3,686 research outputs found
Measuring the galaxy power spectrum with multiresolution decomposition -- II. diagonal and off-diagonal power spectra of the LCRS galaxies
The power spectrum estimator based on the discrete wavelet transform (DWT)
for 3-dimensional samples has been studied. The DWT estimator for
multi-dimensional samples provides two types of spectra with respect to
diagonal and off-diagonal modes, which are very flexible to deal with
configuration-related problems in the power spectrum detection. With simulation
samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show
(1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power
spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS
selection function doesn't cause more than 1- error in the DWT power
spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the
redshift distortion, are approximately scale-independent. These results insure
that the uncertainties of the power spectrum measurement are under control. The
scatter of the DWT power spectra of the six strips of the LCRS survey is found
to be rather small. It is less than 1- of the cosmic variance of mock
samples in the wavenumber range h Mpc. To fit the detected
LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting
redshift distortion parameter is about the same as that obtained from
the Fourier power spectrum. The velocity dispersions for SCDM and
CDM models are also consistent with other detections with
the LCRS. A systematic difference between the best-fitting parameters of
diagonal and off-diagonal power spectra has been significantly measured. This
indicates that the off-diagonal power spectra are capable of providing
information about the power spectrum of galaxy velocity field.Comment: AAS LaTeX file, 41 pages, 10 figures included, accepted for
publication in Ap
Tumour volume response, initial cell kill and cellular repopulation in B16 melanoma treated with cyclophosphamide and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea.
The relationship between tumour volume response and cell kill in B16 melanoma following treatment in vivo with cyclophosphamide (CY) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) was investigated. Tumour volume response, expressed as growth delay, was estimated from measurements of tumour dimensions. Depression of in vitro colony-forming ability of cells from treated tumours was used as the measure of tumour cell kill. The relationship between these parameters was clearly different for the two agents studied. CY produced more growth delay (7.5 days) per decade of tumour cell kill than CCNU (2 to 3.5 days). The possibility that this was due to a technical artefact was rejected in favour of an alternative explanation that different rates of cellular repopulation in tumours treated with CY and CCNU might be responsible. Cellular repopulation was measured directly, by performing cell-survival assays at various times after treatment with doses of CY and CCNU which produced about 3 decades of cell kill. The rate of repopulation by clonogenic cells was much slower after treatment with CY than with CCNU, and this appears to account for the longer duration of the growth delay obtained with CY
Cell yield and cell survival following chemotherapy of the B16 melanoma.
We describe in this paper cell survival studies, using in vitro clonogenic assays, performed on the B16 melanoma treated in situ with various cytotoxic agents. In addition we have determined the effects of these agents on the yield of cells obtained by trypsinization. In untreated tumours the mean cell yield was approximately 10(8)/g, which is 20--30% of the cells actually present in the tissue. The plating efficiency was approximately 40%. Most agents rapidly affected both cell yield and cell survival. For example, within 20--30 h, gamma-radiation and several alkylating agents reduced cell yield by about 40%. The cell yield change was associated with an increase in mean cell size. Cell yield was reduced even more (approximately 70%) by Vinca alkaloids. This large reduction was associated with extensive cell lysis, observed as an increase in the necrotic fraction of tumours from approximately 35% to approximately 70%. Adriamycin, bleomycin and Ara-C also produced a moderate reduction in cell yield (approximately 40%), but actinomycin D did not reduce cell yield and FU increased it by about 30%. Only gamma-radiation, cyclophosphamide, CCNU, BCNU and melphalan produced more than a 90% reduction in cell survival, although there was a small but measurable reduction with all other agents except vinblastine, HN2 and actinomycin D
Clonal variation in the sensitivity of B16 melanoma to m-AMSA.
A hypothesis that m-AMSA may have greater cytotoxicity in melanin-containing tumour tissues, because it may reversibly bind to melanin, leading to prolonged drug exposure, was examined. Clonal lines of B16 melanoma which differed widely in pigmentation level were selected by isolating artificial lung colonies and in vitro soft-agar colonies, and implanting them into mice. Excision cell-survival assays performed 24 h after drug administration showed that in vivo sensitivity to m-AMSA progressively increased as pigmentation level decreased, but that m-AMSA drug levels measured 24 h after treatment were much lower in amelanotic than in melanotic lines. In dose-survival studies the reduced sensitivity of melanotic cell lines was revealed as a large shoulder (Dq = 27 mg/kg) though the terminal slopes for melanotic and amelanotic cell lines were similar (D10 approximately 31 mg/kg). Time-course studies indicated that there was no significant loss of drug from a melanotic cell line for 72 h after drug administration, though in an amelanotic cell line drug levels fell 10-fold in 10 h. There was, however, no evidence for prolonged drug cytotoxicity in the melanotic cell line. Using a fractionated drug-treatment regime, the greater cytotoxicity of m-AMSA to amelanotic tumour tissue was confirmed in a non-invasive regrowth-delay assay
Influence of anaesthetics on tumour-cell kill and repopulation in B16 melanoma treated with melphalan.
The influence of anaesthetics on the in vivo response of B16 melanoma to melphalan was studied using an in vitro cell-survival assay. Three anaesthetics were used, Saffan (Althesin) Sagatal (Nembutal) and Hypnorm. When Saffan was administered to tumour-bearing animals before melphalan there was a significant increase in tumour-cell kill. This effect was not observed with Sagatal or Hypnorm. Maximum increase in tumour-cell kill was achieved when Saffan was administered about 1 h before melphalan, and was dependent on Saffan dose. Clonogenic tumour-cell repopulation after melphalan was rapid (TD - 1 day) and the rate was similar from 2 levels of cell kill. When Saffan was combined with melphalan the repopulation rate was the same as with melphalan alone, and the increased cell kill was reflected in increased growth delay. The in vitro response of B16 melanoma cells to melphalan was unaltered by pretreatment with, or simultaneous exposure to Saffan. The results suggest that the mechanism of the enhanced cell kill in vivo is probably due to an indirect systemic effect, rather than a direct effect on the tumour cells
Temperature determination via STJ optical spectroscopy
ESA's Superconducting Tunnel Junction (STJ) optical photon-counting camera
(S-Cam2) incorporates an array of pixels with intrinsic energy sensitivity.
Using the spectral fitting technique common in X-ray astronomy, we fit black
bodies to nine stellar spectra, ranging from cool flare stars to hot white
dwarfs. The measured temperatures are consistent with literature values at the
expected level of accuracy based on the predicted gain stability of the
instrument. Having also demonstrated that systematic effects due to count rate
are likely to be small, we then proceed to apply the temperature determination
method to four cataclysmic variable (CV) binary systems. In three cases we
measure the temperature of the accretion stream, while in the fourth we measure
the temperature of the white dwarf. The results are discussed in the context of
existing CV results. We conclude by outlining the prospects for future versions
of S-Cam.Comment: 9 pages, 9 figures (11 files); uses aa.cls; accepted for publication
in A&
Puromycin Sensitivity of Ribosomal Label after Incorporation of 14C-Labelled Amino Acids into Isolated Mitochondria from Neurospora crassa
Radioactive amino acids were incorporated into isolated mitochondria from Neurospora crassa. Then the mitochondrial ribosomes were isolated and submitted to density gradient centrifugation. A preferential labelling of polysomes was observed. However, when the mitochondrial suspension was treated with puromycin after amino acid incorporation, no radioactivity could be detected in either the monosomes or the polysomes. The conclusion is drawn that isolated mitochondria under these conditions do not incorporate significant amounts of amino acids into proteins of their ribosomes
The Power Spectrum of Clusters of Galaxies and the Press-Schechter Approximation
We examine the power spectrum of clusters in the Press-Schechter (PS) theory
and in N-body simulations to see how the power spectrum of clusters is related
to the power spectrum of matter density fluctuations in the Universe. An
analytic model for the power spectrum of clusters for their given number
density is presented, both for real space and redshift space. We test this
model against results from N-body simulations and find that the agreement
between the analytic theory and the numerical results is good for wavelengths
Mpc. On smaller scales non-linear processes that are not
considered in the linear PS approximation influence the result. We also use our
analytic model to study the redshift-space power spectrum of clusters in cold
dark matter models with a cosmological constant (CDM) and with a
scale-invariant Harrison-Zel'dovich initial spectrum of density fluctuations.
We find that power spectra of clusters in these models are not consistent with
the observed power spectra of the APM and Abell-ACO clusters. One possible
explanation for the observed power spectra of clusters is an inflationary
scenario with a scalar field with the potential that has a localized steplike
feature. We use the PS theory to examine the power spectrum of clusters in this
model.Comment: 16 pages, 5 figures. Accepted by Ap
Cosmic Mach Number as a Function of Overdensity and Galaxy Age
We carry out an extensive study of the cosmic Mach number (\mach) on scales
of R=5, 10 and 20h^-1Mpc using an LCDM hydrodynamical simulation. We
particularly put emphasis on the environmental dependence of \mach on
overdensity, galaxy mass, and galaxy age. We start by discussing the difference
in the resulting \mach according to different definitions of \mach and
different methods of calculation. The simulated Mach numbers are slightly lower
than the linear theory predictions even when a non-linear power spectrum was
used in the calculation, reflecting the non-linear evolution in the simulation.
We find that the observed \mach is higher than the simulated mean by more than
2-standard deviations, which suggests either that the Local Group is in a
relatively low-density region or that the true value of \Omega_m is ~ 0.2,
significantly lower than the simulated value of 0.37. We show from our
simulation that the Mach number is a weakly decreasing function of overdensity.
We also investigate the correlations between galaxy age, overdensity and \mach
for two different samples of galaxies --- DWARFs and GIANTs. Older systems
cluster in higher density regions with lower \mach, while younger ones tend to
reside in lower density regions with larger \mach, as expected from the
hierarchical structure formation scenario. However, for DWARFs, the correlation
is weakened by the fact that some of the oldest DWARFs are left over in
low-density regions during the structure formation history. For giant systems,
one expects blue-selected samples to have higher \mach than red-selected ones.
We briefly comment on the effect of the warm dark matter on the expected Mach
number.Comment: 43 pages, including 15 figures. Accepted version in ApJ. Included
correlation function of different samples of galaxies, and the cumulative
number fraction distribution as a fcn. of overdensity. Reorganized figures
and added some reference
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