4,230 research outputs found
Extragalactic radio sources with sharply inverted spectrum at metre wavelengths
We present the first results of a systematic search for the rare
extragalactic radio sources showing an inverted (integrated) spectrum, with
spectral index , a previously unexplored spectral domain. The
search is expected to yield strong candidates for , for which
the standard synchrotron self-absorption (characterized by a single power-law
energy distribution of relativistic electron population) would not be a
plausible explanation, even in an ideal case of a perfectly homogeneous source
of incoherent synchrotron radiation. Such sharply inverted spectra, if found,
would require alternative explanations, e.g., free-free absorption, or
non-standard energy distribution of relativistic electrons which differs from a
power-law (e.g., Maxwellian).
The search was carried out by comparing two sensitive low-frequency radio
surveys made with sub-arcminute resolution, namely, the WISH survey at 352 MHz
and TGSS/DR5 at 150 MHz. The overlap region between these two surveys contains
7056 WISH sources classified as `single' and brighter than 100 mJy at 352 MHz.
We focus here on the seven of these sources for which we find .
Two of these are undetected at 150 MHz and are particularly good candidates for
. Five of the seven sources exhibit a
`Gigahertz-Peaked-Spectrum' (GPS).Comment: 8 pages, 2 figures, accepted for publication in MNRA
Photon transport in thin disordered slabs
We examine using Monte Carlo simulations, photon transport in optically 'thin' slabs whose thickness L is only a few times the transport mean free path l∗, with particles of different scattering anisotropies. The confined geometry causes an auto-selection of only photons with looping paths to remain within the slab. The results of the Monte Carlo simulations are borne out by our analytical treatment that incorporates directional persistence by the use of the Ornstein-Uhlenbeck process, which interpolates between the short time ballistic and long time diffusive regimes
Treatment of outliers via interpolation method with neural network forecast performances
Outliers often lurk in many datasets, especially in real data. Such anomalous data can negatively affect statistical analyses, primarily normality, variance, and estimation aspects. Hence, handling the occurrences of outliers require special attention. Therefore, it is important to determine the suitable ways in treating outliers so as to ensure that the quality of the analyzed data is indeed high. As such, this paper discusses an alternative method to treat outliers via linear interpolation method. In fact, assuming outlier as a missing value in the dataset allows the application of the interpolation method to interpolate the outliers thus, enabling the comparison of data series using forecast accuracy before and after outlier treatment. With that, the monthly time series of Malaysian tourist arrivals from January 1998 until December 2015 had been used to interpolate the new series. The results indicated that the linear interpolation method, which was comprised of improved time series data, displayed better results, when compared to the original time series data in forecasting from both Box-Jenkins and neural network approaches
Ferromagnetic Ordering in CeIr2B2: Transport, magnetization, specific heat and NMR studies
We present a complete characterization of ferromagnetic system CeIr2B2 using
powder x-ray diffraction XRD, magnetic susceptibility chi(T), isothermal
magnetization M(H), specific heat C(T), electrical resistivity rho(T,H), and
thermoelectric power S(T) measurements. Furthermore 11B NMR study was performed
to probe the magnetism on a microscopic scale. The chi(T), C(T) and rho(T) data
confirm bulk ferromagnetic ordering with Tc = 5.1 K. Ce ions in CeIr2B2 are in
stable trivalent state. Our low-temperature C(T) data measured down to 0.4 K
yield Sommerfeld coefficient gamma = 73(4) mJ/molK2 which is much smaller than
the previously reported value of gamma = 180 mJ/molK2 deduced from the specific
heat measurement down to 2.5 K. For LaIr2B2 gamma = 6(1) mJ/molK2 which implies
the density of states at the Fermi level D(EF) = 2.54 states/(eV f.u.) for both
spin directions. The renormalization factor for quasi-particle density of
states and hence for quasi-particle mass due to 4f correlations in CeIr2B2 is
12. The Kondo temperature TK ~ 4 K is estimated from the jump in specific heat
of CeIr2B2 at Tc. Both C(T) and rho(T) data exhibit gapped-magnon behavior in
magnetically ordered state with an energy gap Eg ~ 3.5 K. The rho data as a
function of magnetic field H indicate a large negative magnetoresistance (MR)
which is highest for T = 5 K.While at 5 K the negative MR keeps on increasing
up to 10 T, at 2 K an upturn is observed near H = 3.5 T. On the other hand, the
thermoelectric power data have small absolute values (S ~ 7 {\mu}V/K)
indicating a weak Kondo interaction. A shoulder in S(T) at about 30 K followed
by a minimum at ~ 10 K is attributed to crystal electric field (CEF) effects
and the onset of magnetic ordering. 11B NMR line broadening provides strong
evidence of ferromagnetic correlations below 40 K.Comment: 10 pages, 11 figure
Magnetic Behavior in RRhX (R = rare earths; X=B, C) Compounds
We report on the magnetic behavior of RRhB (R = La, Ce, Pr, Nd, Gd, Tb and
Tm) and RRhC (R = La, Ce, Pr and Gd) compounds crystallizing in the cubic
perovskite type structure with space group Pm3m. The heat capacity data on
Pauli-paramagnetic LaRhB and LaRhC indicate a high frequency vibrating motion
of boron and carbon atoms in the unit cell. Ce is in -like nonmagnetic state in
both the compounds. Pr compounds show a dominant crystal field effect with a
nonmagnetic singlet ground state in PrRhB and a nonmagnetic quadrupolar doublet
in PrRhC. Compounds with other rare earths order ferromagnetically at low
temperatures except TmRhB in which the zero field evolution of magnetic
interactions is relatively more complicated. The electrical resistivity of
GdRhB decreases with increasing temperature in the paramagnetic state in the
vicinity of T, which is rarely seen in ferromagnets. The behavior is discussed
to be arising due to the short range spin fluctuation and a possible
contribution from Fermi surface geometry.Comment: 14 Figs and a text fil
Tangled magnetic fields and CMBR signal from reionization epoch
We compute the secondary CMBR anisotropy signal from the reionization of the
universe in the presence of tangled magnetic fields. We consider the tangled
magnetic-field-induced scalar, vector, and tensor modes for our analysis. The
most interesting signal for l<10 arise from tensor perturbations. In
particular, we show that the enhancement observed by WMAP in the TE
cross-correlation signal for l<10 could be explained by tensor TE
cross-correlation from tangled magnetic fields generated during the
inflationary epoch for magnetic field strength B_0=4.5*10^{-9}G and magnetic
field power spectrum spectral index n=-2.9. Alternatively, a mixture of tensor
mode signal with primordial scalar modes give weaker bounds on the value of the
optical depth to the reionization surface, tau_{reion}=0.11 +/- 0.02. This
analysis can also be translated to a limit on the magnetic field strength of
nearly 5*10{-9}G for wave-numbers < 0.05 Mpc^{-1}Comment: 28 pages, 6 figures, submitted to Physical Review
Socioeconomic status and cigarette expenditure among US households: results from 2010 to 2015 Consumer Expenditure Survey
Objectives To examine (1) the association between household socioeconomic status (SES) and whether a household spends money on cigarettes and (2) socioeconomic variations in proportion of total household expenditure spent on cigarettes among smoking households.
Methods We pooled data from six consecutive years, 2010–2015, of the Consumer Expenditure Interview Survey. The interviews involved a structured questionnaire about household income, demographics and expenditures including expenditure on cigarettes. Households that reported cigarette expenditure in the previous 3 months were distinguished as smoking households. SES indicators were household poverty status, education and occupation of the head of household. Logistic regression was used to assess the association of household smoking status with SES. Fractional logistic regression was used to assess the association of cigarette expenditure as a proportion of total household expenditure with SES. The analysis sample size was 39 218.
Results The probability of spending money on cigarettes was higher among lower SES households. Households in poverty compared with those above 300% of poverty threshold had 1.86 (95% CI 1.61 to 2.16), households headed by a person with less than high school education compared with those headed by a person with at least a bachelor’s degree had 3.37 (95% CI 2.92 to 3.89) and households headed by a blue-collar work compared with those headed by a person in a managerial occupation had 1.45 (95% CI 1.26 to 1.66) higher odds of spending money on cigarettes. Similarly, the proportion of total household expenditure spent on cigarettes was higher among lower SES smoking households.
Conclusion Lower SES households are more likely to spend money on cigarettes and spend a larger proportion of their total expenditure on cigarettes. We recommend strategies effective in reducing smoking among low SES smokers
- …