To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years. However, stimulated Raman scattering (SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating (CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area (LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of
is achieved in spectrum at the maximum output laser power of 2.35 kW, and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.
We report here a high-power, wavelength tunable and narrow linewidth
all-fiber laser amplifier based on a tunable diode laser and Er-Yb co-doped fibers. The laser wavelength can be precisely tuned from 1535 nm to 1580 nm, which covers many absorption lines of mid-infrared laser gases, such as
, HCN, CO, and HI. The maximum laser power is
11 W, and the linewidth is about 200–300 MHz, which is close to the absorption linewidth of the above-mentioned gases. This work provides a suitable pump source for high-power wavelength tunable mid-infrared fiber gas lasers based on low-loss hollow-core fibers.
Mark E. Drew, Dept. of Mol. Microbiology, Washington University School of Medicine,
Shawn A. Motyka, Department of Biological Chemistry, Johns Hopkins Medical School,
James C. Morris, Department of Genetics, Biochemistry and Life Science Studies, Clemson University,
Zefeng Wang, Dept. of Mol. Microbiology, Washington University School of Medicine,
Paul T. Englund, Department of Biological Chemistry, Johns Hopkins Medical School
In December 1998 the Ullu lab at Yale published the first report of dsRNA-mediated mRNA degradation in Trypanosoma brucei (Ngo et al., 1998). These experiments used either electroporation of in vitro synthesized dsRNA or transient in vivo expression of single-strand RNA that forms a stem–loop structure capable of inducing RNAi. At that time, the arsenal of genetic techniques available to the trypanosome researcher was limited (Clayton, 1999). For example, gene knockout was possible through homologous recombination, although the diploid genome of T. brucei complicated this approach. Furthermore, essential genes were difficult to examine by knockout, necessitating complex strategies in which inducible ectopic expression needed to be maintained while the genomic knockouts were generated (Wirtz et al., 1999). RNAi raised hopes for a powerful and convenient genetic approach for these eukaryotes.
Our lab has made extensive use of RNAi in studying gene function in T. brucei, the eukaryotic parasite that causes African sleeping sickness. The purpose of this chapter is to review the steps our lab has taken in developing an inducible RNAi system that has allowed us to achieve the goal of bona fide RNAi-based forward genetics in T. brucei. In addition, this chapter will review our development of an easy-to-use, inducible RNAi system, presenting a few examples of how this approach has allowed us to gain new insights into gene function, especially in the case of essential genes.
It has been known for almost a decade and a half
that in trypanosomes all mRNAs are trans-spliced
by addition to the 5′ end of the spliced leader (SL)
sequence. During the same time period the conviction developed
that classical cis-splicing introns are not present
in the trypanosome genome and that the trypanosome gene
arrangement is highly compact with small intergenic regions
separating one gene from the next. We have now discovered
that these tenets are no longer true. Poly(A) polymerase
(PAP) genes in Trypanosoma brucei and Trypanosoma
cruzi are split by intervening sequences of 653 and
302 nt, respectively. The intervening sequences occur at
identical positions in both organisms and obey the GT/AG
rule of cis-splicing introns. PAP mRNAs are trans-spliced
at the very 5′ end as well as internally at the 3′
splice site of the intervening sequence. Interestingly,
11 nucleotide positions past the actual 5′ splice
site are conserved between the T. brucei and T.
cruzi introns. Point mutations in these conserved
positions, as well as in the AG dinucleotide of the 3′
splice site, abolish intron removal in vivo. Our results,
together with the recent discovery of cis-splicing
introns in Euglena gracilis, suggest that both
trans- and cis-splicing are ancient acquisitions
of the eukaryotic cell.
Email your librarian or administrator to recommend adding this to your organisation's collection.