1,912 research outputs found
Electronic structure and magnetic properties of RMnX (R= Mg, Ca, Sr, Ba, Y; X= Si, Ge) studied by KKR method
Electronic structure calculations, using the charge and spin self-consistent
Korringa- Kohn-Rostoker (KKR) method, have been performed for several Mn
compounds ( = Mg, Ca, Sr, Ba, Y; = Si, Ge) of the CeFeSi-type structure.
The origin of their magnetic properties has been investigated emphasizing the
role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-
interatomic distances on the Mn magnetic moment value is delineated from our
computations, supporting many neutron diffraction data. We show that the marked
change of with the Mn-Mn and Mn- distances resulted from a
redistribution between spin-up and spin-down -Mn DOS rather than from
different fillings of the Mn 3-shell. Bearing in mind that the neutron
diffraction data reported for the Mn compounds are rather scattered, the
KKR computations of are in fair agreement with the experimental
values. Comparing density of states near obtained in different magnetic
orderings, one can notice that the entitled Mn systems seem to 'adapt'
their magnetic structures to minimize the DOS in the vicinity of the Fermi
level. Noteworthy, the SrMnGe antiferromagnet exhibits a pseudo-gap behaviour
at , suggesting anomalous electron transport properties. In addition,
the F-AF transition occurring in the disordered LaYMnSi alloy for
the range is well supported by the DOS features of
LaYMnSi. In contrast to the investigated Mn compounds,
YFeSi was found to be non-magnetic, which is in excellent agreement with the
experimental data.Comment: 10 pages + 14 figures, to appear in Eur. Phys. Jour.
Communication system features dual mode range acquisition plus time delay measurement
Communication system combines range acquisition system and time measurement system for tracking high velocity aircraft and spacecraft. The range acquisition system uses a pseudonoise code to determine range and the time measurement system reduces uncontrolled phase variations in the demodulated signal
Direct evidence for the magnetic ordering of Nd ions in NdMnSi and NdMnGe by high resolution inelastic neutron scattering
We have investigated the low energy nuclear spin excitations in
NdMnSi and NdMnGe by high resolution inelastic neutron
scattering. Previous neutron diffraction investigations gave ambiguous results
about Nd magnetic ordering at low temperatures. The present element-specific
technique gave direct evidence for the magnetic ordering of Nd ions. We found
considerable difference in the process of the Nd magnetic ordering at low
temperature in NdMnSi and NdMnGe. Our results are consistent
with those of magnetization and recent neutron diffraction measurements
A Scanning Electron Microscopic Technique for Three-Dimensional Visualization of the Spatial Arrangement of Metaphase, Anaphase and Telophase Chromatids
Chromosome and chromatid alignment in mitotic configurations remains a topic of interest because there is little precise information. For example, reconstruction of mitotic configurations from serial sections collected with transmission electron microscopy has proven to be neither practical nor a sensitive method for conceptualizing these arrangements. Similarly light microscopy has been even more unsatisfactory because of its limited resolution and lack of three-dimensional capabilities. These limitations conceivably could be overcome by visualization of mitotic configurations by scanning electron microscopy (SEM). However, SEM has its limitations, of which the most obvious with regard to visualization of mitotic configurations, is that such structures in dividing cells are obscured from the beam by membranes, cellular organelles, and the mitotic apparatus. These contaminants, we have found, can be removed by the appropriate procedure such that a direct three-dimensional visualization of intact life-like mitotic configurations of chromatids from mammalian cells is possible. We also demonstrate that these configurations, although some artifacts may exist, retain the same basic shape and chromatid arrangements throughout metaphase, anaphase, and telophase when compared to configurations isolated with a non-ionic detergent and neutral buffers
Flexible high-voltage supply for experimental electron microscope
Scanning microscope uses a field-emission tip for the electron source, an electron gun that simultaneously accelerates and focuses electrons from the source, and one auxiliary lens to produce a final probe size at the specimen on the order of angstroms
Land snail diversity in a threatened limestone district near Istanbul, Turkey
The limestone meadows located to the northÂ-northwest of Istanbul, Turkey, are in danger of being overrun by the rapidly expanding city. Past surveys showed that these habitats harbor rare plant species, including endemics to Turkey. To further evaluate the conservation value of these habitats, especially in terms of the often neglected invertebrates, one limestone area to the north of Küçükçekmece Lake and surrounding Sazlidere Dam was surveyed for land snails. Our findings strengthen the case for the protection of these unique habitats. TwentyÂ-four species of land snails were identified in the survey area. Of these, 21 are native to Turkey, including three whose type location is Istanbul. In addition, two species that are at or near the limits of their ranges are considered to represent peripheral populations that may be especially worth conserving. Although the area surrounding Sazlidere Dam is under protection, the other limestone habitats are severely threatened by ongoing development
Diversidad de los caracoles terrestres en una zona caliza amenazada cercana a Estambul, TurquÃa
The limestone meadows located to the north–northwest of Istanbul, Turkey, are in danger of being overrun by the rapidly expanding city. Past surveys showed that these habitats harbor rare plant species, including endemics to Turkey. To further evaluate the conservation value of these habitats, especially in terms of the often neglected invertebrates, one limestone area to the north of Küçükçekmece Lake and surrounding Sazlidere Dam was surveyed for land snails. Our findings strengthen the case for the protection of these unique habitats. Twenty–four species of land snails were identified in the survey area. Of these, 21 are native to Turkey, including three whose type location is Istanbul. In addition, two species that are at or near the limits of their ranges are considered to represent peripheral populations that may be especially worth conserving. Although the area surrounding Sazlidere Dam is under protection, the other limestone habitats are severely threatened by ongoing development.Las praderas calcáreas situadas al NNO de Estambul están en peligro de ser rápidamente invadidas por la ciudad en expansión. Estudios anteriores demostraron que estos hábitats albergan especies vegetales raras, incluyendo algunos endemismos turcos. Con objeto de seguir evaluando el valor conservativo de dichos hábitats, en especial en cuanto a los invertebrados, a menudo ignorados, se han estudiado los caracoles terrestres de una zona calcárea al norte del lago Küçükçekmece y alrededor de la presa Sazlidere. Nuestros descubrimientos enfatizan la necesidad de una polÃtica de protección de estos hábitats únicos. En el área estudiada se identificaron 24 especies de caracoles terrestres. De ellas, 21 son nativas de TurquÃa, incluyendo tres cuya localización tipo es Estambul. Además, se considera que dos especies que se hallan en o cerca de los lÃmites de su zona de distribución representan poblaciones periféricas especialmente merecedoras de conservación. A pesar de que la zona que rodea a la presa Sazlidere está
protegida, el resto de los hábitats calcáreos está muy amenazado por el creciente desarrollo
Chromatid Behavior in Late Mitosis: A Scanning Electron Microscopy Analysis of Mammalian Cell Lines with Various Chromosome Numbers
Chromatid activity during the process of nuclear reformation following metaphase is a period of mitosis where little precise information is available. Nuclear reformation requires that chromosomes, at metaphase and chromatids during anaphase and telophase align, position and associate in a clearly defined sequence to insure the specific design of each nucleus. Four cell lines with chromosome numbers ranging from seven to almost seventy were chosen to determine whether the process of nuclear assembly is the same throughout. Chromosomal alignment at metaphase is found to be radial in all four cell lines. Chromosome positioning is essentially the same in all four, where the smaller chromosomes are located centrally and longer ones are positioned peripherally in a radial alignment. Chromosomal association is directly related to chromosome number. The more chromosomes in a one dimensional plane occupying a given area, the closer the association. In comparing the HeLaS3 and muntjac chromatids, the former has the closer association at metaphase. Since association is the most important aspect of chromatid behavior in nuclear reformation, chromatid positioning becomes a vital process during anaphase movement. Chromatid positions established during anaphase determines later positioning in the interphase nucleus because of the subsequent interconnection of adjacent chromatids by the formation of a fibrous meshwork. This fibrous meshwork, formed in anaphase and early telophase, functions to stabilize chromatids following their positioning and it also serves as a substrate or matrix for the assembly of nuclear envelope
Entamoeba histolytica: Lipid rafts are involved in adhesion of trophozoites to host extracellular matrix components
Adhesion is an important virulence function for Entamoeba histolytica, the causative agent of amoebic dysentery. Lipid rafts, cholesterol-rich domains, function in compartmentalization of cellular processes. In E. histolytica, rafts participate in parasite–host cell interactions; however, their role in parasite–host extracellular matrix (ECM) interactions has not been explored. Disruption of rafts with a cholesterol extracting agent, methyl-β-cyclodextrin (MβCD), resulted in inhibition of adhesion to collagen, and to a lesser extent, to fibronectin. Replenishment of cholesterol in MβCD-treated cells, using a lipoprotein–cholesterol concentrate, restored adhesion to collagen. Confocal microscopy revealed enrichment of rafts at parasite–ECM interfaces. A raft-resident adhesin, the galactose/N-acetylgalactosamine-inhibitable lectin, mediates interaction to host cells by binding to galactose or N-acetylgalactosamine moieties on host glycoproteins. In this study, galactose inhibited adhesion to collagen, but not to fibronectin. Together these data suggest that rafts participate in E. histolytica–ECM interactions and that raft-associated Gal/GalNAc lectin may serve as a collagen receptor
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