اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA Novel Precise Method for Correcting the Temperature in Stellar Atmosphere Models
72
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A mayor problem that arises in the computation of stellar atmosphere models is the self consistent determination of the temperature distribution via the constraint of energy conservation. The energy balance includes the gains due to the absorption of radiation and the losses due to emission. It is well known that within each one of the two above integrals the part corresponding to spectral ranges whose opacity X(nu) is huge can overcome by many orders of magnitude the part that corresponds to the remaining frequencies. On the other hand, at those frequencies where X(nu) is very large, the mean intensity J(nu) of the radiation field shall be equal, up to many significant digits, to the source function S(nu) and consequently to the Planck function B(nu,T). Then their net share to the energy balance shall be null, albeit separately their contributions to the gain and loss integrals are the most important numerically. Thus the spectral range whose physical contribution to the overall balance is null will dominate numerically both sides of the energy balance equation, and consequently the errors on the determination of J(nu) and S(nu) at these frequencies will falsify the balance. It is possible to circumvent the numerical problem brought about by the foregoing circumstances by solving the radiative transfer equation for the variable I(n,nu) - S(nu), instead of the customary intensity I(n,nu). We present here a novel iterative algorithm, based on iteration factors already employed by us with success, which makes it possible a fast correction of the temperature by computing directly the difference between the radiative losses and gains at each step of the iterations.
قيم البحث
اقرأ أيضاً
The most common method to measure direct current high voltage (HV) down to the ppm-level is to use resistive high-voltage dividers. Such devices scale the HV into a range where it can be compared with precision digital voltmeters to reference voltage
s sources, which can be traced back to Josephson voltage standards. So far the calibration of the scale factors of HV dividers for voltages above 1~kV could only be done at metrology institutes and sometimes involves round-robin tests among several institutions to get reliable results. Here we present a novel absolute calibration method based on the measurement of a differential scale factor, which can be performed with commercial equipment and outside metrology institutes. We demonstrate that reproducible measurements up to 35~kV can be performed with relative uncertainties below $1cdot10^{-6}$. This method is not restricted to metrology institutes and offers the possibility to determine the linearity of high-voltage dividers for a wide range of applications.
Telescopes for observing the Cosmic Microwave Background (CMB) usually have shields and baffle structures in order to reduce the pickup from the ground. These structures may introduce unwanted sidelobes. We present a method to measure and model baffl
ing structures of large aperture telescope optics to predict the sidelobe pattern.
We present a high-resolution microwave spectrometer to measure the frequency-dependent complex conductivity of a superconducting thin film near the critical temperature. The instrument is based on a broadband measurement of the complex reflection coe
fficient, $S_{rm 11}$, of a coaxial transmission line, which is terminated to a thin film sample with the electrodes in a Corbino disk shape. In the vicinity of the critical temperature, the standard calibration technique using three known standards fails to extract the strong frequency dependence of the complex conductivity induced by the superconducting fluctuations. This is because a small unexpected difference between the phase parts of $S_{rm 11}$ for a short and load standards gives rise to a large error in the detailed frequency dependence of the complex conductivity near the superconducting transition. We demonstrate that a new calibration procedure using the normal-state conductivity of a sample as a load standard resolves this difficulty. The high quality performance of this spectrometer, which covers the frequency range between 0.1 GHz and 10 GHz, the temperature range down to 10 K, and the magnetic field range up to 1 T, is illustrated by the experimental results on several thin films of both conventional and high temperature superconductors.
We present a novel method for precisely determining the running QCD coupling constant $alpha_s(Q^2)$ over a wide range of $Q^2$ from event shapes for electron-positron annihilation measured at a single annihilation energy $sqrt{s}$. The renormalizati
on scale $Q^2$ of the running coupling depends dynamically on the virtuality of the underlying quark and gluon subprocess and thus the specific kinematics of each event. The determination of the renormalization scale for event shape distributions is obtained by using the Principle of Maximum Conformality (PMC), a rigorous scale-setting method for gauge theories which satisfies all the requirements of Renormalization Group Invariance, including renormalization-scheme independence and consistency with Abelian theory in the $N_C to 0$ limit. In this paper we apply the PMC to two classic event shapes measured in $e^+ e^-$ annihilation: the thrust ($T$) and C-parameter ($C$). The PMC renormalization scale depends differentially on the values of $T$ and $C$. The application of PMC scale-setting determines the running coupling $alpha_s(Q^2)$ to high precision over a wide range of $Q^2$ from $10$ to $250~rm{GeV}^2$ from measurements of the event shape distributions at the $Z^0$ peak. The extrapolation of the running coupling using pQCD evolution gives the value $alpha_s(M^2_Z)=0.1185pm0.0012$ from the thrust, and $alpha_s(M^2_Z)=0.1193^{+0.0021}_{-0.0019}$ from the C-parameter in the $bar{rm{MS}}$ scheme. These determinations of $alpha_s(M^2_Z)$ are consistent with the world average and are more precise than the values obtained from analyses of event shapes currently used in the world average. The highly-consistent results for the $T$ and $C$ event-shape distributions provide an additional verification of the applicability of the PMC to pQCD.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
