231 research outputs found
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Ion Implanted Ge:B Far Infrard Blocked Impurity BandDetectors
Ge Blocked Impurity Band (BIB) photoconductors have the potential to replace stressed Ge:Ga photoconductors for far-infrared astronomical observations. A novel planar BIB device has been fabricated in which ion-implanted boron is used to form the blocking and absorbing layers of necessary purity and compensation. The effect of doping in the infrared active layer on the far-infrared photoconductive response has been studied, and the optimum doping concentration is found to be {approx} 4 x 10{sup 16} cm{sup -3}. Devices doped near this concentration show good blocking characteristics with low dark currents. The spectral response extends to {approx} 45 cm{sup -1}, clearly showing the formation of an impurity band. Under low background testing conditions these devices attain a responsivity of 0.12 A/W and NEP of 5.23 x 10{sup -15} W/Hz{sup -1/2}
Origin of Pure Spin Superradiance
The question addressed in this paper is: What originates pure spin
superradiance in a polarized spin system placed inside a resonator? The term
"pure" means that no initial coherence is imposed on spins, and its appearance
manifests a purely self-organized collective effect. The consideration is based
on a microscopic model with dipole spin interactions. An accurate solution of
evolution equations is given. The results show that the resonator Nyquist noise
does not play, contrary to the common belief, any role in starting spin
superradiance, but the emergence of the latter is initiated by local spin
fluctuations. The decisive role of nonsecular dipole interactions is stressed.Comment: 1 file, 13 pages, RevTe
Engineering the Electronic Band Structure for Multiband Solar Cells
Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications
Nonlinear Spin Dynamics in Ferromagnets with Electron-Nuclear Coupling
Nonlinear spin motion in ferromagnets is considered with nonlinearity due to
three factors: (i) the sample is prepared in a strongly nonequilibrium state,
so that evolution equations cannot be linearized as would be admissible for
spin motion not too far from equilibrium, (ii) the system considered consists
of interacting electron and nuclear spins coupled with each other via hyperfine
forces, and (iii) the sample is inserted into a coil of a resonant electric
circuit producing a resonator feedback field. Due to these nonlinearities,
coherent motion of spins can develop, resulting in their ultrafast relaxation.
A complete analysis of mechanisms triggering such a coherent motion is
presented. This type of ultrafast coherent relaxation can be used for studying
intrinsic properties of magnetic materials.Comment: 1 file, LaTex, 23 page
A (sub)millimetre study of dense cores in Orion B9
We aim to further constrain the properties and evolutionary stages of dense
cores in Orion B9. The central part of Orion B9 was mapped at 350 micron with
APEX/SABOCA. A sample of nine cores in the region were observed in C17O(2-1),
H13CO+(4-3) (towards 3 sources), DCO+(4-3), N2H+(3-2), and N2D+(3-2) with
APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA
870-micron dust continuum data. Many of the LABOCA cores show evidence of
substructure in the higher-resolution SABOCA image. In particular, we report on
the discovery of multiple very low-mass condensations in the prestellar core
SMM 6. Based on the 350-to-870 micron flux density ratios, we determine dust
temperatures of ~7.9-10.8 K, and dust emissivity indices of ~0.5-1.8. The CO
depletion factors are in the range ~1.6-10.8. The degree of deuteration in N2H+
is ~0.04-0.99, where the highest value (seen towards the prestellar core SMM 1)
is, to our knowledge, the most extreme level of N2H+ deuteration reported so
far. The level of HCO+ deuteration is about 1-2%. We also detected D2CO towards
two sources. The detection of subcondensations within SMM 6 shows that core
fragmentation can already take place during the prestellar phase. The origin of
this substructure is likely caused by thermal Jeans fragmentation of the
elongated parent core. A low depletion factor and the presence of gas-phase
D2CO in SMM 1 suggest that the core chemistry is affected by the nearby
outflow. The very high N2H+ deuteration in SMM 1 is likely to be remnant of the
earlier CO-depleted phase.Comment: 20 pages, 10 figures, 10 tables. Accepted for publication in
Astronomy and Astrophysic
On being a good Bayesian
Bayesianism is fast becoming the dominant paradigm in archaeological chronology construction. This paradigm shift has been brought about in large part by widespread access to tailored computer software which provides users with powerful tools for complex statistical inference with little need to learn about statistical modelling or computer programming. As a result, we run the risk that such software will be reduced to the status of black boxes. This would be a dangerous position for our community since good, principled use of Bayesian methods requires mindfulness when selecting the initial model, defining prior information, checking the reliability and sensitivity of the software runs and interpreting the results obtained. In this article, we provide users with a brief review of the nature of the care required and offer some comments and suggestions to help ensure that our community continues to be respected for its philosophically rigorous scientific approach
Disaster Situation and Humanitarian Emergency â In-Between Responses to the Refugee Crisis in Germany
In 2015, the needs of hundreds of thousands of refugees who arrived in Germany could only be met by deploying all available civil protection units. This article presents procedures and practices of state and non-state formal actors in the field of civil protection and related crisis management structures implemented and established across the board in the municipalities, the Federal Government and mass shelters, in particular in Bavaria. From a disaster research and humanitarian studies perspective we use the concept of âpatterns of interpretationâ to analyse the application of the âhumanitarian emergencyâ and the âdisaster situationâ procedures to discuss whether the situation can really be categorized as âeither-orâ or whether the coexistence of the two served a function in managing such a complex situation. Finally, we discuss some developments that occurred after 2015/16 and consider the extent to which these developments shift or expand the existing patterns of interpretation
Nonlinear Spin Dynamics in Nuclear Magnets
A method is developed for solving nonlinear systems of differential, or
integrodifferential, equations with stochastic fields. The method makes it
possible to give an accurate solution for an interesting physical problem: What
are the peculiarities of nonlinear spin dynamics in nonequilibrium nuclear
magnets coupled with a resonator? Evolution equations for nuclear spins are
derived basing on a Hamiltonian with dipole interactions. The ensemble of spins
is coupled with a resonator electric circuit. Seven types of main relaxation
regimes are found: free induction, collective induction, free relaxation,
collective relaxation, weak superradiance, pure superradiance, and triggered
superradiance. The initial motion of spins can be originated by two reasons,
either by an imposed initial coherence or by local spin fluctuations due to
nonsecular dipole interactions. The relaxation regimes caused by the second
reason cannot be described by the Bloch equations. Numerical estimates show
good agreement with experiment.Comment: 1 file, 47 pages, LaTe
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