AK Values Research Articles

Comparison of the Allo-Kramer Shear and Texture Profile Methods of Broiler Breast Meat Texture Analysis

Two experiments were conducted to compare the Allo-Kramer shear (AK) and the texture profile analysis (TPA) methods of determining objective texture using broiler breast meat. In one experiment broilers obtained from a commercial processing plant were killed by cervical dislocation and one half of the breast muscles, pectoralis (p.) major and p. minor, were either removed immediately (hot boned, HB) or left on the carcass for 24 h prior to removal (chill-boned, CB). The breast meat samples were cooked in steam, and one half of the samples from each treatment were sliced to a constant thickness. Samples from the anterior, middle, and posterior sections were analyzed by Allo-Kramer shear or TPA. A second experiment was conducted identical to the first except that all birds were obtained in the form of ready-to-cook carcasses (conventional processed) from a commercial processing plant, aged 24 h, and effects of the AK and TPA methods on breast halves were compared.Processing treatment (HB vs. CB) was found to significantly affect AK and TPA values, except for values of springiness and cohesiveness. Slicing the p. major appeared to affect the results of the TPA method more than the AK method in both experiments. Both the AK and TPA methods detected differences across muscle locations.

Studies on nitrogen metabolism in rats of different age fed on a protein-free diet. 3. Urinary endogenous nitrogen excretion in relation to body size and protein-free feeding duration.

The influence of the time (t = 3, 6, 9, 12 and 16 days) of feeding on a protein-free diet (PFD) and the size of shrunk body mass (SB), increasing with age but decreasing with the duration of feeding on PFD, on the excretion of endogenous urinary nitrogen (EUN) were investigated. The experiment was on 350 male rats from 23 to 275 days of age and mean SB from 39 to 430 grammes, divided into 14 age groups (k = 14). The material and the method of the experiment as well as the composition of PFD were described in detail in part one of this work (Beza, 1986). The linear analysis of covariance showed that the EUN excreted after 3, 6, 9, 12 and 16 days on PFD as well as the average daily EUN did not significantly correlate with the initial body mass (SBi). It were calculated: 1. In relationship EUN(t) the slope ratios bk and intercepts ak, differed between the groups of age significantly. The ak values but not the bk, were closely correlated with the initial body mass SBi (r for ak values = 0.947***) indicating that the amount but not the rate of EUN excretion was closely related to SBi; 2. the daily EUN excretion at 1, 3, 6, 9, 12 and 15 days on PFD in relation to body mass in these days-EUNd(SBd) is described by the equation: EUNd = Ad.SBd 0.872 less than 1, in which Ad decreased from 287 mg N/SBd 0.872 on the first day to 167 mg N/SBd 0.872 on the 15th day on PFD; 3. the daily excretion of EUN(y) in relation to the daily body mass (x1) and to the day on PFD (x2) is described by the equation: EUNd(y) = 286.8.x1(0.872).x2(-0.1993); R = 0.987*** with N in mg, SB in kg. There was a directly proportional relationship between EUNd and SB0d 0.872 only (b1 = 1), whereas between EUNd and SBd 0.67 as well as between EUNd and SBd 0.75 the slope ratios b1 were 1.308 and 1.163, respectively and were significantly higher than one. With prolonged feeding on PFD for 15 days, the rate of EUNd excretion decreased in accordance to b2 = -0.1993 less than 0**, independently of the age and the initial SB of the rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Fatigue crack propagation rate model based on a dislocation mechanism

The most common way to express the fatigue crack propagation rate (FCPR, da/dN) data is in terms of stress intensity range (AK) on a log-log basis. AK is a function of applied stress and crack size, and characterizes the elastic stress field existing at the crack tip. Most metals appear to exhibit a "threshold" value of AK (AKth), below which fatigue crack grows at an undetectable rate. Above the threshold value there is usually an intermediate range of AK over which the FCPR is linearly related to the AK. At higher ranges, the FCPR increases rapidly as the maximum stress intensity approaches the critical value (Kic). The FCPR in the intermediate zone is related to the AK by the Paris equation

Semi-empirical equilibrium model for copper(II) extraction from sulphuric acid solution by LIX 64N-Escaid 100

A semi-empirical model Y= AK(S F −X) −2X 1+K(S F −X) −2X has been developed to describe the equilibrium relationship for the CuH 2SO 4/LIX 64N-Escaid 100 system. Once the empirical parameters A and K for initial concentration of the organic extraction reagent ( ρ 0) and balance concentration of the acidic species in the aqueous feed ( S F) are available, the equilibrium relationships, with either the same ρ 0 but different S F or the same S F but different ρ 0, can be predicted with satisfactory accuracy. Considerable experimental effort for studying both the effects of ρ 0 and S F on the equilibrium relationship can therefore be saved. Another advantage of this method is that the net rate expression, with a given ratio of the apparent rate constants, can also be obtained. From the value of the parameter AK( S F) −2, which represents the maximum distribution coefficient, one can judge the extraction power of solvent extraction systems.

Extracellular Potassium Activity in Attached Leaves and its Relation to Stomatal Function

Apoplastic potassium activities (ak) in leaves of Commelina communis L., Vicia faba L. and Pisum sativum L. var. argenteum were recorded with neutral-carrier-based, potassium-sensitive micro-electrodes. Measurements were carried out in 0.3–1.4 nl volumes contiguous with the extracellular space of attached leaves and were held for periods of 7–68 min. Mean steady-state aK values recorded from all three species were below 50 μM. Similar potassium activities were attained, regardless of the initial values obtained after washing with distilled water or potassium additions, and the activities recorded showed only minimal dependence on the relative vapour pressure difference. Tissue capacity for K+ absorption was increased 15–30-fold in the presence of added Ca2+. By contrast, cyanide reduced both the initial rate of potassium absorption by the tissues and their apparent capacity for the cation. These observations indicate that the free potassium pool in the leaf apoplast is significantly smaller than has previously been assumed. The results contradict the notion that high concentrations of potassium accumulate locally as a result of transpiration, and may indicate the presence in the leaf tissues of potassium transport activity sensitive to Ca2+ and dependent on metabolism.

Extracellular potassium levels and axon excitability during repetitive action potentials in crayfish.

Changes in extracellular K+ levels were measured during repetitive stimulation of the excitor axon of the opener muscle of the crayfish walking leg. Mesaxon channels, through which K+ might diffuse away from the periaxonal ('Frankenhaeuser-Hodgkin') space, were examined in electron micrographs; they were seen every 2-10 micron along the axon, and their average (+/- S.D.) length and width were 3.0 (+/- 1.6) micron and 19.8 (+/- 8.9) nm, respectively. Intracellular recordings revealed a 40 ms after-depolarization following an action potential; this was attributed to elevated levels of extracellular K+. During stimulation at 50 Hz, this resulted in a depolarizing shift of the membrane potential between impulses; the average depolarization was 9.3 mV, which corresponds to a 4.3 mM increase in extracellular K+. Using K+-selective micro-electrodes, changes in extracellular K+ activity, delta aK, were measured at distances ranging from 10 to 50 micron from the axon; during 50 Hz stimulation, delta aK rose within 15 s to a maximum value of 1.1 mM which was maintained at a steady level in most preparations. Conduction failure occurred in several preparations after at least 90 s of stimulation; levels of delta aK were not abnormally high in these cases. Soaking the axon for at least 15 min in saline with extracellular K+ levels at least 18 mM above normal values was necessary to cause blockage in unstimulated nerves. Soaking the preparation for 30 min in 10(-3) M-ouabain resulted in a 48% increase in the maximum values of delta aK during 50 Hz stimulation. It is concluded that K+ accumulates extracellularly during axon stimulation and that the extent of this accumulation is reduced by active uptake mechanisms; however, this accumulation probably cannot directly block action potential conduction, for neither the magnitude nor the kinetics of K+ build-up approach values shown to reduce excitability.

Multiple trapping of random walkers on periodic lattices

Formulas are obtained for the mean absorption time of a set ofk independent random walkers on periodic space lattices containingq traps. We consider both discrete (here we assume simultaneous stepping) and continuous-time random walks, and find that the mean lifetime of the set of walkers can be obtained, via a convolution-type recursion formula, from the generating function for one walker on the perfect lattice. An analytical solution is given for symmetric walks with nearest neighbor transitions onN-site rings containing one trap (orq equally spaced traps), for both discrete and exponential distribution of stepping times. It is shown that, asN → ∞, the lifetime of the walkers is of the form TakN2, whereT is the average time between steps. Values ofak, 2 ⩽ Sk ⩽ 6, are provided.

Acétylcholinestérase: II — Aspects expérimentaux de l'interaction avec les effecteurs réversibles en milieu de force ionique élevée

Interaction of usual effectors with acetylcholinesterase (EC 3.1.1.7) from bovine erythrocytes was examined under conditions of high ionic strength (gamma/2 greater than or equal to 0,1). Detailed kinetic investigation of the hydrolysis of acetylcholine by acetylcholinesterase in the presence of modifiers shows that the effects produced by numerous quaternary nitrogen compounds on the enzyme can be explained on the basis of binding of the effectors to the anionic subsite of the active center. The various kinetic behaviors, that are observed, are dependent on the relative values of the deacetylation rate constant ak of the complex acetylated enzyme-modifier and of the rate constant k-2 defined by : (see article) with respect to the value of the deacetylation rate constant K of the acetylated enzyme. If a identical to [1--(k/k-2)]-1, it is shown that interaction of the enzyme with tetraethylammonium, pentamethonium, hexamethonium and gallamine ions is characterized by : a greater than a and k-2 greater than k therefore, these modifiers accelerate deacetylation. On the other hand, inhibition of acetylcholinestase by methylpyridinium, d-tubocurarine, tetra-n-propylammonium, tetra-n-butylammonium, decamethonium and succinylbischoline is consistent with one of the conditions : a less than a and k-2 greater than or equal to k or a greater than a and k-2 less than k and inhibition by tetramethylammonium, phenyltrimethylammonium, 3-hydroxyphenyl-triethylammonium, N-methylacridinium and bis (3-aminopyridinium)-1,10-decane ions agrees with one of the two previous conditions or with : (see article) consequently, the effect of these ligands on the deacetylation step is undetermined. However, the effects of choline chloride, thiazinamium methyl sulfate and thioridazine hydrochloride are not entirely consistent with this mechanism but support the existence of a functional peripheral anionic site which is distinct from the anionic subsite of the active center.

Plasma insulin studies in patients with lag curves

The significance of the lag curve, i.e. one in which the blood sugar rises rapidly from a normal fasting value to more than 180 mg/100 ml but returns to the fasting value within 120 min, remains controversial. In order to study this further, plasma insulin levels were measured by immunoassay during oral and intravenous glucose tolerance tests in 3 groups of age/weight matched subjects: Group 1, 14 with unexplained lag curves: Group 2, 14 with lag curves following gastric surgery and Group 3, 14 normal subjects. The mean insulin levels were higher in Group 1 than in Group 3 but the hyperglycaemic stimulus was greater. The insulin response in Group 2 did not differ significantly from the controls. The mean blood sugar curves were similar in Groups 1 and 2, but despite this the insulin response was significantly prolonged in Group 1, suggesting a degree of insulin resistance or antagonism. In the intravenous test 2 patients from each of Groups 1 and 2 had aK value in the diabetic range. The meanK value was higher in Group 1 than in Group 2. Both groups showed a similar rather low insulin response.

Estimation Of Local Cyclic Stress Ratio Due To Confined Notch Plasticity

Estimation Of Local Cyclic Stress Ratio Due To Confined Notch Plasticity

Investigation of the impact strength of metal ceramic materials

1. The impact strength of the material based on silicon carbide increases with an increase in temperature in the temperature range under investigation. The impact strength of the material based on chromium carbide is at its maximum in the 850–900° range, while it decreases at higher temperatures. 2. The impact strength of the material based on silicon carbide increases with an increase in the specimen's dimensions at 20° as well as at 1200°. 3. The value of ak, which characterizes the ratio of the energy expended on breaking the specimen to the quantity proportional to the specimen's section modulus, does not depend on the specimen's cross-sectional dimensions.

The thermal conductivity of metals at low temperatures

The thermal conductivity of high-purity samples of thirty-two metals has been measured. These were Ag, Al, Au, Be, Cb, Cd, Ce, Co, Cu, Fe, Ga, In, Ir, La, Mg, Mn, Mo, Ni, Pb, Pd, Pt, Rh, Sb, Sn, Ta, Ti, Tl, U, V, W, Zn and Zr. For most metals measurements were taken from 2 to 40°K, but where necessary they were extended to 90°K. For superconductors they were taken in both the superconducting and normal states. The conductivity was found to be entirely electronic except for Sb and U. Most of the specimens were polycrystalline, but single crystals of Zn, Cd, Sn, Pb, Ga and Ti were measured. For Zn and Ga, specimens of different orientations with respect to the rod axis were obtained, and in both these metals the thermal conductivity was found to be anisotropic. The thermal resistance, W, at low temperatures of nearly all the metals is of the form W — a T 2 + gjT, and the constants a and /? have been calculated. If is the limiting thermal conductivity at high temperatures and 6 is the Debye temperature, then the value of aK^d2 is the same for the metals in any one chemical group. For some metals the electrical resistance was measured at the same time as the thermal conductivity over the full temperature range and hence the Lorenz number, L, was calculated. The limiting value of L at low temperatures for several metals was found to be considerably higher than the theoretical value, in particular for Ti and Zr. A corresponding effect to the minimum in the electrical resistance of Mg has been found in the thermal resistance. A large increase in the thermal conductivity of Fe after a period of time has been ascribed to the precipitation of impurities in the metal. A method is given for estimating the thermal conductivity of a metal at low temperatures.

On the motions of 64 long-period comets

The definitive orbits for 64 long-period comets have been solved to determine Ak, the deviation of the effective solar attraction from that determined by planetary motions (k2 is the Gaussian constant). The weighted mean value of AkIk is -0.53 (+0.10 m.e.) X I0 , highly significant in terms of the statistical weight. The sign is negative as predicted by the icy comet model. Diffuse comets and comets with unusual fading after perihelion display large values of Ak, positive and negative. The Ak data lead to conclusions about the dimensions and mass losses of cometary nuclei on the basis of the icy comet model; they correlate as expected with perihelion distance and "age" but do not correlate with magnitude.