Academic literature on the topic 'Irregular cell space'

The external surface of the cell consists of a phospholipid bilayer which carries a carbohydrate-rich coat called the glycocalyx; ionizable groups within the glycocalyx, such as sialic acid (N-acetyl neuraminate), contribute a net negative charge to the cell surface. Many of the carbohydrates that form the glycocalyx are bound to membrane-associated proteins. Each of these components— phospholipid bilayer, carbohydrate-rich coat, membrane-associated protein—has distinct physicochemical characteristics and is abundant. Plasma membranes contain ∼50% protein, ∼45% lipid, and ∼5% carbohydrate by weight. Therefore, each component influences cell interactions with the external environment in important ways. Cells can become attached to surfaces. The surface of interest may be geometrically complex (for example, the surface of another cell, a virus, a fiber, or an irregular object), but this chapter will focus on adhesion between a cell and a planar surface. The consequences of cell–cell adhesion are considered further in Chapter 8 (Cell Aggregation and Tissue Equivalents) and Chapter 9 (Tissue Barriers to Molecular and Cellular Transport). The consequences of cell–substrate adhesion are considered further in Chapter 7 (Cell Migration) and Chapter 12 (Cell Interactions with Polymers). Since the growth and function of many tissue-derived cells required attachment and spreading on a solid substrate, the events surrounding cell adhesion are fundamentally important. In addition, the strength of cell adhesion is an important determinant of the rate of cell migration, the kinetics of cell–cell aggregation, and the magnitude of tissue barriers to cell and molecule transport. Cell adhesion is therefore a major consideration in the development of methods and materials for cell delivery, tissue engineering, and tissue regeneration. The most stable and versatile mechanism for cell adhesion involves the specific association of cell surface glycoproteins, called receptors, and complementary molecules in the extracellular space, called ligands. Ligands may exist freely in the extracellular space, they may be associated with the extracellular matrix, or they may be attached to the surface of another cell. Cell–cell adhesion can occur by homophilic binding of identical receptors on different cells, by heterophilic binding of a receptor to a ligand expressed on the surface of a different cell, or by association of two receptors with an intermediate linker. Cell–matrix adhesion usually occurs by heterophilic binding of a receptor to a ligand attached to an insoluble element of the extracellular matrix.

How information circulates in the brain was the subject of a heated debate lasting a decade or more among anatomists in the closing years of the last century. One camp argued that neural tissue consisted of a continuum, a syncytium, with no discernible functional units while the opposing view held that the brain consisted of discrete units, the nerve cells, communicating through point-to-point contacts that Sherrington dubbed synapses. Although in principle both views can be supported, in practice the majority of rapid communication occurs via specific point-to-point contacts, at either chemical and electrical synapses. Ephaptic transmission refers to nonsynaptic, electrical interactions between neurons. While such interactions do occur, for instance, among adjacent, parallel axons across the extracellular space, they are, by their very nature, neither very strong among any one pair of processes nor very specific. Their functional significance—if any—is currently not known, and we will not discuss them here (Traub and Miles, 1991; Jefferys, 1995). In the beginning chapter, we introduced the action of fast, chemical synapses. Given their importance, we will now return to this topic in greater depth. We first overview the pertinent biophysical events underlying chemical synaptic transmission and some of the vital statistics of synapses before we come to the mathematical treatment of synaptic input. In the last section, we will summarize our knowledge of electrical synapses and their computational role. Most typically, a synapse consists of a presynaptic axonal terminal and a postsynaptic process that can be located on a dendritic spine, on the trunk of a dendrite, or on the cell body. Figure 4.1 shows some examples of synapses among cortical cells as seen through a high-powered electron microscope. It is not easy at first to identify the synapses amid all the curved, irregular, and densely packed structures making up the neuronal tissue. In a number of locations, such as the retina or the thalamus, a synaptic connection is made between two dendrites, rather than between an axon and a dendrite. These synapses are called dendrodendritic synapses; they are believed to be relatively rare in the adult cortex. Most synapses are small and highly specialized features of the nervous system. As we will see, a chemical synapse converts a presynaptic electrical signal into a chemical signal and back into a postsynaptic electrical signal.

The majority of experiments in neurophysiology are based upon spike trains recorded from individual or multiple nerve cells. If all the action potentials are taken to be identical and only the times at which they are generated are considered, the experimentalist obtains a discrete series of time events {t1,···, tn}, where t¡ corresponds to the occurrence of the i th spike, characterizing the spike train. This spike train is transmitted down the axon to all of the target cells of the neuron, and it is this spike train that contains all of the relevant information that the cell is representing (assuming no dendro-dendritic connections). As alluded to in the preceding chapter, there are two opposing views of neuronal coding, with many interim shades. One view holds that it is the firing rate, averaged over a suitable temporal window (Eqs. 14.1 or 14.2), that is relevant for information processing. The dissenting view, correlation coding, argues that the interactions among spikes, at the single cell as well as between multiple cells, encodes information. A key property of spike trains is their seemingly stochastic or random nature, quite in contrast to switching in digital computers. This randomness is apparent in the highly irregular discharge pattern of a central neuron to a sensory stimulus whose details are rarely reproducible from one trial to the next. The apparent lack of reproducible spike patterns has been one of the principal arguments in favor of the hypothesis that neurons only care about the firing frequency averaged over very long time windows. Such a mean rate code is very robust to “sloppy” hardware but is also relatively inefficient in terms of transmitting the maximal amount of information per spike. Encoding information in the intervals between spikes is obviously much more efficient, in particular if correlated across multiple neurons. Such a scheme does place a premium on postsynaptic neurons that can somehow decode this information. Because little or no information can be encoded into a stream of regularly spaced action potentials, this raises the question of how variable neuronal firing really is.

Sarcoidosis is a multi-organ disease characterized by the formation of non-caseating epithelioid granulomas in many organs. The kidneys are not commonly affected but when the disease involves these organs. It is comprised of non-caseating granulomatous interstitial nephritis (GIN) and hypercalcemia-related disorders. In the latter case, acute kidney injury as initial presentation of the disease is a rare entity, and it is postulated to appear due to several pathogenic processes: (1) interstitial nephritis with or without granulomas, (2) nephrocalcinosis with or without nephrolithiasis, and (3) urethral obstruction. A 71-year-old man presented to the clinic with a history of lethargy, nausea, short memory loss and a 10 kg weight loss all of which appeared within the past 6 months. He was also known with prostate adenoma and was under the care of a urologist. Upon physical examination the following aspects were noted: blood pressure of 160/100 mmHg, heart rate 60 bpm and an irregular enlarged prostate. The chest X-ray was normal and blood samples revealed anemia, hypercalcemia, and increased values of urea and creatinine. An ultrasound of the kidneys was performed and no abnormalities were noted. The urinalysis showed the presence of protein +, glucose+, blood 2+, a few white cells and some granular casts. The next step was to perform a renal biopsy that revealed areas of lymphocytic tubulitis, mild mononuclear interstitial infiltrate, some non-necrotizing epithelioid granulomas comprised of Langerhans-type giant cells and epithelioid macrophages. Peri-tubular interstitial calcifications were also noted. As a result a histological diagnosis was summarized as acute or chronic granulomatous interstitial nephritis with nephrocalcinosis. A CT scan pf the chest was subsequently performed and it revealed calcified lymph nodes in the mediastinum involving the space between the aorta and the trachea and numerous nodules scattered bilateralally over the entire lung parenchyma with no apparent periseptal or perivascular association. These findings were diagnosed as sarcoidosis. The serum ACE level was found abnormal and therefore, a clinical diagnosis of sarcoidosis was made and the patient was started on 40 mg of oral prednisone daily with rapid improvement in the overall general condition. Sarcoidosis is an uncommon disease that should be suspected in front of a patient that presents with hypercalcemia and acute kidney injury. After excluding other causes of hypercalcemia such as multiple myeloma, primary hyperparathyroidism, and paraneoplastic phenomena, a renal biopsy is then indicated to confirm the diagnosis of sarcoidosis.

Motivated by its frequent appearance in practical applications, scientists and engineers have been putting much efforts to pursue the ability to predict fluid flow behavior in sphere packed bed, in particular the fluid-solid interaction therein. The network model has recently been used to predict the fluid flow behavior in a sphere packed bed for a smaller length-scale domain of interest. The major questions for this approach are the representation of the irregular void space as a three dimensional network and the assignment of the flow resistance values. The application of Deluanay Cell to di

Cellular Automata (CA) models are among the most popular models for simulating land use change/growth in urban areas around the world and have experienced a significant development over the last twenty years. These models have their origins on the efforts of devising mathematical rules for biological systems and for evolution developed by mathematicians von Neumann and Stanislaw Ulam in the 1940s. Two main
 features made CA interesting for urban studies, to which they were introduced by Waldo Tobler in the early 1970s. First, their intrinsic spatiality, which is suitable for the simulatio

Summary The representation of faults and fractures using cut-cell meshes often results in irregular non-orthogonal grids. Simple finite volume approaches fail to handle complex meshes because they are highly prone to grid orientation effects and only converges for K-orthogonal grids. Wide stencil approaches and higher order methods are computationally expensive and impractical to adopt in commercial reservoir simulators. In this work, we implement an Enriched Galerkin (EG) discretization for the flow and transport problems on non-orthogonal grids. The EG approximation space combines continuous

The main purpose of this study was to confirm operability and effectiveness of the complex methods developed for theoretical prediction and experimental-computational determining some properties of modern highly porous materials, used as thermal protection shields in objects of space engineering, power engineering, etc. Them concern Fibrous Materials (FM), Open-Cell Reticulated Foams (OCRF) etc. The basis for the method proposed is in the combination of Direct Mathematical Simulation (DMS) for global structure of the complex irregular systems, which have the property of local regularity and In

As offshore reservoirs are depleted, the seabed may subside. Furthermore, the extreme crests estimates are now commonly higher than obtained previously due to improved understanding of statistics of non-linear irregular waves. Consequently, bottom fixed installations which have previously had sufficient clearance between the deck and the sea surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. In the present paper, we investigate the long-term area statistics for maximum crest height under a fixed platform deck for 2nd order short cre

This paper analyzes the leg-seabed interaction due to motions of a 3rd generation jack-up vessel in irregular waves. The proposed model considers hydrodynamic forces on the hull as well as on the legs. The sea floor reaction forces are analyzed with a Coupled Eulerian-Lagrangian (CEL) method. The results are used to develop a mechanical rheological model for the sea floor. With computational efficiency in mind a state-space representation in time domain is derived. The excitation of the system is caused by irregular waves, which are described by the JONSWAP spectrum. The proposed method allows