46 research outputs found
Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter
The Bianchi type III dark energy models with constant deceleration parameter
are investigated. The equation of state parameter is found to be time
dependent and its existing range for this model is consistent with the recent
observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy
clustering statistics. The physical aspect of the dark energy models are
discussed.Comment: 12 pages, 2 figures, Accepted version of IJT
Evolution of Oxygen Metal Electron Transfer and Metal Electronic States During Manganese Oxide Catalyzed Water Oxidation Revealed with In Situ Soft X Ray Spectroscopy
Manganese oxide (MnOx) electrocatalysts are examined herein by inâ
situ soft Xâray absorption spectroscopy (XAS) and resonant inelastic Xâray scattering (RIXS) during the oxidation of water buffered by borate (pHâ
9.2) at potentials from 0.75 to 2.25â
V vs. the reversible hydrogen electrode. Correlation of Lâedge XAS data with previous mechanistic studies indicates MnIV is the highest oxidation state involved in the catalytic mechanism. MnOx is transformed into birnessite at 1.45â
V and does not undergo further structural phase changes. At potentials beyond this transformation, RIXS spectra show progressive enhancement of charge transfer transitions from oxygen to manganese. Theoretical analysis of these data indicates increased hybridization of the MnâO orbitals and withdrawal of electron density from the O ligand shell. Inâ
situ XAS experiments at the O Kâedge provide complementary evidence for such a transition. This step is crucial for the formation of O2 from water
Cnm67p Is a Spacer Protein of the Saccharomyces cerevisiae Spindle Pole Body Outer Plaque
In Saccharomyces cerevisiae, the spindle pole body (SPB) is the functional homolog of the mammalian centrosome, responsible for the organization of the tubulin cytoskeleton. Cytoplasmic (astral) microtubules essential for the proper segregation of the nucleus into the daughter cell are attached at the outer plaque on the SPB cytoplasmic face. Previously, it has been shown that Cnm67p is an integral component of this structure; cells deleted for CNM67 are lacking the SPB outer plaque and thus experience severe nuclear migration defects. With the use of partial deletion mutants of CNM67, we show that the N- and C-terminal domains of the protein are important for nuclear migration. The C terminus, not the N terminus, is essential for Cnm67p localization to the SPB. On the other hand, only the N terminus is subject to protein phosphorylation of a yet unknown function. Electron microscopy of SPB serial thin sections reveals that deletion of the N- or C-terminal domains disturbs outer plaque formation, whereas mutations in the central coiled-coil domain of Cnm67p change the distance between the SPB core and the outer plaque. We conclude that Cnm67p is the protein that connects the outer plaque to the central plaque embedded in the nuclear envelope, adjusting the space between them by the length of its coiled-coil
Supercurrents in Magnesium Diboride/Metal Composite Wire
We have fabricated a series of ex situ copper sheathed powder-in-tube MgB2
wires with 20% by volume Ag, Pb, In, and Ga metal added to the MgB2 powder. We
find the transport critical current of these wires increases significantly with
the addition of specific metals to the core filament. In particular, the
critical current density (Jc) of the MgB2/Ga(20%) wire is in excess of 5x10^4
A/cm^2 at 10K in self field, nearly 50 times that of the MgB2/Ag(20%) wire. The
temperature dependent Jc of all wires is well described as an ensemble of clean
S/N/S junctions in which the relevant parameters are the average thickness of
the N layer, the critical temperature of the S layer, and a scaling term
related to Jc at zero temperature. Eliminating the differences in the filament
microstructure as the primary cause of the enhanced Jc, we suggest that Jc is
determined by the magnitude of the proximity effect induced superconductivity
in the normal metal layer, which is known to be proportional to the
electron-electron interaction in N. We present one-dimensional material
specific calculations that support this, and zero-field cooled DC magnetic
susceptibility data that confirm an increased number of well-connected
superconducting grains exist in the composite wires that contain metal
additions with large electron-electron interactions and long electron mean free
paths.Comment: 36 pages, 10 figures, 3 table
Reorientation of Mispositioned Spindles in Short Astral Microtubule Mutant spc72Î Is Dependent on Spindle Pole Body Outer Plaque and Kar3 Motor Protein
Nuclear migration and positioning in Saccharomyces cerevisiae depend on long astral microtubules emanating from the spindle pole bodies (SPBs). Herein, we show by in vivo fluorescence microscopy that cells lacking Spc72, the SPB receptor of the cytoplasmic Îł-tubulin complex, can only generate very short (<1 ÎŒm) and unstable astral microtubules. Consequently, nuclear migration to the bud neck and orientation of the anaphase spindle along the mother-bud axis are absent in these cells. However, SPC72 deletion is not lethal because elongated but misaligned spindles can frequently reorient in mother cells, permitting delayed but otherwise correct nuclear segregation. High-resolution time-lapse sequences revealed that this spindle reorientation was most likely accomplished by cortex interactions of the very short astral microtubules. In addition, a set of double mutants suggested that reorientation was dependent on the SPB outer plaque and the astral microtubule motor function of Kar3 but not Kip2/Kip3/Dhc1, or the cortex components Kar9/Num1. Our observations suggest that Spc72 is required for astral microtubule formation at the SPB half-bridge and for stabilization of astral microtubules at the SPB outer plaque. In addition, our data exclude involvement of Spc72 in spindle formation and elongation functions
Der1p, a protein required for degradation of malfolded soluble proteins of the endoplasmic reticulum: topology and Der1-like proteins
CPY* and the Power of Yeast Genetics in the Elucidation of Quality Control and Associated Protein Degradation of the Endoplasmic Reticulum
Dissociation from BiP and Retrotranslocation of Unassembled Immunoglobulin Light Chains Are Tightly Coupled to Proteasome Activity
Unassembled immunoglobulin light chains expressed by the mouse plasmacytoma cell line NS1 (Îș(NS1)) are degraded in vivo with a half-life of 50â60 min in a way that closely resembles endoplasmic reticulum (ER)-associated degradation (Knittler et al., 1995). Here we show that the peptide aldehydes MG132 and PS1 and the specific proteasome inhibitor lactacystin effectively increased the half-life of Îș(NS1), arguing for a proteasome-mediated degradation pathway. Subcellular fractionation and protease protection assays have indicated an ER localization of Îș(NS1) upon proteasome inhibition. This was independently confirmed by the analysis of the folding state of Îș(NS1) and size fractionation experiments showing that the immunoglobulin light chain remained bound to the ER chaperone BiP when the activity of the proteasome was blocked. Moreover, kinetic studies performed in lactacystin-treated cells revealed a time-dependent increase in the physical stability of the BiPâÎș(NS1) complex, suggesting that additional proteins are present in the older complex. Together, our data support a model for ER-associated degradation in which both the release of a soluble nonglycosylated protein from BiP and its retrotranslocation out of the ER are tightly coupled with proteasome activity
DER7, encoding α-glucosidase I is essential for degradation of malfolded glycoproteins of the endoplasmic reticulum
Time-Lapse Video Microscopy Analysis Reveals Astral Microtubule Detachment in the Yeast Spindle Pole Mutant cnm67
Saccharomyces cerevisiae cnm67Î cells lack the spindle pole body (SPB) outer plaque, the main attachment site for astral (cytoplasmic) microtubules, leading to frequent nuclear segregation failure. We monitored dynamics of green fluorescent proteinâlabeled nuclei and microtubules over several cell cycles. Early nuclear migration steps such as nuclear positioning and spindle orientation were slightly affected, but late phases such as rapid oscillations and insertion of the anaphase nucleus into the bud neck were mostly absent. Analyzes of microtubule dynamics revealed normal behavior of the nuclear spindle but frequent detachment of astral microtubules after SPB separation. Concomitantly, Spc72 protein, the cytoplasmic anchor for the Îł-tubulin complex, was partially lost from the SPB region with dynamics similar to those observed for microtubules. We postulate that in cnm67Î cells Spc72âÎł-tubulin complex-capped astral microtubules are released from the half-bridge upon SPB separation but fail to be anchored to the cytoplasmic side of the SPB because of the absence of an outer plaque. However, successful nuclear segregation in cnm67Î cells can still be achieved by elongation forces of spindles that were correctly oriented before astral microtubule detachment by action of Kip3/Kar3 motors. Interestingly, the first nuclear segregation in newborn diploid cells never fails, even though astral microtubule detachment occurs