GCRT J1745-3009 as a Transient White Dwarf Pulsar

A transient radio source in the direction of the Galactic Center, GCRT J1745-3009, exhibited 5 peculiar consecutive outbursts at 0.33 GHz with a period of 77.13 minutes and a duration of ~10 minutes for each outburst. It has been claimed to be the prototype of a hitherto unknown class of transient radio sources. We interpret it as a transient white dwarf pulsar with a period of 77.13 minutes. The ~10-minute flaring duration corresponds to the epoch when the radio beam sweeps our line of sight. The bursting epoch corresponds to the episodes when stronger sunspot-like magnetic fields emerge into the white dwarf polar cap region during which the pair production condition is satisfied and the white dwarf behaves like a radio pulsar. It switches off as the pair production condition breaks down.Comment: minor changes, ApJL, in pres

Stability analysis for the background equations for inflation with dissipation and in a viscous radiation bath

The effects of bulk viscosity are examined for inflationary dynamics in which dissipation and thermalization are present. A complete stability analysis is done for the background inflaton evolution equations, which includes both inflaton dissipation and radiation bulk viscous effects. Three representative approaches of bulk viscous irreversible thermodynamics are analyzed: the Eckart noncausal theory, the linear and causal theory of Israel-Stewart and a more recent nonlinear and causal bulk viscous theory. It is found that the causal theories allow for larger bulk viscosities before encountering an instability in comparison to the noncausal Eckart theory. It is also shown that the causal theories tend to suppress the radiation production due to bulk viscous pressure, because of the presence of relaxation effects implicit in these theories. Bulk viscosity coefficients derived from quantum field theory are applied to warm inflation model building and an analysis is made of the effects to the duration of inflation. The treatment of bulk pressure would also be relevant to the reheating phase after inflation in cold inflation dynamics and during the radiation dominated regime, although very little work in both areas has been done, the methodology developed in this paper could be extended to apply to these other problems.Comment: 27 pages, 14 figures, Published version JCA

Evolution and CNO yields of Z=10^-5 stars and possible effects on CEMP production

Our main goals are to get a deeper insight into the evolution and final fates of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to investigate their C, N, and O yields. Using the Monash University Stellar Evolution code we computed and analysed the evolution of stars of metallicity Z = 10^-5 and masses between 4 and 9 M_sun, from their main sequence until the late thermally pulsing (super) asymptotic giant branch, TP-(S)AGB phase. Our model stars experience a strong C, N, and O envelope enrichment either due to the second dredge-up, the dredge-out phenomenon, or the third dredge-up early during the TP-(S)AGB phase. Their late evolution is therefore similar to that of higher metallicity objects. When using a standard prescription for the mass loss rates during the TP-(S)AGB phase, the computed stars lose most of their envelopes before their cores reach the Chandrasekhar mass, so our standard models do not predict the occurrence of SNI1/2 for Z = 10^-5 stars. However, we find that the reduction of only one order of magnitude in the mass-loss rates, which are particularly uncertain at this metallicity, would prevent the complete ejection of the envelope, allowing the stars to either explode as an SNI1/2 or become an electron-capture SN. Our calculations stop due to an instability near the base of the convective envelope that hampers further convergence and leaves remnant envelope masses between 0.25 M_sun for our 4 M_sun model and 1.5 M_sun for our 9 M_sun model. We present two sets of C, N, and O yields derived from our full calculations and computed under two different assumptions, namely, that the instability causes a practically instant loss of the remnant envelope or that the stars recover and proceed with further thermal pulses. Our results have implications for the early chemical evolution of the Universe.Comment: 12 pages, 13 figures, accepted for publication in A&

Broadband telecom transparency of semiconductor-coated metal nanowires: more transparent than glass

Metallic nanowires (NW) coated with a high permittivity dielectric are proposed as means to strongly reduce the light scattering of the conducting NW, rendering them transparent at infrared wavelengths of interest in telecommunications. Based on a simple, universal law derived from electrostatics arguments, we find appropriate parameters to reduce the scattering efficiency of hybrid metal-dielectric NW by up to three orders of magnitude as compared with the scattering efficiency of the homogeneous metallic NW. We show that metal@dielectric structures are much more robust against fabrication imperfections than analogous dielectric@metal ones. The bandwidth of the transparent region entirely covers the near IR telecommunications range. Although this effect is optimum at normal incidence and for a given polarization, rigorous theoretical and numerical calculations reveal that transparency is robust against changes in polarization and angle of incidence, and also holds for relatively dense periodic or random arrangements. A wealth of applications based on metal-NWs may benefit from such invisibility

On the Nature of Precursors in the Radio Pulsar Profiles

In the average profiles of several radio pulsars, the main pulse is accompanied by the preceding component. This so called precursor is known for its distinctive polarization, spectral, and fluctuation properties. Recent single-pulse observations hint that the sporadic activity at the extreme leading edge of the pulse may be prevalent in pulsars. We for the first time propose a physical mechanism of this phenomenon. It is based on the induced scattering of the main pulse radiation into the background. We show that the scattered component is directed approximately along the ambient magnetic field and, because of rotational aberration in the scattering region, appears in the pulse profile as a precursor to the main pulse. Our model naturally explains high linear polarization of the precursor emission, its spectral and fluctuation peculiarities as well as suggests a specific connection between the precursor and the main pulse at widely spaced frequencies. This is believed to stimulate multifrequency single-pulse studies of intensity modulation in different pulsars.Comment: 5 pages, no figures. Accepted for publication in MNRAS Letter

WKB formalism and a lower limit for the energy eigenstates of bound states for some potentials

In the present work the conditions appearing in the WKB approximation formalism of quantum mechanics are analyzed. It is shown that, in general, a careful definition of an approximation method requires the introduction of two length parameters, one of them always considered in the text books on quantum mechanics, whereas the second one is usually neglected. Afterwards we define a particular family of potentials and prove, resorting to the aforementioned length parameters, that we may find an energy which is a lower bound to the ground energy of the system. The idea is applied to the case of a harmonic oscillator and also to a particle freely falling in a homogeneous gravitational field, and in both cases the consistency of our method is corroborated. This approach, together with the Rayleigh--Ritz formalism, allows us to define an energy interval in which the ground energy of any potential, belonging to our family, must lie.Comment: Accepted in Modern Physics Letters

An Empirical Model for the Radio Emission from Pulsars

A model for slow radio pulsars is proposed which involves the entire magnetosphere in the production of the observed radio emission. It is argued that observations of pulsar profiles suggest that a feedback mechanism exists between the star surface and the null charge surface, requiring particle flow in both directions. In their flow to and from the surface the particles execute an azimuthal drift around the magnetic pole, thereby creating a ring of discrete `emission nodes' close to the surface. Motion of the nodes is observed as the well-known subpulse `drift', but is interpreted here as a small residual component of the real particle drift. The nodes can therefore move in either direction, or even remain stationary. A precise fit is found for the pulsar PSR0943+10. Azimuthal interactions between different regions of the magnetosphere depend on the angle between the magnetic and rotation axes and influence the conal type, as observed. The requirement of intermittent weak pair-production in an outergap suggests a natural evolutionary link between radio and gamma-ray pulsars.Comment: 17 pages 8 figure

Routine first-trimester screening for fetal trisomies in twin pregnancy: cell-free DNA test contingent on results from combined test

Objective: To report on the routine clinical implementation of cell-free (cf)DNA analysis of maternal blood for trisomies 21, 18 and 13 contingent on the results of the first-trimester combined test in twin pregnancies. Methods: Screening for trisomies 21, 18 and 13 was carried out by a combination of maternal age, fetal nuchal translucency (NT) thickness, and serum free ß-hCG and PAPP-A at 11-13 weeks’ gestation in 959 twin pregnancies in two UK NHS hospitals. Women in the high-risk group (risk >1 in 100) were offered options of invasive testing, cfDNA testing or no further testing and those in the intermediate-risk group (risk 1 in 101 to 1 in 2500 in the first phase of the study and 1 in 101 to 1 in 500 in the second phase) were offered cfDNA or no further testing. The trisomic status of the pregnancies was determined by prenatal or postnatal karyotyping or examination of the neonates. Results: In 42 (4.4%) of the 959 pregnancies there was termination, miscarriage or stillbirth with no known karyotype or there was loss to follow up. The 917 pregnancies with known trisomic status of both twins, included 6 that were discordant for trisomy 21, 4 discordant for trisomy 18 and 896 with no trisomies 21, 18 or 13. Following combined screening, 47 (5.1%), 203 (22.2%) and 667 (72.7%) of the pregnancies were classified as high-risk, intermediate-risk and low-risk, respectively. The high-risk group included 5 (83.3%) cases of trisomy 21 and 3 (75.0%) of trisomy 18. The cfDNA test was carried out in 224 pregnancies and results were provided in 214 (95.5%); this group included 6 with trisomy 21, 3 with trisomy 18 and 206 with no trisomies 21, 18 or 13. The cfDNA test correctly classified as screen positive all 6 cases of trisomy 21 and 2 of the 3 with trisomy 18 and as screen negative for each of the trisomies all 206 unaffected pregnancies. Contingent screening, led to prenatal detection of all cases of trisomy 21 and 3 of 4 with trisomy 18. Conclusions: The study has demonstrated the feasibility of introducing cfDNA testing, contingent on the results of the first-trimester combined test for major trisomies, in a routine population of twin pregnancies

Keratoacanthoma-like nodules as first manifestation of metastatic epithelioid trophoblastic tumor

Cutaneous metastases are rarely the initial manifestation of a previously undiagnosed malignancy and keratoacanthoma-like lesions are a notoriously unusual presentation pattern of cutaneous dissemination of a primary tumor. Herein, we report a 40-year-old woman presenting to our dermatology department with multiple keratoacanthoma-like scalp nodules. Subsequent investigation determined it to be the first manifestation of a disseminated endometrial epithelioid trophoblastic tumor, eventually causing the patient's death. Epithelioid trophoblastic tumor, a rare form of gestational trophoblastic disease, is a recently described neoplasm whose cutaneous metastasis has not been previously reported in the literature

Dynamics of cholesteric structures in an electric field

Motivated by Lehmann-like rotation phenomena in cholesteric drops we study the transverse drift of two types of cholesteric fingers, which form rotating spirals in thin layers of cholesteric liquid crystal in an ac or dc electric field. We show that electrohydrodynamic effects induced by Carr-Helfrich charge separation or flexoelectric charge generation can describe the drift of cholesteric fingers. We argue that the observed Lehmann-like phenomena can be understood on the same basis.Comment: 4 pages, 4 figures, submitted to PR