Characteristics investigation on heat transfer growth of sonochemically synthesized ZnO-DW based nanofluids inside square heat exchanger

Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...     

The effect of rapid rotation on a vertical bridgman furnace at large Rayleigh number

In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate.     

The effects of oxygenation on the optical properties of dimethyl-dithienothiophenes: comparison between experiments and first-principles calculations

Modifications of the optical properties of dimethyl-dithienothiophenes due to the oxygen functionalization of the central sulfur atom are investigated. We have measured the absorption, photoluminescence (PL) and PL excitation spectra, the PL quantum efficiencies, and the PL decay times. These experimental results are interpreted and compared with first-principles time-dependent density-functional theory calculations, which predict, for the considered systems, excitation and emission energies with an accuracy of 0.1 eV. It is found that the oxygenation strongly changes optical and photophysical properties. These effects are related to the modifications of the energetically lowest-unoccupied molecular orbital and the energetically second highest occupied one, which change the relative position of the two lowest singlet and triplet excited states.     

Synthesis of the C3-C19 segment of phorboxazole B

[reaction: see text]. Three segment-coupling Prins approaches to the C3-C19 segment of phorboxazole B have been developed. One successful strategy utilized a novel TMSBr-mediated cyclization that proceeded with complete axial selectivity. Displacement of bromide with cesium acetate provided the C13 hydroxyl stereocenter of 22. Additionally, treatment of alpha-acetoxy ether 20 with TFA enabled a more concise synthesis of the C3-C19 target 13 by allowing direct access to the equatorial alcohol.     

Open-shell localized Hartree-Fock method based on the generalized adiabatic connection Kohn-Sham formalism for a self-consistent treatment of excited states

An effective exact-exchange Kohn-Sham approach for the treatment of excited electronic states, the generalized adiabatic connection open-shell localized Hartree-Fock (GAC-OSLHF) method is presented. The GAC-OSLHF method is based on the generalized adiabatic connection Kohn-Sham formalism and therefore capable of treating excited electronic states, which are not the energetically lowest of their symmetry. The method is self-interaction free and allows for a fully self-consistent computation of excited valence as well as Rydberg states. Results for atoms and small- and medium-size molecules are presented and compared to restricted open-shell Hartree-Fock (ROHF) and time-dependent density-functional results as well as to experimental data. While GAC-OSLHF and ROHF results are quite close to each other, the GAC-OSLHF method shows a much better convergence behavior. Moreover, the GAC-OSLHF method as a Kohn-Sham method, in contrast to the ROHF approach, represents a framework which allows also for a treatment of correlation besides an exchange by appropriate functionals. In contrast to the common time-dependent density-functional methods, the GAC-OSLHF approach is capable of treating doubly or multiply excited states and can be easily applied to molecules with an open-shell ground state. On the nodal planes of the energetically highest occupied orbital, the local multiplicative GAC-OSLHF exchange potential asymptotically approaches a different, i.e., nonzero, value than in other regions, an asymptotic behavior which is known from exact Kohn-Sham exchange potentials of ground states of molecules.     

Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights

We report the first transition metal catalyst- and ligand-free conjugate addition of lithium tetraorganozincates (R₄ZnLi₂) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R₄ZnLi₂ provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 °C) and short reaction time (30 min). This is particularly remarkable when employing β-nitroacrylates and β-nitroenones, where despite the presence of other electrophilic groups, selective 1,4 addition to the C=C is preferred. Structural and spectroscopic studies confirmed the formation of tetraorganozincate species in solution, the nature of which has been a long debated issue, and allowed to unveil the key role played by donor additives on the aggregation and structure of these reagents. Thus, while chelating N,N,N’,N’-tetramethylethylenediamine (TMEDA) and (R,R)-N,N,N’,N’-tetramethyl-1,2-diaminocyclohexane (TMCDA) favour the formation of contacted-ion pair zincates, macrocyclic Lewis donor 12-crown-4 triggers an immediate disproportionation process of Et₄ZnLi₂ into equimolar amounts of solvent-separated Et₃ZnLi and EtLi.     

Evaluations of particulate mass loading from visibility observations and atmospheric turbidity measurements

Summary Two extinction models for continental and rural particles were defined by using a very accurate computer programme based on Mie extinction theory for spherical particles. The first extinction model gives several sets of volume extinction coefficients at seven visible and near-infra-red wave-lengths, calculated for twenty-seven Junge-type size distribution curves (with Junge parameter ranging from 1.8 to 4.4) and for eight relative-humidity values of the air. This model also gives the corresponding values of ?ngstr?m's exponent α and mean particle mass. The second extinction model gives similar sets of data, calculated for two lognormal size distribution curves of tropospheric and large rural particles at five relative-humidity values of the air. These monomodal models can be used to determine bimodal extinction models consisting of variable number fractions of tropospheric and rural particles. Evaluations of the particulate mass loading can be obtained from measurements of visual range and atmospheric turbidity, choosing the most appropriate extinction model on the basis of the spectral features characterizing atmospheric attenuation. Measurements of visibility and atmospheric turbidity in two rural localities of the Po Valley were examined by employing both the present extinction models and other extinction models commonly used. The comparison of the results shows that the Junge-type extinction model can be reliably used in cases in which the exponent α is equal to or larger than 1.4. For smaller values of α, the Junge-type extinction model and bimodal model were found to give realistic evaluations of the lower and upper limits of particulate mass loading.

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Riassunto Usando un programma di calcolo assai accurato, basato sulla teoria di Mie per l'estizione da particelle sferiche, si sono definiti due modelli di estinzione per particelle di origine continentale e rurale. Il primo di questi modelli fornisce diverse serie spettrali dei coefficienti di estinzione da particelle su percorso unitario, relativi a sette lunghezze d'onda nel visibile e vicino infrarosso e calcolati per ventisette distribuzioni dimensionali del tipo di Junge (con parametro di Junge che varia da 1.8 a 4.4) e per otto valori dell'umidità relativa dell'aria. Inoltre, questo modello fornisce i valori corrispondenti dell'esponente di ?ngstr?m α e della massa media delle particelle. Il secondo modello fornisce insiemi simili di dati calcolati per due distribuzioni dimensionali di tipo lognormale, relative a particelle troposferiche e a grandi particelle di origine rurale, e per cinque valori di umidità relativa dell'aria. Questi modelli monomodali possono essere usati per definire modelli bimodali di estinzione, composti da particelle troposferiche e rurali in percentuali numeriche variabili. Scegliendo il modello piú appropriato di estinzione sulla base delle caratteristiche spettrali di attenuazione atmosferica, si possono ricavare valutazioni del contenuto atmosferico di massa delle particelle da misure di visibilità e torbidità atmosferica. Misure di questo tipo, effettuate in due località rurali della pianura padana, sono state esaminate sia mediante i modelli di estinzione qui proposti sia mediante altri modelli di estinzione usati comunemente. Il confronto tra i risultati mostra che il modello di estinzione del tipo di Junge può dare risultati realistici nei casi in cui l'esponente α è maggiore di o egule a 1.4. Per valori minori di α, il modello di Junge e il modello bimodale forniscono rispettivamente una stima di minima e una stima di massima del contenuto atmosferico di massa delle particelle.

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Резюме Предлагаются две модели экстинции для континентальных и селяских частиц, используя очень точную программу, основанную на теории Ми сферических частиц. Первая модель экстинции дает несколько систем для коэффициентов общемной экстинции при семи длинах волн в видимом и ближнем инфракрасном диапазонах, которые вычислены для 27 распределений по размерам типа Джунджа (с параметром Джунджа в области от 1.8 до 4.4) и для восьми значений относительной влажности воздуха. Эта модель также дает соответствуюшие величины для экспоненты Ангстрема α и среднюю массу частиц. Вторая модель экстинции дает аналогичные системы данных, вычисленных для двух log-нормальных распределений по размерам для тропосферных и больших сельских частиц при пяти значениях относительной влажности воздуха. Эти мономодальные модели могут быть использованы для определения бимодальных моделей экстинции, которые учитывают изменяющиеся численные относительные содержания тропосферных и сельских частиц. Выбирая наиболее соответствуюшую модель экстинции на основе спектральных особенностей, характеризующих атмосфернэе ослабление, можно оденить массовое содержание микрочастиц из измерениц видимости и помутнения атмосферы. Анализируются измерения видимости и помутнения атмосферы в двух сельских райохах долины По, используя предложенные модели экстинции и обычно пременяемые модели экстинции. Сравнение результатов показывает, что модель экстинции типа Джунджа может быть надежно использована в случаях, когда экспонента α равна или больше, чем 1.4. Для меньших значений α получается, что модель экстинции типа Джунджа и бимодальная модель дают реалистические оценки для нижнего и верхнего пределов массового содержания микрочастиц.

     

Minkowski iteration of sets

The Minkowski addition, ⊕, is a natural generalization of vector addition. However, ⊕ and scalar multiplication do not follow all the usual laws of vector space operations. This is reflected upon the properties of a new operation, °, which maps vector sets into vector sets. The study of a linear iterative process (with ° acting recurrently on vector sets) brings out the outstanding value of vector balls and convex hulls for obtaining explicit solutions or bounds.     

Upper limits on gravitational-wave emission in association with the 27 Dec 2004 giant flare of SGR1806-20

At the time when the giant flare of SGR1806-20 occurred, the AURIGA "bar" gravitational-wave (GW) detector was on the air with a noise performance close to stationary Gaussian. This allows us to set relevant upper limits, at a number of frequencies in the vicinities of 900 Hz, on the amplitude of the damped GW wave trains, which, according to current models, could have been emitted, due to the excitation of normal modes of the star associated with the peak in x-ray luminosity.     

Achieving geodetic motion for LISA test masses: ground testing results

The low-frequency resolution of space-based gravitational wave observatories such as LISA (Laser Interferometry Space Antenna) hinges on the orbital purity of a free-falling reference test mass inside a satellite shield. We present here a torsion pendulum study of the forces that will disturb an orbiting test mass inside a LISA capacitive position sensor. The pendulum, with a measured torque noise floor below 10 fN m/square root of Hz from 0.6 to 10 mHz, has allowed placement of an upper limit on sensor force noise contributions, measurement of the sensor electrostatic stiffness at the 5% level, and detection and compensation of stray dc electrostatic biases at the millivolt level.