909 research outputs found

    The Use of Cryogenic HEMT Amplifiers in Wide Band Radiometers

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    Advances in device fabrication, modelling and design techniques have made wide band, low noise cryogenic amplifiers available at frequencies up to 106 GHz. Microwave radiometry applications as used in radio astronomy capitalize on the low noise and large bandwidths of these amplifiers. Radiometers must be carefully designed so as to preclude sensitivity degradations caused by small, low frequency gain fluctuations inherent in these amplifiers

    Offset balancing in pseudo-correlation radiometers for CMB measurements

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    Radiometeric CMB measurements need to be highly stable and this stability is best obtained with differential receivers. The residual 1/f noise in the differential output is strongly dependent on the radiometer input offset which can be cancelled using various balancing strategies. In this paper we discuss a software method implemented in the Planck-LFI pseudo-correlation receivers which uses a tunable "gain modulation factor, r, in the sky-load difference. Numerical simulations and experimental data show how proper tuning of the parameter r ensures a very stable differential output with knee frequencies of the order of few mHz. Various approaches to calculate r using the radiometer total power data are discussed with some examples relevant to Planck-LFI. Although the paper focuses on pseudo-correlation receivers and the examples are relative to Planck-LFI, the proposed method and its analysis is general and can be applied to a large class of differential radiometric receivers.Comment: 12 pages, 8 figures, accepted for publication in A&A (updated version with few editorial changes

    The correlation between the energy gap and the pseudogap temperature in cuprates: the YCBCZO and LSHCO case

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    The paper analyzes the influence of the hole density, the out-of-plane or in-plane disorder, and the isotopic oxygen mass on the zero temperature energy gap (2Δ(0)2\Delta\left(0\right)) for Y1xCaxBa2(Cu1yZny)3O7δ\rm{Y}_{1-x}\rm{Ca}_{x}\rm{Ba}_2\left(\rm{Cu}_{1-y}\rm{Zn}_{y}\right)_{3}\rm{O}_{7-\delta} (YCBCZO) and La1.96xSrxHo0.04CuO4\rm{La}_{1.96-x}\rm{Sr}_{x}\rm{Ho}_{0.04}\rm{CuO}_{4} (LSHCO) superconductors. It has been found that the energy gap is visibly correlated with the value of the pseudogap temperature (TT^{\star}). On the other hand, no correlation between 2Δ(0)2\Delta\left(0\right) and the critical temperature (TCT_{C}) has been found. The above results mean that the value of the dimensionless ratio 2Δ(0)/kBTC2\Delta\left(0\right)/k_{B}T_{C} can vary very strongly together with the chemical composition, while the parameter 2Δ(0)/kBT2\Delta\left(0\right)/k_{B}T^{\star} does not change significantly. In the paper, the analytical formula which binds the zero temperature energy gap and the pseudogap temperature has been also presented.Comment: 7 pages, 4 figures, 3 table

    Specifc Heat and Thermodynamic Critical Field for Calcium under the Pressure at 120 GPa

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    The free energy difference between the superconducting and normal state for Calcium under the pressure at 120 GPa has been determined. The numerical calculations have been made in the framework of the imaginary axis Eliashberg approach. On the basis of the obtained results the specific heat in the superconducting C^{S}(T) and normal C^{N}(T) state, as well as, the thermodynamic critical field H_{C}(T) have been obtained. It has been shown that the characteristic values of the considered thermodynamic quantities do not obey the BCS universal laws. In particular, {\Delta}C(T_{C})/C^N(T_{C})=2.48 and T_{C}C^{N}(T_{C})/H_{C}^{2}(0)=0.154.Comment: 3 pages, 4 figure

    Session A-4: National Archives Resources and the Common Core

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    Discover the online resources of the National Archives and learn how they can support Common Core standards and help build the literacy skills of your students. We will explore sample U.S. history activities relating to the Civil War, American Indians, and World War II during this session

    The Anisotropy in the Cosmic Microwave Background At Degree Angular Scales

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    We detect anisotropy in the cosmic microwave background (CMB) at degree angular scales and confirm a previous detection reported by Wollack et al. (1993). The root-mean-squared amplitude of the fluctuations is 447+13μ44^{+13}_{-7} \muK. This may be expressed as the square root of the angular power spectrum in a band of multipoles between leff=6922+29l_{eff}=69^{+29}_{-22}. We find δTl=l(2l+1)/4π=427+12μ\delta T_l = \sqrt{l(2l+1)/4\pi} = 42^{+12}_{-7} \muK. The measured spectral index of the fluctuations is consistent with zero, the value expected for the CMB. The spectral index corresponding to Galactic free-free emission, the most likely foreground contaminant, is rejected at approximately 3σ3\sigma. The analysis is based on three independent data sets. The first, taken in 1993, spans the 26 - 36 GHz frequency range with three frequency bands; the second was taken with the same radiometer as the first but during an independent observing campaign in 1994; and the third, also take in 1994, spans the 36-46 GHz range in three bands. For each telescope position and radiometer channel, the drifts in the instrument offset are 4 μ\le 4~\muK/day over a period of one month. The dependence of the inferred anisotropy on the calibration and data editing is addressed.Comment: 16 pages, 2 figures. Saskatoon 1993/1994 combined analysi