Simulation and measurement of turbulent heat transfer in a channel with a surface-mounted rectangular heated block

Present study numerically and experimentally investigates the turbulent forced convective flow over a heated block mounted on one principal wall of an adiabatic channel. In the computation, thek-?, low-Reynolds-number, two-equation model was adopted for the turbulence closure. In the experiment, the flow measurement was performed by the laser Doppler velocimetry and the mass transfer measurement was carried out via the naphthalene sublimation technique. By virtue of the analogy between heat and mass transfer, the results could then be converted to predict the heat transfer coefficient. The effects of the Reynolds number and the aspect ratio of the block on heat transfer and fluid flow are thoroughly investigated. Distributions of the velocity and the turbulent kinetic energy are presented to gain an insight into the influence of the fluid flow on the heat transfer from the block. The Nusselt number hump is found on every face of the block, which is attributed to the separating bubble there. It is worth noting that the Nusselt number hump is located near the reattachment point of the separating bubble. In the absence of the separating bubble, the Nusselt number decreases or increases monotonously. Comparisons between numerical and experimental results of the local velocity and the heat transfer coefficient show reasonable agreement.     

Mass-analyzed threshold ionization spectroscopy of deuterium-substituted isotopomers of o-fluoroaniline and m-fluoroaniline cations

We applied the resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic and cation spectra of deuterium-substituted isotopomers of o-fluoroaniline (OFA) and m-fluoroaniline (MFA). The origins of the S₁ ← S₀ electronic transitions and adiabatic ionization energies of these isotopomers were precisely determined.     

Wind identification along a flight trajectory,part 3: 2D-dynamic approach

This paper deals with the identification of the wind profile along a flight trajectory by means of a two-dimensional dynamic approach. In this approach, the wind velocity components are computed as the difference between the inertial velocity components and the airspeed components. The airspeed profile as well as the nominal thrust, drag, and lift profiles are obtained from the available DFDR measurements. The actual values of the thrust, drag, and lift are assumed to be proportional to the respective nominal values via multiplicative parameters, called the thrust, drag, and lift factors. The thrust, drag, and lift factors plus the inertial velocity components at impact are determined by matching the flight trajectory computed from DFDR data with the flight trajectory available from ATCR data. This leads to a least-square problem which is solved analytically under the additional requirement of closeness of the multiplicative factors to unity. Application of the 2D-dynamic approach to the case of Flight Delta 191 shows that, with reference to the last 180 sec before impact, the values of the multiplicative factors were 1.09, 0.84, and 0.89; this implies that the actual values of the thrust, drag, and lift were 9% above, 16% below, and 11% below their respective nominal values. For the last 60 sec before impact, the aircraft was subject to severe windshear, characterized by a horizontal wind velocity difference of 123 fps and a vertical wind velocity difference of 80 fps. The 2D-dynamic approach is applicable to the analysis of windshear accidents in take-off or landing, especially for the case of older-generation, shorter-range aircraft which do not carry the extensive instrumentation of newer-generation, longer-range aircraft. The same methodology can be extended to the investigation of aircraft accidents originating from causes other than windshear (e.g., icing, incorrect flap position, engine malfunction), above all if its precision is further increased by combining the 2D-dynamic approach and the 2D-kinematic approach.     

Photostability of amino acids: internal conversion versus dissociation

Photodissociation dynamics for various tryptophan chromophores was studied at 193 or 248 nm using multimass ion imaging techniques. The competition between internal conversion to the ground electronic state and dissociation from the repulsive excited state reveals size-dependent photostability for these amino acid chromophores. As the size of chromophore increases, internal conversion to the ground state becomes the major nonradiative process. For tryptophan and larger chromophores, dissociation directly from the repulsive state is completely quenched.     

Computational study of reaction pathways for the formation of indium nitride from trimethylindium with HN3: comparison of the reaction with NH3 and that on TiO2 rutile (110) surface

The reactions of trimethylindium (TMIn) with HN3 and NH3 are relevant to the chemical vapor deposition of indium nitride thin film. The mechanisms and energetics of these reactions in the gas phase have been investigated by density functional theory and ab initio calculations using the CCSD(T)/Lanl2dz//B3LYP/Lanl2dz and CCSD(T)/Lanl2dz//MP2/Lanl2dz methods. The results of both methods are in good agreement for the optimized geometries and relative energies. These results suggest that the reaction with HN3 forms a new stable product, dimethylindiumnitride, CH3-In=N-CH3 via another stable In(CH3)2N3 (dimethylindium azide, DMInA) intermediate. DMInA may undergo unimolecular decomposition to form CH3InNCH3 by two main possible pathways: (1) a stepwise decomposition process through N2 elimination followed by CH3 migration from In to the remaining N atom and (2) a concerted process involving the concurrent CH3 migration and N2 elimination directly giving N2+CH3InNCH3. The reaction of TMIn with NH3 forms a most stable product DMInNH2 following the initial association and CH4-elimination reaction. The required energy barrier for the elimination of the second CH4 molecule from DMInNH2 is 74.2 kcal/mol. Using these reactions, we predict the heats of formation at 0 K for all the products and finally for InN which is 123+/-1 kcal/mol predicted by the two methods. The gas-phase reaction of HN3 with TMIn is compared with that occurring on rutile TiO2 (110). The most noticeable difference is the high endothermicity of the gas-phase reaction for InN production (53 kcal/mol) and the contrasting large exothermicity (195 kcal/mol) released by the low-barrier Langmuir-Hinshelwood type processes following the adsorption of TMIn and HN3 on the surface producing a horizontally adsorbed InN(a), Ti-NIn-O(a), and other products, CH4(g)+N2(g)+2CH3O(a) [J. Phys. Chem. B 2006, 110, 2263].     

Ultraviolet-durable superhydrophobic zinc oxide-coated mesh films for surface and underwater-oil capture and transportation

In this paper, we report a simple and an inexpensive method for fabricating superhydrophobic/superoleophilic mesh films from microstructured ZnO coatings. The microstructured ZnO coatings, which do not contain any fluorinated compounds, maintain their superhydrophobicity and superoleophilicity after ultraviolet irradiation and display environmental stability. Furthermore, those microstructured ZnO-coated mesh films exhibit good selectivity (even underwater) and excellent recyclability, making them promising candidates for many potential applications, including liquid-liquid separation, water treatment, and liquid transportation.     

Reversible Phase Transformation and Mechanochromic Luminescence of ZnII‐Dipyridylamide‐Based Coordination Frameworks

A 1D double‐zigzag framework, {[Zn(paps)₂(H₂O)₂](ClO₄)₂}_n ( 1 ; paps=N,N′‐bis(pyridylcarbonyl)‐4,4′‐diaminodiphenyl thioether), was synthesized by the reaction of Zn(ClO₄)₂ with paps. However, a similar reaction, except that dry solvents were used, led to the formation of a novel 2D polyrotaxane framework, [Zn(paps)₂(ClO₄)₂]_n ( 2 ). This difference relies on the fact that water coordinates to the Zn^II ion in 1 , but ClO₄^? ion coordination is found in 2 . Notably, the structures can be interconverted by heating and grinding in the presence of moisture, and such a structural transformation can also be proven experimentally by powder and single‐crystal X‐ray diffraction studies. The related N,N′‐bis‐ (pyridylcarbonyl)‐4,4′‐diaminodiphenyl ether (papo) and N,N′‐(methylenedi‐para‐phenylene)bispyridine‐4‐carboxamide (papc) ligands were reacted with Zn^II ions as well. When a similar reaction was performed with dry solvents, except that papo was used instead of paps, the product mixture contained mononuclear [Zn(papo)(CH₃OH)₄](ClO₄)₂ ( 5 ) and the polyrotaxane [Zn(papo)₂(ClO₄)₂]_n ( 4 ). From the powder XRD data, grinding this mixture in the presence of moisture resulted in total conversion to the pure double‐zigzag {[Zn(papo)₂(H₂O)₂](ClO₄)₂}_n ( 3 ) immediately. Upon heating 3 , the polyrotaxane framework of 4 was recovered. The double‐zigzag {[Zn(papc)₂(H₂O)₂](ClO₄)₂}_n ( 6 ) and polyrotaxane [Zn(papc)₂(ClO₄)₂]_n ( 7 ) were synthesized in a similar reaction. Although upon heating the double‐zigzag 6 undergoes structural transformation to give the polyrotaxane 7 , grinding solid 7 in the presence of moisture does not lead to the formation of 6 . Significantly, the bright emissions for double‐zigzag frameworks of 1 and 3 and weak ones for polyrotaxane frameworks of 2 and 4 also show interesting mechanochromic luminescence.     

Simultaneous determination of deoxycytidine diphosphate and deoxycytidine triphosphate by capillary electrophoresis with transient isotachophoretic stacking: a sensitive monitoring method for ribonucleotide reductase activity

A simple and rapid capillary electrophoretic method was developed for simultaneous determination of sub‐micromolar 2′‐deoxycytidine 5′‐diphosphate (dCDP) and 2′‐deoxycytidine 5′‐triphosphate (dCTP) levels in enzyme assays without using radioactively labeled substrates. The separation was performed at 25°C using MES in the BGE as the terminating ion, the chloride ions in the sample buffer as the leading ion, and PEG 4000 in the BGE as the EOF suppressor for sample stacking by transient isotachophoresis (tITP). Several parameters affecting the separation were investigated, including the pH of the BGE, the concentration of sodium chloride in the sample buffer, and the concentrations of MES and PEG 4000 in the running buffer. Good separation with high separation efficiency was achieved within 6 min under optimal conditions. In comparison with the simple CZE method, the present tITP‐CZE method enabled a 150‐fold increase in the injection time without any decrease in resolution and the sensitivity was enhanced up to two orders of magnitude with the new method. The linear range of the method was 0.1–10 μM for dCDP and dCTP. The limits of detection of dCDP and dCTP were 85 and 73 nM, respectively. The proposed method was successfully applied for the activity assay of ribonucleotide reductase from Hep G2 and Sf9 cells.     

Neuroprotective effect of agmatine in rats with transient cerebral ischemia using MR imaging and histopathologic evaluation

Purpose

This study aimed to further investigate the effects of agmatine on brain edema in the rats with middle cerebral artery occlusion (MCAO) injury using magnetic resonance imaging (MRI) monitoring and biochemical and histopathologic evaluation.

Materials and methods

Following surgical induction of MCAO for 90 min, agmatine was injected 5 min after beginning of reperfusion and again once daily for the next 3 post-operative days. The events during ischemia and reperfusion were investigated by T2-weighted images (T2WI), serial diffusion-weighted images (DWI), calculated apparent diffusion coefficient (ADC) maps and contrast-enhanced T1-weighted images (CE-T1WI) during 3 h–72 h in a 1.5 T Siemens MAGNETON Avanto Scanner. Lesion volumes were analyzed in a blinded and randomized manner. Triphenyltetrazolium chloride (TTC), Nissl, and Evans Blue stainings were performed at the corresponding sections.

Results

Increased lesion volumes derived from T2WI, DWI, ADC, CE-T1WI, and TTC all were noted at 3 h and peaked at 24 h–48 h after MCAO injury. TTC-derived infarct volumes were not significantly different from the T2WI, DWI-, and CE-T1WI-derived lesion volumes at the last imaging time (72 h) point except for significantly smaller ADC lesions in the MCAO model (P < 0.05). Volumetric calculation based on TTC-derived infarct also correlated significantly stronger to volumetric calculation based on last imaging time point derived on T2WI, DWI or CE-T1WI than ADC (P < 0.05). At the last imaging time point, a significant increase in Evans Blue extravasation and a significant decrease in Nissl-positive cells numbers were noted in the vehicle-treated MCAO injured animals. The lesion volumes derived from T2WI, DWI, CE-T1WI, and Evans blue extravasation as well as the reduced numbers of Nissl-positive cells were all significantly attenuated in the agmatine-treated rats compared with the control ischemia rats (P < 0.05).

Conclusion

Our results suggest that agmatine has neuroprotective effects against brain edema on a reperfusion model after transient cerebral ischemia.