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At least 433 records · Page 24Linked to original sources
PubMed2006

Localization-delocalization transition in a system of quantum kicked rotors.

The quantum dynamics of atoms subjected to pairs of closely spaced delta kicks from optical potentials are shown to be quite different from the well-known paradigm of quantum chaos, the single delta-kick system. We find the unitary matrix has a new oscillating band structure corresponding to a cellular structure of phase space and observe a spectral signature of a localization-delocalization transition from one cell to several. We find that the eigenstates have localization lengths which scale with a fractional power L approximately h(-0.75) and obtain a regime of near-linear spectral variances which approximate the "critical statistics" relation summation2(L) approximately or equal to chi(L) approximately 1/2 (1-nu)L, where nu approximately 0.75 is related to the fractal classical phase-space structure. The origin of the nu approximately 0.75 exponent is analyzed.

Journal Article↗
PubMed1978

Cellular fine structure in the invasive nodules of different histogenetic types of malignant melanoma.

Ultrastructural studies were carried out on the invasive nodule of forty malignant melanomas. The findings support the concept that the fine structure of lentigo maligna melanoma is often characteristic, and differs from that of superficial spreading and nodular melanoma. The melanosomes in lentigo maligna melanoma are usually ellipsoidal and resemble those of normal melanocytes, whereas the melanosomes in superficial spreading and nodular melanoma are most often spheroidal and abnormal in appearance. Superficial spreading and nodular melanomas cannot be distinguished reliably by their ultrastructure. Melanosomal appearances could not be related to the presence of a pre-existing naevus or the depth of invasion of the tumour nodule.

Humans↗
PubMed2002

Protein-protein interactions: lessons learned.

Protein-Protein (P-P) interactions play a pivotal role in determining cellular structure and in all cellular processes. The nature of P-P interactions is complex, and despite the large amount of research that has occurred in the field, is still poorly understood. Abnormal P-P interactions are particularly important because of their association with a variety of diseases, including cancer. This review examines P-P interactions with particular emphasis on the discovery of new anti-tumor drugs, including underlying physical forces that determine affinity and specificity and discusses classical and newer strategies used to discover inhibitors of P-P interactions, providing a number of recent cancer-related case studies and commentary.

Animals↗
PubMed1994

A method for light microscopy examination of cellular and structural interrelations in undemineralized tooth specimens.

This study examines ameloblasts and odontoblasts in relation to mineralizing enamel and dentin in thin undemineralized tooth sections from unerupted and partly erupted human third molars. The material comprised 12 freshly removed third molars. After fixation for 24 h the specimens were dehydrated and embedded in hydroxyethylmethacrylate. Undemineralized sections 10-15 microns thick were prepared with a cutting-grinding system, and radiomicrographs were taken. Postsecretory ameloblasts were seen in different morphologic stages ranging from ruffle- and smooth-ended ameloblasts to cuboidal and squamous cells adhering to incomplete and fully mineralized enamel. The former occurred in the most coronal tooth part, whereas the latter were seen cervically. It was not possible to identify systematic modulation cycles as seen in postsecretory rat incisor ameloblasts. The well-defined subodontoblastic region with cell-free and cell-rich layers was established before tooth eruption. The function of the subodontoblastic region is not fully understood, but our findings suggest that the establishment of the region plays a role in maintaining the specific odontoblast phenotype in the coronal region possibly linked to progressive dentin mineralization.

Ameloblasts↗
PubMed1975

[Change in cellular surface structures and volume under the action of colchicine].

Effect of colchicine upon the surface structures and volume of embryonic pig kidney cells and mouse ascite carcinoma Krebs II cells involved an increase of the cells volume. This was confirmed by the scanning electron microscopy data. The surface of colchicine-treated pig cells has less microvilli due, probably, to their enlarged volume. Swelling of mitochondrial matrix as well as some other ultrastructural changes in cytoplasm of the drug-treated cells suggest that the increase in the volume is a result of cell hydration. Disturbance of the osmotic equilibrium following the depolymerization of microtubles in the mitotic spindle and cytoplasm, is discussed.

Animals↗