1,128 research outputs found
Deletion mutants in COP9/Signalosome subunits in fission yeast Schizosaccharomyces pombe display distinct phenotypes
The COP9/signalosome complex is highly conserved in evolution and possesses significant structural similarity to the 19S regulatory lid complex of the proteasome. It also shares limited similarity to the translation initiation factor eIF3. The signalosome interacts with multiple cullins in mammalian cells. In the fission yeast Schizosaccharomyces pombe, the Csn1 subunit is required for the removal of covalently attached Nedd8 from Pcu1, one of three S. pombe cullins. It remains unclear whether this activity is required for all the functions ascribed to the signalosome. We previously identified Csn1 and Csn2 as signalosome subunits in S. pombe. csn1 and csn2 null mutants are DNA damage sensitive and exhibit slow DNA replication. Two further putative subunits, Csn4 and Csn5, were identified from the S. pombe genome database. Herein, we characterize null mutations of csn4 and csn5 and demonstrate that both genes are required for removal of Nedd8 from the S. pombe cullin Pcu1 and that their protein products associate with Csn1 and Csn2. However, neither csn4 nor csn5 null mutants share the csn1 and csn2 mutant phenotypes. Our data suggest that the subunits of the signalosome cannot be considered as a distinct functional unit and imply that different subunits of the signalosome mediate distinct functions
Photoelectron spectra of anionic sodium clusters from time-dependent density-functional theory in real-time
We calculate the excitation energies of small neutral sodium clusters in the
framework of time-dependent density-functional theory. In the presented
calculations, we extract these energies from the power spectra of the dipole
and quadrupole signals that result from a real-time and real-space propagation.
For comparison with measured photoelectron spectra, we use the ionic
configurations of the corresponding single-charged anions. Our calculations
clearly improve on earlier results for photoelectron spectra obtained from
static Kohn-Sham eigenvalues
Violation of the `Zero-Force Theorem' in the time-dependent Krieger-Li-Iafrate approximation
We demonstrate that the time-dependent Krieger-Li-Iafrate approximation in
combination with the exchange-only functional violates the `Zero-Force
Theorem'. By analyzing the time-dependent dipole moment of Na5 and Na9+, we
furthermore show that this can lead to an unphysical self-excitation of the
system depending on the system properties and the excitation strength.
Analytical aspects, especially the connection between the `Zero-Force Theorem'
and the `Generalized-Translation Invariance' of the potential, are discussed.Comment: 5 pages, 4 figure
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Dosimetric comparison study between intensity modulated radiation therapy and three-dimensional conformal proton therapy for pelvic bone marrow sparing in the treatment of cervical cancer.
The objective was to compare intensity-modulated radiation therapy (IMRT) with 3D conformal proton therapy (3DCPT) in the treatment of cervical cancer. In particular, each technique's ability to spare pelvic bone marrow (PBM) was of primary interest in this study. A total of six cervical cancer patients (3 postoperative and 3 intact) were planned and analyzed. All plans had uniform 1.0 cm CTV-PTV margin and satisfied the 95% PTV with 100% isodose (prescription dose = 45 Gy) coverage. Dose-volume histograms (DVH) were analyzed for comparison. The overall PTV and PBM volumes were 1035.9 ± 192.2 cc and 1151.4 ± 198.3 cc, respectively. In terms of PTV dose conformity index (DCI) and dose homogeneity index (DHI), 3DCPT was slightly superior to IMRT with 1.00 ± 0.001, 1.01 ± 0.02, and 1.10 ± 0.02, 1.13 ± 0.01, respectively. In addition, 3DCPT demonstrated superiority in reducing lower doses (i.e., V30 or less) to PBM, small bowel and bladder. Particularly in PBM, average V10 and V20 reductions of 10.8% and 7.4% (p = 0.001 and 0.04), respectively, were observed. However, in the higher dose range, IMRT provided better sparing (> V30). For example, in small bowel and PBM, average reductions in V45 of 4.9% and 10.0% (p = 0.048 and 0.008), respectively, were observed. Due to its physical characteristics such as low entrance dose, spread-out Bragg peak and finite particle range of protons, 3DCPT illustrated superior target coverage uniformity and sparing of the lower doses in PBM and other organs. Further studies are, however, needed to fully exploit the benefits of protons for general use in cervical cancer
A 16S rDNA-Based Quantitative Assay for Monitoring \u3ci\u3eLactobacillus Plantarum\u3c/i\u3e in Silage
Ensilage of herbaceous biomass can be enhanced by applying pre-selected fermentative bacteria, however insufficient is known about the population dynamics of such starter cultures under a range of ensiling conditions. Classical methods for species-specific quantification of bacteria are labour intensive. An alternative approach is the detection of bacteria based on molecular markers for species-specific regions within their genomic DNA (e.g. the 16S rDNA sequence). In this study, a quantitative marker assay using the real-time PCR technique (Q-PCR) is described for Lactobacillus plantarum, a bacterium often used for silage starter cultures
Physical signatures of discontinuities of the time-dependent exchange-correlation potential
The exact exchange-correlation (XC) potential in time-dependent
density-functional theory (TDDFT) is known to develop steps and discontinuities
upon change of the particle number in spatially confined regions or isolated
subsystems. We demonstrate that the self-interaction corrected adiabatic
local-density approximation for the XC potential has this property, using the
example of electron loss of a model quantum well system. We then study the
influence of the XC potential discontinuity in a real-time simulation of a
dissociation process of an asymmetric double quantum well system, and show that
it dramatically affects the population of the resulting isolated single quantum
wells. This indicates the importance of a proper account of the discontinuities
in TDDFT descriptions of ionization, dissociation or charge transfer processes.Comment: 17 pages, 6 figure
Dust rings and filaments around the isolated young star V1331 Cygni
We characterize the small and large scale environment of the young star V1331
Cygni with high resolution HST/WFPC2 and Digitized Sky Survey images. In
addition to a previously known outer dust ring (~30'' in diameter), the
HST/WFPC2 scattered light image reveals an inner dust ring for the first time.
This ring has a maximum radius of 6.5'' and is possibly related to a molecular
envelope. Large-scale optical images show that V1331 Cyg is located at the tip
of a long dust filament linking it to the dark cloud LDN 981. We discuss the
origin of the observed dust morphology and analyze the object's relation to its
parent dark cloud LDN 981. Finally, based on recent results from the
literature, we investigate the properties of V1331 Cyg and conclude that in its
current state the object does not show suffcient evidence to be characterized
as an FU Ori object.Comment: 15 pages ApJ preprint style including 3 figures, accepted for
publication in ApJ (Feb. 2007
Coupling a single atomic quantum bit to a high finesse optical cavity
The quadrupole S -- D optical transition of a single trapped
Ca ion, well suited for encoding a quantum bit of information, is
coherently coupled to the standing wave field of a high finesse cavity. The
coupling is verified by observing the ion's response to both spatial and
temporal variations of the intracavity field. We also achieve deterministic
coupling of the cavity mode to the ion's vibrational state by selectively
exciting vibrational state-changing transitions and by controlling the position
of the ion in the standing wave field with nanometer-precision
Tracing kinematical and physical asymmetries in the jet from DG Tau B
Stellar jets can be highly asymmetric and have multiple velocity components.
To clarify the origin of jet asymmetries and constrain their launch mechanism
we study the physical and kinematical structure of the flow emitted by DG Tau
B. The analysis of deep spectra taken at the KECK telescope allows us to infer
the physical properties (the electron and total density, ne and nh, the
ionisation fraction, xe, and the temperature, te) and the spatial distribution
of the velocity components in the two jet lobes. The presence of dust grains in
the jet is investigated by estimating the gas-phase abundance of calcium with
respect to its solar value. At the base of the jet the lines are broad (~100
km/s) and up to three velocity components are detected. At 5" from the source,
however, only the denser and more excited high velocity components survive and
the lines are narrower (~10-30 km/s). The jet is strongly asymmetric both in
velocity and in its physical structure. The red lobe, slower (~140 km/s) and
more collimated, presents low ionisation fractions (xe~0.1-0.4) and
temperatures (te<5e3 K), while the total density is up to ~2.5e4 ccm. The blue
lobe, faster (~-320 km/s) and less collimated, is also less dense (nh~1e4 ccm)
but highly excited (te up to ~5e4 K and xe up to 0.9). The estimated mass loss
rate is similar in the two lobes (~6-8e-9 Msol/yr), suggesting that the
ejection power is comparable on the two sides of the system, as expected from a
magneto-centrifugal ejection mechanism, and that the observed asymmetries are
due to different mass load and propagation properties in an inhomogeneous
environment. Calcium is strongly depleted, indicating that the jet contains
dust grains and, therefore, should originate from a region of the disk
extending beyond the dust sublimation radius. The depletion is lower for higher
velocities, consistent with dust destruction by shocks.Comment: 14 pages, 9 figures, accepted by A&
He I 10830 as a Probe of Winds in Accreting Young Stars
He I 10830 profiles acquired with Keck's NIRSPEC for 6 young low mass stars
with high disk accretion rates (AS 353A, DG Tau, DL Tau, DR Tau, HL Tau and SVS
13) provide new insight into accretion-driven winds. In 4 stars the profiles
have the signature of resonance scattering, and possess a deep and broad
blueshifted absorption that penetrates more than 50% into the 1 micron
continuum over a continuous range of velocities from near the stellar rest
velocity to the terminal velocity of the wind, unlike inner wind signatures
seen in other spectral features. This deep and broad absorption provides the
first observational tracer of the acceleration region of the inner wind and
suggests that this acceleration region is situated such that it occults a
significant portion of the stellar disk. The remaining 2 stars also have blue
absorption extending below the continuum although here the profiles are
dominated by emission, requiring an additional source of helium excitation
beyond resonant scattering. This is likely the same process that produces the
emission profiles seen at He I 5876
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