Transit-time devices as local oscillators for frequencies above 100 GHz

Very promising preliminary experimental results have been obtained from GaAs IMPATT diodes at F-band frequencies (75 mW, 3.5 percent at 111.1 GHz and 20 mW, 1.4 percent at 120.6 GHz) and from GaAs TUNNETT diodes at W-band frequencies (26 mW, 1.6 percent at 87.2 GHz and 32 mW, 2.6 percent at 93.5 GHz). These results indicate that IMPATT, MITATT and TUNNETT diodes have the highest potential of delivering significant amounts of power at Terahertz frequencies. As shown recently, the noise performance of GaAs W-band IMPATT diodes can compete with that of Gunn devices. Since TUNNETT diodes take advantage of the quieter tunnel injection, they are expected to be especially suited for low-noise local oscillators. This paper will focus on the two different design principles for IMPATT and TUNNETT diodes, the material parameters involved in the design and some aspects of the present device technology. Single-drift flat-profile GaAs D-band IMPATT diodes had oscillations up to 129 GHz with 9 mW, 0.9 percent at 128.4 GHz. Single-drift GaAs TUNNETT diodes had oscillations up to 112.5 GHz with 16 mW and output power levels up to 33 mW and efficiencies up to 3.4 percent around 102 GHz. These results are the best reported so far from GaAs IMPATT and TUNNETT diodes

On the IYB-property in some solvable groups

A finite group G is called Involutive Yang-Baxter (IYB) if there exists a bijective 1-cocycle χ:G⟶M for some ZG -module M. It is known that every IYB-group is solvable, but it is still an open question whether the converse holds. A characterization of the IYB property by the existence of an ideal I in the augmentation ideal ωZG complementing the set 1−G leads to some speculation that there might be a connection with the isomorphism problem for ZG . In this paper we show that if N is a nilpotent group of class two and H is an IYB-group of order coprime to that of N, then N⋊H is IYB. The class of groups that can be obtained in that way (and hence are IYB) contains in particular Hertweck’s famous counterexample to the isomorphism conjecture as well as all of its subgroups. We then investigate what an IYB structure on Hertweck’s counterexample looks like concretely

Time to reappraise or distract? Temporal and situational context in emotion regulation in daily life

Contextual factors influence how people regulate their everyday emotions. While daily life is rich with situations that evoke emotion regulation, few studies have broadly investigated the role of context in regulating emotions in response to naturally occurring negative events. In this study, we use a structured diary technique - the Experience Sampling Method - to test how different types of contextual factors are associated with using reappraisal and distraction to regulate daily emotions in N = 74 young adults from the general population. The following contextual factors were assessed: time of the day, weekday, tiredness, event stressfulness, and event type. We found that higher stressfulness of negative events was associated with using more distraction within- and between-person and using more reappraisal between persons. Time of day and weekday were not associated with reappraisal or distraction use, suggesting that variation in people’s external environments due to temporal patterns does not influence reappraisal or distraction use. However, tiredness was positively associated with distraction and reappraisal use within persons. Exploratory analyses suggested that experiencing time pressure affords less distraction use, and that experiencing physical discomfort affords less reappraisal use. These findings underscore the dynamic nature of emotion regulation, and the importance of context in everyday emotion regulation

African Malaria Control Programs Deliver ITNs and Achieve What the Clinical Trials Predicted

Thomas Eisele and Richard Steketee discuss new research in PLoS Medicine by Stephen Lim and colleagues that examined the association of insecticide-treated nets with the reduction of P. falciparum prevalence in children under 5 and all-cause post-neonatal mortality

D-band (110-170 GHz) InP gunn devices

This paper reports on the development of InP Gunn sources for operation in the D-band (110-170 GHz). n+-n-n+ structures with flat doping as well as graded doping profiles have been considered. Oscillations were obtained at 108.3 GHz from a 1 [mu]m structure with a uniform n doping of 2.5 x 1016 cm-3. The CW RF output power was 33 mW. A 1 [mu]m graded structure with an n doping increasing linearly from 7.5 x 1015 to 2.0 x 1016 cm-3 has resulted in 20 mW at 120 GHz and 10 mW at 136 GHz. These results are believed to correspond to a fundamental mode operation and represent the state-of-the-art performance from InP Gunn devices at these frequencies. This improvement in performance is attributed in part to a processing technique based on the use of etch-stop layers and InGaAs cap layers. An etch-stop layer allows low-profile mesas (2-3 [mu]m) and InGaAs cap layers help reduce the contact resistance, thus minimizing series resistances in the device. In addition, a physical model based on the Monte Carlo method was developed to aid in the design of structures for high frequency operation. Experimental results obtained from a 1.7 [mu]m Gunn device operating at W-band frequencies were used to estimate appropriate InP material parameters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30504/1/0000133.pd

Baryon stopping and strange baryon/antibaryon production at SPS energies

The amount of proton stopping in central Pb+Pb collisions from 20-160 AGeV as well as hyperon and antihyperon rapidity distributions are calculated within the UrQMD model in comparison to experimental data at 40, 80 and 160 AGeV taken recently from the NA49 collaboration. Furthermore, the amount of baryon stopping at 160 AGeV for Pb+Pb collisions is studied as a function of centrality in comparison to the NA49 data. We find that the strange baryon yield is reasonably described for central collisions, however, the rapidity distributions are somewhat more narrow than the data. Moreover, the experimental antihyperon rapidity distributions at 40, 80 and 160 AGeV are underestimated by up to factors of 3 - depending on the annihilation cross section employed - which might be addressed to missing multi-meson fusion channels in the UrQMD model.Comment: 18 pages, including 7 eps figures, to be published in Phys. Rev.

Anomalous quantum confined Stark effects in stacked InAs/GaAs self-assembled quantum dots

Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs) are predicted to exhibit a strong non-parabolic dependence of the interband transition energy on the electric field, which is not encountered in single SAD structures nor in other types of quantum structures. Our study based on an eight-band strain-dependent ${\bf k}\cdot{\bf p}$ Hamiltonian indicates that this anomalous quantum confined Stark effect is caused by the three-dimensional strain field distribution which influences drastically the hole states in the stacked SAD structures.Comment: 4 pages, 4 figure

Renormalization scale uncertainty in tne DIS 2+1 jet cross-section

The deep inelastic scattering 2+1 jet cross- section is a useful observable for precision tests of QCD, e.g. measuring the strong coupling constant alpha(s). A consistent analysis requires a good understanding of the theoretical uncertainties and one of the most fundamental ones in QCD is due to the renormalization scheme and scale ambiguity. Different methods, which have been proposed to resolve the scale ambiguity, are applied to the 2+1 jet cross-section and the uncertainty is estimated. It is shown that the uncertainty can be made smaller by choosing the jet definition in a suitable way.Comment: 24 pages, uuencoded compressed tar file, DESY 94-082, TSL-ISV-94-009