9,231 research outputs found
The periods of the intermediate polar RX J0153.3+7446
We present the first optical photometry of the counterpart to the candidate
intermediate polar RX J0153.3+7446. This reveals an optical pulse period of
2333s +/- 5s. Reanalysis of the previously published ROSAT X-ray data reveals
that the true X-ray pulse period is probably 1974s +/- 30s, rather than the
1414 s previously reported. Given that the previously noted orbital period of
the system is 3.94 h, we are able to identify the X-ray pulse period with the
white dwarf spin period and the optical pulse period with the rotation period
of the white dwarf in the binary reference frame, as commonly seen in other
intermediate polars. We thus confirm that RX J0153.3+7446 is indeed a typical
intermediate polar.Comment: 4 pages, submitted to A&A Letter
The spin periods of magnetic cataclysmic variables
We have used a model of magnetic accretion to investigate the rotational equilibria of magnetic cataclysmic variables (mCVs). This has enabled us toderive a set of equilibrium spin periods as a function of orbital period and magnetic moment which we use to estimate the magnetic moments of all known intermediate polars. We further show how these equilibrium spin periods relate to the polar synchronisation condition and use these results to calculate the theoretical histogram describing the distribution of magnetic CVs as a function of P_spin / P_orb. We demonstrate that this is in remarkable agreement with the observed distribution assuming that the number of systems as a function of white dwarf magnetic moment is distributed according to N(mu_1) ~ mu_1^-2
The X-ray properties of the magnetic cataclysmic variable UUColumbae
Aims. XMM-Newton observations to determine for the first time the broad-band X-ray properties of the faint, high galactic latitude intermediate polar UUCol are presented.
Methods. We performed X-ray timing analysis in different energy ranges of the EPIC cameras, which reveals the dominance of the 863 s white dwarf rotational period. The spin pulse is strongly energy dependent. Weak variabilities at the beat 935 s and at the 3.5 h orbital periods are also observed, but the orbital modulation is detected only below 0.5 keV. Simultaneous UV and optical photometry shows that the spin pulse is anti-phased with respect to the hard X-rays. Analysis of the EPIC and RGS spectra reveals
the complexity of the X-ray emission, which is composed of a soft 50 eV black–body component and two optically thin emission components at 0.2 keV and 11 keV strongly absorbed by dense material with an equivalent hydrogen column density of 1023 cm−2 that partially (50%) covers the X-ray source.
Results. The complex X-ray and UV/optical temporal behaviour indicates that accretion occurs predominantly (∼80%) via a disc with a partial contribution (∼20%) directly from the stream. The main accreting pole dominates at high energies whilst the secondary pole mainly contributes in the soft X-rays and at lower energies. The bolometric flux ratio of the soft-to-hard X-ray emissions is found to be consistent with the prediction of the standard accretion shock model. We find the white dwarf in UUCol accretes at a low rate and possesses a low magnetic moment. It is therefore unlikely that UUCol will evolve into a moderate field strength polar, so that the soft X-ray intermediate polars still remain an enigmatic small group of magnetic cataclysmic variables
X-ray Orbital Modulations in Intermediate Polars
We present an analysis of 30 archival ASCA and RXTE X-ray observations of 16
intermediate polars to investigate the nature of their orbital modulation. We
show that X-ray orbital modulation is widespread amongst these systems, but not
ubiquitous as indicated by previous studies that included fewer objects. Only
seven of the sixteen systems show a clearly statistically significant
modulation depth whose amplitude decreases with increasing X-ray energy.
Interpreting this as due to photoelectric absorption in material at the edge of
an accretion disc would imply that such modulations are visible for all system
inclination angles in excess of 60 degrees. However, it is also apparent that
the presence of an X-ray orbital modulation can appear and disappear on a
timescale of ~years or months in an individual system. This may be evidence for
the presence of a precessing, tilted accretion disc, as inferred in some low
mass X-ray binaries.Comment: Accepted for publication in Astronomy & Astrophysics. 9 pages of
text, plus 5 pages of tables, plus 33 pages of figure
Modelling chemotherapy resistance in palliation and failed cure
The goal of palliative cancer chemotherapy treatment is to prolong survival and improve quality of life when tumour eradication is not feasible. Chemotherapy protocol design is considered in this context using a simple, robust, model of advanced tumour growth with Gompertzian dynamics, taking into account the effects of drug resistance. It is predicted that reduced chemotherapy protocols can readily lead to improved survival times due to the effects of competition between resistant and sensitive tumour cells. Very early palliation is also predicted to quickly yield near total tumour resistance and thus decrease survival duration. Finally, our simulations indicate that failed curative attempts using dose densification, a common protocol escalation strategy, can reduce survival times
Electrically conductive fibers thermally isolate temperature sensor
Mounting assembly provides thermal isolation and an electrical path for an unbacked thermal sensor. The sensor is suspended in the center of a plastic mounting ring from four plastic fibers, two of which are coated with an electrically conductive material and connected to electrically conductive coatings on the ring
Cancer and nonextensive statistics
We propose a new model of cancer growth based on nonextensive entropy. The
evolution equation depends on the nonextensive parameter q. The exponential,
the logistic, and the Gompertz growth laws are particular cases of the
generalized model. Experimental data of different tumors have been shown to
correspond to all these tumor-growth laws. Recently reported studies suggest
the existence of tumors that follow a power law behavior. Our model is able to
fit also these data for q<1. We show that for q<1, the commonly used
constant-intensity therapy is unable to reduce the tumor size to zero. As is
the case of the Gompertzian tumors, for- q<1 a late-intesification schedule is
needed. However, these tumors with q<1 are even harder to cure than the
Gompertzian ones. While for a Gompertzian tumor a linearly-increasing cell-kill
function is enough to reduce the tumor size to zero following an exponential
decay, in the case of tumors with q<1, the exponential decay is obtained only
with an exponentially increasing cell-kill function. This means that these
tumors would need an even more aggressive treatment schedule. We have shown
that for Gompertzian tumors a logarithmic late-intensification is sufficient
for the asymptotic reduction of the tumor-size to zero. This is not the fastest
way but it is more tolerable for patients. However for the tumors with q<1 we
would need at least a linearly increasing therapy in order to achieve a
similarly effective reduction. When q>1, tumor size can be reduced to zero
using a traditional constant-intensity therapy.Comment: 5 figure
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