Coherent communication link using diode-pumped lasers

Work toward developing a diffraction limited, single frequency, modulated transmitter suitable for coherent optical communication or direct detection communication is discussed. Diode pumped, monolithic Nd:YAG nonplanar ring oscillators were used as the carrier beam. An external modulation technique which can handle high optical powers, has moderate modulation voltage, and which can reach modulation rates of 1 GHz was invented. Semiconductor laser pumped solid-state lasers which have high output power (0.5 Watt) and which oscillate at a single frequency, in a diffraction limited beam, at the wavelength of 1.06 microns were built. A technique for phase modulating the laser output by 180 degrees with a 40-volt peak to peak driving voltage is demonstrated. This technique can be adapted for amplitude modulation of 100 percent with the same voltage. This technique makes use of a resonant bulk modulator, so it does not have the power handling limitations of guided wave modulators

Prototype laser-diode-pumped solid state laser transmitters

Monolithic, diode-pumped Nd:YAG ring lasers can provide diffraction-limited, single-frequency, narrow-linewidth, tunable output which is adequate for use as a local oscillator in a coherent communication system. A laser was built which had a linewidth of about 2 kHz, a power of 5 milliwatts, and which was tunable over a range of 30 MHz in a few microseconds. This laser was phase-locked to a second, similar laser. This demonstrates that the powerful technique of heterodyne detection is possible with a diode-pumped laser used as the local oscillator. Laser diode pumping of monolithic Nd:YAG rings can lead to output powers of hundreds of milliwatts from a single laser. A laser was built with a single-mode output of 310 mW. Several lasers can be chained together to sum their power, while maintaining diffraction-limited, single frequency operation. This technique was demonstrated with two lasers, with a total output of 340 mW, and is expected to be practical for up to about ten lasers. Thus with lasers of 310 mW, output of up to 3 W is possible. The chaining technique, if properly engineered, results in redundancy. The technique of resonant external modulation and doubling is designed to efficiently convert the continuous wave, infrared output of our lasers into low duty-cycle pulsed green output. This technique was verified through both computer modeling and experimentation. Further work would be necessary to develop a deliverable system using this technique

Fertility preservation in pre-pubertal girls with cancer : the role of ovarian tissue cryopreservation

Copyright © 2016 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.With increasing numbers of survivors of cancer in young people future fertility and ovarian function are important considerations that should be discussed before treatment commences. Some young people, by nature of the treatment they will receive, are at high risk of premature ovarian insufficiency and infertility. For them, ovarian tissue cryopreservation (OTC) is one approach to fertility preservation that remains both invasive and for young patients experimental. There are important ethical and consent issues that need to be explored and accepted before OTC can be considered established in children with cancer. In this review we have discussed a framework for patient selection which has been shown to be effective in identifying those patients at high risk of premature ovarian insufficiency (POI) and who can be offered OTC safely.PostprintPeer reviewe

Perinatal germ cell development and differentiation in the male marmoset (Callithrix jacchus):similarities with the human and differences from the rat

STUDY QUESTION: Is perinatal germ cell (GC) differentiation in the marmoset similar to that in the human? SUMMARY ANSWER: In a process comparable with the human, marmoset GC differentiate rapidly after birth, losing OCT4 expression after 5–7 weeks of age during mini-puberty. WHAT IS KNOWN ALREADY: Most of our understanding about perinatal GC development derives from rodents, in which all gonocytes (undifferentiated GC) co-ordinately lose expression of the pluripotency factor OCT4 and stop proliferating in late gestation. Then after birth these differentiated GC migrate to the basal lamina and resume proliferation prior to the onset of spermatogenesis. In humans, fetal GC differentiation occurs gradually and asynchronously and OCT4(+) GC persist into perinatal life. Failure to switch off OCT4 in GC perinatally can lead to development of carcinoma in situ (CIS), the precursor of testicular germ cell cancer (TGCC), for which there is no animal model. Marmosets show similarities to the human, but systematic evaluation of perinatal GC development in this species is lacking. Similarity, especially for loss of OCT4 expression, would support use of the marmoset as a model for the human and for studying CIS origins. STUDY DESIGN, SIZE AND DURATION: Testis tissues were obtained from marmosets (n = 4–10 per age) at 12–17 weeks' gestation and post-natal weeks 0.5, 2.5, 5–7, 14 and 22 weeks, humans at 15–18 weeks' gestation (n = 5) and 4–5 weeks of age (n = 4) and rats at embryonic day 21.5 (e21.5) (n = 3) and post-natal days 4, 6 and 8 (n = 4 each). PARTICIPANTS/MATERIALS, SETTING AND METHODS: Testis sections from fetal and post-natal marmosets, humans and rats were collected and immunostained for OCT4 and VASA to identify undifferentiated and differentiated GC, respectively, and for Ki67, to identify proliferating GC. Stereological quantification of GC numbers, differentiation (% OCT4(+) GC) and proliferation were performed in perinatal marmosets and humans. Quantification of GC position within seminiferous cords was performed in marmosets, humans and rats. MAIN RESULTS AND ROLE OF CHANCE: The total GC number increased 17-fold from birth to 22 post-natal weeks in marmosets; OCT4(+) and VASA(+) GC proliferated equally in late gestation and early post-natal life. The percentage of OCT4(+) GC fell from 54% in late fetal life to <0.5% at 2.5 weeks of age and none were detected after 5–7 weeks in marmosets. In humans, the percentage of OCT4(+) GC also declined markedly during the equivalent period. In marmosets, GC had begun migrating to the base of seminiferous cords at ∼22 weeks of age, after the loss of GC OCT4 expression. LIMITATIONS, REASONS FOR CAUTION: There is considerable individual variation between marmosets. Although GC development in marmosets and humans was similar, there are differences with respect to proliferation during fetal life. The number of human samples was limited. WIDER IMPLICATIONS OF THE FINDINGS: The similarities in testicular GC differentiation between marmosets and humans during the perinatal period, and their differences from rodents, suggest that the marmoset may be a useful model for studying the origins of CIS, with relevance for the study of TGCC. STUDY FUNDING/COMPETING INTERESTS: This work was supported by Grant G33253 from the Medical Research Council, UK. No external funding was sought and there are no competing interests

Edge states of graphene bilayer strip

The electronic structure of the zig-zag bilayer strip is analyzed. The electronic spectra of the bilayer strip is computed. The dependence of the edge state band flatness on the bilayer width is found. The density of states at the Fermi level is analytically computed. It is shown that it has the singularity which depends on the width of the bilayer strip. There is also asymmetry in the density of states below and above the Fermi energy.Comment: 9 page

Instances and connectors : issues for a second generation process language

This work is supported by UK EPSRC grants GR/L34433 and GR/L32699Over the past decade a variety of process languages have been defined, used and evaluated. It is now possible to consider second generation languages based on this experience. Rather than develop a second generation wish list this position paper explores two issues: instances and connectors. Instances relate to the relationship between a process model as a description and the, possibly multiple, enacting instances which are created from it. Connectors refers to the issue of concurrency control and achieving a higher level of abstraction in how parts of a model interact. We believe that these issues are key to developing systems which can effectively support business processes, and that they have not received sufficient attention within the process modelling community. Through exploring these issues we also illustrate our approach to designing a second generation process language.Postprin

105110^{51} Ergs: The Evolution of Shell Supernova Remnants

This paper reports on a workshop hosted by the University of Minnesota, March 23-26, 1997. It addressed fundamental dynamical issues associated with the evolution of shell supernova remnants and the relationships between supernova remnants and their environments. The workshop considered, in addition to classical shell SNRs, dynamical issues involving X-ray filled composite remnants and pulsar driven shells, such as that in the Crab Nebula. Approximately 75 participants with wide ranging interests attended the workshop. An even larger community helped through extensive on-line debates prior to the meeting. Each of the several sessions, organized mostly around chronological labels, also addressed some underlying, general physical themes: How are SNR dynamics and structures modified by the character of the CSM and the ISM and vice versa? How are magnetic fields generated in SNRs and how do magnetic fields influence SNRs? Where and how are cosmic-rays (electrons and ions) produced in SNRs and how does their presence influence or reveal SNR dynamics? How does SNR blast energy partition into various components over time and what controls conversion between components? In lieu of a proceedings volume, we present here a synopsis of the workshop in the form of brief summaries of the workshop sessions. The sharpest impressions from the workshop were the crucial and under-appreciated roles that environments have on SNR appearance and dynamics and the critical need for broad-based studies to understand these beautiful, but enigmatic objects. \\Comment: 54 pages text, no figures, Latex (aasms4.sty). submitted to the PAS

California Extremely Large Telescope: Conceptual Design for a Thirty-Meter Telescope

Following great success in the creation of the Keck Observatory, scientists at the California Institute of Technology and the University of California have begun to explore the scientific and technical prospects for a much larger telescope. The Keck telescopes will remain the largest telescopes in the world for a number of years, with many decades of forefront research ahead after that. Though these telescopes have produced dramatic discoveries, it is already clear that even larger telescopes must be built if we are to address some of the most profound questions about our universe. The time required to build a larger telescope is approximately ten years, and the California community is presently well-positioned to begin its design and construction. The same scientists who conceived, led the design, and guided the construction of the Keck Observatory have been intensely engaged in a study of the prospects for an extremely large telescope. Building on our experience with the Keck Observatory, we have concluded that the large telescope is feasible and is within the bounds set by present-day technology. Our reference telescope has a diameter of 30 meters, the largest size we believe can be built with acceptable risk. The project is currently designated the California Extremely Large Telescope (CELT)

Heart Fatty Acid Binding Protein and cardiac troponin: development of an optimal rule-out strategy for acute myocardial infarction

Background: Improved ability to rapidly rule-out Acute Myocardial Infarction (AMI) in patients presenting with chest pain will promote decongestion of the Emergency Department (ED) and reduce unnecessary hospital admissions. We assessed a new commercial Heart Fatty Acid Binding Protein (H-FABP) assay for additional diagnostic value when combined with cardiac troponin (using a high sensitivity assay). Methods: H-FABP and high-sensitivity troponins I (hs-cTnI) and T (hs-cTnT) were measured in samples taken on-presentation from patients, attending the ED, with symptoms triggering investigation for possible acute coronary syndrome. The optimal combination of H-FABP with each hs-cTn was defined as that which maximized the proportion of patients with a negative test (low-risk) whilst maintaining at least 99 % sensitivity for AMI. A negative test comprised both H-FABP and hs-cTn below the chosen threshold in the absence of ischemic changes on the ECG. Results: One thousand seventy-nine patients were recruited including 248 with AMI. H-FABP 99 % sensitivity for AMI whilst classifying 40.9 % of patients as low-risk. The combination of H-FABP < 3.9 ng/mL and hs-cTnT < 7.6 ng/L with a negative ECG maintained the same sensitivity whilst classifying 32.1 % of patients as low risk. Conclusions: In patients requiring rule-out of AMI, the addition of H-FABP to hs-cTn at presentation (in the absence of new ischaemic ECG findings) may accelerate clinical diagnostic decision making by identifying up to 40 % of such patients as low-risk for AMI on the basis of blood tests performed on presentation. If implemented this has the potential to significantly accelerate triaging of patients for early discharge from the ED