Motivated by the potentially large number of devices and simulations involved in optoelectronic system design, and the associated need for compact optoelectronic device models, we present a simple ...thermal model of vertical-cavity surface-emitting laser (VCSEL) light-current (LI) characteristics based on the laser rate equations and a thermal offset current. The model was implemented in conventional SPICE-like circuit simulators, including HSPICE, and used to simulate key features of VCSEL LI curves, namely, thermally dependent threshold current and output-power roll-over for a range of ambient temperatures. The use of the rate equations also allows simulation in other non-dc operating regimes. Our results compare favorably to experimental data from three devices reported in the literature.
The increasing interest in vertical-cavity surface-emitting lasers (VCSEL's) requires the corresponding development of circuit-level VCSEL models for use in the design and simulation of ...optoelectronic applications. Unfortunately, existing models lack either the computational efficiency or the comprehensiveness warranted by circuit-level simulation. Thus, in this paper we present a comprehensive circuit-level model that accounts for the thermal and spatial dependence of a VCSEL's behavior. The model is based on multimode rate equations and empirical expressions for the thermal dependence of the active-layer gain and carrier leakage, thereby facilitating the simulation of VCSEL's in the context of an optoelectronic system. To confirm that our model is valid, we present sample simulations that demonstrate its ability to replicate typical dc, small-signal, and transient operation, including temperature-dependent light-current (LI) curves and modulation responses, multimode behavior, and diffusive turn-off transients. Furthermore, we verify our model against experimental data from four devices reported in the literature. As the results will show, we obtained excellent agreement between simulation and experiment.
Carrier diffusion and spatial hole burning can have a severe impact on vertical cavity surface emitting laser (VCSEL) performance. In particular, these phenomena can produce secondary pulses, bumps, ...and optical tails in the VCSEL turn-off transient which limit both the system bit rate and the bit error rate (BER). To study these effects, laser rate equation models that include both spatial and temporal dependence are often employed; however, simulations which require discretization of both space and time, while accurate, typically consume vast amounts of computational power. In this paper, we demonstrate that models based on well-accepted spatially independent rate equations can be used to simulate these effects. These models exhibit the advantages of the full spatio-temporal approach but execute much more quickly. We also integrate these models into electronic computer-aided design (CAD) tools which will enable circuit and system designers to simultaneously simulate electrical and optical performance.
Since it was established in 1997, the ESHRE PGD Consortium has been collecting data from international preimplantation genetic diagnosis (PGD) centres. Ten papers have been published, including data ...from January 1997 to December 2007.
The data collection originally used a hard-copy format, then an excel database and finally a FileMaker Pro database. The indications are divided into five categories: PGD for chromosome abnormalities, sexing for X-linked disease, PGD for single gene defects, preimplantation genetic screening (PGS) and PGD for social sexing. The main end-points are pregnancy outcome and follow-up of deliveries.
In data collection I, 16 centres contributed data, which increased to 57 centres by data X (average of 39 centres per data collection). These centres contributed data on over 27 000 cycles that reached oocyte retrieval. Of these cycles, 61% were for aneuploidy screening, 17% for single gene disorders, 16% for chromosomal abnormalities, 4% for sexing of X-linked disease and 2% for social sexing. Cumulatively, 5187 clinical pregnancies gave rise to 4140 deliveries and 5135 newborns (singletons: 3182, twins: 921, triplets: 37).
In this paper, we present an overview of the first 10 years of PGD data, highlighting trends. These include the introduction of laser-assisted biopsy, an increase in polar body and trophectoderm biopsy, new strategies, methodologies and technologies for diagnosis, including recently arrays, and the more frequent use of freezing biopsied embryos. The Consortium data reports represent a valuable resource for information about the practice of PGD.
Since 2004, there have been 11 randomized controlled trials (RCTs) mainly for advanced maternal age (AMA), which have shown no benefit of performing preimplantation genetic screening (PGS). Ten of ...the RCTs have been performed at the cleavage stage and one at the blastocyst stage. It is probable that the high levels of chromosomal mosaicism at cleavage stages, which may result in the tested cell not being representative of the embryo, and the inability to examine all of the chromosomes using fluorescence in situ hybridization, have contributed to the lack of positive outcome from the RCTs. We suggest that future RCTs should examine alternative biopsy timing (polar body and/or trophectoderm biopsy), and should apply technologies that allow more comprehensive testing to include all chromosomes (microarray-based testing) to determine if PGS shows an improvement in delivery rate. Currently there is no evidence that routine PGS is beneficial for patients with AMA and conclusive data (RCTs) on repeated miscarriage, implantation failure and severe male factor are missing. To evaluate benefits of PGS, an ESHRE trial has recently been started on patients with AMA using polar body biopsy and array-comparative genomic hybridization, which should bring more information on this patient group in the near future.
A systematic investigation of Planacon MCP-PMTs was performed using 64 XP85002/FIT-Q photosensors. These devices are equipped with microchannel plates of reduced resistance. Results of a study of ...their gain stability over time and saturation level in terms of the average anode current are presented. This information allows one to determine the lower limit of the MCP resistance for stable Planacon operation. The spread of the electron multiplication characteristics for the entire production batch is also presented, indicating the remarkably low voltage requirements of these MCP-PMTs. Detection efficiency and noise characteristics, such as dark count rate and afterpulsing level, are also reviewed.
Francisella tularensis is an important human pathogen responsible for causing tularemia. F. tularensis has long been developed as a biological weapon and is now classified as a category A agent by ...the Centers for Disease Control because of its possible use as a bioterror agent. F. tularensis represses inflammasome; a cytosolic multi-protein complex that activates caspase-1 to produce proinflammatory cytokines IL-1β and IL-18. However, the Francisella factors and the mechanisms through which F. tularensis mediates these suppressive effects remain relatively unknown. Utilizing a mutant of F. tularensis in FTL_0325 gene, this study investigated the mechanisms of inflammasome repression by F. tularensis. We demonstrate that muted IL-1β and IL-18 responses generated in macrophages infected with F. tularensis live vaccine strain (LVS) or the virulent SchuS4 strain are due to a predominant suppressive effect on TLR2-dependent signal 1. Our results also demonstrate that FTL_0325 of F. tularensis impacts proIL-1β expression as early as 2 h post-infection and delays activation of AIM2 and NLRP3-inflammasomes in a TLR2-dependent fashion. An enhanced activation of caspase-1 and IL-1β observed in FTL_0325 mutant-infected macrophages at 24 h post-infection was independent of both AIM2 and NLRP3. Furthermore, F. tularensis LVS delayed pyroptotic cell death of the infected macrophages in an FTL_0325-dependent manner during the early stages of infection. In vivo studies in mice revealed that suppression of IL-1β by FTL_0325 early during infection facilitates the establishment of a fulminate infection by F. tularensis. Collectively, this study provides evidence that F. tularensis LVS represses inflammasome activation and that F. tularensis-encoded FTL_0325 mediates this effect.
Background: The mechanism of repression of inflammasome caused by Francisella tularensis is not known.
Results:F. tularensis represses AIM2 and NLRP3 inflammasomes in a FTL_0325-dependent fashion.
Conclusion: Repression of inflammasome by F. tularensis results in fulminate infection.
Significance: This study advances the understanding of mechanisms of immune suppression caused by F. tularensis.
The 10th report of the European Society of Human Reproduction and Embryology (ESHRE) PGD Consortium is presented, documenting cycles collected for the calendar year 2007 and follow-up of the ...pregnancies and babies born until October 2008 which resulted from these cycles. Since the beginning of the data collections there has been a steady increase in the number of cycles, pregnancies and babies reported annually. For data collection X, 57 centres participated, reporting on 5887 cycles to oocyte retrieval (OR), along with details of the follow-up on 1516 pregnancies and 1206 babies born. A total of 729 OR were reported for chromosomal abnormalities, 110 OR for sexing for X-linked diseases, 1203 OR for monogenic diseases, 3753 OR for preimplantation genetic screening and 92 OR for social sexing. Data X is compared with the cumulative data for data collections I–IX.
PDF
