231 research outputs found
Relativistic quasiparticle time blocking approximation. II. Pygmy dipole resonance in neutron-rich nuclei
Theoretical studies of low-lying dipole strength in even-even spherical
nuclei within the relativistic quasiparticle time blocking approximation
(RQTBA) are presented. The RQTBA developed recently as an extension of the
self-consistent relativistic quasiparticle random phase approximation (RQRPA)
enables one to investigate effects of coupling of two-quasiparticle excitations
to collective vibrations within a fully consistent calculation scheme based on
covariant energy density functional theory. Dipole spectra of even-even
Sn -- Sn and Ni -- Ni isotopes calculated within
both RQRPA and RQTBA show two well separated collective structures: the
higher-lying giant dipole resonance (GDR) and the lower-lying pygmy dipole
resonance (PDR) which can be identified by a different behavior of the
transition densities of states in these regions.Comment: 28 pages, 13 figure
Low-lying dipole response in the Relativistic Quasiparticle Time Blocking Approximation and its influence on neutron capture cross sections
We have computed dipole strength distributions for nickel and tin isotopes
within the Relativistic Quasiparticle Time Blocking approximation (RQTBA).
These calculations provide a good description of data, including the
neutron-rich tin isotopes Sn. The resulting dipole strengths have
been implemented in Hauser-Feshbach calculations of astrophysical neutron
capture rates relevant for r-process nucleosynthesis studies. The RQTBA
calculations show the presence of enhanced dipole strength at energies around
the neutron threshold for neutron rich nuclei. The computed neutron capture
rates are sensitive to the fine structure of the low lying dipole strength,
which emphasizes the importance of a reliable knowledge of this excitation
mode.Comment: 15 pages, 4 figures, Accepted in Nucl. Phys.
Discrimination of healthy and cancer cells of the bladder by metabolic state, based on autofluorescence
Bladder cancer is among the most common cancers worldwide (4th in men). It is responsible for high patient morbidity and displays rapid recurrence and progression. Lack of sensitivity of gold standard techniques (white light cystoscopy, voided urine cytology) means many early treatable cases are missed. The result is a large number of advanced cases of bladder cancer which require extensive treatment and monitoring. For this reason, bladder cancer is the single most expensive cancer to treat on a per patient basis. In recent years, autofluorescence spectroscopy has begun to shed light into disease research. Of particular interest in cancer research are the fluorescent metabolic cofactors NADH and FAD. Early in tumour development, cancer cells often undergo a metabolic shift (the Warburg effect) resulting in increased NADH. The ratio of NADH to FAD ("redox ratio") can therefore be used as an indicator of the metabolic status of cells. Redox ratio measurements have been used to differentiate between healthy and cancer breast cells and to monitor cellular responses to therapies. Here, we have demonstrated, using healthy and bladder cancer cell lines, a statistically significant difference in the redox ratio of bladder cancer cells, indicative of a metabolic shift. To do this we customised a standard flow cytometer to excite and record fluorescence specifically from NADH and FAD, along with a method for automatically calculating the redox ratio of individual cells within large populations. These results could inform the design of novel probes and screening systems for the early detection of bladder cancer
SN 2006bp: Probing the Shock Breakout of a Type II-P Supernova
HET optical spectroscopy and unfiltered ROTSE-III photometry spanning the
first 11 months since explosion of the Type II-P SN 2006bp are presented. Flux
limits from the days before discovery combined with the initial rapid
brightening suggest the supernova was first detected just hours after shock
breakout. Optical spectra obtained about 2 days after breakout exhibit narrow
emission lines corresponding to HeII 4200, HeII 4686, and CIV 5805 in the rest
frame, and these features persist in a second observation obtained 5 hours
later; however, these emission lines are not detected the following night nor
in subsequent observations. We suggest that these lines emanate from material
close to the explosion site, possibly in the outer layers of the progenitor
that have been ionized by the high energy photons released at shock breakout. A
P-Cygni profile is observed around 4450 A in the +2 and +3 day spectra.
Previous studies have attributed this feature to high velocity H-beta, but we
discuss the possibility that this profile is instead due to HeII 4687. Further
HET observations (14 nights in total) covering the spectral evolution across
the photometric plateau up to 73 days after breakout and during the nebular
phase around day +340 are presented, and expansion velocities are derived for
key features. The measured decay slope for the unfiltered light curve is 0.0073
+/- 0.0004 mag/day between days +121 and +335, which is significantly slower
than the decay of rate 56Co. We combine our HET measurements with published
X-ray, UV, and optical data to obtain a quasi-bolometric light curve through
day +60. We see a slow cooling over the first 25 days, but no sign of an early
sharp peak; any such feature from the shock breakout must have lasted less than
~1 day.[ABRIDGED]Comment: ApJ accepted, 43 page
A Parameter Study of Type II Supernova Light Curves Using 6 M_odot He Cores
Results of numerical calculations of Type II supernova light curves are
presented. The model progenitor stars have 6 cores and various
envelopes, originating from a numerically evolved 20 star. Five
parameters that affect the light curves are examined: the ejected mass, the
progenitor radius, the explosion energy, the Ni mass, and the extent of
Ni mixing. The following affects have been found: 1) the larger the
progenitor radius the brighter the early--time light curve, with little affect
on the late--time light curve, 2) the larger the envelope mass the fainter the
early light curve and the flatter the slope of the late light curve, 3) the
larger the explosion energy the brighter the early light curve and the steeper
the slope of the late light curve, 4) the larger the Ni mass the
brighter the overall light curve after 20 to 50 days, with no affect on the
early light curve, 5) the more extensive the Ni mixing the brighter the
early light curve and the steeper the late light curve. The primary parameters
affecting the light curve shape are the progenitor radius and the ejected mass.
The secondary parameters are the explosion energy, Ni mass and Ni
mixing. I find that while in principle the general shape and absolute magnitude
of a light curve indicate a unique set of parameters, in practice it is
difficult to avoid some ambiguity in the parameters. I find that the
nickel--powered diffusion wave and the recombination of helium produce a
prominent secondary peak in all our calculations. The feature is less prominent
when compositional mixing, both Ni mixing and mixing between the
hydrogen and helium layers, occurs. The model photospheric temperatures and
velocities are presented, for comparison to observation.Comment: 39 pages, 15 figures. Astrophysical Journal (Accepted, Dec. 20, 2004
Covariant response theory beyond RPA and its application
The covariant particle-vibration coupling model within the time blocking
approximation is employed to supplement the Relativistic Random Phase
Approximation (RRPA) with coupling to collective vibrations. The Bethe-Salpeter
equation in the particle-hole channel with an energy dependent residual
particle-hole (p-h) interaction is formulated and solved in the shell-model
Dirac basis as well as in the momentum space. The same set of the coupling
constants generates the Dirac-Hartree single-particle spectrum, the static part
of the residual p-h interaction and the particle-phonon coupling amplitudes.
This approach is applied to quantitative description of damping phenomenon in
even-even spherical nuclei with closed shells Pb and Sn. Since
the phonon coupling enriches the RRPA spectrum with a multitude of
phphonon states a noticeable fragmentation of giant monopole and
dipole resonances is obtained in the examined nuclei. The results are compared
with experimental data and with results of the non-relativistic approach.Comment: 12 pages, 4 figures, Proceedings of the NSRT06 Conferenc
Isospin Character of the Pygmy Dipole Resonance in 124Sn
The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn
with the (a,a'g) coincidence method at E=136 MeV. The comparison with results
of photon-scattering experiments reveals a splitting into two components with
different structure: one group of states which is excited in (a,a'g) as well as
in (g,g') reactions and a group of states at higher energies which is only
excited in (g,g') reactions. Calculations with the self-consistent relativistic
quasiparticle time-blocking approximation and the quasiparticle phonon model
are in qualitative agreement with the experimental results and predict a
low-lying isoscalar component dominated by neutron-skin oscillations and a
higher-lying more isovector component on the tail of the giant dipole
resonance
Structure of the bacteriophage PhiKZ non-virion RNA polymerase
Bacteriophage ΦKZ (PhiKZ) is the archetype of a family of massive bacterial viruses. It is considered to have therapeutic potential as its host, Pseudomonas aeruginosa, is an opportunistic, intrinsically antibiotic resistant, pathogen that kills tens of thousands worldwide each year. ΦKZ is an incredibly interesting virus, expressing many systems that the host already possesses. On infection, it forms a ‘nucleus’, erecting a barrier around its genome to exclude host endonucleases and CRISPR-Cas systems. ΦKZ infection is independent of the host transcriptional apparatus. It expresses two different multi-subunit RNA polymerases (RNAPs): the virion RNAP (vRNAP) is injected with the viral DNA during infection to transcribe early genes, including those encoding the non-virion RNAP (nvRNAP), which transcribes all further genes. ΦKZ nvRNAP is formed by four polypeptides thought to represent homologues of the eubacterial β/β′ subunits, and a fifth with unclear homology, but essential for transcription. We have resolved the structure of ΦKZ nvRNAP to better than 3.0 Å, shedding light on its assembly, homology, and the biological role of the fifth subunit: it is an embedded, integral member of the complex, the position, structural homology and biochemical role of which imply that it has evolved from an ancestral homologue to σ-factor
From Normal to Obesity and Back: The Associations between Mitochondrial DNA Copy Number, Gender, and Body Mass Index.
Mitochondrial DNA (mtDNA) encodes core subunits of oxidative phosphorylation complexes and, as a result of intricate regulatory crosstalk between nuclear and mitochondrial genomes, the total number of mtDNA copies fits the requirements of each cell type. Deviations from the physiological number of mtDNA copies are expected to be deleterious and might cause some inherited diseases and normal ageing. We studied 46 obese patients with type 2 diabetes (T2DM) one year after a laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB). The results were compared with normal-weight patients without T2DM (control group 1) (body mass index (BMI) = 22.5 ± 3.01 kg/m <sup>2</sup> ) and patients with obesity without T2DM (control group 2) (BMI = 36 ± 3.45 kg/m <sup>2</sup> ). We detected an increase of mtDNA copy number in the cells of the buffy coat obtained from peripheral blood, sampled one year after bariatric surgery. We also found that average mtDNA copy number as well as its dynamics (before and after the surgery) are gender-specific. To the best of our knowledge, this is the first evidence for the restoration of mtDNA copy number in obese patients after LSG and RYGB
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