Prime interchange graphs of classes of matrices of zeros and ones

Let R = (r₁,…, r_m) and S = (s₁,…, s_n) be nonnegative integral vectors, and let $\text{U}$(R, S) denote the class of all m × n matrices of 0's and 1's having row sum vector R and column sum vector S. An invariant position of $\text{U}$(R, S) is a position whose entry is the same for all matrices in $\text{U}$(R, S). The interchange graph G(R, S) is the graph where the vertices are the matrices in $\text{U}$(R, S) and where two matrices are joined by an edge provided they differ by an interchange. We prove that when 1 ≤ r_i ≤ n ? 1 (i = 1,…, m) and 1 ≤ s_j ≤ m ? 1 (j = 1,…, n), G(R, S) is prime if and only if $\text{U}$(R, S) has no invariant positions.     

Bonding corneal tissue: applications of photoactivated diazopyruvoyl cross-linking agent

Photoactivated bis-diazopyruvamide-N,N'-bis(3-diazopyruvoyl)-2,2'-(ethylenedioxy)bis-(ethylamine), (DPD)-was previously shown to bond materials containing type I collagen. However, tensile strength of bonded collagenous tissue ( approximately 78% water) was low compared with that of dehydrated collagenous gelatin ( approximately 14% water). Here we investigated the role of water in corneal tissue bond strength and in bonding corneal tissue to glass. Bonding corneal tissue to glass may be of value in surgically anchoring keratoprostheses to corneas to alleviate problems with extrusion. Bovine corneal samples were lyophilized for various times resulting in tissue hydrations of zero (no water content) to approximately 3.7 (normal water content). The lyophilized corneal tissue was bonded to solid gelatin sheets, to other corneal samples and to glass using 0.3M DPD in chloroform. Control runs used chloroform only. Samples were irradiated with 100 or 200 J of 320-500 nm light. Strong bonds formed with all three materials when corneal tissue hydration was 1. No bonding occurred with chloroform alone. Formation of strong bonds only occurs with hydration levels 相似文献   

Technical considerations for the use of 15N-DNA stable-isotope probing for functional microbial activity in soils

Stable-isotope DNA probing is a culture-independent technique that may provide a link between function and phylogeny of active microorganisms. The technique has been used in association with 13C substrates while here we evaluate feasibility and limitations of 15N-DNA stable-isotope probing (SIP) using labelled and unlabelled pure microbial cultures or soil extracts. Our results showed that (15)N-DNA probing is feasible for cultures as well as soil samples. Limitations of 15N-DNA-SIP are (a) the need for relatively large quantities of DNA to visualise bands (although molecular resolution is much higher) and (b) 15N-DNA enrichment needed to ideally be >50 at%; however, this requirement can be lowered to approx. 40 atom% 15N with pure cultures using a modified CsCl centrifugation method (140K g for 69 h). These advances in 15N-DNA-SIP methodology open new opportunities to trace active microbial populations utilising specific N substrates in situ.     

Cyclohexanol dehydrogenation over Cu/SiO2 and CuO/SiO2: A comparison

Various CuO/SiO₂ catalysts were prepared and characterized by XRD, surface area and metal area measurements. While dehydrogenation activity for cyclohexanol was observed at 473–573 K on reduced catalysts, it was observed only at 573 K on the unreduced catalyst.IICT Communication No: 3261     

The effects of varying metal precursor fluxes on the growth of InAlN by metal organic vapour phase epitaxy

InAlN is a relatively new addition to the palette of nitride semiconductor alloys, with potential applications in distributed Bragg reflectors and high electron mobility transistors. However relatively little is known about the effects of different growth conditions on InAlN’s structure and properties and more importantly what these effects can tell us about the surface processes of growth. Here we have investigated the effects of varying various metal fluxes. First, we varied the total fluxes of all the precursors while maintaining their ratios. This led to an increase in growth rate, of itself very desirable, but at the considerable cost of significantly roughened surfaces. Analysis of these surfaces using power spectral density functions suggests that they were all produced by a combination of stochastic roughening and smoothing by surface diffusion, suggesting that at a given temperature increasing the growth rate will always lead to roughening. In addition, we examined the effect of varying just the trimethylindium flux (and therefore varying the indium to gallium ratio). As this flux was increased the indium incorporation initially increased but then levelled off, and for further increases the amount of indium on the surface as droplets increases significantly, suggesting that there is a limit to the indium incorporation that than be achieved at a given temperature and pressure. This suggests that there are practical limits to simultaneously achieving high growth rates, high indium contents and low surface roughnesses.     

Constructing and disrupting listeners' models of auditory space

A major problem for an auditory system exposed to sound in a reverberant environment is to distinguish reflections from true sound sources. Previous research indicates that the process of recognizing reflections is malleable from moment to moment. Three experiments report how ongoing input can prevent or disrupt the fusion of the delayed sound with the direct sound, a necessary component of the precedence effect. The buildup of fusion can be disrupted by presenting stimuli in alternation that simulate different reflecting surfaces. If buildup of fusion is accomplished first and then followed by an aberrant configuration, breakdown of the precedence effect occurs but it depends on the duration of the new sound configuration. The Djelani and Blauert (2001) finding that a brief disruption has no effect on fusion was confirmed; however, it was found that a more lengthy disruption produces breakdown.     

A new chiral lanthanide NMR probe for the determination of the enantiomeric purity of alpha-hydroxy acids and the absolute configuration of alpha-amino acids in water

A water-soluble, enantiopure lanthanide complex, SSS-[Ln x L3], has been assessed as an effective chiral derivatizing agent for the determination of the enantiomeric purity of alpha-hydroxy acids in aqueous solution. The complex displays superior chemical shift non-equivalence (DeltaDeltadelta approximately 2-11 ppm) for the diastereomeric resonances of interest compared to lanthanide shift reagents reported in the literature (DeltaDeltadelta <0.1 ppm, typically). 1H NMR studies have also revealed that SSS-[Ln x L3] can be used to determine the absolute configuration of alpha-amino acids at physiological pH, in water. The ability of SSS-[Ln x L3] to signal anion binding and, in particular, to distinguish between diastereomers through optical techniques such as lanthanide luminescence and circular dichroism has also been assessed.     

Imaging the dynamics of gas phase reactions

Ion imaging methods are making ever greater impact on studies of gas phase molecular reaction dynamics. This article traces the evolution of the technique, highlights some of the more important breakthroughs with regards to improving image resolution and in image processing and analysis methods, and then proceeds to illustrate some of the many applications to which the technique is now being applied--most notably in studies of molecular photodissociation and of bimolecular reaction dynamics.     

Interaction of the glycoalkaloid tomatine with DMPC and sterol monolayers studied by surface pressure measurements and Brewster angle microscopy

The interaction of the glycoalkaloid tomatine with monolayers of dimyristoylphosphatidylcholine (DMPC) and cholesterol, as well as other selected sterols, has been investigated using surface pressure measurements at constant area and Brewster angle microscopy (BAM). The interaction of tomatine with sterol monolayers is found to vary with the structure of the sterol. The interaction of tomatine with cholesterol-containing monolayers results in a surface pressure increase accompanied by the appearance of a mottled texture. Morphological changes are observed that suggest the formation of tomatine-cholesterol complexes that aggregate at the water-air interface. No morphology change observable by BAM is observed for monolayers containing epicholesterol, suggesting that the stereochemistry of hydrogen bonding between the sterol and the sugar units on tomatine is of particular significance. Strong interactions are observed with cholestanol- and coprostanol-containing monolayers, and BAM reveals formation of spiked aggregates upon interaction with 7:3 mole ratio DMPC/coprostanol mixed monolayers. More modest surface pressure changes are observed for cholestenone- and epicoprostanol-containing monolayers. A much smaller surface pressure increase is observed when tomatine is injected beneath a pure DMPC monolayer.