Heat transfer enhancement in a turbulent natural convection boundary layer along a vertical flat plate

An experimental study on heat transfer enhancement for a turbulent natural convection boundary layer in air along a vertical flat plate has been performed by inserting a long flat plate in the spanwise direction (simple heat transfer promoter) and short flat plates aligned in the spanwise direction (split heat transfer promoter) with clearances into the near-wall region of the boundary layer. For a simple heat transfer promoter, the heat transfer coefficients increase by a peak value of approximately 37% in the downstream region of the promoter compared with those in the usual turbulent natural convection boundary layer. It is found from flow visualization and simultaneous measurements of the flow and thermal fields with hot- and cold-wires that such increase of heat transfer coefficients is mainly caused by the deflection of flows toward the outer region of the boundary layer and the invasion of low-temperature fluids from the outer region to the near-wall region with large-scale vortex motions riding out the promoter. However, heat transfer coefficients for a split heat transfer promoter exhibit an increase in peak value of approximately 60% in the downstream region of the promoter. Flow visualization and PIV measurements show that such remarkable heat transfer enhancement is attributed to longitudinal vortices generated by flows passing through the clearances of the promoter in addition to large-scale vortex motions riding out the promoter. Consequently, it is concluded that heat transfer enhancement of the turbulent natural convection boundary layer can be substantially achieved in a wide area of the turbulent natural convection boundary layer by employing multiple column split heat transfer promoters. It may be expected that the heat transfer enhancement in excess of approximately 40% can be accomplished by inserting such promoters.     

Variational formulation of stability problems for thin-walled members

Summary The governing equations for thin-walled members subjected to axial force, biaxial bending and torsion are formulated by variational method. The resulting equations differ slightly with currently accepted governing equations. Numerical examples are solved for simple problems to illustrate some of the features of the proposed equations.

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Übersicht Die beschreibenden Differentialgleichungen für dünnwandige Bauglieder, die durch achsiale Kräfte, biachsiale Biegung und Torsion beansprucht sind, werden nach einem Variationsverfahren aufgestellt. Die so erhaltenen Gleichungen unterscheiden sich etwas von den zur Zeit üblichen Gleichungen. Um die Eigenschaften der jetzt vorgeschlagenen Gleichungen zu zeigen, werden numerische Ergebnisse für einige einfache Aufgaben angegeben.

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On leave from University of Tokyo, Tokyo Japan.     

Partial Protection of Carbohydrate Derivatives. Part 21. Lead(II) Nitrate Mediated Triisopropylsilyl Ether Formation; Preparation of 2′-Deoxy-3′-O-triisopropylsilylribonucleosides

Introduction of the triisopropylsilyl protecting group to the 3′-position of 5′-O-aroyl-2′-deoxyribonucleosides wa effectively performed by the use of triisopropylsilyl chlor ide in DMF in the presence of pyridine and lead(II) nitrate the latter was substituted in this reaction for silver nitr ate. Simple treatment of the resulting triisopropylsilyl ethers with sodium methoxide in THF gave 2′-deoxy-3′-O-tri-isopropylsilylribonucleosides in excellent yields.     

Micro-PIV measurement and CFD analysis of a thin liquid flow between rotating and stationary disks

Abstract  

A strongly sheared flow in a thin liquid layer between rotating and stationary disks is studied experimentally and numerically to clarify the characteristics of the flow in rotation-shearing chemical reactors. The disk diameter is 10 mm and the separation between the disks is 500 μm. The rotational speeds that are examined are 300, 500 and 700 rpm. The micro-PIV technique is used to measure the velocity in the liquid layer. A commercial CFD software is also used to obtain the results for the comparison and validation purposes. The overall velocity distributions revealed by the micro-PIV measurement are in good agreement with the CFD results. Both results show some interesting characteristics of the flow field, including the presence of a secondary flow and its influence on the tangential velocity profiles. The near-wall measurement in the micro-PIV technique is appreciably improved by the use of a simple digital, high-pass filtering technique that is applied to the acquired particle images. It is found that the flow characteristics in the thin liquid layer can be evaluated efficiently if the micro-PIV technique is used together with the high-pass filtering technique that is examined here.     

0-extended supergravity and Chern-Simons theories

We give generalizations of extended Poincaré supergravity with arbitrarily many supersymmetries in the absence of central charges in three dimensions by gauging its intrinsic global SO(N) symmetry. We call these ₀ (Aleph-null) supergravity theories. We further couple a non-Abelian supersymmetric Chern-Simons theory and an Abelian topological BF theory to ₀ supergravity. Our result overcomes the previous difficulty for supersymmetrization of Chern-Simons theories beyond N = 4. This feature is peculiar to the Chern-Simons and BF theories including supergravity in three dimensions. We also show that dimensional reduction schemes for four-dimensional theories such as N = 1 self-dual supersymmetric Yang-Mills theory or N = 1 supergravity theory that can generate ₀ globally and locally supersymmetric theories in three dimensions. As an interesting application, we present ₀ supergravity Liouville theory in two dimensions after appropriate dimensional reduction from three dimensions.     

How is it possible to obtain buried interface information through very thick films using a hard-X-ray PEEM?

We analyze the excitation of secondary electrons by hard-X-rays in subsurface layers. By studying core-excited photoelectron lines and their plasmon satellites in photoemission spectra, we show how electrons excited by hard-X-rays can carry information from deep regions deep within the sample to the surface. It is believed that the decay of high-energy photoelectrons via plasmon-loss is strongly related to the production of secondary electrons. For high-energy electrons, however, the momentum transfer to plasmons is small compared to the electron’s initial momentum, so the lateral position on the surface from which the secondary electrons are emitted is close to that of the atom initially excited by the hard-X-rays. This explains why the spatial resolution of hard-X-ray photoelectron emission microscope (HX-PEEM) images is good even if the buried interface is covered by a film with a thickness many times the inelastic mean free path of the primary electrons. This argument explains well recent HX-PEEM results.     

Supersymmetric grand unified theory with soft breaking of intermediate mass scale

We consider a supersymmetric GUT with the soft breaking of supersymmetry at an intermediate mass scale. A realistic and natural unified model is constructed.     

Photo-induced aromatic assembly of benzocycloalka[1,2-b] furan and spiro[furan-2(3H),1′-benzocycloalkane] derivatives

The photo-induced benzannulation of benzocycloalka[1,2-b]furans produced hydrohelicene-type compounds in good yields. A similar photoreaction of the spiro[furan-2(3H),1′-benzocycloalkane]s afforded dihydrophenalene derivatives in moderate yields. Benzo[kl]xanthene was also formed by a similar photoreaction of spiro[furan-2(3H),9′-xanthene]. The reaction pathway was elucidated by the ¹H NMR spectrum of the reaction mixture and the alternative synthesis of the intermediate.     

One-pot synthesis of 2-oxa-7-azaspiro[4.4]nonane-8,9-diones using Mn(III)-based oxidation of 4-acylpyrrolidine-2,3-diones

2-Oxa-7-azaspiro[4.4]nonane-8,9-diones were newly synthesized in good yields by the Mn(III)-based reaction of a mixture of 1,1-diarylethenes and 4-acylpyrrolidine-2,3-diones. Under the stated reaction conditions, the pyrrolidinedione ring remained intact and became one of the two rings of the 2-oxa-7-azaspiro[4.4]nonanedione scaffold. The procedure was simple and the product was easily separated. The structure determination and the mechanism for the formation of the 2-oxa-7-azaspiro[4.4]nonanediones were also discussed.