Compact single-shot electro-optic detection system for THz pulses with femtosecond time resolution at MHz repetition rates.

Electro-optical detection has proven to be a valuable technique to study temporal profiles of THz pulses with pulse durations down to femtoseconds. As the Coulomb field around a relativistic electron bunch resembles the current profile, electro-optical detection can be exploited for non-invasive bunch length measurements at accelerators. We have developed a very compact and robust electro-optical detection system based on spectral decoding for single-shot longitudinal bunch profile monitoring at the European X-ray Free Electron Laser (XFEL) for electron bunch lengths down to 200 fs (rms). Apart from the GaP crystal and the corresponding laser optics at the electron beamline, all components are housed in 19 in. chassis for rack mount and remote operation inside the accelerator tunnel. An advanced laser synchronization scheme based on radio-frequency down-conversion has been developed for locking a custom-made Yb-fiber laser to the radio-frequency of the European XFEL accelerator. In order to cope with the high bunch repetition rate of the superconducting accelerator, a novel linear array detector has been employed for spectral measurements of the Yb-fiber laser pulses at frame rates of up to 2.26 MHz. In this paper, we describe all sub-systems of the electro-optical detection system as well as the measurement procedure in detail and discuss the first measurement results of longitudinal bunch profiles of around 400 fs (rms) with an arrival-time jitter of 35 fs (rms).

The Human Genome Project and the clinician.

The Florida Supreme Court's decision in Pate v Threlkel is an early warning sing of the massive impact human genome research will have on medical practice. Genetic screening is a scientific tool whose widespread use in clinical medicine will expand due to the combined influences of the federally funded Human Genome Project, biotechnology market forces, and corporate and societal pressures to both use and further develop the technique. Once testing becomes cost-effective, clinicians, by virtue of their position as "knowledgeable professionals" and as the primary source of health information for patients with genetic disorders, will be required to act as gatekeepers to the genetic heritage of their patients. This will seriously impact the legal definitions of reasonable care, a physician's duty to warn, the concept of informed consent, and the confidentiality of medical records.

The role of promoter insertion in the induction of neoplasia.

It has been shown in several retroviral systems that proviral DNA can integrate into the host genome in such a manner that expression of a nearby oncogene is enhanced. This enhancement results from either a direct promotion of transcription from a strong promoter within the proviral 3' LTR or from less well defined activation in which sequences known as 'enhancers' mediate an increase in the transcription of nearby genes. As a result of this observation, potential oncogenes can now be found by identifying genes whose activity is modulated by the nearby insertion of transcriptional activating elements during oncogenesis. It has also been shown that the genome of a retroviral-like IAP can similarly become integrated adjacent to an oncogene and produce an increase in transcription of that gene. Other examples of possible nonviral promoter insertion events that take place in the oncogenesis of the human Burkitt's lymphoma are discussed elsewhere in this volume.

Molecular cloning, sequence analysis and in vitro expression of a rat tRNA gene cluster.

A rat genomic DNA fragment containing a tRNA gene cluster was isolated from a lambda phage library. Hybridization and nucleotide sequence analysis revealed the presence of a 83 bp tRNALeuCUG gene and a 72 bp tRNAAspGUG gene. Both genes possessed intact coding regions and putative transcription termination signals at their respective 3' ends. In vitro transcription analysis of the two subcloned genes in a HeLa cell S-100 system demonstrated the specific synthesis of a number of RNAs by RNA polymerase III. Studies carried out in the presence of alpha-amanitin showed that the larger RNAs are precursors for the final processed transcripts of the tRNALeu and tRNAAsp genes, respectively. Further nucleotide sequence analysis of the cluster revealed the presence of tRNAGly and a tRNAGlu pseudogenes with missing areas within their coding regions which are essential for transcription by RNA polymerase III. Within the region of DNA between the tRNALeu and tRNAAsp genes is a sequence which is 65% homologous to a region of the rat B1 element. The significance of this latter structure within the gene cluster is unknown.