Effect of size, shape and hardness of particles in suspension on oral texture and palatability

Trans-species, multiple site (particularly common site between species), mutagenic rodent carcinogens are less affected by the influences of polymorphic genes than are chemicals inducing more limited carcinogenic effects. Trans-species carcinogens, therefore, should represent a first priority for attention for human health risk.     

Effect of size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys

The effect of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys was investigated. Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering, using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles and their hardness were increased as sintering temperature and time were increased, thereby deteriorating fracture toughness. The dynamic torsional test results indicated that in the specimens whose tungsten particles were coarse and irregularly shaped, cleavage fracture occurred predominantly with little shear deformation, whereas shear deformation was concentrated into the center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle size because the cleavage fracture mode would be beneficial for the “self-sharpening” of the tungsten heavy alloys.     

The role of histones and their modifications in the informative content of chromatin

It is traditionally accepted that the DNA sequence cannot by itself explain all the mechanisms necessary for the development of living beings, especially in eukaryotes. Indeed part of the information used in these processes is stored in other ways, generally called 'epigenetic', whose molecular mechanisms are mostly unknown. The ultimate explanation for them might reside in the non-DNA moiety of chromatin which may play an active role in heredity ('chromatin information'). Histones are the universal structural component of chromatin. However, recent studies strongly suggest that histones, and their modifications--especially the reversible acetylation of lysines--may act as a recognition signal for regulatory proteins and they may participate, for this reason, in gene regulation. This type of information could be maintained through its replication and, ultimately, it could form the molecular basis of certain processes related to the development of the eukaryotic organisms.     

Breast reconstruction after mastectomy: problems in position, size, and shape

Having learned that healed mastectomy wounds will stretch sufficiently to accommodate an implanted prosthesis, we must pay more attention to the position, and shape of the breast mound created by the prosthesis. We have briefly discussed our methods and the considerations we feel are important in this regard, but, even after extensive experience, we confess that the problems are still with us. Clearly, surgical methods and prostheses must improve.     

Changes in pulmonary artery size before and after total cavopulmonary connection

The aim of any abdominal wall reconstruction is maximal functional stability and adequate soft tissue coverage. The anatomy, elevation and clinical application of the myofascial tensor fasciae latae transposition flap and of the microvascular musculocutaneous latissimus dorsi free flap are presented. Repairing extensive fascial defects and recurrent hernias with the tensor fasciae latae transposition flap provides strong, dynamic, and functional reconstruction of fascial continuity to prevent a further recurrence. Adequate functional and aesthetic repair of a full-thickness abdominal wall defect can be optimally managed by the innervated microsurgical latissimus dorsi free flap.     

Sliding wear behavior of some Al-Si alloys: Role of shape and size of Si particles and test conditions

In this investigation, effects of the shape and size of silicon particles have been studied on the sliding wear response of two Al-Si alloys, namely, LM13 and LM29. The LM13 alloy comprised 11.70 pct Si, 1.02 pct Cu, 1.50 pct Ni, 1.08 pct Mg, 0.70 pct Fe, 0.80 pct Mn, and remainder Al. The LM29 alloy contained 23.25 pct Si, 0.80 pct Cu, 1.10 pct Ni, 1.21 pct Mg, 0.71 pct Fe, 0.61 pct Mn, and remainder Al. Wear tests were conducted under the conditions of varying sliding speed and applied pressure. The alloys were also characterized for their microstructural features and mechanical properties. The presence of primary silicon particles in the alloy led to a higher hardness but lower tensile properties. Further, refinement in the size of the primary particles improved the mechanical properties of the alloy system. The wear behavior of the alloys was influenced by the presence of primary Si particles and was a function of their size. Samples with refined but identical microconstituents (e.g., pressure cast vs gravity cast LM29 in terms of the size of primary Si particles and dendritic arm spacing) exhibited better wear characteristics. Their overall effect was further controlled by the test conditions. It was observed that test conditions leading to the generation of an optimal degree of frictional heating offer the best wear resistance. This was attributed to the reduced microcracking tendency of the alloy system otherwise introduced by the Si particles. The reduced microcracking tendency in turn allows the Si phase to carry load more effectively and impart better thermal stability to the alloy system. This caused improved wear resistance under the circumstances. Further, the primary Si particles improved the wear resistance of the alloy system (e.g., gravity-cast LM29 vs gravity-cast LM13) under high operating temperature conditions. Additional thermal stability and protection offered to the matrix by the primary Si phase, under the conditions of reduced microcracking tendency, were the reasons for the improved wear characteristics of the alloy system. Conversely, a reverse effect was produced at low operating temperatures in view of the predominating microcracking tendency. The study suggests that shape, size, microcracking tendency, and thermal stability of different microconstituents greatly control the mechanical and tribological properties of these alloys. The extent of effective load transfer between the phases plays an important role in this regard. Further, the overall effect of these factors is significantly governed by the test conditions.     

The organization of histones and DNA in chromatin: evidence for an arginine-rich histone kernel

We have examined the role played by various histones in the organization of the DNA of the nucleosome, using staphylococcal nuclease as a probe of DNA conformation. When this enzyme attacks chromatin, a series of fragments evenly spaced at 10 base pair intervals is generated, reflecting the histone-DNA interactions within the nucleosome structure. To determine what contribution the various histones make to DNA organization, we have studied the staphylococcal nuclease digestion patterns of complexes of DNA with purified histones. Virtually all possible combinations of homogeneous histones were reconstituted onto DNA. Exhaustive digestion of a complex containing the four histones H2A, H2B,H3, and H4 yields a DNA fragment pattern very similar to that of whole chromatin. The only other combinations of histones capable of inducing chromatin-like DNA organization are H2A/H2B/H4 and those mixtures containing both H3 and H4. From an examination of the kinetics of digestion of H3/H4 reconstitutes, we conclude that although the other histones have a role in DNA organization within the nucleosome, the arginine-rich histone pair, H3/H4, can organize DNA segments the length of the nucleosome core in the absence of all other histones.     

Changes of callus diameter during axial loading and after fixator removal in leg lengthening

We retrospectively reviewed nine tibial lengthenings in seven achondroplastic patients. The callotasis method was used, and a unilateral type lengthener, either the Dynamic Axial Fixator (Orthofix, Italy; eight legs) or the High Functional Fixator (Matsumoto Co., Japan; one leg), was applied. The distracted length averaged 14.6 (range 10-18) cm. The minimum diameter of the callus was measured using a ruler on anteroposterior and lateral radiographs. The callus diameter ratio (%) was calculated as the callus diameter divided by the original diaphysis diameter. For periods during axial loading and after removal of the fixator in each patient, a single regression line was drawn on the callus diameter ratio data using the least squares method, and the diameter change rate (%/day) was evaluated by inclination of this line. The diameter change rates during axial loading were negative in six legs, but those after fixator removal were positive in all legs, and the latter were significantly greater than the former. The diameter change rates after fixator removal on the anteroposterior radiographs were negatively correlated with the callus diameter ratio at the time of fixator removal (r = 0.84, P = 0.0008). Simple axial loading may not be a sufficient mechanial environment for restoration of the physiological shape, and it is important to be aware that we cannot expect the callus diameter to increase by this means alone.     

Measuring the shape and size of microcracks in bone

Microcracks in bone are normally measured from two-dimensional, transverse sections but this provides incomplete information about their three-dimensional shape and size. The methods of stereology can usefully be applied in such a case. This problem has been addressed using a theoretical model and a numerical simulation. Results show that the data are consistent with a crack shape which is elliptical, with axis ratio approximately 4.5:1 and with size variation (expressed as the ratio of standard deviation to mean length) of at least 0.1. Measured lengths will, on average, be smaller and have more scatter than true lengths. Errors caused by omitting small cracks are relatively unimportant. Knowledge of the true crack dimensions, and their variability, is important for the analysis of damage, stress fracture, remodelling and adaptation.     

Subunit structure of a naturally occurring chromatin lacking histones F1 and F3

Macronuclei of the ciliated protozoan Tetrahymena pyriformis contain at least five classes of histones, including two with properties like those of histones F3 and F1 of higher eukaryotes. Micronuclei isolated under identical conditions contain little or no detectable F3 or F1. Digestion of both macronuclei and micronuclei with staphylococcal nuclease results in DNA fragments of discrete sizes. The electrophoretic mobilities of the larger fragments suggest that they are oligomers of the smallest ones. These results indicate that the periodic subunit structure observed in the chromatin of higher organisms also occurs in protozoans, and that this structure does not depend on the presence of either histone F1 or F3, even in an organism which has the genetic information for synthesizing these proteins.     

A class of chromatin particles associated with nonhistone proteins

Unfixed nucleoproteins may be banded isopycnically in metrizamide (2(3-acetamido-5-N-methylacetamido-2,4,6-triiodobenzamido)-2-deoxy-D-glucose) according to the protein/nucleic acid ratio. Unsheared or lightly sheared chromatin bands sharply (p=1.2 g/ml); it has a protein/DNA ratio of 1.4. Chromatin sheared by sonication to approximately 350 base pairs of DNA contains two components with protein/nucleic acid ratios of approximately 1.3 (p=1,185 g/ml) and 2 (p=1.245 g/ml). When chromatin is digested exhaustively with staphylococcal nuclease, two density components are found, one with a protein/DNA ratio of 1.5 (p=1.21 g/ml), the other with a protein/DNA ratio of 2 (p=1.24 g/ml). In both instances the denser particle (p=1.24 g/ml) contains nearly all the nonhistone proteins, while both dense and light fractions contain histones in similar amounts. The base sequence complexity of DNA from the fractions is not distinguishable from that of total DNA and there is no evidence of any concentration of sequences complementary to polysomal polyadenylated RNA molecules.