A research note on factors affecting the determination of myofibrillar fragmentation

The myofibrillar fragmentation index (MFI) was determined for a section of ovine Longissimus muscle, aged for either 1 or 3 days and processed from either the fresh or frozen state. Additionally samples were homogenized at one of three speeds (5000, 10,000 or 15,000 rpm). Speed of homogenisation and 'state' of the sample both had a significant effect (P < 0.001) on MFI values as did the interaction between speed and state (P < 0.001), with other interactions terms not being significant. Age of the sample had no significant (P > 0.05) effect on MFI values with least square means (s.e.) for Day 1 and Day 3 being 92 and 93 (1.16), respectively. As homogenisation speed increased, the difference between values for fresh and frozen samples was diminished, such that at 15,000 rpm there was no effect of 'state' on values. Overall the 'state' and the speed of homogenisation have a large impact on values and there was more variation between samples at the slowest speed (5000 rpm). At the slowest speed myofibrils consist of more sarcomeres and can be observed to still exhibit intermyofibril linkages. The results suggest a homogenisation speed of 15,000 rpm was preferable when determining MFI values.     

对烃类检测的进一步研究

目前，ＡＶＯ烃类检测尚存在一些不足之外，其中的一类ＡＶＯ异常被认为是正的烃类检测（ＨＣＩ），这类异常的反射波振幅随偏移距的增大而增大。虽然这是一类常见的ＡＶＯ异常，但并不是唯一的与烃类有关的异常。因此，应用现有的ＨＣＩ，根据负指标的其它异常就可能检测不到烃类。而利用岩石特性的相关性（速度和密度）能列加可靠地进行烃类检测，利用这种岩石物理特性的相关性可提出更普遍性的烃类检测法，这种新ＨＣＩ法受地震数     

In situ preparation of thin sodium films as an expendable filter in the vacuum ultraviolet

The use of a sodium film as a filter for wavelengths between 40 and 80 nm is discussed, and a technique to prepare these films is described. Sodium films of 230 nm thickness were demonstrated to have a transmission of 55% at 100 degrees K at a wavelength 41 nm. The transmission decreased to 40% after 18 h in a vacuum of 5x10(-8) Torr. Films of this thickness were shown to attenuate 20.5-nm radiation appearing in second order at 41 nm by at least a factor of 50.     

Electron transfer capacities and reaction kinetics of peat dissolved organic matter

Information about electron-transfer reactions of dissolved organic matter (DOM) is lacking. We determined electron acceptor and donor capacities (EAC and EDC) of a peat humic acid and an untreated peat DOM by electrochemical reduction and reduction with metallic Zn and H2S (EAC), and by oxidation with complexed ferric iron (EDC) at pH 6.5. DOC concentrations (10-100 mg L(-1)) and pH values (4.5-8) were varied in selected experiments. EAC reached up to 6.2 mequiv x (g C)(-1) and EDC reached up to 1.52 mequiv-(g C)(-1). EDC decreased with pH and conversion of chelated to colloidal iron, and the electron-transfer capacity (ETC) was controlled by the redox potential Eh of the reactant (ETC = 1.016x Eh - 0.138; R(2) = 0.87; p = 0.05). The kinetics could be adequately described by pseudo first-order rate laws, one or two DOM pools, and time constants ranging from 2.1 x 10(-3) d-1 to 1.9 x 10(-2) d(-1) for the fast pool. Reactions were completed after 24-160 h depending on the redox couple applied. The results indicate that DOM may act as a redox buffer over electrochemical potentials ranging from -0.9 to +1.0 V.     

Dual biomarkers of anaerobic hydrocarbon degradation in historically contaminated groundwater

This study reports that ongoing in situ anaerobic hydrocarbon biodegradation at a manufactured gas plant impacted site is occurring, 9 years after the initial investigation. Groundwater samples from the site monitoring wells (MW) were analyzed for biomarkers by GC-MS, end-point PCR, and quantitative PCR (qPCR). Metabolic biomarkers included specific intermediates of anaerobic naphthalene and/or 2-methylnaphthalene degradation: 2-naphthoic acid (2-NA); 5,6,7,8-tetrahydro-2-NA (TH-2-NA); hexahydro-2-NA (HH-2-NA); and carboxylated-2-methylnaphthalene (MNA). The analogues of gene bssA, encoding alpha subunit of enzyme benzylsuccinate synthase, were used as a genetic biomarker. Results indicate 1-2 orders of magnitude higher abundance of total bacteria in the impacted wells than in the unimpacted wells. End-point PCR analysis of bssA gene, with degenerate primers, indicated the presence of hydrocarbon degrading bacteria within the plume. In qPCR analysis, using primers based on toluene-degrading denitrifying or sulfate-reducing/methanogenic bacteria, bssA genes were detected only in MW-24, located downstream from the source. Metabolic biomarkers were detected in multiple wells. The highest abundance of 2-NA (6.7 μg/L), TH-2-NA (2.6 μg/L), HH-2-NA, and MNA was also detected in MW-24. The distribution of two independent biomarkers indicates that the site is enriched for anaerobic hydrocarbon biodegradation and provides strong evidence in support of natural attenuation.     

Link between heart disease, cholesterol, and Alzheimer's disease: a review

Increased prevalence of Alzheimer's disease-like beta-amyloid deposits in the neuropil and within neurons occurs in the brains of non-demented individuals with heart disease. Heart disease is a prevalent finding in Alzheimer's disease, and may be a forerunner to the dementing disorder. In the cholesterol-fed rabbit model of human coronary heart disease there is production and accumulation of beta-amyloid in the brain. This accumulation of beta-amyloid can be reversed by removing cholesterol from the rabbits' diet. In culture cells, a cholesterol challenge has been shown to increase production of beta-amyloid, and dramatic reductions of cholesterol produced by HMG Co-A reductase inhibitors decrease production of beta-amyloid. Increased beta-amyloid production is also produced by dietary cholesterol in a number of transgenic mouse models of Alzheimer's disease. Administration of HMG Co-A reductase inhibitors may block beta-amyloid production caused by dietary cholesterol in rabbits. Clinical trials testing the benefit of HMG Co-A reductase inhibitors in the treatment of Alzheimer's disease are underway.     

Desorption characteristics of uncoated silicon microcantilever surfaces for explosive and common nonexplosive vapors

We measured the desorption of explosive trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and hexahydro-1,3,5-triazine (RDX) vapors from piezoresistive silicon microcantilevers under ambient air. Depending on the amount of vapor loaded on the cantilever, TNT desorption took a few minutes to tens of minutes (for nanogram quantities). On the other hand, no significant loss of PETN or RDX was observed after many hours. We also measured desorption of common “nonexplosive” compounds (water, acetone, and ethyl alcohol) and observed that desorption was too fast to be measured. There is a good correlation between the desorption time and the melting point (or the vapor pressure) of a particular substance. In principle, this method can be used to measure desorption rates of various substances from cantilever surfaces.     

Experimental determination of the boundary condition for diffuse photons in a homogeneous turbid medium

We present a simple experimental method that permits an empirical determination of the effective boundary condition and the extrapolated end point for the diffuse photon density in a homogeneous turbid medium.