909 research outputs found

### The Use of Cryogenic HEMT Amplifiers in Wide Band Radiometers

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

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

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 ($2\Delta\left(0\right)$) for
$\rm{Y}_{1-x}\rm{Ca}_{x}\rm{Ba}_2\left(\rm{Cu}_{1-y}\rm{Zn}_{y}\right)_{3}\rm{O}_{7-\delta}$
(YCBCZO) and $\rm{La}_{1.96-x}\rm{Sr}_{x}\rm{Ho}_{0.04}\rm{CuO}_{4}$ (LSHCO)
superconductors. It has been found that the energy gap is visibly correlated
with the value of the pseudogap temperature ($T^{\star}$). On the other hand,
no correlation between $2\Delta\left(0\right)$ and the critical temperature
($T_{C}$) has been found. The above results mean that the value of the
dimensionless ratio $2\Delta\left(0\right)/k_{B}T_{C}$ can vary very strongly
together with the chemical composition, while the parameter
$2\Delta\left(0\right)/k_{B}T^{\star}$ 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

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

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

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 $44^{+13}_{-7}
\mu$K. This may be expressed as the square root of the angular power spectrum
in a band of multipoles between $l_{eff}=69^{+29}_{-22}$. We find $\delta T_l =
\sqrt{l(2l+1)/4\pi} = 42^{+12}_{-7} \mu$K. 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 $3\sigma$.
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 $\le 4~\mu$K/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

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