scholarly journals IUE Observations of White Dwarfs and Hot Subdwarfs

1979 ◽  
Vol 53 ◽  
pp. 107-108
Author(s):  
J. B. Oke
Keyword(s):  
White Dwarfs ◽  
Low Resolution ◽  
Energy Distributions ◽  
International Ultraviolet Explorer ◽  
Non Linear ◽  
Level Shifts ◽  
Radiation Induced ◽  
Hot Subdwarfs ◽  
Multichannel Spectrometer ◽  
Selection Of

The International Ultraviolet Explorer (IUE) has been used by Greenstein and Oke to obtain low resolution spectra from 1150 to 3200 Å of a selection of white dwarfs and hot subdwarfs.The observations can be converted to absolute fluxes so that, by including energy distributions measured with the multichannel spectrometer on the Hale telescope, fluxes can be derived between 1150 and 11000 Å. The IUE absolute fluxes show erratic level shifts of up to 20 percent and probably also smaller changes in the slope. These shifts are probably associated with the level of the radiation induced background coupled with uncertainties in the calibration of the non-linear detectors. In many cases, these anomalies in the fluxes are obvious, but they do decrease the accuracy with which temperatures and gravities can be determined.

scholarly journals A Spectrophotometry Atlas of White Dwarfs Compiled from the IUE Archives

1989 ◽  
Vol 114 ◽  
pp. 149-151
Author(s):  
Steven R. Swanson ◽  
Gary Wegner
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Low Resolution ◽  
Convective Mixing ◽  
The Past ◽  
Molecular Features ◽  
International Ultraviolet Explorer

In the past ten years, more than 775 low resolution spectra of white dwarfs have been taken with the International Ultraviolet Explorer satellite (IUE). This wealth of information has yielded many new discoveries in the field of white dwarf research; a few of which include: the λ1400 and λ1600 quasi-molecular features discovered in hydrogen rich DA white dwarfs (Greenstein 1980; Wegner 1982, 1984; Nelan and Wegner 1985; and Koester et. al. 1985), strong C I lines in some DQ white dwarfs (Koester, Weidemann, and Vauclair 1980; Wegner 1981a,b), and the absence of these same lines in hotter DB white dwarfs by Wegner and Nelan (1987) which may indicate convective mixing (Pelletier et al. 1986).

scholarly journals Relationship between Age and Value of Information for a Noisy Ornstein–Uhlenbeck Process

Entropy ◽  
2021 ◽  
Vol 23 (8) ◽  
pp. 940
Author(s):  
Zijing Wang ◽  
Mihai-Alin Badiu ◽  
Justin P. Coon
Keyword(s):  
Value Of Information ◽  
Markov Models ◽  
Upper Bounds ◽  
Distribution Functions ◽  
Lower And Upper Bounds ◽  
Uhlenbeck Process ◽  
Source Data ◽  
Non Linear ◽  
Queue Model ◽  
Selection Of

The age of information (AoI) has been widely used to quantify the information freshness in real-time status update systems. As the AoI is independent of the inherent property of the source data and the context, we introduce a mutual information-based value of information (VoI) framework for hidden Markov models. In this paper, we investigate the VoI and its relationship to the AoI for a noisy Ornstein–Uhlenbeck (OU) process. We explore the effects of correlation and noise on their relationship, and find logarithmic, exponential and linear dependencies between the two in three different regimes. This gives the formal justification for the selection of non-linear AoI functions previously reported in other works. Moreover, we study the statistical properties of the VoI in the example of a queue model, deriving its distribution functions and moments. The lower and upper bounds of the average VoI are also analysed, which can be used for the design and optimisation of freshness-aware networks. Numerical results are presented and further show that, compared with the traditional linear age and some basic non-linear age functions, the proposed VoI framework is more general and suitable for various contexts.

On Hardware Implementation of Balanced S-boxes

2021 ◽  
Vol 12 (1) ◽  
pp. 8-20
Author(s):  
E. A. Kurganov ◽  
Keyword(s):  
Boolean Functions ◽  
Hardware Implementation ◽  
Circuit Complexity ◽  
Lookup Table ◽  
Synthesis Methods ◽  
Main Indicator ◽  
Non Linear ◽  
Symmetric Ciphers ◽  
Depth And Complexity ◽  
Selection Of

An S-box is a non-linear transformation that takes n bits as input and returns m bits. This transformation is most easily represented as a nm lookup table. Most often, only balanced S-boxes are used in cryptography. This means that the number of input bits is equal to the number of output bits. The S-box is an important part of most symmetric ciphers. The selection of the correct substitution makes the link between the key and the ciphertext more complex (non-linear), which makes it much more difficult to hack. This paper deals with a hardware implementation of S-boxes. This implementation can be realized by using logical conjunction, disjunction, negation and delay blocks. The main indicator of productivity of such implementations is a circuit depth, namely the maximum length of a simple way of the circuit and a circuit complexity, namely the quantity of logic elements (negation elements are not taken into account). The article considers the standard synthesis methods (based on DNF, Shannon, Lupanov), proposes a new algorithm to minimize the complexity of an arbitrary Boolean functions system and a way to reduce the complexity of the circuit obtained after simplification by the ESPRESSO algorithm of DNF of the function related to the output of the S-box. To compare the efficiency of the methods, the C++ program was created that generates a circuit in the Verilog language. The estimates of depth and complexity are obtained for the schemes produced as a result of the programs operation. The article ends with a comparison of the efficiency of S-box schemes of known cryptographic standards obtained as the output of the program (with each other and with the result of the Logic Friday program).

In vitro Technique for Selection of Radiation Induced Mutants of Tall Fescue

2013 ◽  
Vol 19 (1) ◽  
pp. 63-68
Author(s):  
Ki-Won Lee ◽  
Jin Young Moon ◽  
Hee Chung Ji ◽  
Gi Jun Choi ◽  
Ki-Yong Kim ◽  
...  
Keyword(s):  
Tall Fescue ◽  
In Vitro Technique ◽  
Induced Mutants ◽  
Radiation Induced ◽  
Selection Of

scholarly journals Generalized Theory of Shell Flash and Accreting White Dwarfs

1981 ◽  
Vol 93 ◽  
pp. 191-206
Author(s):  
Daiichiro Sugimoto ◽  
Shigeki Miyaji
Keyword(s):  
White Dwarfs ◽  
Dissipative System ◽  
Finite Amplitude ◽  
Recurrence Time ◽  
Near Surface ◽  
Giant Stars ◽  
Deep Interior ◽  
Non Linear ◽  
Red Giant ◽  
Linear Oscillation

Shell flashes take place both in deep interior of red giant stars and near surface of accreting white dwarfs. Theories of shell flashes have been thus far presented piece by piece in different papers. It is the purpose of the present review to construct and generalize them in order to reach better understanding. A non-linear yet almost analytical theory is presented which treats the development of the shell flash in finite amplitude. Recurrence of the shell flashes is also shown to be well understood as a non-linear oscillation in dissipative system which tends to be its limit cycle. As a result strength of the peak energy-generation and recurrence time of the shell flashes are related with mass of the accreting white dwarfs, accretion rate, etc.

scholarly journals IUE Observations of Quasars

1980 ◽  
Vol 92 ◽  
pp. 125-126
Author(s):  
M. Schmidt ◽  
R. F. Green ◽  
J. R. Pier ◽  
F. B. Estabrook ◽  
A. L. Lane ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Resonance Transition ◽  
Energy Distributions ◽  
International Ultraviolet Explorer ◽  
Visible Spectra ◽  
Line Transfer ◽  
Net Flux ◽  
Low Dispersion

Spectra of six quasars have been obtained with the International Ultraviolet Explorer Satellite. Five of the six show no evidence for strong Lyα absorption between the redshifted and rest wavelengths, for .23≤ zem ≤1.72. In addition, the quasar PG 1115+080 at z=1.72 shows no evidence for strong He I absorption from the resonance transition at λ584 Å. These results confirm that the intergalactic medium must be both tenuous and hot enough to produce an optical depth <0.1 in neutral hydrogen and helium. In no case was the Lyman edge detected in absorption near zem. Four of the objects produce an average Lyα/Hβ intensity ratio of 6.3, in disagreement with the theoretical prediction for Case B optically thick recombination of 30. Also, two of the objects show Lyγ in emission, a result unexpected from Case B line transfer assumptions. The Lyα emission line in 3C 351 shows the identical sharp core plus 20,000 km s−1 broad wings observed in Hβ and Mg II, implying a common origin in the same dynamical ensemble of emitting regions. These quasars show systematically steeper spectral indices when the energy distributions are fit from the ultraviolet through the visible than those derived from the visible spectra alone. PG 1115+080 shows a featureless continuum down to an observed λ1173 Å. The ionizing spectrum, with fν αν−2.0, therefore persists beyond 2 Rydbergs. The spectrum of PG 1247+268, with z=2.038, contains a strong absorption line at observed λ2697 Å, with no net flux detected from λ2000 Å down to the observed limit at λ1150 Å. This result is interpreted as absorption in Lyα and the Ly edge at z=1.218. Low dispersion optical spectra show no evidence for Mg II or C IV absorption in the same system; the signal to noise ratio is too low in the IUE spectrum to confirm Lyβ. We conclude that the line of sight intersects a metal-poor cloud with τ ≲ 1 in the Ly continuum, at (1+zem)/(1 + zabs) = 1.37.

scholarly journals The Status of the Absolute Calibration of Stellar Fluxes Between 912 and 1200 Å

1985 ◽  
Vol 111 ◽  
pp. 479-483
Author(s):  
R. S. Polidan ◽  
J. B. Holberg
Keyword(s):  
Planetary Nebula ◽  
White Dwarfs ◽  
Main Sequence ◽  
Absolute Calibration ◽  
Energy Distributions ◽  
B Stars ◽  
The Status ◽  
The Absolute ◽  
Flux Calibration

Recent results have shed new light on the status of the calibration of absolute stellar fluxes between 912 and 1200 Å. Observations of hot white dwarfs, subdwarfs and planetary nebula nuclei with the Voyager ultraviolet spectrometers provide evidence that the current calibration agrees very well with extrapolations of IUE energy distributions shortwards of 1200 Å. Voyager observations of main sequence B-stars used as flux calibration sources have revealed that many are variable in brightness in the 912–1200 Å region. We conclude there is no current observational motivation for any revision of the 912 to 1200 Å calibration described by Holberg et al. (1982).

scholarly journals Model Atmospheres for Very Cool Hydrogen-Rich White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 236-239
Author(s):  
France C. Allard ◽  
Rainer Wehrse
Keyword(s):  
White Dwarfs ◽  
Gas Pressure ◽  
Special Consideration ◽  
Solar Photosphere ◽  
Energy Distributions ◽  
Effective Temperatures ◽  
Cool White Dwarfs

In recent years cool white dwarfs have been studied for various aspects ( see e.g.Winget et al.,1987 Winget and van Horn, 1987, Koester, 1987, Llebert, 1980) and much effort has been Invested in attempts to interpret the energy distributions of these stars ( Greenstein, 1984, Zeldler-K.T. et al, 1986, Llebert et al., 1987, and others). However, it seems that in spite of these efforts the spectra in particular of the very cool objects with effective temperatures below about 6000 K are not yet fully under-stood, since they are extremely diverse and each objects needs special consideration. In addition, the analyses are extremely difficult because the principal constiuents of the atmospheres ( H, He ) and elements, which may donate the majority of electrons, are essentially invisible. Since usually only one ionlsatlon stage of an element is present, this implies that the gas pressure Pg is high ( compared e.g. to the solar photosphere ), the accurate value of Pg, however, cannot be determined reliably.

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