Exploring a critical diameter for thermo-acoustic instability of downward propagating flames in tubes

Thermo-acoustic oscillations are observed when a flame ignited at open end of a tube propagates towards the closed end due to interaction between unsteady heat release rate fluctuations from flame and acoustic fluctuations. In our past work, it was found that thermo-acoustic instability increases with decreasing diameter from 7.0 cm to 3.0 cm. A recent study in flame propagation in Hele–Shaw cells showed that thermo-acoustic instability is not observed for plate separation less than or equal to 0.4 cm. Thermoacoustic instabilities cannot be observed in very narrow tubes due to excessive damping from the wall. This opens up the possibility of a critical diameter where thermo-acoustic instability would be maximum. In this work we perform flame propagation experiments with diameter of combustion tube in the range 0.5 cm to 3 cm for a fixed length of 70.2 cm. It was found that thermo-acoustic parametric instability begins at lowest laminar burning velocity when the diameter is around 1.0 cm. This diameter is termed as critical diameter. Critical diameter is found to be independent of Lewis number of mixtures. Existence of a critical diameter is thus proved experimentally. Growth rates of primary instability increase with decreasing diameter and show a maximum around the critical diameter and decrease with further decrease in tube diameter. But, growth rates of secondary instability as well as maximum pressure fluctuation amplitude decreases continuously with decreasing diameter. Mechanisms responsible for these observations and existence of a critical diameter are clarified.     

On-site analysis of archaeological artifacts excavated from the site on the outcrop at Northwest Saqqara,Egypt, by using a newly developed portable fluorescence spectrometer and diffractometer

Blue-painted pottery was produced in the New Kingdom, Egypt, and decorated with blue, red, and black pigment. In this study, two newly developed portable instruments, a portable X-ray fluorescence spectrometer and a portable X-ray powder diffractometer, were brought to the site on the outcrop at Northwest Saqqara, an archaeological site in Egypt, to verify their performance in on-site analysis of excavated artifacts at the site. Pigments used for the blue-painted pottery and plasters in the New Kingdom were analyzed by these instruments on the basis of both their chemical compositions and crystal-structural information. The blue pigments were identified as two different pigments, Egyptian blue and cobalt blue. The diffraction pattern of the blue pigment of the painted pottery exhibited that of spinel structure. The XRF spectrum of the blue pigment obtained by the same instrument from the same position indicates the presence of Mn, Co, Fe, Ni, and Zn. The possibility of compositional transitions of the cobalt blue pigment with time was revealed on by detailed analysis of the XRF data. The reason for the transitions is considered together with the archaeological background of the New Kingdom, Egypt.     

A graph theoretical approach to the effect of mutation on the flexibility of the DNA binding domain of p53 protein

Tumor suppressor protein p53 becomes inactive due to mutation on its DNA binding core domain leading to misbehavior of this protein and preventing its interaction with DNA. In the present study, changes of the protein conformation by five hot spot mutations of T-p53C were assessed preventing the mutants wild-type (WT) behavior. While studies of this nature were undertaken both experimentally and theoretically, the focus is fundamentally on the effects of the mutation on the dynamics of the protein. Hence, the basic concept underlying this study is the change in flexibility or rigidity of the protein. It was found that stable variant T-p53C (PDB-ID: 1uol) that is structurally and functionally very close to wild-type p53 is the most rigid structure and each single carcinogenic mutation on it makes the structure more flexible. We hypothesize that these changes of the molecule’s flexibility disrupt the network of hydrogen bonds associated with the interaction of WT not only at interaction but in the internal structures of the mutants as well, which prevents them from interacting in the WT fashion loosing the anti-cancer properties of WT.     

X-ray diffraction and magnetic susceptibility of sodium fullerides NaxC60

The X-ray diffraction (XRD), magnetic susceptibility and electron spin resonance (ESR) measurements have been carried out for Na_xC₆₀. The XRD profiles with x<4 can be assigned to a face-centered cubic (fcc) lattice, while those with 4≦x to a hexagonal one. The temperature dependence of magnetic susceptibility χ for Na_xC₆₀ using SQUID was fitted to the Curie law, and estimated temperature-independent component χ₀. The composition x dependence of the χ₀ for Na_xC₆₀ shows two maxima at around x=3 and x=10, and minimum at x=6. The absence of Pauli contribution at x=6 was confirmed using ESR. A trace of superconducting transition at 14 K has been found for some Na_xC₆₀ specimens with 8<x<9.     

Interaction of Cupidin/Homer2 with two actin cytoskeletal regulators, Cdc42 small GTPase and Drebrin, in dendritic spines

Background  

Homer is a postsynaptic scaffold protein that links various synaptic signaling proteins, including the type I metabotropic glutamate receptor subunits 1α and 5, the inositol 1,4,5-trisphosphate receptor, Shank and Cdc42 small GTPase. Overexpression of Homer induces changes in dendritic spine morphology in cultured hippocampal neurons. However, the molecular basis underpinning Homer-mediated spine morphogenesis remains unclear. In this study, we aimed to elucidate the structural and functional properties of the interaction between Cupidin/Homer2 and two actin-cytoskeletal regulators, Cdc42 small GTPase and Drebrin.     

Synthesis and biological activity of novel 5-(omega-aryloxyalkyl)oxazole derivatives as brain-derived neurotrophic factor inducers

A novel series of 5-(omega-aryloxyalkyl)oxazole derivatives was prepared and their effects on brain-derived neurotrophic factor (BDNF) production were evaluated in human neuroblastoma (SK-N-SH) cells. Syntheses were performed by construction of an oxazole ring as a key reaction. Most of the 5-(omega-aryloxyalkyl)oxazole derivatives markedly increased BDNF production in SK-N-SH cells. 4-(4-Chlorophenyl)-2-(2-methyl-1H-imidazol-1-yl)-5-[3-(2-methoxyphenoxy)propyl]-1, 3-oxazole, one of the most promising compounds, showed potent activity (EC(50)=7.9 microM) and the improvement of the motor nerve conduction velocity and the tail-flick response accompanied by a recovery of the brain-derived neurotrophic factor level in the sciatic nerve of streptozotocin (STZ)-diabetic rats.     

Rearrangement of the main-chain and subsequent thermal degradation of polyphenylene-ether

Studies of the thermal rearrangement and degradation of polyphenylene-ether (PPE) have been carried out by TGA (thermo-gravimetric analysis), GC-MS (gas chromatography-mass spectroscopy) and ¹H-NMR. 2,6-Xylenol was a major scission product in the temperature range 420–700 °C, and 3,5-xylenol, as a scission product, decreased with increasing temperature. Four monomeric and eight dimeric scission products were observed at relatively high temperatures. The distribution of the scission products, which changed with increasing temperature, led to the suggestion that rearrangement of the PPE main-chain occurred to form diphenyl methylene groups, followed by thermal degradation.     

One-Handed Helical Polyacetylenes Bearing Axially-Chiral 2-Arylpyridyl-N-Oxide Units for Efficient Chromatographic Enantioseparation of Chiral Aromatic and Aliphatic Alcohols

A series of poly(biarylylacetylene)s (PBAs) bearing axially-chiral (S)-and (R)-pyridyl-N-oxide residues with a methoxy, propoxy, or acetyloxy substituent at the 3-position of the biaryl units was synthesized. All the PBAs formed a preferred-handed helix, while the helical sense preference was varied depending on the substituents despite the same twist-sense of the biaryl units. Among them, the propoxy-bound helical PBA showed an exceptionally high chiral recognition ability as a chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) and efficiently resolved not only various chiral aromatic alcohols, but also a variety of chiral aliphatic alcohols; the latter still remains difficult to resolve by commercially-available CSPs in HPLC. Such practically-useful both handed helical PBA-based CSPs can be produced from the racemic PBA composed of fully racemic monomer units through deracemization of the biaryl units with a chiral alcohol.     

Oscillatory Reaction of a Pendant Drop in a Liquid–Air System under Microwave Irradiation

A Belousov–Zhabotinsky reaction in a pendant drop under microwave radiation was observed under nonstirring conditions. The period decreased as the irradiation power and time were increased because the droplet temperature increased. Moreover, the color change of the solution during the oscillatory reaction depended on the irradiation power and time although the droplet temperature returned to room temperature quickly. Irradiation at higher powers or longer times suspended the oscillatory reaction. However, for moderate irradiation powers or times, the oscillatory reaction stopped after irradiation because the concentration distribution of the reagents became homogeneous. After a time, the oscillatory reaction restarted because a concentration gradient developed again. Accordingly, the effect of the microwave irradiation history continued because the oscillatory reaction stopped even after the irradiation was stopped. This is because the rotation of the polar molecule caused by the irradiation produced a flat concentration distribution for the reagents through increased molecular diffusion.     

Future directions for higher-efficiency HIT solar cells using a Thin Silicon Wafer

To reduce the power generation cost of heterojunction with intrinsic thin layer (HIT) solar cells, it is necessary to use a thinner crystalline silicon wafer, as well as to improve the conversion efficiency. We have experimentally confirmed that V_OC of the HIT solar cell increases with decreasing the wafer thickness, and can reach a very high V_OC of 747 mV with a 58-μm-thick wafer owing to a sufficiently low surface recombination velocity. We also indicate the future directions for improving the efficiency. The uniformization of the texture size of the silicon surface and reduction of the carrier density in TCO film while maintaining an equal or lower conductivity are effective for improving the optical confinement.