 rings. In the absence of counterions, defects are delocalized. Counterions induce localization. For dications two polarons on the same chain are preferred over a bipolaren. Intragap absorptions arise in charged species, no matter whether defects are localized or delocalized. Cations and dications give rise to two sub-band transitions. The cation peaks have lower energies than those of dications. The first excitations of cations have lower oscillator strengths than the second; for dications the second peak is weaker than the first. For very long oligomers, the second sub-band absorption vanishes and a third one appears at higher energy. The behavior of pyrrole oligomers is analogous to that of thiophene oligomers. Theoretical UV spectra for cations and dications of short oligomers (six to eight rings) match experimental spectra of polypyrrole at low and at high doping levels, respectively. The error in the theoretical calculations is about 0.4 eV, slightly larger than for thiophene oligomers at the same level of theory. © 2008 American Chemical Society

Gas sensing properties of carbon nanotubes modified with calixarene molecules measured by QCM techniques

1st International Congress on Advances in Applied Physics and Materials Science (APMAS), Antalya, Turkey, 12-15 May, 2011This study focuses on the characterization and optimization of calixarene modified carbon nanotube thin films for gas detection. Calixarene molecules were synthesized individually by considering their functional groups to attract the gas. Calixarene modified carbon nanotube based sensors were fabricated using drop-casting method on a quartz crystal microbalance gold electrode. Carbon monoxide, carbondioxide, oxygen and dry air were used as active gases for adsorption process, while high-purity nitrogen gas was used for desorption process. The selectivity and sensitivity of calixarene modified carbon nanotube are investigated in detail. Our experimental results show that functional calixarene modified carbon nanotube coated quartz crystal microbalance sensors are very sensitive and selective to gas of CO 2 at room temperature operation.This research was supported by TÜBİTAK under project numbers TBAG 109 T240 and 110 M349 and IYTE research project number 2010IYTE2

A photoprogrammable electronic nose with switchable selectivity for VOCs using MOF films

Advanced analytical applications require smart materials and sensor systems that are able to adapt or be configured to specific tasks. Based on reversible photochemistry in nanoporous materials, we present a sensor array with a selectivity that is reversibly controlled by light irradiation. The active material of the sensor array, or electronic nose (e-nose), is based on metal–organic frameworks (MOFs) with photoresponsive fluorinated azobenzene groups that can be optically switched between their trans and cis state. By irradiation with light of different wavelengths, the trans–cis ratio can be modulated. Here we use four trans–cis values as defined states and employ a four-channel quartz-crystal microbalance for gravimetrically monitoring the molecular uptake by the MOF films. We apply the photoprogrammable e-nose to the sensing of different volatile organic compounds (VOCs) and analyze the sensor array data with simple machine-learning algorithms. When the sensor array is in a state with all sensors either in the same trans- or cis-rich state, cross-sensitivity between the analytes occurs and the classification accuracy is not ideal. Remarkably, the VOC molecules between which the sensor array shows cross-sensitivity vary by switching the entire sensor array from trans to cis. By selectively programming the e-nose with light of different colors, each sensor exhibits a different isomer ratio and thus a different VOC affinity, based on the polarity difference between the trans- and cis-azobenzenes. In such photoprogrammed state, the cross-sensitivity is reduced and the selectivity is enhanced, so that the e-nose can perfectly identify the tested VOCs. This work demonstrates for the first time the potential of photoswitchable and thus optically configurable materials as active sensing material in an e-nose for intelligent molecular sensing. The concept is not limited to QCM-based azobenzene-MOF sensors and can also be applied to diverse sensing materials and photoswitches

The effect of stair case electron injector design on electron overflow in InGaN light emitting diodes

Effect of two-layer (In0.04Ga0.96N and In0.08Ga0.92N) staircase electron injector (SEI) on quantum efficiency of light-emitting-diodes (LEDs) in the context of active regions composed of single and quad 3 nm double heterostructures (DHs) is reported. The experiments were augmented with the first order model calculations of electron overflow percentile. Increasing the two-layer SEI thickness from 4 + 4 nm up to 20 + 20 nm substantially reduced, if not totally eliminated, the electron overflow in single DH LEDs at low injections without degrading the material quality evidenced by the high optical efficiency observed at 15K and room temperature. The improvement in quad 3 nm DH LEDs with increasing SEI thickness is not so pronounced as the influence of SEI is less for thicker active regions, which in and of themselves necessarily thermalize the carriers. (C) 2013 AIP Publishing LLC

Nondestructive atomic compositional analysis of BeMgZnO quaternary alloys using ion beam analytical techniques

The atomic composition with less than 1-2 atom % uncertainty was measured in ternary BeZnO and quaternary BeMgZnO alloys using a combination of nondestructive Rutherford backscattering spectrometry with 1 MeV He + analyzing ion beam and non- Rutherford elastic backscattering experiments with 2.53 MeV energy protons. An enhancement factor of 60 in the cross-section of Be for protons has been achieved to monitor Be atomic concentrations. Usually the quantitative analysis of BeZnO and BeMgZnO systems is challenging due to difficulties with appropriate experimental tools for the detection of the light Be element with satisfactory accuracy. As it is shown, our applied ion beam technique, Page 2 of 22 Accepted Manuscript supported with the detailed simulation of ion stopping, backscattering, and detection processes allows of quantitative depth profiling and compositional analysis of wurtzite BeZnO/ZnO/sapphire and BeMgZnO/ZnO/sapphire layer structures with low uncertainty for both Be and Mg. In addition, the excitonic bandgaps of the layers were deduced from optical transmittance measurements. To augment the measured compositions and bandgaps of BeO and MgO co-alloyed ZnO layers, hybrid density functional bandgap calculations were performed with varying the Be and Mg contents. The theoretical vs. experimental bandgaps show linear correlation in the entire bandgap range studied from 3.26 eV to 4.62 eV. The analytical method employed should help facilitate bandgap engineering for potential applications, such as solar blind UV photodetectors and heterostructures for UV emitters and intersubband devices

Volumetric evaluation of temporal bone structures in the cases with bilateral tinnitus: clinical and morphometrical study

Background: Tinnitus is the recognition of sound in the absence of any external auditory stimulus to the noise of ringing in the ears. Middle ear aeration carries important role for ossicular coupling and normal hearing. There is restricted morphometric data on the cases with bilateral tinnitus. Materials and methods: In this study we evaluated hearing findings of 18 cases with subjective nonpulsatile bilateral tinnitus and also morphometry and volumetry of temporal bone substructures on the computed tomography images using stereological method compared with the gender and age matched 12 healthy subjects. Duration of tinnitus, exposing acoustic trauma or/and high level noise levels, evaluation of middle ear volume, jugular bulb levels, distances between jugular bulb and both oval window and middle ear were evaluated. Results: Both males and females with tinnitus showed worse hearing thresholds through bone and air conductions than healthy subjects but it was not statistically significant. Pure tone thresholds through bone and air conductions were not statistically different in both sexes with bilateral tinnitus. Right middle ear volume of the cases with bilateral tinnitus was mean 5.57 cm3 for males and 5.64 cm3 for females; and also the left middle ear volume of the cases with bilateral tinnitus was mean 5.87 cm3 for males and 5.65 cm3 for females. There were no significant differences between the cases with bilateral tinnitus and the control subjects according to the side of the body. < strong > Conclusions: The data on the hearing findings and morphometrical evaluation of the cases with bilateral tinnitus may be important for anatomists and clinicians. (Folia Morphol 2018; 77, 1: 57–64)