1,329 research outputs found
Astrophysical Fluids of Novae: High Resolution Pre-decay X-ray spectrum of V4743 Sagittarii
Eight X-ray observations of V4743 Sgr (2002), observed with Chandra and
XMM-Newton are presented. The nova turned off some time between days 301.9 and
371, and the X-ray flux subsequently decreased from day 301.9 to 526 following
an exponential decline time scale of days. We use the absorption
lines present in the SSS spectrum for diagnostic purposes, and characterize the
physics and the dynamics of the expanding atmosphere during the explosion of
the nova. The information extracted from this first stage is then used as input
for computing full photoionization models of the ejecta in V4743 Sgr. The SSS
spectrum is modeled with a simple black-body and multiplicative Gaussian lines,
which provides us of a general kinematical picture of the system, before it
decays to its faint phase (Ness et al. 2003). In the grating spectra taken
between days 180.4 and 370, we can resolve the line profiles of absorption
lines arising from H-like and He-like C, N, and O, including transitions
involving higher principal quantum numbers. Except for a few interstellar
lines, all lines are significantly blue-shifted, yielding velocities between
1000 and 6000 km/s which implies an ongoing mass loss. It is shown that
significant expansion and mass loss occur during this phase of the explosion,
at a rate . Our measurements show that the efficiency of the amount of
energy used for the motion of the ejecta, defined as the ratio between the
kinetic luminosity and the radiated luminosity , is
of the order of one.Comment: 25 pages, 9 figures. Accepted in book: Recent Advances in Fluid
Dynamics with Environmental Applications, pp.365-39
The Status of the Scholarship of Teaching and Learning in Dental Education
The purpose of this study was to determine the current status of the Scholarship of Teaching and Learning (SoTL) within academic dentistry. A twenty-two-item survey was distributed to faculty members of American Dental Education Association (ADEA) member schools asking about their awareness of SoTL practices, perceived barriers to SoTL application, and ways to enhance SoTL activity. Four hundred thirty surveys with equal distribution of assistant, associate, and full professors were received (this may be considered a response rate of 5.4 percent out of roughly 8,000 ADEA faculty members). Almost 70 percent of the respondents indicated that they highly valued SoTL; only 2.1 percent indicated they did not. The extent to which the respondents valued SoTL was positively correlated with their perception of SoTLâs value among other faculty members in their program (r(322)=0.374, p\u3c0.001), school (r(299)=0.204, p\u3c0.001), and institution (r(233)=0.296, p\u3c0.002). However, the respondents were generally unsure how SoTL was applied at their institutions. Respondents from private institutions reported making more SoTL presentations at conferences than did those from public institutions (t(303)=-2.761, p=0.006) and stronger promotion of SoTL in their institutional policies (t(330)=-3.004, p=0.003). Barriers to changing the perception and application of SoTL appeared to exist at both organizational and individual levels, and ADEA was perceived to be well positioned to assist with both
First Light Measurements of Capella with the Low Energy Transmission Grating Spectrometer aboard the Chandra X-ray Observatory
We present the first X-ray spectrum obtained by the Low Energy Transmission
Grating Spectrometer (LETGS) aboard the Chandra X-ray Observatory. The spectrum
is of Capella and covers a wavelength range of 5-175 A (2.5-0.07 keV). The
measured wavelength resolution, which is in good agreement with ground
calibration, is 0.06 A (FWHM). Although in-flight
calibration of the LETGS is in progress, the high spectral resolution and
unique wavelength coverage of the LETGS are well demonstrated by the results
from Capella, a coronal source rich in spectral emission lines. While the
primary purpose of this letter is to demonstrate the spectroscopic potential of
the LETGS, we also briefly present some preliminary astrophysical results. We
discuss plasma parameters derived from line ratios in narrow spectral bands,
such as the electron density diagnostics of the He-like triplets of carbon,
nitrogen, and oxygen, as well as resonance scattering of the strong Fe XVII
line at 15.014 A.Comment: 4 pages (ApJ letter LaTeX), 2 PostScript figures, accepted for
publication in ApJ Letters, 200
Screening tests for active pulmonary tuberculosis in children
Objectives
This is a protocol for a Cochrane Review (diagnostic). The objectives are as follows:
To determine the sensitivity, specificity, and positive and negative predictive value of 1) the presence of one or more tuberculosis symptoms, or symptom combinations; 2) chest radiography; 3) Xpert MTB/RIF; 4) Xpert Ultra; and 5) combinations of the aforementioned tests as screening tests for detecting active pulmonary tuberculosis in children in the following groups.
Household contacts of a person with active tuberculosis;
School contacts of a person with active tuberculosis;
Other close contacts of a person with active tuberculosis;
Children living with HIV;
Children with pneumonia;
Other risk groups (e.g. children with a history of previous tuberculosis, malnourished children);
Children in the general population in high burden settings Secondary objectives
To compare the accuracy of the different index tests, including different applications of tests (e.g. CXR with any abnormality versus, more specifically, CXR with abnormality suggestive of tuberculosis); we are interested in the accuracy of the index tests in any setting (i.e. community, outpatient, and inpatient).
To investigate potential sources of heterogeneity in accuracy estimates in relation to age group, HIV status, whether the study was conducted in a high tuberculosis burden country, and whether the child received a single screening or more than one screening
Silicate dust in the environment of RS Ophiuchi following the 2006 eruption
We present further Spitzer Space Telescope observations of the recurrent nova
RS Ophiuchi, obtained over the period 208-430 days after the 2006 eruption. The
later Spitzer IRS data show that the line emission and free-free continuum
emission reported earlier is declining, revealing incontrovertible evidence for
the presence of silicate emission features at 9.7 and 18microns. We conclude
that the silicate dust survives the hard radiation impulse and shock blast wave
from the eruption. The existence of the extant dust may have significant
implications for understanding the propagation of shocks through the red giant
wind and likely wind geometry.Comment: 12 pages, 4 figures, accepted for publication in ApJ (Letters
A gene expression signature distinguishes innate response and resistance to proteasome inhibitors in multiple myeloma
Extensive interindividual variation in response to chemotherapy is a major stumbling block in achieving desirable efficacy in the treatment of cancers, including multiple myeloma (MM). In this study, our goal was to develop a gene expression signature that predicts response specific to proteasome inhibitor (PI) treatment in MM. Using a well-characterized panel of human myeloma cell lines (HMCLs) representing the biological and genetic heterogeneity of MM, we created an in vitro chemosensitivity profile in response to treatment with the four PIs bortezomib, carfilzomib, ixazomib and oprozomib as single agents. Gene expression profiling was performed using next-generation high-throughput RNA-sequencing. Applying machine learning-based computational approaches including the supervised ensemble learning methods Random forest and Random survival forest, we identified a 42-gene expression signature that could not only distinguish good and poor PI response in the HMCL panel, but could also be successfully applied to four different clinical data sets on MM patients undergoing PI-based chemotherapy to distinguish between extraordinary (good and poor) outcomes. Our results demonstrate the use of in vitro modeling and machine learning-based approaches to establish predictive biomarkers of response and resistance to drugs that may serve to better direct myeloma patient treatment options
Changes in the red giant and dusty environment of the recurrent nova RS Ophiuchi following the 2006 eruption
We present near-infrared spectroscopy of the recurrent nova RS Ophiuchi (RS Oph) obtained on several occasions after its latest outburst in 2006 February. The 1â5 ÎŒm spectra are dominated by the red giant, but the H i, He i and coronal lines present during the eruption are present in all our observations. From the fits of the computed infrared spectral energy distributions to the observed fluxes, we find Teff= 4200 ± 200 K for the red giant. The first overtone CO bands at 2.3 ÎŒm, formed in the atmosphere of the red giant, are variable. The spectra clearly exhibit an infrared excess due to dust emission longward of 5 ÎŒm; we estimate an effective temperature for the emitting dust shell of 500 K, and find that the dust emission is also variable, being beyond the limit of detection in 2007. Most likely, the secondary star in RS Oph is intrinsically variable
Density functional method for nonequilibrium electron transport
We describe an ab initio method for calculating the electronic structure,
electronic transport, and forces acting on the atoms, for atomic scale systems
connected to semi-infinite electrodes and with an applied voltage bias. Our
method is based on the density functional theory (DFT) as implemented in the
well tested Siesta approach (which uses non-local norm-conserving
pseudopotentials to describe the effect of the core electrons, and linear
combination of finite-range numerical atomic orbitals to describe the valence
states). We fully deal with the atomistic structure of the whole system,
treating both the contact and the electrodes on the same footing. The effect of
the finite bias (including selfconsistency and the solution of the
electrostatic problem) is taken into account using nonequilibrium Green's
functions. We relate the nonequilibrium Green's function expressions to the
more transparent scheme involving the scattering states. As an illustration,
the method is applied to three systems where we are able to compare our results
to earlier ab initio DFT calculations or experiments, and we point out
differences between this method and existing schemes. The systems considered
are: (1) single atom carbon wires connected to aluminum electrodes with
extended or finite cross section, (2) single atom gold wires, and finally (3)
large carbon nanotube systems with point defects.Comment: 18 pages, 23 figure
Feasibility study of parameter estimation of random sampling jitter using the bispectrum
An actual sampling process can be modeled as a random process, which consists of the regular (uniform) deterministic sampling process plus an error in the sampling times which constitutes a zero-mean noise (the jitter). In this paper we discuss the problem of estimating the jitter process. By assuming that the jitter process is an i.i.d. one, with standard deviation that is small compared to the regular sampling time, we show that the variance of the jitter process can be estimated from the n th order spectrum of the sampled data, n =2, 3, i.e., the jitter variance can be extracted from the 2nd-order spectrum or the 3rd-order spectrum (the bispectrum) of the sampled data, provided the continuous signal spectrum is known. However when the signal skewness exceeds a certain level, the potential performance of the bispectrum-based estimation is better than that of the spectrum-based estimation. Moreover, the former can also provide jitter variance estimates when the continuous signal spectrum is unknown while the latter cannot. This suggests that the bispectrum of the sampled data is potentially better for estimating any parameter of the sampling jitter process, once the signal skewness is sufficiently large.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43577/1/34_2005_Article_BF01183740.pd
- âŠ