Small Transition Zone Research Articles

Adaptive mesh refinement for the phase field method: A FEniCS implementation

This paper reports insightful implementation details of the global adaptive refinement procedure for the phase-field method recently published in Freddi and Mingazzi (2022). Phase field approaches reproduce cracks within solids in a smeared manner. The small transition zone between broken and unbroken material, whose width is controlled by an internal scale length parameter, permits to precisely replicate complex sharp crack topologies only if an extremely fine mesh is adopted. Starting from a coarse mesh, the proposed refinement process utilizes an energetic criterion to selectively refine the elements on which cracks may propagate. In fully broken areas, where the phase field is no longer evolving, a specific refinement is adopted to capture the high displacement gradient. The implementation is performed within the open-source finite element software FEniCS (ver. 19.1.0) which provides a framework for automated solutions of partial differential equations. The fundamental aspects of the code are described starting from the functional definition to the various steps of the refinement technique. A representative example is illustrated to supply further information on the code functionality. The code can be downloaded from https://github.com/LorenzoMingazzi/AGu-AGal and be used to easily apply the proposed refinement strategy to different problems or as a starting point for more sophisticated formulations.

Transitional Anal Cells Mediate Colonic Re-epithelialization in Colitis

Epithelial wound healing is compromised and represents an unleveraged therapeutic target in inflammatory bowel disease (IBD). Intestinal epithelial cells exhibit plasticity that facilitates dedifferentiation and repair during the response to injury. However, it is not known whether epithelial cells of a neighboring organ can be activated to mediate re-epithelialization in acute colitis. Histological findings of a permanent squamous tissue structure in the distal colon in human IBD could suggest diverse cellular origins of repair-associated epithelium. Here, we tested whether skin-like cells from the anus mediate colonic re-epithelialization in murinecolitis. We studied dextran sulfate sodium-induced colitis and interleukin 10-deficient colitis in transgenic mice. We performed lineage tracing, 3-dimensional (3D) imaging, single-cell transcriptomics, and biophysical modeling to map squamous cell fates and to identify squamous cell types involved in colonic repair. In acute and chronic colitis, we found a large squamous epithelium, called squamous neo-epithelium of the colon (SNEC), near the anorectal junction. Neighboring squamous cells of the anus rapidly migrate into the ulcerated colon and establish this permanent epithelium of crypt-like morphology. These squamous cells derive from a small unique transition zone, distal to the border of colonic and anal epithelium, that resists colitic injury. The cells of this zone have a pre-loaded program of colonic differentiation and further upregulate key aspects of colonic epithelium during repair. Transitional anal cells represent unique reserve cells capable of rebuilding epithelial structures in the colon after colitis. Further study of these cells could reveal novel approaches to direct mucosal healing in inflammation and disease.

Tracking of Oil Water Contact in a Barail Main Reservoir

To supplement the current understanding of the reservoir and also to increase the confidence level in decision making, an understanding in the variation of Oil Water Contact is very much important. In this paper, a study of an integrated and efficient methodology for establishment of complex Oil Water Contacts in Barail Main Sand (water drive reservoir) for a part of one oilfield of Upper Assam Basin has been discussed. The Barail Formation which is the main producing reservoir exhibits unique behaviour in terms of fluid distribution. The aim of the study is to map the movement of Oil Water Contact with respect to time and production in the study area. The study is mainly based on the structural contour map drawn based on the open hole log data of drilled wells in different time frame throughout the development of the study area. Using Oil Field Management software a cross section had been prepared taking Oil Water Contact as base among the selected wells to track its trend in these wells of the study area. The present study shows that Oil Water Contact is disturbed upon the start of production and sensitive to the rate and volume of withdrawal from localized area. Aquifer is very active and vertical sweep efficiency in the reservoir is very good due to its reservoir properties which resulted a small transition zones as it is evident from the open hole logs of the wells drilled in different time span. The study also shows that as a result of the thinning of oil column and sand incursion owing to the high drawdown in the study area, the tracking of movement of Oil Water Contact is found to be very important.

Numerical study of the cone angle effects on transition and convection heat transfer for hypersonic inflatable aerodynamic decelerator aeroshell

The inevitable boundary-layer transition and severe heating argumentation of Hypersonic Inflatable Aerodynamic Decelerator (HIAD) pose challenge for survivability of a Thermal Protection System (TPS). In the current study, the effects of sphere-cone angle on hypersonic heating and boundary-layer transition of stacked tori HIADs with 60°, 65° and 70° sphere-cone are demonstrated minutely by solving compressible Navier-Stokes equations with k-ω-γ transition model. Transition and heating augmentation triggered on the leeward where the shape deformation causes crossflows and local flow separations are sensitive to the cone angle. Smaller cone angle withstands severer heating flux. The study reveals that the first-mode disturbance and crossflow instability are dominators to the transition. Whereas the contribution of second-mode disturbance could be negligible. Larger cone angle postpones transition onsets as a result of weaker crossflow and more limited affected region of the first-mode disturbance. The 70° sphere-cone model, whose crossflow is lower than the critical value is only determined by the first mode, and thus has a quite smaller transition zone as compared to the other two models.

Congenital intestinal stenosis and Hirschsprung\u2019s disease: two extremely rare pathologies in a newborn puppy

BackgroundHirschsprung’s disease (HSCR) is a common congenital malformation of the enteric nervous system (ENS). During fetal development, ganglion cells of the ENS are derived from neural crest cells that migrate to the bowel. These cells reside principally in two ganglionated plexus: 1) The myenteric plexus, extending from the esophagus to the anus, and 2) submucous plexus, extending from the duodenum to the anus. In large animal species, there is a third plexus called Henle’s or Schabadasch’s plexus.ENS ganglion cells play a key role in normal gastrointestinal motility, respond to sensory stimuli and regulate blood flow. Both plexus show a high degree of independence from the central nervous system. Alterations in the embryonic development of the ENS can induce multiple pathologies in animal models and humans.Case presentationThe present case was a female the fifth born in a litter of 5 puppies. At about 2–3 weeks of age, she suffered from abdominal distension, pain, and constipation. At approximately 8–10 weeks of age, the puppy started to vomit abundantly, and the regurgitated food appeared undigested. Progressive abdominal distention was observed, with quite visible peristaltic movements and more frequent vomiting episodes. The abdominal radiographs, based on AP and side projections, revealed an enlargement of the abdominal diameter and an increased width in the epigastric region. At 12 weeks of age, exploratory surgery revealed a stenotic segment in the jejunum, followed by a small transition zone and then a significantly reduced diameter. Immunohistochemical examinations were performed using antibodies against calretinin, S-100 protein, CD56, neuron specific enolase (NSE) and synaptophysin, which are the biological markers for diagnosing HSCR.ConclusionA reduced number of ganglion cells (1–3 cells per ganglion) were found. There was no specific staining pattern for many of these; while for others, the pattern was compatible with HSCR. Surgical intervention to remove the stenotic section prolonged the life of the puppy for 13 years. Extremely rare pathologies such as that discussed herein should be studied to understand the pathophysiology and be able to diagnose small species in veterinary medicine in a timely fashion. To our knowledge, this is the first report of congenital intestinal stenosis and Hirschprung’s disease in a newborn puppy.

Mechanical characterization of as-cast AA7075/6060 and CuSn6/Cu99.5 compounds using an experimental and numerical push-out test

The present paper describes an experimental method and innovative numerical approach in the mechanical testing of rotationally symmetric, as-cast bilayer compounds using a push-out test. Specimens consisting of AA7075/6060 and CuSn6/Cu99.5 were fabricated by static and semi-continuous compound casting, respectively. Optical and mechanical testing methods showed a cohesive bonding character and a negligibly small transition zone between the joining partners. The shear strength was investigated by using an experimental push-out test. The experiments were reviewed by means of a finite element analysis. Therefore, Johnson-Cock failure parameters were determined for each casting material. Subsequently, a multi-sectional numerical model was built up to simulate the mechanical behavior of an as-cast bimetal sample during push-out testing. Lastly, a numerical parameter study yielded a strong dependency between optimized loads at the interface and the ratio of die clearance and sample thickness as well as the interface position.

Simulation of control characteristics of liquid column vibration absorber using a quasi-elliptic flow path estimation method

Tuned liquid column dampers (TLCDs) and liquid column vibration absorbers (LCVAs) are good substitutes for mechanical dampers to counter seismic activity exerted to tall buildings. The existing simplified effective length method could predict good results corresponding to test outcomes on TLCDs and LCVAs with small transition zones, but is found to yield larger discrepancy as larger transition zones are needed, often due to limited space constraints. The numerical panel method could be effectively employed to give more accurate results, but is not simple to formulate and needs to be re-modified for each new configuration. This paper proposes a new quasi-elliptic flow path estimation method to simulate control characteristics of TLCDs and LCVAs with relatively large transition boundary between the vertical columns and the horizontal cross-over duct, since liquid velocity’s variation inside the large transition boundary cannot be assumed to occur at a single point. The simulation results are compared with experimental investigations conducted on a shake table, yielding satisfactorily better outcomes for large transition zones, as well as for small transition zones. This new formulation has been verified with a few other studies and has been found to be an excellent viable option with a respectable better, or at least comparable, accuracy level.

A vanishing viscosity approach to the evolution of microstructures in finite plasticity

AbstractMaterial microstructures in finite single‐slip crystal plasticity occur and evolve due to deformation. Their formation is not arbitrary, they tend to form structured spatial patterns. This hints at a universal underlying process. As in the approach of D. Kochmann and K. Hackl, we use a variational framework, focusing on the Lagrange functional to describe the evolving mircrostructure. We modify this approach by introducing a small smooth transition zone between the domains in order to improve the numerical treatment. We present explicit time‐evolution equations for the volume fractions and the internal variables. We outline a numerical scheme. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Inhibition of electrokinetic ion transport in porous materials due to potential drops induced by electrolysis

In this work we present non-destructive measurements of sodium ion concentration profiles during the electrokinetic removal of sodium chloride from porous materials using Nuclear Magnetic Resonance (NMR). The effect of both protons and hydroxyl ions, generated due to the electrolysis of water, on the transport of the salt ions is studied by tracking the acidic and alkaline fronts using pH-indicator paper. In addition, the electrical potential distribution within the specimen is monitored to assess its influence on the process. To support the observations we compare the experimental results with a theoretical model based on the Poisson–Nernst–Plank equations. In this model we use the chemical equilibrium condition for the self-electrolysis of water in the description of the transport of protons and hydroxyl ions. In addition we use the electro-neutrality condition to compute the transport of salt ions through the material. At the edges of the system the electrical current is distributed over the chemical active species, i.e. protons, hydroxyl and chloride ions, according to the Butler–Volmer description for charge transfer at electrodes. Both the experimental and model results show in the final stage of the electrokinetic remediation process a sharp transition from the acidic to alkaline region at one third of the length of the specimen away from the positively biased electrode, i.e. the anode. From the model results we found that the formation of chlorine gas at the anode does not influence the position of this transition area. In this transition region we also observe a large gradient in electrical potential and a corresponding local deficit of ions. As a result of the large potential gradient in this small transition zone the electrical field in the acidic and alkaline region diminishes. Consequently, electrokinetic ion transport though the material will stagnate.

Ion beam based composition and texture control of titanium nitride

Titanium nitride was formed by electron beam evaporation of titanium in an atmosphere of backfilled nitrogen. The growing film was simultaneously irradiated with argon ions. From of a single-aperture ion source, a Gaussian-shaped ion beam was extracted. Each position on the sample was correlated with a particular ion beam current density. With this method, on a single substrate a large variation in ion irradiation intensity could be obtained. Since the titanium evaporation rate was uniform over this area, the parameter varied over the sample surface was only the ion-to-atom arrival ratio. It turns out that with a constant Ti condensation rate and nitrogen impact rate, the Ti:N ratio in the film is a strong function of the argon ion impact rate. Ion-beam induced nitrogen sorption saturates at a certain ion irradiation intensity. While under all conditions the TiN (mono)phase is obtained, it shows different preferred crystal orientations in dependence on ion bombardment intensity. At low level, the film grows in (111)-orientation, at high levels in (100)-orientation. In a small transition zone, (110)-orientation prevails. Thus, the orientation can be selected by the ion beam intensity, which is relevant for application.

Effect of CALIPSO cloud–aerosol discrimination (CAD) confidence levels on observations of aerosol properties near clouds

CALIPSO aerosol backscatter enhancement in the transition zone between clouds and clear sky areas is revisited with particular attention to effects of data selection based on the confidence level of cloud–aerosol discrimination (CAD). The results show that backscatter behavior in the transition zone strongly depends on the CAD confidence level. Higher confidence level data has a flatter backscatter far away from clouds and a much sharper increase near clouds (within 4km), thus a smaller transition zone. For high confidence level data it is shown that the overall backscatter enhancement is more pronounced for small clear-air segments and horizontally larger clouds. The results suggest that data selection based on CAD reduces the possible effects of cloud contamination when studying aerosol properties in the vicinity of clouds.

Elucidating Marine Biogeography with Macrophytes: Quantitative Analysis of the North Atlantic Supports the Thermogeographic Model and Demonstrates a Distinct Subarctic Region in the Northwestern Atlantic

Quantitative analysis of North Atlantic macrophyte (seaweed) abundance was used to test the thermogeographic model (TM) of marine biogeography. The TM uses coastal area and seawater temperature over Pleistocene time to reveal long-term climate/ area clusters that predict biogeographic regions. An earlier study with the TM predicted 20 of 24 classical biogeographic regions; the 4 omitted regions were either weak, disputed, or structurally (sandy/silty regions) inapplicable to the TM. The TM predicted a new western North Atlantic Subarctic Region, centered on the Strait of Belle Isle and lying between Newfoundland and Labrador. In contrast, Nova Scotia and the Gulf of Maine were found to be a Boreal/Subarctic transition zone. The predictions of the TM were earlier supported with coralline algal abundances, and here are supported by a test with macrophyte assemblages.Seaweed assemblages were studied at 51 primary SCUBA stations with 4–7 standard depth zones at each station from southern Labrador to Cape Elizabeth, ME. Meter-square quadrats were taken at each station, followed by at-sea sorting, identification, and weighing of biomass by species. A permanent record of these studies is provided by archived underwater photography and voucher herbarium samples, including tissue in silica gel to support future DNA analyses. Comparisons of European seaweed assemblages were accomplished by re-analyzing semi-quantitative data available in the literature.We demonstrate with the biomass data that a 3000-km stretch of coast (i.e., northern Gulf of St. Lawrence, northeastern Newfoundland, and southern Labrador) that is centered on the Strait of Belle Isle has a unique assemblage of seaweeds. In its location and marine climate, this coast closely matches the Subarctic Region predicted by the TM. Based on graphic demonstration, this Subarctic Region is radically different from that of Nova Scotia and the Gulf of Maine, and its dominant species derive from the North Pacific Ocean. Several different statistical approaches applied to the macrophyte data demonstrate the strength of these findings, while also finding that a subset of Subarctic species persists in deeper water to the south in the transition zone (i.e., southwestern Nova Scotia, Gulf of Maine). Only a very small proportion of the seaweed flora of the Subarctic Region is Arctic in origin (<4%). Earlier geographic analyses of biodiversity did not discover the Subarctic Region because rare species hide the strength of assemblages based on abundance.Many of the dominant seaweeds in the transitional region of the Gulf of Maine and Nova Scotia occur widely in Europe, and are Boreal in origin. Such Boreal species form 47–80% of the macrophyte biomass at depths shallower than 5 m in the northwestern Atlantic transition zone southwest of the Subarctic Region. In deeper water (>5 m), however, European Boreal species are only 22–25% of the macrophyte biomass. Although many of the dominant, shallow sublittoral species of the European Boreal flora have made the North Atlantic passage, only about 10% (by biomass) of mid-depth species (2.5–5 m) have crossed and even fewer of the deeper European species are found in the northwestern Atlantic. A few European “Boreal” seaweeds reach further north into the Subarctic Region, but only at low levels of biomass and primarily at mid-depths (2.5–5 m). The Subarctic is inhospitable for establishment of such species in shallow water because of low winter temperatures and sea ice, and in deeper water by low summer temperatures (<5 °C).Few ecologists have had the opportunity to work in the Subarctic Region; instead, most of the recent descriptive and experimental studies of northwestern Atlantic ecosystems are based on studies in the smaller transition zone in the Gulf of Maine and southwestern Nova Scotia. Consequently, we provide detailed photographic, tabular, and graphic descriptions of the seaweed assemblages within the Subarctic and their interactions with

Optimal Intercity Transportation Services With Heterogeneous Demand and Variable Fuel Price

Optimal Intercity Transportation Services With Heterogeneous Demand and Variable Fuel Price

Higher-Order Feature-Preserving Geometric Regularization

We introduce two fourth-order regularization methods that remove geometric noise without destroying significant geometric features. These methods leverage ideas from image denoising and simplification of high contrast images in which piecewise affine functions are preserved up to infinitesimally small transition zones. We combine the regularization techniques with active contour models and apply them to segmentation of polygonal objects in aerial images. To avoid loss of features during the computation of the external driving forces we use total variation-based inverse scale-space techniques on the input data. Furthermore, we use the models for feature-preserving removal of geometric texture on surfaces.

Role of transition zones in marine ice sheet dynamics

It has been suggested that rapid thinning of the West Antarctic ice sheet is due to increased melting under ice shelves caused by a gradual ocean warming (Shepherd et al., 2004). Payne et al. (2004) showed that such melting could lead to an acceleration of grounded ice flow. In this paper, we analyze the response of a marine ice sheet to different perturbations near the grounding line using a numerical ice sheet model that takes into account longitudinal stress coupling and grounding line migration at subgrid precision, based on a novel technique. Results show that stress transmission or longitudinal coupling across the grounding line plays a decisive role. The grounding line migration is a function of the length scale over which the basal conditions change from frozen to the bed to floating, the “transition zone.” We demonstrate that thinning of the ice shelf due to bottom melting has a negligible effect on the grounded ice mass. Only perturbations at the grounding line or reduction in buttressing of the ice shelf substantially thins the grounded ice sheet. Inclusion of lateral drag does not alter these results qualitatively. Marine ice sheets with large transition zones, such as ice streams, seem highly sensitive to such perturbations compared to ice sheets with small transition zones, such as an abrupt ice sheet/ice shelf junction.

Laser in situ Keratomileusis for High Myopia Using a Small Ablation Zone and Large Aspheric Transition Zone

To evaluate the efficacy and predictability of laser in situ keratomileusis (LASIK) using the Nidek NAVEX system with a small ablation (optical, OZ) zone and a large aspheric transition zone (OATz). We report a prospective nonrandomized study of LASIK for high myopia using a small ablation in 23 eyes of 18 patients. The optical zone was between 3 and 3.8 mm and transition zone (TZ) was between 7 and 7.8 mm. Preoperative examination included best-spectacle corrected visual acuity (BSCVA), refraction, and corneal topography. All eyes were measured by the Nidek OPD-Scan and data were imported to FinalFit software. Aspheric profile (OATz) numbers 5 to 7 were used. BSCVA, uncorrected spectacle visual acuity (UCVA), refraction, and subjective evaluation of glare and night vision by questionnaire were recorded after surgery. At baseline, mean spherical equivalent refraction was -7.03 +/- 2.39 D (range -5.50 to -15.50 D). Postoperative UCVA was better than 20/25 in 95.65% of eyes 3 months after LASIK. Postoperative refraction was within +/- 0.50 D of emmetropia in 91.3% of eyes and within +/- 1.00 D in all eyes. No eye lost lines of BSCVA; 52.17% of eyes gained 1 line and 13.04% of eyes gained 2 lines. No patient reported significant glare or night vision problems on subjective questionnaire. LASIK with a small ablation (optical) zone and high aspheric transition zone using the Nidek NAVEX system was effective, predictable, and relatively safe for correction of high myopia.

A classification of duct modes based on surface waves

For the relatively high frequencies relevant in a turbofan engine duct, the modes of a lined section may be classified in two categories: genuine acoustic 3D duct modes resulting from the finiteness of the duct geometry, and 2D surface waves that exist only near the wall surface in a way essentially independent of the rest of the duct. Per frequency and circumferential order there are at most four surface waves. They occur in two kinds: two acoustic surface waves that exist with and without mean flow, and two hydrodynamic surface waves that exist only with mean flow. The number and location of the surface waves depends on the wall impedance Z and mean flow Mach number. When Z is varied, an acoustic mode may change via small transition zones into a surface waves and vice versa. Compared to the acoustic modes, the surface waves behave—for example as a function of the wall impedance—rather differently as they have their own dynamics. They are therefore more difficult to find. A method is described to trace all modes by continuation in Z from the hard-wall values, by starting in an area of the complex Z-plane without surface waves.

Residual Vision in Transition Zones in Patients with Cerebral Blindness

Using high resolution perimetry in repeated sessions, we investigated 27 patients with homonymous visual field defects in order to detect islands of vision within the damaged area, and to determine color- and form-recognition abilities within these zones of residual vision. In most patients we found circumscribed areas within the “blind” field in which the stimulus was detected in about 50% of presentations. Only one patient had an island of vision greater than 5° within the defective area. We also found an area of variable performance between the blind and the intact field. Borders of field defects were classified as being: (a) sharp (small transition zone), (b) medium, or (c) fuzzy (scattered deficits). We propose that transition zones are functional representations of partially spared neuronal structures in areas of the brain which are only partially injured.

Clinical relevance of the individual prostate cancer focus.

The course of stage A prostate cancer is difficult to predict because some of the tumors sampled at TURP are histologically "latent" (resembling cancer discovered incidentally at autopsy) and others have the ability to progress clinically. TURP selectively samples cancer in the transition zone, but, as we noted, the pattern of cancer in the TURP was a limited predictor of residual cancer. Furthermore, peripheral zone cancer appeared histologically to have a higher grade, volume for volume, than transition zone cancer and, in our study, was more frequently associated with extraprostatic spread of cancer. Peripheral zone cancer, while sampled in a minority of TURPs (less than 20%), is associated with histological predictors of poor prognosis. In the ploidy study, peripheral zone cancer was sampled in 5 patients, 4 of whom had nondiploid residual cancer in the radical prostatectomy specimen. Three of these 5 had extracapsular extension and 2 had seminal vesicle invasion. The frequent pattern in stage A1 is, therefore, a low-volume, diploid, transition zone cancer in the TURP specimen. In most cases this was associated with one or more small diploid transition zone or peripheral zone cancers in the radical prostatectomy specimen. However, in some cases, a residual nondiploid cancer was present that could eventually cause progression. The pattern of cancer in stage A2 differs from that in stage A1 in that most large transition zone cancers are selected into this stage and some of these are nondiploid. Stage A2, therefore, includes the minority of transition zone cancers that are nondiploid as well as a considerable number of peripheral zone cancers that are nondiploid. In both stages A1 and A2 nondiploid peripheral zone cancers outnumbered nondiploid transition zone cancers. The relationship of tumor volume with ploidy is clearly different for peripheral zone and transition zone cancers. Eight peripheral zone cancers less than 2.0 cc were nondiploid but only 1 transition zone cancer less than 2.0 cc was nondiploid. Furthermore, all peripheral zone cancers greater than 2.0 cc were nondiploid whereas only 50% of transition zone cancers greater than 2.0 cc were nondiploid. There was a significant difference between tumor volume of diploid and nondiploid cancers. Presumably, nondiploid cell lines have a growth advantage and are more poorly differentiated than diploid cancers. Whether DNA ploidy changes occur as a consequence of tumor growth and tumor cell heterogeneity is unclear because of range in volume of tumors studied.(ABSTRACT TRUNCATED AT 400 WORDS)

The premyofibril: evidence for its role in myofibrillogenesis.

When cardiac muscle cells are isolated from embryonic chicks and grown in culture they attach to the substrate as spherical cells with disrupted myofibrils, and over several days in culture, they spread and extend lamellae. Based on antibody localizations of various cytoskeletal proteins within the spreading cardiomyocyte, three types of myofibrils have been identified: 1) fully formed mature myofibrils that are centrally positioned in the cell, 2) premyofibrils that are closest to the cell periphery, and 3) nascent myofibrils located between the premyofibrils and the mature myofibrils. Muscle-specific myosin is localized in the A-bands in the mature, contractile myofibrils, and along the nascent myofibrils in a continuous pattern, but it is absent from the premyofibrils. Antibodies to non-muscle isoforms of myosin IIB react with the premyofibrils at the cell periphery and with the nascent myofibrils, revealing short bands of myosin between closely spaced bands of alpha-actinin. In the areas where the nascent myofibrils border on the mature myofibrils, the bands of non-muscle myosin II reach lengths matching the lengths of the mature A-bands. With the exception of a small transition zone consisting of one myofibril, or sometimes several sarcomeres, bordering the nascent myofibrils, there is no reaction of these non-muscle myosin IIB antibodies with the mature myofibrils in spreading myocytes. C-protein is found only in the mature myofibrils, and its presence there may prevent co-polymerization of non-muscle and muscle myosins. Antibodies directed against the non-muscle myosin isoforms, IIA, do not stain the cardiomyocytes. In contrast to the cardiomyocytes, the fibroblasts in these cultures stain with antibodies to both non-muscle myosin IIA and IIB. The premyofibrils near the leading edge of the lamellae show no reaction with antibodies to either titin or zeugmatin, whereas the nascent myofibrils and mature myofibrils do. The spacings of the banded alpha-actinin staining range from 0.3 to 1.4 microns in the pre- and nascent myofibrils and reach full spacings (1.8-2.5 microns) in the mature myofibrils. Based on these observations, we propose a premyofibril model in which non-muscle myosin IIB, titin, and zeugmatin play key roles in myofibrillogenesis. This model proposes that pre- and nascent myofibrils are composed of minisarcomeres that increase in length, presumably by the concurrent elongation of actin filaments, the loss of the non-muscle myosin II filaments, the fusion of dense bodies or Z-bodies to form wide Z-bands, and the capture and alignment of muscle myosin II filaments to form the full spacings of mature myofibrils.