Membrane-transferring regions of gp41 as targets for HIV-1 fusion inhibition and viral neutralization

12 páginas, 4 figurasThe fusogenic function of HIV-1 gp41 transmembrane Env subunit relies on two different kinds of structural elements: i) a collapsible ectodomain structure (the hairpin or six-helix bundle) that opens and closes, and ii) two membrane- transferring regions (MTRs), the fusion peptide (FP) and the membrane-proximal external region (MPER), which ensure coupling of hairpin closure to apposition and fusion of cell and viral membranes. The isolation of naturally produced short peptides and neutralizing IgG-s, that interact with FP and MPER, respectively, and block viral infection, suggests that these conserved regions might represent useful targets for clinical intervention. Furthermore, MTR-derived peptides have been shown to be membrane-active. Here, it is discussed the potential use of these molecules and how the analysis of their membrane activity in vitro could contribute to the development of HIV fusion inhibitors and effective immunogensThe authors wish to thank financial support obtained from Spanish MICINN (BIO2008- 00772) (JLN) and University of the Basque Country (GIU 06/42 and DIPE08/12) (NH and JLN).Peer reviewe

Characterization, Analysis and Modelling of DC and Dynamic Properties of GaN HFETs Grown on Silicon

Due to the increase in the demand for more efficient and reliable power switches, gallium nitride based devices have been long foreseen as eventual replacement for silicon technology. Due to their superior material properties, GaN-based devices are able to deliver much higher output power and handle higher driving voltages than their silicon counterparts for the same die area. GaN-based devices still face significant hurdles towards an industrial integration in the current power electronics, as these devices still fall short from their actual potential with record devices still significantly distant from the theoretical material limits.GaN on silicon (or GaN-on-Si) represents a viable solution for a wider adoption of GaN devices. On one hand, GaN-on-Si technology will benefit from the well-established Si foundries for device processing. On the other hand, the availability of large-diameter silicon wafers will bring down manufacturing costs. Growing GaN on a foreign substrate such as silicon will add, nonetheless, epitaxial complexity higher dislocation densities which can jeopardize the device performance.During the course of this work, DC and dynamic properties of power transistors fabricated on GaN-on-Si wafers are intensively investigated. The analysis is focused on the voltage-blocking capabilities and the losses in conduction during dynamic operation of these transistors. These two parameters were chosen as they represent the most straightforward criteria in choosing an efficient and reliable transistor for a power switch.The voltage-blocking capabilities of the devices are limited by the leakage current flowing through the device in the off-state. The source of this leakage current is due to carrier injection from the grounded silicon substrate and the background doping of the GaN buffer. To tackle the first problem, the source of the injected carriers was suppressed via altering the initial growth conditions of the GaN-on-Si epitaxial stack. To address the second challenge, compensation doping of the GaN buffer using carbon was adopted. Losses in electrical conduction during dynamic operation in GaN devices stems from incomplete recovery of trapped charge carriers. This phenomenon takes place either on the device surface or in the GaN buffer due to surface traps or bulk traps, respectively. Proper surface passivation with PECVD SiNX proves to be the most effective in suppressing surface trapping. This leaves buffer trapping — for example due to carbon compensation doping — as the main contributor to conduction losses during dynamic operation.Specially devised back-gated techniques are used to characterize buffer trapping mechanisms. These techniques were adopted to investigate the effects of various growth parameters and carbon incorporation techniques on the dynamic properties of the GaN buffers. The analysis pointed to the intricate role of charge transport and charge injection in trapping/de-trapping of charge carriers in the GaN buffer

Design and Analysis of a 50GHz InP DHBT Class-E Power Amplifier Providing 2.3 mW/μm²

For the commercial success of mm-wave 5G technologies, there is a need for high-output power and efficient power amplifier systems. In this paper, we demonstrate the capability of InP DHBT devices at the V band and achieve a high power density of 2.3 mW/μm2 at 50GHz. The simulated and measured class E is analysed and compared with an analytical HBT switching model. A single-stage, single-finger of 0.85×6μm2 (emitter area) class E power amplifier is designed to reach this high power density with a PAE of 28.3%