The limits of filopodium stability

Filopodia are long, finger-like membrane tubes supported by cytoskeletal filaments. Their shape is determined by the stiffness of the actin filament bundles found inside them and by the interplay between the surface tension and bending rigidity of the membrane. Although one might expect the Euler buckling instability to limit the length of filopodia, we show through simple energetic considerations that this is in general not the case. By further analyzing the statics of filaments inside membrane tubes, and through computer simulations that capture membrane and filament fluctuations, we show under which conditions filopodia of arbitrary lengths are stable. We discuss several in vitro experiments where this kind of stability has already been observed. Furthermore, we predict that the filaments in long, stable filopodia adopt a helical shape

A varactor tuned low-cost 24 GHz harmonic VCO

We present a low-cost 24 GHz VCO that is based on a microstrip design combined with discrete packaged devices. The output frequency is generated by a harmonic oscillator. The tunabilty was reached using a varactor diode. Two versions of the VCO were built, one has a wide tuning range of 1.1 GHz and the other one has a high output power of 3.7 dBm

Tuning of structure inversion asymmetry by the δ\delta-doping position in (001)-grown GaAs quantum wells

Structure and bulk inversion asymmetry in doped (001)-grown GaAs quantum wells is investigated by applying the magnetic field induced photogalvanic effect. We demonstrate that the structure inversion asymmetry (SIA) can be tailored by variation of the delta-doping layer position. Symmetrically-doped structures exhibit a substantial SIA due to impurity segregation during the growth process. Tuning the SIA by the delta-doping position we grow samples with almost equal degrees of structure and bulk inversion asymmetry.Comment: 4 pages 2 figure