The genes for the beta (rpoB) and beta' (rpoC) subunits of Escherichia coli RNA polymerase are the distal members of a complex transcriptional unit that contains four upstream ribosomal protein genes. The RNA polymerase subunit genes are transcribed at a lower frequency than the ribosomal protein genes as a result of termination at an attenuator preceding rpoB. A purified in vitro transcription...

We have investigated the mechanism of transcription termination by T7 RNA polymerase using templates encoding variants of the transcription-termination structure (attenuator) of the regulatory region of the threonine (thr) operon of Escherichia coli. The thr attenuator comprises the following two distinct structural elements: a G + C-rich inverted repeat, which encodes an RNA hairpin structure,...

The Lorentz group is the fundamental language for space-time symmetries of relativistic particles. This group can these days be derived from the symmetries observed in other branches of physics. It is shown that this group can be derived from optical filters. The group O(2,1) is appropriate for attenuation filters, while the O(3) group describes phase-shift filters. The combined operation leads...

In this paper, we present a THz attenuator based on the sub-wavelength metal s tructures. The T Hz attenuator is designed and fabricated on a copper foil. We measured TH z transmission of the at tenuator by means of terahertz time domain spectroscopy. The experimental results s how th at the attenuator ca n h ave a good frequency selectivity which depends on the polarization of THz radiati on. ...

We present a scheme to generate a 10 GHz optical frequency comb that is bandwidth reconfigurable on a time scale of tens of nanoseconds via electronic control of the drive signal to a phase modulator. When such a comb is used as the source for a radio-frequency (RF) photonic filter employing dispersive propagation, the RF filter bandwidth varies in inverse proportion to the optical bandwidth. A...

This paper presents the 4~6GHz 6-bit MMIC digital attenuator with low phase shift. Phase compensation techniques were used in the MMIC design to reduce the phase shift. This attenuator is fabricated with 0.25μm GaAs PHEMT process. Simulation results of the developed MMIC chips in the 4~6GHz show that the 6-bit MMIC digital attenuator has 0.5dB resolution and 31.5dB dynamic attenuation range, in...

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling tube (TWT) and studied by simulations experiments. The ASML SWS simplifies the fabrication assembly process of traditional planar metal meander-lines (MLs) structures, employing an to support ML on bottom enclosure rather than welding them together sides. To reduce surface roughness molybd...

This paper presents the x-band 5-bit MMIC digital attenuator with low phase shift. Phase compensation techniques were used in the MMIC design to reduce the phase shift. This attenuator is fabricated with 0.2μm GaAs PHEMT process. Measurement results of the developed MMIC chips in the xband show that the 5-bit MMIC digital attenuator has 0.5dB resolution and 15.5dB dynamic attenuation range, inp...

We introduce a technique for ultrawideband measurement of terahertz pulses called dithered-edge sampling ~DES!. The technique makes use of a photoconductive receiver, but the detection bandwidth is much wider than that of the receiver alone. The key to increasing the bandwidth is the addition of an ultrafast optically triggered attenuator that chops the terahertz pulse before its detection. The...